Climate Change Extinction Risk
The impacts of climate change are intensifying, and according to the most recent United Nations Emissions Gap Report, we need to take dramatic action if we are to remain below 1.5C of warming. The climate crisis significantly threatens global biodiversity, and effective conservation policies and efforts to mitigate disastrous outcomes rely on accurate models and predictions. To increase certainty in available models, UConn Department of Ecology and Evolutionary Biology Professor Mark Urban analyzed 485 studies, comprising over 5 million projections, to create a global assessment of climate change extinctions. The study is published in Science. Urban met with UConn Today to discuss his findings.
Can you discuss the analysis and why meta-analyses like this are important?
Although many scientists have made predictions about extinction risks from climate change for specific regions or species, it is critical that we understand the big picture for how climate change affects all species. One way to understand the broader picture is to analyze all the analyses – called a meta-analysis – which estimates an overall effect (in this case of extinction risk) while accounting for uncertainty. The meta-analysis also provides the opportunity to test how results vary by different factors, such as species, region, and model assumptions for this research.
In 2015, I performed a meta-analysis on climate change extinctions and thought I was done. However, an explosion of new studies, and, frankly, my dissatisfaction with other assessments, led me to redo this analysis in 2024. My goal was to provide the most up-to-date, transparent, and comprehensive assessment of extinction risk from climate change – that is performing the global assessment I thought was needed to inform decisions about greenhouse gas emissions.
One thing that I wanted to know was if methods for predicting extinctions had changed over time. I found that scientists now incorporate more sophisticated techniques, especially by including more biological information about individual species such as about their dispersal or interactions with other species. Even expert assessments now commonly include biologically informed analyses of species-specific risks. These newer and more sophisticated predictive approaches should not only provide a better understanding of future extinction risks, but also pinpoint the species most at risk so we can find ways to protect them.
What were your findings, and did anything surprise you?
Whereas past assessments indicated high uncertainties, this analysis suggests with increasing certainty that climate change has caused and will cause global extinctions. Climate change results in an accelerating risk of global extinction, rising from 2% currently to 30% under the highest-emission scenario. Current policies and actions place the world on a path to a 2.8 degrees Celsius rise in global temperature, which would still result in 5% of species being at risk. This study presents a choice for decisionmakers: Will we curb emissions now and only need to protect 2% of species at risk, or will we choose another path that will fundamentally alter the nature of our world.
The biggest surprise was that I wasn’t surprised. I thought that the results would change with newer, more sophisticated studies. Part of me expected that the early models had exaggerated the risks. I was looking for some good news and was surprised that nothing had changed. At first, I was a bit disappointed, but then I realized an outcome that was both consistent and more certain was exactly what was needed to compel decisionmakers to take action to reduce emissions and increase conservation efforts.
Can you discuss extinction debt and how Earth’s hidden biodiversity impacts extinction risk assessment?
Extinction risk estimates indicate how many species could eventually become extinct at some point in the future. The analogy I like to give is a water jug with a crack in it. We know that the water will eventually flow out, but we do not know exactly when. Extinction debt characterizes all those species that are declining toward extinction (losing water) and will eventually become extinct without interventions. The bad news is that many species might be declining or about to decline due to climate change impacts, but we have not yet recognized these threats. The good news is that we could still mitigate climate change or deploy successful conservation measures to ensure that the debt is not paid.
Earth’s hidden biodiversity refers to the large number of species that remain unnamed or undiscovered. By some estimates, five times more species exist than have been named. Many of these species are likely to have small range sizes or live in threatened hyper-diverse regions like the tropics. These more threatened species are usually not included in extinction models. Thus, the actual extinction risk from climate change could be higher than current estimates. Discovering, researching, and protecting biodiversity will be a grand challenge for scientists in the coming years.
What are your thoughts on the future after the most recent COP?
A huge mismatch exists in that climate change and its impacts are accelerating quickly, but global actions to reduce climate change remain incremental. Although the recent COP 29 (shorthand for the United Nations’ annual summit for climate change negotiations) made some limited progress, much more is needed to prevent the worst effects of climate change. We have now reached 1.5 degrees Celcius and are experiencing the predicted impacts from heat waves, floods, droughts, hurricanes, and extinctions. And every day we wait, it costs us more to mitigate and adapt. Therefore, the world is at a crucial point where actions need to be stronger than impacts. Science already tells us what will happen and what needs to be done, and technological advances have provided us with suitable solutions. We just need courageous leaders to do what needs to be done.
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