Unchecked human population growth and consumption are key drivers of the current threats facing wildlife and wild spaces. Understanding the evidence-backed consequences of human population growth and the barriers to working on this issue is important for developing and prioritizing solutions.
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Abbitt, R. J. F., Scott, J. M., & Wilcove, D. S. (2000). The geography of vulnerability: Incorporating species geography and human development patterns into conservation planning. Biological Conservation, 96(2), 169–175. https://doi.org/10.1016/S0006-3207(00)00064-1
What is the research about?
This study mapped the distribution of restricted-range birds and butterflies not listed as threatened or endangered in the continuous United States, along with projected increases in human population and development.
What are the key takeaways?
Anticipated human impact was estimated using projected change in density, increase in developed land area, increase in urban road mileage, and total amount of undeveloped nonfederal land available for potential development. These methods could be used in other countries to identify species and areas of vulnerability before they become endangered.
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Ament, J. M., Collen, B., Carbone, C., Mace, G. M., & Freeman, R. (2019). Compatibility between agendas for improving human development and wildlife conservation outside protected areas: Insights from 20 years of data. People and Nature, 1(3), 305–316. https://doi.org/10.1002/pan3.10041
What is the research about?
The study analyzes the connections among trends in human development and wildlife over time, specifically using bird and mammal population abundance trends. The analyses focused on low‐ and lower‐middle income countries to observe wildlife trends occurring simultaneously with human development. This also helps to avoid measuring signals of historical change, including the effects of extinction filters, which are when countries that have already experienced significant development and species loss don’t show an accurate representation of these correlations.
What are the key takeaways?
Results indicate negative relationships between human population growth and wildlife abundance, for both bird and mammals, across 298 wildlife populations in 33 countries. There was also a positive correlation between wildlife abundance trends with economic growth, suggesting that as countries develop environmental regulations improve and help place a higher priority on conservation. The potential unintended consequences and compatibility between the conservation and development agendas indicate a need to better coordinate these strategies.
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Andermann, T., Faurby, S., Turvey, S. T., Antonelli, A., & Silvestro, D. (2020). The past and future human impact on mammalian diversity. Science Advances, 6(36), eabb2313. https://doi.org/10.1126/sciadv.abb2313
What is the research about?
This study estimates the specific times of changes in extinction rates from mammal extinctions in the past 126,000 years. The results provide a comprehensive assessment of the human impact on past and predicted future extinctions of mammals.
What are the key takeaways?
The changes in extinction rates reviewed coincide with human colonization patterns. Human population density predicts the mammalian extinction patterns with 96% accuracy. Total land mass occupied by humans predicts past extinctions with 97.1% accuracy. This study predicts an unprecedented increase in rate of extinctions in the near future based on current trends.
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Arnocky, S., Dupuis, D., & Stroink, M. L. (2012). Environmental concern and fertility intentions among Canadian university students. Population and Environment, 34(2), 279–292. https://doi.org/10.1007/s11111-011-0164-y
What is the research about?
To better understand how individuals understand reduced fertility as a solution to environmental problems this study looked at two types of environmental concern: (1) concerns about humans’ role in affecting the natural environment and the importance of environmental protection (2) concerns with health risks due to pollution.
What are the key takeaways?
The results showed that that pollution-related health concern was related to lower fertility intention. Future research could investigate additional distinction between limiting one’s reproduction out of environmental concern for the world at large as compared with more self-oriented environmental concerns.
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Austin, K. F., & Banashek, C.,. 2018. Gender Inequality and Environmental Well-Being: A Cross-National Investigation of Ecosystem Vitality and Environmental Health. Sustainability in Environment, 3(3), pp. 257. 10.22158/SE.V3N3P257
What is the research about?
This study looks at the relationship between gender inequality and environment across 114 countries. The gender inequality was quantified using the Global Gender Gap Index, which includes economic, educational, health-based and political indicators. Environmental quality was quantified through 2 indexes: ecosystem performance and environmental health. Ecosystem performance encompassed trends in carbon intensity, species protection, terrestrial protection, marine protection, fish stocks, tree cover loss, nitrogen balance, nitrogen use efficiency and wastewater treatment. Environmental health encompassed drinking-water quality, unsafe sanitation, air pollution, exposure to NO2, fine particulate matter exposure, household air quality, and environmental risk exposure.
What are the key takeaways?
Countries with greater gender inequality tended to have lower environmental performance. Higher levels of economic growth (GDP) were also associated with lower environmental performance. Women were affected by the effects of climate change more than men and also are more likely to support progressive environmental policy. Gender inequality can be reduced by increasing women’s empowerment with more access to education, health and economic resources. The empowerment of women can also lead to increased environmental stewardship.
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Baisero, D., Visconti, P., Pacifici, M., Cimatti, M., & Rondinini, C. (2020). Projected Global Loss of Mammal Habitat Due to Land-Use and Climate Change. One Earth, 2(6), 578–585. https://doi.org/10.1016/j.oneear.2020.05.015
What is the research about?
This study modeled impacts of land-use and climate change on future habitat for 2,827 terrestrial mammals under five different global scenarios based on climate projections and alternative socioeconomic development scenarios (which include population) between 2015 and 2050.
What are the key takeaways?
Habitat available to mammals declined under all five combinations of scenarios. Mammal habitat declined globally by 5-16% depending on the scenario and regionally up to 25%. Pathways of sustainable development more aggressive than the lowest-impact scenario may be needed to slow the current rates of biodiversity loss. Mammals especially need a mix of actions at different levels, and a global shift of socioeconomic development scenarios moving toward sustainability and climate-change mitigation.
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Bar-On, Y. M., Phillips, R., & Milo, R. (2018). The biomass distribution on Earth. Proceedings of the National Academy of Sciences of the United States of America, 115(25), 6506–6511. https://doi.org/10.1073/pnas.1711842115
What is the research about?
This study presents a survey of the composition of living organisms in our world to help gain a better understanding of biological relationships and dynamics.
What are the key takeaways?
The biomass of humans is more than eight times that of wild mammals, and the biomass of poultry is almost three times that of wild birds. The combination of humans and livestock outweigh all vertebrates except for fish. Also, total plant biomass has been halved since the start of human civilization, which has consequences for carbon sequestration. This is partly due to human advances and associated impacts we’ve made with agriculture, livestock domestication and industry in order to support our growing population.
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Barnes, M. D., Craigie, I. D., Harrison, L. B., Geldmann, J., Collen, B., Whitmee, S., … Woodley, S. (2016). Wildlife population trends in protected areas predicted by national socio-economic metrics and body size. Nature Communications, 7:12747. https://doi.org/10.1038/ncomms12747
What is the research about?The study analyzes correlates of population change in 1,902 populations of birds and mammals from 447 protected areas globally.
What are the key takeaways?
Protected areas are maintaining populations of monitored birds and mammals within their boundaries. Indicators of greater human wealth and development were associated with more positive population trends. This could be due to more resource availability for protected area management and people in these populations being less likely to extract resources from the protected areas. Human-caused drivers of wildlife abundance change appear to have more influence than those drivers affecting ecological dimensions. Managing sociopolitical dimensions like wealth, development and corruption, instead of exclusively ecological dimensions like size, shape and age of protected area, is important to wildlife conservation in protected areas.
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Barrett, S., Dasgupta, A., Dasgupta, P., Neil Adger, W., Anderies, J., van den Bergh, J., … Wilen, J. (2020). Social dimensions of fertility behavior and consumption patterns in the Anthropocene. Proceedings of the National Academy of Sciences of the United States of America, 117(12), 6300–6307. https://doi.org/10.1073/pnas.1909857117
What is the research about?
