But the report also contains crucial reasons for hope. It does not find evidence for a single temperature threshold beyond which climate change will spiral out of control. It suggests that the feedback loops that come with high levels of warming — such as melting permafrost that releases more carbon into the atmosphere — are dwarfed by the current human emissions. The scale of increasing temperatures and escalating extremes is directly related to the amount of greenhouse gases people choose to unleash.
In other words, climate change is not a pass/fail course. There is no chance that the world will avoid the effects of warming — we’re already experiencing them — but neither is there any point at which we are doomed.
“The general conclusion is that every bit of warming matters in terms of creating outcomes that are different,” said lead author Claudia Tebaldi, a climate scientist at the Pacific Northwest National Laboratory.
And that means a safer future is still within our grasp.
The world is at a fork in the road on climate. Nations are gearing up for a major U.N. summit this fall in Scotland, where they are expected to significantly increase their commitments to curb greenhouse gases. Depending on the ambition of those commitments — and the actions that follow — we will find ourselves on one of several very different paths.
In the best-case scenario, people rapidly switch from fossil-fuel-powered energy sources to renewable ones. We change the way we travel, construct homes and grow food. We restore ecosystems so they can more effectively soak up carbon dioxide.
If we manage to reach “net zero” emissions in the next few decades, the report finds, we have a good shot at limiting warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) over preindustrial levels — just a few tenths of a degree hotter than the world is now. The world would still have to cope with longer heat waves, more frequent droughts and more intense rainfall during storms. But the scale of those changes would likely be within our capacity to adapt.
That scenario will be difficult to achieve, but it’s still possible, the report says. And even if the world misses that warming target, “we shouldn’t throw up our hands and give up and let everything burn to the ground,” Tebaldi said.
Think about it like a person dealing with health problems as they age, she continued.
“You have the choice of spending your time feeling the doom and gloom of getting old … fearing the future,” she said. “Or you can get up every day and remind yourself that that day is likely going to be the best you have … and you better make the best of it.”
Yes, the planet will get hotter. Sea levels will rise further. Extreme weather will worsen, and more people will suffer.
But any reduction in emissions means that the world is better off than it otherwise would be. Warming of 1.6 degrees Celsius is still preferable to warming of 1.7 degrees, which is better than 2.
And all of those options are better than the scenario in which we do nothing. If the world continues along its current emissions trajectory, the IPCC scientists say, global average temperatures are likely to exceed 2 degrees Celsius (3.6 degrees Fahrenheit) by the middle of the century. By the time today’s infants are collecting social security, average warming could be on its way to 4 degrees Celsius (7.2 degrees Fahrenheit).
In that much hotter reality, major storms will carry 10 percent more rain, and droughts will happen four times as often. The chance of “compound events” — when multiple natural disasters collide to cause drastically more chaos — is significantly higher.
Such intense warming also increases the risk of triggering runaway changes in weather patterns and irreversible losses across the natural world, the report warns. One of the scariest possibilities is the sudden shutdown of the Atlantic Meridional Overturning Circulation, the system of currents that transports heat through the oceans. Recent studies have suggested that the circulation may be close to a tipping point; if it collapses, it could bring extreme cold to Europe and parts of North America, raise sea levels along the U.S. East Coast and disrupt seasonal monsoons that provide water to much of the world.
But the amount of warming needed to disrupt the AMOC is still uncertain. Indeed, the worst-case warming scenario is so far outside the realm of human experience, so much faster than anything observed in the geologic record, that all of the consequences are hard to predict.
Instead of panicking at uncertainty, we should let it motivate us, said University of Oxford researcher Fredi Otto, another lead author of the report.
“We should really use the fact that we cannot exclude these things … to really not go there,” she said. “We don’t want to experience if our world has that potential.”
So what can the average person do about it? Anything that reduces the amount of greenhouse gases in the atmosphere and helps the world adapt to the changes that are already underway.
You can back efforts that will shift the economy away from fossil fuels — by far the biggest source of planet-warming emissions. That could look like giving testimony at a zoning board meeting in favor of renewable energy infrastructure. It could mean lobbying your city’s education department to make its school bus fleet electric. It could involve submitting a supportive comment on legislation that would regulate pollution. (Pretty much all federal agencies are required to accept public comment on rules before they are finalized.)
You can support companies that are taking meaningful steps to curb emissions and stop buying from ones that resist climate action. You can move your retirement account to an investment fund that supports green industries. You can make changes in your own life: eating less meat, switching your gas appliances to electric, using public transit or riding a bike.
And you can do it all knowing that your actions are helping to make the world a little bit cooler and the future a little bit safer.
“Something is always better than nothing,” Tebaldi said. “Every little bit counts.”