When you’re sipping coffee in the morning, half a degree Celsius probably won’t push the drink into tongue-scalding temperatures. But in the global climate system, half a degree of warming is enough to upturn ecosystems everywhere.
Even though countries pledged in the 2015 Paris Agreement to limit global warming to less than 2° C and to aim for only 1.5° C, scientists hadn’t fully analyzed the differences in how those two climate benchmarks would affect the planet. Now, a team of climate scientists has parsed out what an extra half-degree would mean. What they found isn’t pretty.
While 1.5 degrees of warming would lead to greater heat extremes and droughts, the changes would be comparable to extremes that we’ve lived through in modern times. But with 2°, the climate system gets pushed over the edge—we would live under a new climate regime. Water availability would fall by 30% in a broad belt around the equator. Regions closer to the poles, in contrast, would experience more frequent extreme storm systems. Big chunks of the global crop harvest would fail, especially in tropical countries that are already vulnerable to food shortages.
Reef ecosystems would also hang in the balance. The study’s authors write that “this warming difference is likely to be decisive for the future of tropical coral reefs.” Here’s Damian Carrington, reporting for the Guardian:
Coral reefs, which provide vital nurseries for many fish on which people rely on for food, would be particularly affected by an additional 0.5C of warming. “In a [2C] scenario, virtually all tropical coral reefs are projected to be at risk of severe degradation due to temperature-induced bleaching from 2050 onwards.” This is reduced to 70% by 2100 for the 1.5C scenario, the scientists found.
Jacob Schewe, one of the research team and at the Potsdam Institute for Climate Impact Research in Germany, said: “Some researchers have argued that there is little difference in climate change impacts between 1.5C and 2C. Indeed, it is necessary to account for natural variability, model uncertainties, and other factors that can obscure the picture. We did that in our study, and by focusing on key indicators at the regional level, we clearly show that there are significant differences in impacts.”
For now, the amount of warming stands at 1.34° C. So far in the United States, this has meant that shifts in average temperatures have actually led to conditions many people prefer, the AP reports. Winters have been 1° F warmer on average, and summer heat has only increased by a fraction of a degree. Since the effects of climate change will—in many cases—be gradual until we reach 2° C, it could be difficult for some Americans to realize what’s happening until too late.