This study looks at how decisions around family planning and consumption behaviors aren’t exclusively individual decisions but also influenced by social pressures. Our individual needs appear small but have major impacts in aggregate and over time, when these demands are ingrained as social norms due to competitive and conformist behavior.
What are the key takeaways?
Continued growth of fertility and per capita GDP is not sustainable. Technology is often touted as the solution to many of our environmental issues, but it has not been a cure-all for habitat destruction and biodiversity loss. Social change is an important part of the solution, along with policy changes. These are most effective at the local and national level, rather than regional and global level.
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Benson, J. F., Abernathy, H. N., Sikich, J. A., & Riley, S. P. D. (2021). Mountain lions reduce movement, increase efficiency during the Covid-19 shutdown. Ecological Solutions and Evidence, 2(3), e12093. https://doi.org/10.1002/2688-8319.12093
What is the research about?
This study used the 2020 Covid-19 shutdowns as a natural experiment to observe 12 mountain lions’ space use, movement and resource selection in relation to reduced human activity in the Los Angeles area.
What are the key takeaways?
The mountain lions in this study did not expand their space use or travel greater distances in response to reduced human activity. They did avoid human infrastructure like trails and development less, though, which may have allowed them to travel more efficiently and therefore cover shorter distances.
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Berger, J., Wangchuk, T., Briceño, C., Vila, A., & Lambert, J. E. (2020). Disassembled Food Webs and Messy Projections: Modern Ungulate Communities in the Face of Unabating Human Population Growth. Frontiers in Ecology and Evolution, 8:128. https://doi.org/10.3389/fevo.2020.00128
What is the research about?
This study reviews how human population growth and its related disruptions alter wildlife community dynamics and ecological relationships of ungulates now and in the future.
What are the takeaways?
Many formerly predictable patterns and processes have diminished, and ecological surprises are becoming more regular occurrences. Disturbed habitat and altered communities can still offer important contributions to biodiversity, but we must continue to protect what we still have. Scientists need to be more involved outside academic literature and to participate in policy direction, speaking out and outreach. It’s important to help the public understand the relevance of food webs, biodiversity and community composition to shape policy, motivate politicians and elected officials, and influence state and federal agencies.
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Bologna, M., & Aquino, G. (2020). Deforestation and world population sustainability: a quantitative analysis. Scientific Reports, 10(1), 1–9. https://doi.org/10.1038/s41598-020-63657-6
What is the research about?
This study presents an analysis of how current population growth trends will affect deforestation.
What are the key takeaways?
Human activities are responsible for driving climate change through water and air contamination (mostly greenhouse effect) and deforestation. Results of this study show that based on the current growth and consumption rates and best estimate of technological rate growth, we have very low probability, less than 10% in the most optimistic scenario, to survive without facing a catastrophic collapse. Our civilization’s best chance for survival is shifting away from a culture strongly ruled by economy.
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Boucher, J. L.,. 2016. Culture, Carbon, and Climate Change: A Class Analysis of Climate Change Belief, Lifestyle Lock-in, and Personal Carbon Footprint. Social Ecology: Journal for Environmental Thought and Sociological Research, 25, pp. 53–80. 10.17234/SocEkol.25.1.3
What is the research about?
This study investigated the relationship between income and consumption and whether climate change beliefs can affect individual emissions in the United States.
What are the key takeaways?
The link between income, consumption and resulting individual emissions was reconfirmed. The theory of being locked-in to one’s level of consumption by societal and institutional parameters was examined based on level of concern about human-caused climate change in conjunction with consumption. Level of concern affected consumption among those who are the most concerned, but no effect on the rest. Recommendations for policy change at the governmental and institutional level, such as higher taxes and limits on emissions are suggested to most effectively change behavior.
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Bradshaw, C. J. A., Giam, X., & Sodhi, N. S. (2010). Evaluating the relative environmental impact of countries. PLoS ONE, 5(5), e10440. https://doi.org/10.1371/journal.pone.0010440
What is the research about?
This study ranks countries by their proportional (relative to resource availability) and total environmental impact focused on consumption, deforestation, pollution and biodiversity loss. Of 228 countries considered, 179 (proportional) and 171 (absolute) had sufficient data for correlations and ranking based on natural forest loss, habitat conversion, marine captures, fertilizer use, water pollution, carbon emissions and species threat. Those results were then compared to socioeconomic indicators: human population size, human population density, human population growth rate and wealth. These country rankings can provide a better understanding of which countries could improve on their environmental impact, along with countries that are doing especially well and may serve as models for policy change.
What are the key takeaways?
Countries with higher total human populations and densities had greater proportional environmental impact, and those with lower population growth rates had a slightly lower proportional environmental impact. However, overall wealth was the most important indicator of environmental impact. Improving environmental performance doesn’t fall exclusively on less-developed countries, but wealthier developed countries have plenty room for improvement, too.
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Bradshaw, C. J. A., & Di Minin, E. (2019). Socio-economic predictors of environmental performance among African nations. Scientific Reports, 9(1), 1–13. https://doi.org/10.1038/s41598-019-45762-3
What is the research about?
This study tested hypotheses looking at the socioeconomic predictors of ecosystem change and degradation for countries across Africa, hypothesizing that human density and economic development increase the likelihood of cumulative environmental damage.
What are the key takeaways?
Much of the research investigating environmental change has not focused on the wider socioeconomic conditions contributing to environmental degradation. Models indicate that increasing population density and overall economic activity are some of the strongest predictors of increased environmental degradation. The study suggests that dedicated family planning, to reduce population growth, and economic development that limits agricultural expansion are needed to support environmental sustainability.
Bradshaw, C. J. A., Ehrlich, P. R., Beattie, A., Ceballos, G., Crist, E., Diamond, J., … Blumstein, D. T. (2021). Underestimating the Challenges of Avoiding a Ghastly Future. Frontiers in Conservation Science, 1, 615419. https://doi.org/10.3389/fcosc.2020.615419
What is the research about?
This commentary summarizes the severity of major environmental change scenarios, including continued biodiversity loss as part of the current mass extinction, severe climate events and ecological overshoot. It points to the “inertia” of human population trends as one of the main contributing factors.
What are the key takeaways?
While there’s plenty of scientific evidence for these problems, awareness can still be improved. It’s important to clearly state how broad the problems and required solutions are in order to reach our sustainability goals. The choice at hand is no longer “environment vs. economy” but whether we can exit overshoot by design instead of disaster. The lack of change in population trends shouldn’t discourage us but rather motivate us to increase our efforts.
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Brown, M. L., Donovan, T. M., Schwenk, W. S., & Theobald, D. M. (2014). Predicting impacts of future human population growth and development on occupancy rates of forest-dependent birds. Biological Conservation, 170, 311–320. https://doi.org/10.1016/j.biocon.2013.07.039
What is the research about?
This paper models predictions of how human development will affect several bird species in the northeastern United States.
What are the key takeaways?
97% of towns experienced reductions in the occupancy of species within their town borders. There were also declines in the probability of species occupying an area when development was predicted to increase. These types of predictive modeling studies are important for evaluating the environmental costs of development.
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Campbell-Staton, S. C., Arnold, B. J., Gonçalves, D., Granli, P., Poole, J., Long, R. A., & Pringle, R. M.,. 2021. Ivory poaching and the rapid evolution of tusklessness in African elephants. Science, 374(6566), pp. 483–487. 10.1126/SCIENCE.ABE7389
What is the research about?
This study tested whether the increase in the number of tuskless female elephants was by chance with a population bottleneck or caused by selective pressure from ivory poaching.
What are the key takeaways?
The survival of tuskless females was five times that of females with tusks. Human-driven selective pressure resulted in rapid evolution of a physical trait in these elephants. There will likely be downstream environmental consequences since elephants are ecosystem engineers that often use their tusks to modify their surrounding habitat.
