Even if global temperatures begin to decline after peaking this century due to climate change, the risks to biodiversity could persist for decades after, finds a new study by UCL and University of Cape Town researchers. The paper — published in Philosophical Transactions of the Royal Society B: Biological Sciences journal — models the potential impacts on global biodiversity if temperatures increase by more than 2°C compared to pre-industrial levels before beginning to decline again. The Paris Agreement signed in 2015 aims to limit global warming to well below 2°C, preferably to 1.5°C. However, as global greenhouse gas emissions continue to increase, many scenarios now feature a multiple decades-long 'overshoot' of the Paris Agreement limit, then factor in the effects of potential carbon dioxide removal technology to reverse dangerous rises in temperature by 2100. Climate change and other human influences are already causing an ongoing biodiversity crisis, with mass die-offs in forests and coral reefs, altered species distributions and reproductive events, and many other ill effects. Co-author Alex Pigot of the UCL Centre for Biodiversity and Environment Research at UCL Biosciences said: "We have investigated what will happen to global biodiversity if climate change is only brought under control after a temporary overshoot of the agreed target to provide evidence that has long been missing from climate change research." "We found that huge numbers of animal species will continue to endure unsafe conditions for decades after the global temperature peak. Even if we collectively manage to reverse global warming before species are irreversibly lost from ecosystems, the ecological disruption caused by unsafe temperatures could well persist for an additional half century or more. Urgent action is needed to ensure we never approach, let alone exceed, the 2°C limit." The study examined more than 30,000 species in locations around the world and found that for more than a quarter of the locations studied, the chances of returning to pre-overshoot normalcy are either uncertain or non-existent. The paper focuses on one overshoot scenario in which CO2 emissions keep growing until 2040 then reverse their course and fall into negative territory after 2070 thanks to deep carbon cuts and massive deployment of carbon dioxide removal technology. This means that, for several decades in this century, global temperatures surpass 2°C and then fall below this level around 2100. The researchers looked at when and how quickly the species in a particular location would get exposed to potentially dangerous temperatures, how long that exposure would last, how many species it would affect, and whether they would ever get de-exposed, returning to their thermal niche. According to previous research published in Nature, the research team found that, for most regions, exposure to unsafe temperatures will arrive suddenly and many species will simultaneously be pushed beyond their thermal niche limits. However, the return of these species to conditions comfortably within their thermal niches will be gradual and will lag behind the global temperature decline due to continually volatile climatic conditions within local sites and lasting changes to ecosystems. The effective overshoot for biodiversity risks is projected to be between 100 and 130 years, around twice as long as the actual temperature overshoot of around 60 years.
