How Hot Will It Get? Exploring the Different Heating Scenarios of Climate Change
Key Highlights :
It's no secret that the Earth is getting hotter. In recent years, temperatures have been breaking or nearly breaking records in Phoenix, Arizona, China, Death Valley, California, and Rome. Heat waves are normal, but continuously breaking, nearly breaking, or obliterating heat records isn't. This sustained heat is expected to increase in the coming years as added global warming exacerbates heat waves, and overall temperatures will continue to rise until emissions of heat-trapping greenhouse gasses drop to zero. So, how hot will it get?
The answer is dependent on the most unpredictable part of the climate change equation: Us. More specifically, the amount of fossil fuel emissions, largely from carbon dioxide and methane, humanity loads into the atmosphere. Scientists have created different heating scenarios based ultimately on the choices made by prodigious carbon emitters, world governments, and beyond. It's exceedingly unlikely that we're on the worst pathway, wherein Earth would warm by some 9 or 10 F (around 5 C) above the pre-Industrial Revolution levels of the late 19th century. But, crucially, it will also be challenging to end up with the best, most optimistic outcome, which would mean limiting warming to some 2.7 F (or 1.5 C) above pre-Industrial Revolution levels by this century's end.
Already, Earth has warmed by 2 F (1.2 C) since the late 19th century. About 10 years ago, things looked dire. Fossil fuel use and carbon emissions were continually rising each year. But coal use, while not declining, has largely stopped its yearly growth. What's more, renewable energy – the likes of wind and solar – has vastly expanded, now providing some 13 percent of energy in the U.S. (though renewables are still currently outpaced by fossil fuels both in the U.S. and globally).
This energy change has considerably decreased the likelihood of a worst-case climate scenario. On the other end of extreme scenarios is SSP1-1.9, which would limit warming to just some 2.7 F (1.5 C) above pre-Industrial Revolution levels by the century's end. That's the warming target global leaders hoped to hit when they signed the historic Paris Agreement in 2016. But it's likely humanity will blow through this ambitious warming goal, as soon as the 2030s.
This probably leaves us in the middle ground, which still means significant warming. Crucially, high warming amounts, up to perhaps some 7 F (around 4 C), are still possible and can't be completely ruled out. But such warming is at the extreme edge of what's likely. So how much warming is currently realistic? Something close to the SSP2-4.5 trajectory, which is the middle orange line above, explained Hausfather. That's in the 4.8 F (2.6 to 2.7 C) range above pre-Industrial levels.
Roughly is an important caveat here, because other factors — such as how exactly Earth will respond to future CO2 levels in the atmosphere — are uncertain. Some 4.8 F (2.6 C) of warming this century is still a lot. That's a future any reasonable person would want to avoid. Already, just some 2 F (1.2 C) of warming has stoked momentous changes. The heating has: increased the frequency and intensity of heat waves, worsened air quality, and caused more extreme weather events. Clearly, a world at some 2 F (1.2 C) is problematic, and for some, catastrophic.
So what happens at 3.6 F (2 C), which is around a doubling of today's heat? "A lot of these impacts will double in frequency or severity," Lehner said. That's why limiting the warming, as much as possible, is critical — not just for ourselves, but for the future residents of Earth. They will experience serious sea level rise. But, it doesn't have to be devastating. "Every 10th of a degree matters," Lehner said.