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Cardillo, M., Purvis, A., Sechrest, W., Gittleman, J. L., Bielby, J., & Mace, G. M. (2004). Human population density and extinction risk in the world’s carnivores. PLoS Biology, 2(7). https://doi.org/10.1371/journal.pbio.0020197
What is the research about?
This is a global-scale analysis of biological and external predictors of extinction risk among carnivores based on human population density.
What are the key takeaways?
Biology is a stronger predictor of extinction risk to carnivores than exposure to high-density human populations. However, biology interacts with human population density to determine extinction risk: Biological traits explain 80% of variation in risk for carnivore species with high levels of exposure to human populations, compared to 45% for carnivores generally. Inherent ecological and life-history traits determine how resilient populations can be when exposed to threats. The study demonstrates how a model predicting extinction risk based on biology can be combined with projected human population density to identify species that might move toward extinction faster than based on biology alone. Maintaining the stability of particularly susceptible species before they become threatened could be more cost-effective in the long term than attempts to rescue them from the brink of extinction after large declines occur.
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Cavicchioli, R., Ripple, W. J., Timmis, K. N., Azam, F., Bakken, L. R., Baylis, M., … Webster, N. S. (2019). Scientists’ warning to humanity: microorganisms and climate change. Nature Reviews Microbiology, 17(9), 569–586. https://doi.org/10.1038/s41579-019-0222-5
What is the research about?
This article provides a series of examples and consequences of how microorganisms affect climate change (such as production and consumption of greenhouse gases) but also how they will be affected by climate change and other human activities. Together they create a feedback loop that accelerates climate change, worsens pollution, threatens agriculture and increases the spread of disease.
What are the key takeaways?
Some of the consequences that are shown as directly connected to human population growth include the increasing spread of animal, human and crop pathogens and increasing antimicrobial resistance of microorganisms.
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Ceballos, G., Ehrlich, P. R., Barnosky, A. D., García, A., Pringle, R. M., & Palmer, T. M. (2015). Accelerated modern human-induced species losses: Entering the sixth mass extinction. Science Advances, 1(5), e1400253. https://doi.org/10.1126/sciadv.1400253
What is the research about?
The study assesses, using conservative assumptions, whether human activities are causing a mass extinction.
What are the key takeaways?
Even under conservative assumptions that minimize evidence of a burgeoning mass extinction, the average rate of vertebrate species loss over the last century is up to 100 times higher than the background rate. This analysis emphasizes that humans have started to destroy other species at an accelerating rate, initiating a mass extinction episode that has not been seen for 65 million years. Avoiding a true sixth mass extinction will require efforts much more drastic than what is already being done to prevent the loss of already threatened species and to reduce pressures on their populations, such as habitat loss, overexploitation for economic gain, and climate change.
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Ceballos, G., Ehrlich, P. R., & Dirzo, R. (2017). Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines. Proceedings of the National Academy of Sciences of the United States of America, 114(30), E6089–E6096. https://doi.org/10.1073/pnas.1704949114
What is the research about?
This study demonstrates that the current mass extinction is even worse than previously thought. This is because this analysis includes not just the extinction of entire species but declines in ranges and individual populations.
What were the key takeaways?
In addition to global species extinctions, there are widespread population declines and extirpations. The study found that the rate of population loss in terrestrial vertebrates is extremely high — even in “species of low concern.” In this sample, comprising nearly half of known vertebrate species, 32% (8,851/27,600) are decreasing in population size and range. In the 177 mammals for which there were detailed data, all have lost 30% or more of their geographic ranges, and more than 40% of the species have experienced severe population declines (>80% range shrinkage).
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Ceballos, G., & Ehrlich, P. R. (2002). Mammal population losses and the extinction crisis. Science, 296(5569), 904–907. https://doi.org/10.1126/science.1069349
What is the research about?
This study compares the past and current distributions of 173 declining mammal species from six continents.
What are the key takeaways?
The species studied have, together, lost over half of their past range area, with the most loss occurring where human activities are intense.
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Ceballos, G., Ehrlich, P. R., & Raven, P. H. (2020). Vertebrates on the brink as indicators of biological annihilation and the sixth mass extinction. Proceedings of the National Academy of Sciences, 201922686. https://doi.org/10.1073/pnas.1922686117
What is the research about?
This study evaluates how many vertebrates are on the brink of extinction (i.e., have fewer than 1,000 individuals left) and the timing and distribution of these species losses.
What are the key takeaways?
Human activity is causing the current extinction crisis and will continue to accelerate it if we don’t take necessary action. 94% of the species loss analyzed in this study occurred in the past century. Many of the species with under 1,000 individuals remaining have overlapping ranges. This interconnectedness could mean that more species loss will keep increasing the already high extinction rate as ecosystem functions change. The occurrence of species at risk and species on the brink are concentrated in areas of heavy human population with high levels of biodiversity loss. The extinction crisis should be elevated to a national and global emergency for governments and institutions to act with the level of urgency required to conserve species.
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Cincotta, R. P., Wisnewski, J., & Engelman, R. (2000). Human population in the biodiversity hotspots. Nature, 404(6781), 990–992. https://doi.org/10.1038/35010105
What is the research about?
This study looks at estimates of population growth and population density in 25 biodiversity hotspots.
What are the key takeaways?
The population density in these biodiversity hotspots was 71% greater than the global average. Population growth rates were highest in the 19 hotspots within developing countries, but growth rates in the hotspots within developed countries were also higher than the global average for developed regions. It’s likely that substantial human-caused habitat degradation will continue in the hotspots and that demographic change remains an important factor in global biodiversity conservation. These results emphasize that continuing the declines in human fertility globally will also be important for conservation.
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Clinchy, M., Zanette, L. Y., Roberts, D., Suraci, J. P., Buesching, C. D., Newman, C., & Macdonald, D. W. (2016). Fear of the human “super predator” far exceeds the fear of large carnivores in a model mesocarnivore. Behavioral Ecology, 27(6), 1826–1832. https://doi.org/10.1093/beheco/arw117
What is the research about?
This study tested how badgers reacted to the sounds of both extinct and extant large carnivores and humans. The study measured how the badgers’ level of fearfulness affected their foraging behavior.
What are the key takeaways?
Hearing humans affected time it took badgers to start feeding, amount of awareness, time spent foraging, number of feeding visits, and number of badgers feeding. Hearing extant predators had far lesser effects on latency to feed, and hearing extinct predators had no effects. Fear of humans cannot replace the fear of large carnivores for mesocarnivores because humans are perceived as far more frightening. This refutes the argument that humans can serve as a substitute for large carnivores in terms of community-level dynamics where large carnivores no longer exist.
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Cohen, J. E.,. 2003. Human Population: The Next Half Century. In Science(Vol. 302, Issue 5648, pp. 1172–1175). 10.1126/science.1088665
What is the research about?
This article reviews past and projected global demographics in terms of fertility, mortality and population broken out by region, country an income level.
What are the key takeaways?
The 20th century may be the last where younger people outnumber older people. Migration remains one of the more difficult variables to predict based on the instability of factors that can cause it. Demographic shifts can also spur changes in family structure.
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Crist, E., Mora, C., & Engelman, R. (2017). The interaction of human population, food production, and biodiversity protection. Science, 356(6335), 260–264. https://doi.org/10.1126/science.aal2011
What is the research about?
This paper reviews the various proposed solutions and feasibility of feeding the world’s population. While some recommendations, such as changes in diet and reducing food waste, would help, there is still a reliance on intensification that continues the cycle of environmental degradation. The absence of addressing population growth has also paved the way for this reliance on technological advances to improve well-being.
