One in six of the planet’s species will be lost forever to extinction if climate change continues on its current track.
That’s the conclusion of a new meta-analysis of 131 published studies, looking at everything from Costa Rica’s insects to Arctic foxes to California oak trees. The analysis is one of the most comprehensive studies of how biodiversity will fare in a warmer climate. It found that the rate of biodiversity loss doesn’t rise linearly but actually accelerates with each degree of warming – highlighting the need for an urgent change of course.
“If the world does not come together and control greenhouse gas emissions and we allow the Earth to warm considerably we will face a potential loss of one in six species,” warned study author Dr. Mark Urban, an ecologist at the University of Connecticut. “Many species will be able to shift their ranges and keep up with climate change whereas others will not either because their habitat has disappeared or because they can’t reach their habitat anymore.”
The basic premise behind the studies included in the meta-analysis is that climate change reduces the geographic range in which a species can live, and that loss of living space can drive a species to extinction. “Species were predicted to become extinct if their range fell below a minimum threshold,” explained author Dr. Mark Urban in the paper published in Science.
But each study had developed its own model for that process. For instance, they assumed different rates of climate change, and they defined different amounts of range loss as fatal for a species. In this latest analysis, Dr. Urban used statistical methods to combine the data from all of the studies to work out likely extinction rates for different scenarios, like more or less global warming, or higher or lower thresholds of range loss.
Based on predictions about range loss in the 131 studies, 2.8 percent of the world’s species are now at risk. A 2⁰ C increase in global average temperature (compared to pre-industrial levels) would put 5.2 percent of species at risk. Some political leaders around the world have set a goal of limiting global warming to 2⁰ C, though most climate experts now doubt that that goal remains within reach.
At 3⁰ C, Dr. Urban’s model predicts that 8.5 percent of the world’s species would face extinction. But 3⁰ C is still pretty optimistic. The current rate of climate change puts the world’s temperatures on track to increase 4.3⁰ C by the 2060s, which Dr. Urban says would put 16 percent of species at risk for extinction. That would mean the loss of about 1 species out of every 6 in the world today by around the middle of this century unless action is taken to reduce emissions.
According to Dr. Urban’s analysis, the regions hardest hit will be South America, Australia, and New Zealand. In a world that is 4.3⁰ C warmer by mid-century, South America could lose a staggering 23 percent of its species. Australia and New Zealand could lose 14 percent of their species.
These regions are particularly vulnerable, said Dr. Urban, because they’re home to many endemic species (those that live only in one place), which already have very small ranges. Any loss of range could have a big impact on a species which only calls one very small area home. And because Australia and New Zealand are isolated from other landmasses, most of their endemic species can’t move to another habitat even if one existed.
The results highlight how crucial such dispersal ability is to many species’ future survival. As rising temperatures make one habitat unlivable for a species, it may also open up new habitats where the climate wasn’t suitable before. Species who can migrate to those new habitats will have better chances, but species trapped by natural or man-made barriers will be in dire trouble.
Other factors, which many of the studies don’t take into account, can influence a species’ response to climate change. For instance, the risk of extinction is lower for species which can evolve quickly enough to adapt to changing environments, which usually means species with short generations. Interaction between species, such as predation or symbiosis, could shift the odds either way, depending on the interaction. Invasive species, overharvesting, and pollution also increase extinction risks.
“While all species affected by climate change will not become extinct, there will undoubtedly be unwanted changes to contend with,” wrote Dr. Urban. “Even species not threatened directly by extinction could experience substantial changes in abundance, distribution, and in their interactions with other species. In turn, this may affect ecosystems, crop growth, and the spread of disease, and have other unanticipated consequences.”
The findings offer a “sobering estimate of climate change-induced biodiversity loss,” wrote University of Washington biologist Dr. Janneke Hille Ris Lambers in a commentary that accompanies Dr. Urban’s report. The study is only one of many that makes the case that “climate change will have enormous impacts on the organisms with which we share our planet,” she wrote. Despite the uncertainties inherent in making these kinds of predictions, she added, “we should not wait … before taking action, preferentially by curbing emissions.”
The dire projections from Dr. Urban’s analysis mirror those of another recent report, in which an international team of 18 scientists warned that humans are “eating away at our own life support systems” at a rate unseen in the past 10,000 years, damaging the environment so gravely that the Earth will cease to be a “safe operating space” for our species.