We’re at a turning point: The choices that the world makes now will determine how livable the planet is later this century. We know what climate change looks like in 2021. This summer was the hottest on record; hundreds died in unprecedented heat in the Pacific Northwest, and there were widespread power outages in the Middle East, where temperatures topped 125 degrees Fahrenheit. In basements in New York City and subways in China, people were trapped by floods. Massive wildfires burned in Canada and Siberia and Greece. In Madagascar, after four years without rain, the country is facing the first famine caused entirely by climate change.
But this isn’t the “new normal.” As emissions keep growing, things can get much, much worse. The planet has heated up so far a little more than 1 degree Celsius. By the end of the century, we may have managed to limit warming to 1.5 degrees Celsius, the most ambitious goal in the Paris climate agreement. Or, if we’re slower to act, the average temperature may have soared up to 2 or 3 degrees Celsius, or more—differences that sound small, but in reality, will shape very different futures. (Consider the fact that 3 million years ago when the planet was hotter by 3 degrees Celsius, sea levels were as much as 50 feet higher, and giant camels lived in Arctic forests—not things that are going to happen this century but that illustrate the scale of what’s possible with a change of only a few degrees.)
Everything depends on how quickly businesses and governments and the rest of society change course this decade, and the next, and the next. “If we work around the edges of emissions reductions, kind of what we’re doing right now, let’s face it—we’ll definitely be into a 3-to-4-degree Celsius warming level [by the end of the century],” says Kim Cobb, a climate scientist at Georgia Tech. “If not more.” In a recent report, the United Nations warned that the plans countries have to cut emissions put the Earth on track to warm up more than 2.7 degrees Celsius by 2100, something the report emphasizes would be catastrophic—and that’s only if countries actually succeed in meeting those pledges. The numbers may seem abstract, but here’s a look at how they translate into impacts.
To imagine the planet after 3 degrees of warming, take the example of Australia, where catastrophic wildfires, fueled by ongoing drought and heat, burned an area larger than the state of Florida in late 2019 and early 2020—blanketing cities in smoke and killing or displacing 3 billion animals. Climate change has already increased the number of extreme fire risk days in the country. If the global temperature heats up by 3 degrees, something that’s plausible under the current path, the number of extreme fire risk days could double or even quadruple.
A recent report details other ways the country is likely to change. With 3 degrees of global warming, as many as 250,000 properties along the coast will risk flooding. Australia will also face more extreme heat. In Melbourne, the number of days hotter than 95 degrees Fahrenheit could double, from 11 to 24. In Darwin, in the country’s northern territory, the number of days hotter than 95 degrees Fahrenheit could jump from 11 to an average of 265 days.
Heat will impact daily life: Outdoor sports, for example, might have to move inside. Outdoor work will become more dangerous. But it will also impact larger systems. In the ocean, coral reefs will likely disappear; heat has already killed about half of the Great Barrier Reef. Hotter, more acidic oceans will impact fishing. Because of heat, drought, and the increasing numbers of pests, it will be harder to grow food; and yields of key crops could fall between 5% and 50%.
The rest of the world will face similar challenges, with the specific set of problems varying in each location. In low-lying Bangladesh, as sea levels rise, millions of people will likely be forced to relocate. Large swaths of major cities will flood, from Shanghai (where 17.5 million people may be displaced) to Alexandria, Egypt, to Miami; globally, hundreds of millions of people may have to relocate.
In some tropical countries, the combined levels of heat and humidity may grow so high during heat waves that it surpasses the limit of what human bodies can survive. (In India, this type of extreme heat stress may happen even at lower levels of climate change.) Droughts that are currently considered once-in-a-century events could happen every two to five years in much of the world, including parts of the U.S. As farms struggle with droughts, heat, and sometimes extreme rain, food prices will rise. The Amazon rainforest may not survive. Antarctic ice sheets will melt faster, pushing sea levels higher.
It’s very possible that the world will heat up even more, depending on both how slowly we act and how the natural world changes—rainforests, for example, which have played a critical role in absorbing carbon, are beginning to emit more carbon than they absorb. If the planet passes 4 degrees Celsius of warming, life will be considerably bleaker. The risk of extreme heat, hurricanes, fires, and other impacts will increase even more. Many of the glaciers that feed rivers in Asia will be lost. Much of Europe could become a desert. The area where people can live—and feasibly grow food—will significantly shrink. “A [4-degree Celsius] warmer world may well be survivable, but it would be eminently poorer than the one we currently enjoy,” journalist Gaia Vince writes in the Guardian.