What are the key takeaways?
Tackling both population and consumption is necessary to undo the environmental damages that have been done. Human-rights solutions like gender equity, along with educating women and investing in improved universal family planning services, are key elements of slowing population growth. Intensification of agriculture isn’t enough to compensate for our food supply because current rates are already unsustainable.
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Crooks, K. R., Burdett, C. L., Theobald, D. M., King, S. R. B., Di Marco, M., Rondinini, C., & Boitani, L. (2017). Quantification of habitat fragmentation reveals extinction risk in terrestrial mammals. Proceedings of the National Academy of Sciences of the United States of America, 114(29), 7635–7640. https://doi.org/10.1073/pnas.1705769114
What is the research about?
This study modelled the amount and effects of habitat fragmentation on over 4,000 terrestrial mammals.
What are the key takeaways?
Species experiencing more fragmentation have an increased risk of extinction. On average, less than half of a species’ range is made up of highly suitable habitat. Habitat fragmentation driven by human activity differs from natural fragmentation caused by landscape, like elevation or bodies of water, and this distinction is important for prioritizing conservation and protection efforts.
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Czech, B., Krausman, P. R., & Devers, P. K. (2000). Economic associations among causes of species endangerment in the United States. BioScience, 50(7), 593–601. https://doi.org/10.1641/0006-3568(2000)050[0593:EAACOS]2.0.CO;2
What is the research about?
This study gives a comprehensive list of the current causes of species endangerment in the United States and Puerto Rico. Habitat loss was broken out into subcategories that correspond to different economic sectors to provide a better understanding of what needs to be done to protect species.
What are the key takeaways?
Looking at the association the different causes of endangerment have helps give a clearer illustration of the magnitude of the effect. Urbanization and agriculture were the most frequently associated threats. Forty-five percent of the species endangered by urbanization are also endangered by agriculture, and 55% of the species endangered by agriculture are also threatened by urbanization. Many of the threats studied are also due to infrastructure and human activity. The wide extent of humanity’s continuously growing impact suggests that conservation policy could constitute macroeconomic policy and vice versa.
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Dabelko, G. D. (2011). Population and Environment Connections The Role of U.S. Family Planning Assistance in U.S. Foreign Policy. Retrieved from www.cfr.org.
What is the research about?
This paper provides a comprehensive review of how population growth is related to water and food scarcity around the world and how population interacts with climate change. It also discusses how consumption factors and addressing population have played out in the policy field.
What are the key takeaways?
Limited access to reproductive healthcare and resulting population growth can be viewed as a source of vulnerability to climate change and related impacts such as drought. Empowerment within a human rights-based approach avoids making unrealistic claims when addressing complex, interconnected issues like climate change. Including family planning within adaptation and vulnerability strategies helps meet development goals and avoids the perception of imposing high-income country conservation or mitigation agendas.
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Dalton, M., O’Neill, B., Prskawetz, A., Jiang, L., & Pitkin, J.,. 2008. Population aging and future carbon emissions in the United States. Energy Economics, 30(2), pp. 642–675. 10.1016/j.eneco.2006.07.002
What is the research about?
This study analyzes how demographic composition, not just absolute population size number, can affect consumption emissions in the United States; quantified using households instead of individuals.
What are the key takeaways?
An aging population’s effects on emissions may be equal to, or larger than, technological change away from carbon-intensive fuels, demonstrating the importance of incorporating demographics into future emissions simulations as population growth declines.
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Díaz, S., Settele, J., Brondízio, E. S., Ngo, H. T., Agard, J., Arneth, A., … Zayas, C. N. (2019). Pervasive human-driven decline of life on Earth points to the need for transformative change. Science, Vol. 366. https://doi.org/10.1126/science.aax3100
What is the research about?
This review summarizes the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) Global Assessment report.
What are the key takeaways?
Various areas of nature are in decline due to human activity, including: ecosystem extent and condition; species extinction risk; ecological communities; biomass and species abundance; and nature for Indigenous people and local communities. Many practices of Indigenous peoples and local communities are beneficial to maintaining and enhancing biodiversity. Some key leverage points for the transformative change needed are supporting diverse visions, reducing inequalities, and incorporating justice and inclusion into conservation.
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Di Marco, M., Venter, O., Possingham, H. P., & Watson, J. E. M. (2018). Changes in human footprint drive changes in species extinction risk. Nature Communications, 9(1), 1–9. https://doi.org/10.1038/s41467-018-07049-5
What is the research about?
This study quantified cumulative human pressure on the terrestrial environment and how it relates to species extinction risk of land mammals around the world.
What are the key takeaways?
Degree of human pressure and changes in human pressure were the strongest predictors of extinction risk. Pinpointing a threshold point of human pressure for species could be a useful tool for conservation plans.
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Elhacham, E., Uri, L. Ben, Grozovski, J., Bar-On, Y. M., & Milo, R. (2020). Global human-made mass exceeds all living biomass. Nature, 588, 442–444. https://doi.org/10.1038/s41586-020-3010-5
What is the research about?
This study compared the quantified the amount of anthropogenic (human-made) mass to all living biomass on Earth.
What are the key takeaways?
In 2020 the Earth is just about at the tipping point where human-made mass surpasses all living biomass. Anthropogenic mass has doubled roughly every 20 years. Globally, there is double the amount of plastic mass (8 Gigatons) as there is of animal mass (4 Gt), and there are 1,100 Gt of buildings and infrastructure compared to 900 Gt of trees and shrubs.
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Ganivet, E. (2019). Growth in human population and consumption both need to be addressed to reach an ecologically sustainable future. Environment, Development and Sustainability, 22, 4979–4998. https://doi.org/10.1007/s10668-019-00446-w
What is the research about?
This paper gives an overview of how increasing human population growth continues to negatively affect biodiversity, how we can change perceptions about population, and various noncoercive solutions like education and increasing access to contraception.
What are the key takeaways?
The habitat destruction driven by agricultural land-use change for food production and urban expansion to support our growing population show no signs of slowing down. There is substantial evidence to refute the argument that population is no longer an issue or something we can afford to ignore. There are several countries that have successfully implemented noncoercive population policies involving contraception and education to reduce their fertility rates than can be looked to as examples.
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Gaynor, K. M., Hojnowski, C. E., Carter, N. H., & Brashares, J. S. (2018). The influence of human disturbance on wildlife nocturnality. Science, 360(6394), 1232–1235. https://doi.org/10.1126/SCIENCE.AAR7121
What is the research about?
This review analyzes 76 studies encompassing 62 species of medium- to large-sized mammals and the effects that human presence has on changing the timing of their activity patterns.
What are the key takeaways?
Mammals are shifting their activity to being more active at night to avoid humans in areas where humans are active during the day. This response was seen across size, habitat type and continent. Human activity included lethal (hunting), non-lethal (hiking and recreation) and infrastructure (roads, agriculture and development). Wildlife responded with similar shifts in activity to both lethal and non-lethal activity which could indicate that any human activity is seen as a threat even without direct risk. While these shifts can help reduce human-wildlife conflict, it also can have cascading effects on ecosystems in terms of social behaviors, competition and evolution.
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Helm, S., Kemper, J. A., & White, S. K. (2021). No future, no kids–no kids, no future?: An exploration of motivations to remain childfree in times of climate change. Population and Environment, 1–22. https://doi.org/10.1007/s11111-021-00379-5
What is the research about?
This paper includes 2 studies looking at how climate anxiety affects reproductive intentions. One study reviewed comments on articles about choosing to be childfree because of climate change. The other involved conducting a series of interviews in New Zealand and the United States.
What are the key takeaways?
