In the past, research has predicted that global warming could lead to the extinction of more than one-fifth of animal and plant species. This research has largely been based on theoretical models. However, now observations can confirm whether reality matches theory. The paper Erosion of Lizard Diversity by Climate Change and Altered Thermal Niches (Sinervo 2010) compares global observations of lizard populations from 1975 to present day. The result? Rapidly warming temperatures are causing lizard species to go extinct before our eyes.
How does climate change affect lizard populations? While lizards bask in the morning sun to warm up, they retreat to the shade when temperatures get too hot to avoid heat stress. As it gets hotter, they have less time to forage for food. Warmer springs are particularly devastating as this is when lizards reproduce and need extra food.
Sinervo 2010 first analysed observations of lizard populations in Mexico. Since 1975 when observations began, 12% of local populations have gone extinct. Looking at weather station data, they found a correlation between the change in maximum temperature and local extinctions. The number of hours that lizards were forced to retreat to shade were significantly higher at extinction sites.
There are two ways species can compensate for climate change: adapt or migrate. Temperatures are changing too rapidly for most species to evolve in order to adapt to warmer temperatures. That leaves migration. What is being observed is species are relocating to cooler regions in response to warming temperatures. Lizard populations from lower elevations are expanding up to cooler, higher habitats. This appears to be exacerbating extinction of species already living in higher elevations.
Another important result they found is if we manage to reduce CO2 emissions over the next few decades, this will reduce the number of species extinctions in 2080 but have little effect on the extinctions by 2050. A slow down in global warming will lag atmospheric CO2 levels by decades. This lead the authors to conclude that lizards have already crossed a threshold for extinctions.
JR: Here is the abstract for the Science paper:
It is predicted that climate change will cause species extinctions and distributional shifts in coming decades, but data to validate these predictions are relatively scarce. Here, we compare recent and historical surveys for 48 Mexican lizard species at 200 sites. Since 1975, 12% of local populations have gone extinct. We verified physiological models of extinction risk with observed local extinctions and extended projections worldwide. Since 1975, we estimate that 4% of local populations have gone extinct worldwide, but by 2080 local extinctions are projected to reach 39% worldwide, and species extinctions may reach 20%. Global extinction projections were validated with local extinctions observed from 1975 to 2009 for regional biotas on four other continents, suggesting that lizards have already crossed a threshold for extinctions caused by climate change.