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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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