Main themes from the comments in study 1 included: the concern about too many people in the world and the associated pressure from their resource consumption, and what it means for the environment to have a child now, whether that’s worries about the state of the environment for future children or the impact on one’s own carbon footprint due to having children. Study 2 involved interviews with young male, female and non-binary individuals who considered their knowledge of climate change to play an important part in their reproductive decision-making. Participants all expressed concern about contributing to population growth and overconsumption by having kids, but also recognized the societal pressures that can counter their choice to be childfree. These findings should encourage policymakers to take these perspectives into consideration when developing adaptation and mitigation strategies.
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Hickel, J., & Kallis, G.,. 2020. Is Green Growth Possible? New Political Economy, 25(4), pp. 469–486. 10.1080/13563467.2019.1598964
What is the research about?
This review critiques the theory of “green growth,” the idea that gross domestic product can be decoupled from carbon emissions and resource use, and also whether this can be achieved fast enough to avoid global warming of 1.5°C or 2°C.
What are the key takeaways?
Current predictions of decoupling resource use and growth often leave out the effects of transportation, an important component of resource use in our global economy that is critical to developing effective and realistic recommendations. With decoupling growth and carbon emissions, many models are overly optimistic of, and do not provide evidence for, the parameters they cite, making their predictions questionable. The most likely way to reduce emissions to avoid warming by 1.5°C is by reducing global energy demand 40% by 2050 with significant reduction in production and consumption.
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Imasiku, K., & Ntagwirumugara, E. (2020). An impact analysis of population growth on energy‐water‐food‐land nexus for ecological sustainable development in Rwanda. Food and Energy Security, 9(1). https://doi.org/10.1002/fes3.185
What is the research about?
This study analyzed the ecological balance of human activities in Rwanda and how policymakers have increasingly focused on energy–water–food nexus sectors separately, without including land usage and population.
What are the key takeaways?
Population has an increasing effect on all nexus sectors — food, land, water, and energy. Since these sectors are interconnected, stress on any of them would cause socioeconomic and environmental stress. Leaving population growth out of sustainable development plans will likely result in insufficient solutions. Rwanda has made progress with educating citizens about family planning, but there are still cultural norms of having many children, and cultural change is not easy.
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Jha, S., & Bawa, K. S. (2006). Population Growth, Human Development, and Deforestation in Biodiversity Hotspots. Conservation Biology, 20(3), 906–912. https://doi.org/10.1111/j.1523-1739.2006.00398.x
What is the research about?
This study measured the effect of human population growth and development on deforestation rates in regions with high species diversity.
What are the key takeaways?
The relationship between human population growth, human development and deforestation was not always predictable or constant over time. Human population growth and human development were also found to have interacting effects on deforestation as well. Areas with lower development have higher rates of deforestation in biodiversity hotspots, as forests are more directly relied on for shelter, fuel, food and expansion; but as development increases, which often includes expanded trade and urbanization, the decrease in deforestation can vary. This indicates the need for broader conservation efforts that include a closer look at the policies and economies that may also affect deforestation.
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KC, S., & Lutz, W. (2017). The human core of the shared socioeconomic pathways: Population scenarios by age, sex and level of education for all countries to 2100. Global Environmental Change, 42, 181–192. https://doi.org/10.1016/j.gloenvcha.2014.06.004
What is the research about?
This paper analyzes different population scenarios with the addition of education level to the usual metric of age and sex.
What are the key takeaways?
Education is key in empowering individuals and driving sustainable development. Variation in future fertility, mortality, and education trends would result in very different future population sizes based on subsequent differences in age and education structures. The difference between the population predictions is driven by level of female educational attainment and level of education specific fertility.
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Lee, R., Mason, A., Amporfu, E., An, C. B., Bixby, L. R., Bravo, J., … Zhang, Q. (2014). Is low fertility really a problem? Population aging, dependency, and consumption. Science, 346(6206), 229–234. https://doi.org/10.1126/science.1250542
What is the research about?
This study analyzes how changes in fertility rate and subsequent population aging will affect standards of living.
What are the key takeaways?
Higher fertility and younger populations are often favored by government budgets that depend on the younger portion of the population to support the older portion. However, lower fertility, older population and population decline are associated with improved standards of living.
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Lidicker, W. Z. (2020). A Scientist’s Warning to humanity on human population growth. Global Ecology and Conservation, Vol. 24, p. e01232. https://doi.org/10.1016/j.gecco.2020.e01232
What is the research about?
This review goes over nine ecological principles that explain our current planetary situation and nine social behaviors that would be beneficial for humanity to respond with. It also provides 20 predictions of what may happen if current trends don’t change.
What are the key takeaways?
Population growth cannot continue forever when there’s an exhaustible supply of resources and our growing population is using those resources at an increasingly faster rate. The six guidelines recommended to respond include: Pay attention to science, remain optimistic, engage in respectful dialogue, encourage cooperation, balance between individual and common benefits and don’t underestimate need for rapid progress. Education through at least secondary school is important for everyone, and all women of reproductive age should have access to contraception.
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Lutz, W. (2017). How population growth relates to climate change. Proceedings of the National Academy of Sciences of the United States of America, 114(46), 12103–12105. https://doi.org/10.1073/pnas.1717178114
What is the research about?
This commentary critiques climate-economy models (CEMs) and their ethics, which often make certain assumption about how population growth interacts with climate change.
What are the key takeaways?
CEMs still use gross domestic product and income as a measure for human wellbeing, which then leads to the questionable practice of putting a price on the value of a human life lost due to climate change. CEMs also disregard humans as agents who can adapt to challenges presented by climate change. The alternative model of shared socioeconomic pathways (SSPs) illustrate that future population growth can depend on other socioeconomic trends that factor into climate change mitigation and adaptation, which is missing from CEMs. SSPs also take into account the differences between groups of people in terms of age, gender, work, education, income and location.
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Marín-Beltrán, I., Demaria, F., Ofelio, C., Serra, L. M., Turiel, A., Ripple, W. J., Mukul, S. A., & Costa, M. C.,. 2021. Scientists’ warning against the society of waste. Science of The Total Environment, pp. 151359. 10.1016/J.SCITOTENV.2021.151359
What is the research about?
This study quantifies the increases in resource extraction and the subsequent rates that humanity is wasting them. Resources were separated into categories of freshwater, food, metals, fossil fuels and nonmetallic minerals.
What are the key takeaways?
Resource extraction is happening at a disproportionately higher rate than would be predicted by population growth rates. More than 30% of extracted resources are wasted or mismanaged. We need a series of reforms and strategies to shift from a linear economy to a circular economy where outputs can be utilized in a different way and not simply destined for a landfill. A combination of active citizen participation with governmental institutional support would facilitate such reforms.
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Marques, A., Martins, I. S., Kastner, T., Plutzar, C., Theurl, M. C., Eisenmenger, N., … Pereira, H. M. (2019). Increasing impacts of land use on biodiversity and carbon sequestration driven by population and economic growth. Nature Ecology and Evolution, 3(4), 628–637. https://doi.org/10.1038/s41559-019-0824-3
What is the research about?
This study assesses how socioeconomic activities affect biodiversity by looking at bird species richness and reduced carbon sequestration through land-use change.
What are the key takeaways?
Population growth and economic growth between 2000-2011 led to decreases in bird diversity and carbon sequestration. Increasing development and human population will continue to drive biodiversity and carbon sequestration loss. These losses are not always caused by the population of the region they occur in, as international trade complicates these relationships.
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McKee, J., Chambers, E., & Guseman, J. (2013). Human Population Density and Growth Validated as Extinction Threats to Mammal and Bird Species. Human Ecology, 41(5), 773–778. https://doi.org/10.1007/s10745-013-9586-8
What is the research about?
This study tested the hypothesis that human population growth and human population density are correlated with the number of threatened species. The study also aimed to establish whether this can be quantified for future population growth.
What are the key takeaways?
This is the first study to show that continued change in human population densities quantitatively relates to species biodiversity threats. Predictions about extinction threat in 2010 were strongly correlated with observed data. Human population growth was found to be statistically significant with the increase in number of threatened species. Countries that experience a decline in population had a decrease in the number of threatened species, which was due to recovery efforts, not extinction.
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McKee, J. K., Sciulli, P. W., David Fooce, C., & Waite, T. A. (2004). Forecasting global biodiversity threats associated with human population growth. Biological Conservation, 115(1), 161–164. https://doi.org/10.1016/S0006-3207(03)00099-5
What is the research about?
This study tests a model of the association between human population density and the number of threatened mammal and bird species by country.
What are the key takeaways?
Using the model with projected population sizes of each country, the number of threatened species in the average nation is expected to increase 7% by 2020 and 14% by 2050, as predicted by human population growth alone. The results strongly support the idea that reducing human population growth is a necessary step in conserving global biodiversity.
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McKinney, M. L. (2001). Role of human population size in raising bird and mammal threat among nations. Animal Conservation, 4(1), 45–57. https://doi.org/10.1017/S1367943001001056
What is the research about?
This study investigated the relationship between human population size and the extinction threat level of birds and mammals in 150 countries.
What are the key takeaways?
There was a significant relationship between human population size and the threat levels of birds and mammals. Surprisingly, the amount of land area did not influence the level of threat despite the expectation that more land would lower threat levels since it provides more space for wildlife. This could be because human impacts are so extensive that it takes only a few people to cause high extinction threat levels.
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Mora, C., & Sale, P. (2011). Ongoing global biodiversity loss and the need to move beyond protected areas: a review of the technical and practical shortcomings of protected areas on land and sea. Marine Ecology Progress Series, 434, 251–266. https://doi.org/10.3354/meps09214
What is the research about?
If protected areas are failing to protect biodiversity, support for conservation could be lost and we need to consider different solutions. This paper reviews the existing literature and data on the ability of protected areas to prevent the loss of biodiversity without additional actions that address stabilizing population growth and associated ecological demands.
What are the key takeaways?
We will not be able to slow down biodiversity loss without changing our current levels of consumption. Reducing human population growth and consumption is cited as the only scenario to effectively address the underlying causes of biodiversity loss. The authors call for prioritizing solutions that fulfill human needs and also protect human welfare, along with noting the effectiveness of advocating from social, economic and ecological perspectives.
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Murtaugh, P. A., & Schlax, M. G. (2009). Reproduction and the carbon legacies of individuals. Global Environmental Change, 19(1), 14–20. https://doi.org/10.1016/j.gloenvcha.2008.10.007
What is the research about?
This study estimates the additional carbon dioxide emissions produced when a person has children.
What are the key takeaways?
In the United States each child adds about 9,441 tons of CO2 to the carbon legacy of their parent, which is over 5 times the parent’s lifetime emissions. Reproductive decisions should be discussed when making suggestions for how individuals can reduce their own environmental impact. Having one less child saves 20 times more emissions than six other green actions (improved fuel economy, reducing miles driven, improving energy efficiency at home, recycling, etc.) combined over the course of a lifetime.
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Naidoo, R., & Adamowicz, W. L. (2001). Effects of economic prosperity on numbers of threatened species. Conservation Biology, 15(4), 1021–1029. https://doi.org/10.1046/j.1523-1739.2001.0150041021.x
What is the research about?
This studied analyzed the connection between numbers of threatened species and per capita gross national product in over 100 countries. Results were broken out into seven categories of taxa (birds, mammals, reptiles, amphibians, fish, invertebrates and plants).
What are the key takeaways?
Most taxa saw an increase in number of threatened species with an increase in per capita gross domestic product, with the exception of birds, which had a decrease in number of threatened species. Getting a better understanding of this relationship between economics, biology and conservation would be useful for future policy developments.
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Ordaz-Németh, I., Sop, T., Amarasekaran, B., Bachmann, M., Boesch, C., Brncic, T., Caillaud, D., Campbell, G., Carvalho, J., Chancellor, R., Davenport, T. R. B., Dowd, D., Eno-Nku, M., Ganas-Swaray, J., Granier, N., Greengrass, E., Heinicke, S., Herbinger, I., Inkamba-Nkulu, C., … Kühl, H. S.,. 2021. Range-wide indicators of African great ape density distribution. American Journal of Primatology, 4, pp. e23338. 10.1002/AJP.23338
What is the research about?
This study investigated how different socioeconomic factors can affect great ape density throughout Africa.
What are the key takeaways?
Areas with high human footprint index and gross domestic product had the lowest densities of great apes. Only 10.7% of apes were in areas with legal protections, so conservation outside of these protected areas is necessary.
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O’Bryan, C. J., Allan, J. R., Holden, M., Sanderson, C., Venter, O., Di Marco, M., … Watson, J. E. M. (2020). Intense human pressure is widespread across terrestrial vertebrate ranges. Global Ecology and Conservation, 21, e00882. https://doi.org/10.1016/j.gecco.2019.e00882
What is the research about?
This study assesses the extent of intense cumulative human pressures on the geographic range of more than 20,000 terrestrial vertebrate species. This included several metrics that illustrate the intense effects of a growing human population, such as more space for people (population density and built environments), more food to feed them (crop lands and pasture lands), and more systems to support them (roads, railways, electric infrastructure).
What are the key takeaways?
There is substantial scientific evidence pointing to the destructive effects of interacting threats on biodiversity, but many species lack information on their exposure to cumulative human pressures since most studies focus on specific individual threats. Results show that 85% (17,517) of the terrestrial vertebrate species assessed have over half of their range exposed to intense human pressure, with 16% (3,328) of the species being entirely exposed to this amount of pressure.
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O’Neill, B. C., Dalton, M., Fuchs, R., Jiang, L., Pachauri, S., & Zigova, K. (2010). Global demographic trends and future carbon emissions. Proceedings of the National Academy of Sciences of the United States of America, 107(41), 17521–17526. https://doi.org/10.1073/pnas.1004581107
What is the research about?
This study provided an assessment for how various scenarios of changes in demography could affect carbon dioxide emissions globally. This assessment took a more detailed approach that included population size, age structure and urbanization, which have been left out or oversimplified in previous analyses.
What are the key takeaways?
The results show that slowing population growth could provide 16-29% of the emissions reductions needed to stay below a 2 degree Celsius temperature increase. Population composition can also affect emissions, and aging can reduce emissions by up to 20% in developed countries. This analysis also suggest that improved family planning policies could help in certain regions (like the United States and developing regions other than China) that account for half of the total reductions that results from lower population growth.
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Pezzulo, C., Nilsen, K., Carioli, A., Tejedor-Garavito, N., Hanspal, S. E., Hilber, T., James, W. H. M., Ruktanonchai, C. W., Alegana, V., Sorichetta, A., Wigley, A. S., Hornby, G. M., Matthews, Z., & Tatem, A. J.,. 2021. Geographical distribution of fertility rates in 70 low-income, lower-middle-income, and upper-middle-income countries, 2010–16: a subnational analysis of cross-sectional surveys. The Lancet Global Health, 9(6), pp. e802–e812. 10.1016/S2214-109X(21)00082-6
What is the research about?
This study analyzed the geographical variation of fertility rates within 70 different countries to better understand patterns of fertility determinants like contraception use and education.
What are the key takeaways?
There was significant variation in fertility rates across regions within countries. While higher fertility rates tended to be correlated with lower rates of contraceptive use, access to family planning and education, not all patterns were the same. For example, higher teen pregnancy rates were not always seen with overall higher total fertility rates. Also, there was sometimes more similarity in total fertility rates of spatially close regions, even if they were separated by their countries’ border. This illustrates the need for policies and programs that are tailored at a more fine-grain scale (rather than exclusively at the national level) to specific areas and their needs.
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Ripple, W. J., Wolf, C., Newsome, T. M., Barnard, P., & Moomaw, W. R. (2020). World Scientists’ Warning of a Climate Emergency. BioScience, 70(1), 8–12. https://doi.org/10.1093/biosci/biz088
What is the research about?
This paper with over 11,000 scientist signatories from around the world declares that Earth is facing a climate emergency and identifies key solutions.
What are the key takeaways?
The climate crisis is closely correlated to excessive consumption of the wealthy lifestyle. Economic and population growth are among the key drivers of increasing CO2 emissions. Population must be stabilized — and, ideally, gradually reduced — within a framework that guarantees human rights. There are proven policies that strengthen human rights while lowering fertility rates and lessening the impacts of population growth on greenhouse gas emissions and biodiversity loss. These policies improve availability of family planning services, remove barriers to access and achieve gender equity, including primary and secondary education as a global standard, especially women and girls.
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Ricketts, T. H., Dinerstein, E., Boucher, T., Brooks, T. M., Butchart, S. H. M., Hoffmann, M., … Wikramanayake, E. (2005). Pinpointing and preventing imminent extinctions. Proceedings of the National Academy of Sciences of the United States of America, 102(51), 18497–18501. https://doi.org/10.1073/pnas.0509060102
What is the research about?
This study evaluated locations of species facing impending extinction. It also looked at the level of protection these areas have and the amount of human activity happening nearby.
What are the key takeaways?
794 highly threatened species that exist in single locations were identified across 595 sites. The average human population density surrounding these areas is three times the global average and twice the average of similar ecosystems. The average human footprint of surrounding areas was over double the global average. Prioritizing conservation of these areas and preventing further species loss needs site-specific actions, but also needs to consider actions the broader surrounding area.
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Schneider-Mayerson, M. (2021). The environmental politics of reproductive choices in the age of climate change. Environmental Politics, 1–21. https://doi.org/10.1080/09644016.2021.1902700
What is the research about?
This study asked 607 Americans identified as climate leftists: How are people who are factoring climate change into their reproductive choices thinking about these decisions?
What are the key takeaways?
Environmental political considerations factor into some people’s reproductive plans and reproductive choices. This was broken down into 4 categories: parental investment in environmental politics; children as future environmentalists; the opportunity cost of parenting; and fertility as a sociopolitical tool. For those who identify climate change as a reason to have children, they view their families as motivation to work toward a better future and raise future environmentalists. For those that see climate change as a reason not to have children, some discussed the tradeoff in energy needed to be involved in environmental politics vs parenting, while others see their choice as a statement about the urgency of the climate crisis.
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Schneider-Mayerson, M., & Leong, K. L. (2020). Eco-reproductive concerns in the age of climate change. Climatic Change, 163(2), 1007–1023. https://doi.org/10.1007/s10584-020-02923-y
What is the research about?
This article reviews the results of the first empirical study asking young people how climate change factors into their reproductive choices.
What are the key takeaways?
Nearly 60% of respondents reported being “very” or “extremely concerned” about the carbon footprint of having kids. Over 96% of respondents were “very” or “extremely concerned” about the well-being of their current, future or hypothetical children in a world changed for the worse by climate change. The amount to which climate change was factored in varied widely and was often one of several factors respondents considered in their decision whether or not to have kids.
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Scovronick, N., Budolfson, M. B., Dennig, F., Fleurbaey, M., Siebert, A., Socolow, R. H., … Wagner, F. (2017). Impact of population growth and population ethics on climate change mitigation policy. Proceedings of the National Academy of Sciences of the United States of America, 114(46), 12338–12343. https://doi.org/10.1073/pnas.1618308114
What is the research about?
This study looked at how future population is valued affects climate change mitigation decisions. Two approaches to valuing population were explored: increasing the number of people who are happy or increasing the average level of people’s happiness.
What are the key takeaways?
Whether lowering population growth entails overall improvements in wellbeing — rather than merely cost savings — depends on the ethical approach to valuing population. One way values additional people that increase the number of people who are happy over the climate damages and necessary mitigation costs and the other values a smaller population to avoid those costs. These considerations need to be discussed when deciding climate policy.
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Sellers, S. (2020). Gender and Climate Change in the United States: A Reading of Existing Research. Retrieved from www.wedo.org.
What is the research about?
This report reviews the current literature about climate change and focuses on how gender plays a part in climate change experiences in the United States.
What are the key takeaways?
Both men and women face disproportionate effects of climate change in different ways. Men who often have greater exposure to the outdoors based on their jobs will have more encounters with heat-related or infectious diseases. Women are more affected by gender-based violence, which has been linked to natural disasters due to increases in mental and emotional stress. Women also face poor maternal and infant health outcomes related to consistently high temperatures. Indigenous women are disproportionately affected by the sex trafficking spurred by extractive industries like mining and oil drilling. Natural disasters can affect contraceptive use, particularly for people of color, potentially resulting in more unprotected sex and increased rates of unintended pregnancy. Disasters can limit one’s access to their doctor to receive contraception or disrupt their use of contraception if they had to evacuate. After Hurricane Ike Black women were more than twice as likely than white women to lack access to contraception.
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Seto, K. C., Güneralp, B., & Hutyra, L. R. (2012). Global forecasts of urban expansion to 2030 and direct impacts on biodiversity and carbon pools. Proceedings of the National Academy of Sciences of the United States of America, 109(40), 16083–16088. https://doi.org/10.1073/pnas.1211658109
What is the research about?
This study provides forecasts of urban land-cover change and the effects on habitat in biodiversity hotspots and tropical carbon storage and biomass.
What are the key takeaways?
Urban land cover is expected to triple by 2030 from 2000 amounts if current trends in population density continue. Some of the highest rates in growth are predicted to happen in areas that were relatively undeveloped in 2000. Critical biodiversity hotspot habitat will be lost if these patterns continue. The long-term environmental impacts of infrastructure associated with sprawl and urbanization need to be considered when developing urbanization policies.
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Smith, J. A., Suraci, J. P., Clinchy, M., Crawford, A., Roberts, D., Zanette, L. Y., & Wilmers, C. C. (2017). Fear of the human ‘super predator’ reduces feeding time in large carnivores. Proceedings of the Royal Society B: Biological Sciences, 284(1857), 20170433. https://doi.org/10.1098/rspb.2017.0433
What is the research about?
This study observed the reactions of pumas to predator (human) and non-predator control (frog) sounds at puma feeding sites to measure fear responses to humans and the effects on feeding.
What are the key takeaways?
Pumas fled more often, took longer to return, and reduced their overall feeding time by more than half in response to hearing the human “super predator,” which demonstrates that fear is driving an ecological cascade from humans to increased puma predation on deer. The fear of humans can cause a strong reduction in feeding by pumas and may alter the ecological role of large carnivores.
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Song, Y., Zajic, C. J., Hwang, T., Hakkenberg, C. R., & Zhu, K.,. 2021. Widespread Mismatch Between Phenology and Climate in Human-Dominated Landscapes. AGU Advances, 2(4), pp. e2021AV000431. 10.1029/2021AV000431
What is the research about?
This study investigated how global human activity and land use affects how plants shift their timing of regular seasonal events in relation to the warming climate.
What are the key takeaways?
Plants are predicted to change their seasonal cycle timing based on climate change, but their adaptations are currently being outpaced in human-dominated landscapes, which can have a negative effect on biodiversity and ecosystem productivity. This relationship is exacerbated with increased population density.
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Stephenson, J., Newman, K., & Mayhew, S. (2010). Population dynamics and climate change: What are the links? Journal of Public Health, 32(2), 150–156. https://doi.org/10.1093/pubmed/fdq038
What is the research about?
This paper describes the relationship between population growth and climate change through mitigation and adaptation. It also reviews recommendations for action.
What are the key takeaways?
Climate change is driven by consumer behavior in population in addition to population numbers.
The main cause of climate change is high consumption by those in higher-income nations with lower population growth, while lower-income, high-fertility nations face a greater impact.
Almost all (37 of 40) National Adaptation Programs of Action (NAPA) reports refer to population growth as a significant factor that exacerbates the harmful impacts of climate change. “Contraction and convergence” is a strategy that seeks to reduce overall carbon emissions to a sustainable level, where high-consuming countries drastically reduce their emissions and low-consuming countries increase their emissions to a sustainable “ceiling.” Population is a major factor in the feasibility of this strategy.
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Venter, O., Sanderson, E. W., Magrach, A., Allan, J. R., Beher, J., Jones, K. R., Possingham, H. P., Laurance, W. F., Wood, P., Fekete, B. M., Levy, M. A., & Watson, J. E. M.,. 2016. Sixteen years of change in the global terrestrial human footprint and implications for biodiversity conservation. Nature Communications, 7. 10.1038/NCOMMS12558
What is the research about?
This study measured change in the extent of cumulative human pressure on the planet using several variables, including: built environments, crop land, pasture land, human population density, night-time lights, railways, roads and navigable waterways.
What are the key takeaways?
Humanity’s footprint has increased by 9% over the past 16 years. Land suitable for agriculture was particularly vulnerable to increased human pressure. Areas with a high biodiversity and high numbers of threatened species are also experiencing high levels of human pressure. Habitat restoration could be most beneficial in recently developed areas before they experience drastic species loss.
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Wackernagel, M., Schulz, N. B., Deumling, D., Linares, A. C., Jenkins, M., Kapos, V., … Randers, J. (2002). Tracking the ecological overshoot of the human economy. Proceedings of the National Academy of Sciences of the United States of America, 99(14), 9266–9271. https://doi.org/10.1073/pnas.142033699
What is the research about?
This study quantifies the amount of human demand on the environment as a measure of impact on the biosphere.
What are the key takeaways?
Humanity’s demands have surpassed Earth’s capacity since the 1980s. Our demands increased from 70% of the biosphere’s capacity in 1961 to 120% in 1999. These measurement methods can also be used to estimate the effectiveness of solutions.
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Wake, D., & Vredenburg, V. (2008). Are we in the midst of the sixth mass extinction? A view from the world of amphibians. Proc. Natl Acad. Sci. USA, 105, 11466–11473.
What is the research about?
This study provides a global assessment demonstrating that one third or more of 6,300 species of amphibians are threatened with extinction.
What are the key takeaways?
Many pollutants that are detrimental to amphibians are byproducts of human activities. Humans are also responsible for the introduction of exotic species that have consequences for amphibians. And as humans continue to spread into new areas, they risk transmitting novel infectious diseases to populations of species that have not encountered it before.
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Weinzettel, J., Hertwich, E. G., Peters, G. P., Steen-Olsen, K., & Galli, A. (2013). Affluence drives the global displacement of land use. Global Environmental Change, 23(2), 433–438. https://doi.org/10.1016/j.gloenvcha.2012.12.010
What is the research about?
This study seeks to better understand how international supply chains to final consumption impact the use of land and water by modeling agricultural, food, and forestry products while also including the land requirements of manufactured goods and services.
What are the key takeaways?
Increasing affluence is often suggested as a driver for the human impact on biologically productive areas and identified among the causes of biodiversity loss, but international trade complicates these relationships. The land and ocean area footprint of nations increased by a third for each doubling of income, with all variables analyzed on a per capita basis. This increase came largely from imports, which increased proportionally to income, demonstrating the disproportionate impact wealthier countries have because of higher consumption.
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Wiedmann, T., Lenzen, M., Keyßer, L. T., & Steinberger, J. K. (2020). Scientists’ warning on affluence. Nature Communications, 11(1), 1–10. https://doi.org/10.1038/s41467-020-16941-y
What is the research about?
This study reviews the evidence for how the consumption of affluent, high-income nations bears the most responsibility for emissions, pollution and environmental degradation.
What are the key takeaways?
Income is strongly correlated with consumption, which affects environmental impact, so income inequalities will also lead to major differences in impact as well. Capitalist and growth-driven economies are responsible for increasing affluence, resource consumption and resulting environmental pressures. Reducing consumption is more important that just making consumption “greener.” Sustainable lifestyles exist between an upper bound of sustainable use (environmental ceiling) and a lower bound of necessary use of environmental resources to meet needs and avoid poverty (social foundation).
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Williams, J. N. (2013). Humans and biodiversity: Population and demographic trends in the hotspots. Population and Environment, 34(4), 510–523. https://doi.org/10.1007/s11111-012-0175-3
What is the research about?
This study seeks to quantify the amount of population growth occurring in biodiversity hotspots in order to understand and better mitigate habitat loss.
What are the key takeaways?
The population growth rate declined from 1.6% to 1.3% in biodiversity hotspots but the total population increased by 187 million people. These slower growth rates are the result of trends in decreasing fertility, aging populations and increased urbanization. The hotspots are mostly populated by younger people who haven’t entered their reproductive years or are in the early stages. This means that populations in these priority conservation areas will grow, despite declining birth rates. As a result, biodiversity conservation in these areas may face obstacles.
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Woodroffe, R. (2000). Predators and people: using human densities to interpret declines of large carnivores. Animal Conservation, 3(2), 165–173. https://doi.org/10.1111/j.1469-1795.2000.tb00241.x
What is the research about?
This paper explores the effect of people on predators by looking at the relationship between carnivore extinctions to past and projected human population densities.
What are the key takeaways?
There is a correlation between high human density and loss of carnivore populations from an area. Variations in species sensitivity probably has more to do with local human activities rather than species life history. This is due to differences in the culture, policy and trade of local areas which impact humans’ relationships with resident predators. The effect of these factors could mean that even as human population growth slows, carnivore extinction rates could increase.
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World Wildlife Fund. (2020). Living Planet Report 2020 - Bending the curve of biodiversity loss.Retrieved from https://livingplanet.panda.org/en-us/
What is the research about?
This report gives an overview of how the continued destruction of nature from human activity is having disastrous effects on wildlife populations, human health and all aspects of our lives.
What are the key takeaways?
One of the biggest causes of biodiversity loss has been land-use change driven by the doubling of the world’s human population, a fourfold increase in the global economy, and a tenfold increase in trade. Human population growth is categorized as an indirect driver underlying human pressure and activities that contribute to the direct drivers of biodiversity loss.
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York, R., Rosa, E. A., & Dietz, T.,. 2003. Footprints on the earth: The environmental consequences of modernity. American Sociological Review, 68(2), pp. 279–300. 10.2307/1519769
What is the research about?
This study tests the accuracy of several environmental impact theories (human ecology, modernization and political economy) using an iteration of the Impacts=Population x Affluence x Technology (IPAT) framework and ecological footprint as measurement.
What are the key takeaways?
Population affects environmental impact proportionally, which is consistent with human ecology theory. GDP per capita drives increased environmental impact, which is consistent with political economy theory. Thus, both population and consumption have environmental consequences. This is also contrary to modernization theory, which predicts a plateau and decline after a certain level of development is reached, along with the finding that urbanization increases impacts. Even a slow growth rate in affluent countries with high consumption can be considered a substantial environmental threat.
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