At first glance, Monday's long-awaited report from the Intergovernmental Panel on Climate Change was bleak. It found that some consequences of human-driven emissions are irreversible for centuries to millennia, and that warming will continue to some extent over the next two to three decades, regardless of how much emissions drop.
But the assessment also emphasizes that the worst-case climate disasters aren't inevitable: Every half-degree of warming that can be averted makes a huge difference — including in the intensity and frequency of extreme heat, rainfall, and drought. Even incremental reductions in emissions today would stave off more catastrophic events in the coming decades.
The IPCC report comes from a working group of hundreds of scientists whose last assessment was in 2013. This new report shows that human-caused emissions have led the planet to warm by 1.1 degrees Celsius in the last 170 years. Some glacial melting and sea-level rise will continue for millennia, no matter what happens next.
But Youba Sokona, vice-chair of the IPCC, highlighted a more optimistic takeaway: "We are in the right moment to completely change the direction we are taking," he told Insider.
In the IPCC's worst-case scenario, global emissions would double by 2050, causing temperatures to rise an average of 2.4 degrees Celsius between 2041 and 2060. But in the best-case scenario, the global temperature would rise just 1.5 degrees between now and 2040, then dip back down by the end of the century.
That means there's still time to act.
"It is virtually certain that global surface temperature rise and associated changes can be limited through rapid and substantial reductions in global greenhouse-gas emissions," the IPCC authors wrote.
The world has some time to lower emissions
In the Paris agreement, world leaders pledged to cut greenhouse-gas emissions enough to keep global temperatures from rising more than 1.5 degrees Celsius above pre-industrial levels. Now, Earth's temperature is very likely to blow past that mark in the next 20 years, according to the IPCC report.
But the Paris agreement's larger goal was to avoid a 2-degree rise at all costs. That's still possible, scientists say.
"It's very likely that we'll exceed 1.5 degrees," Greg Flato, a climate scientist from the Canadian Center for Climate Modeling and one of the new report's co-authors, told Insider. "It's possible to exceed slightly and stabilize if we follow a pathway of deep emissions cuts by midcentury."
Already, the world cut carbon emissions by 2.5 billion tons in 2020, since pandemic-related lockdowns meant fewer vehicles on the road, planes in the sky, and less collective electricity use at peak times. That's a roughly 6% decline from the year prior, following decades of rising global emissions.
"The lesson we can learn from that is that we can change our behavior drastically in the short term," Sokona said.
The IPCC found that every trillion tons of carbon emitted leads the world's temperature to rise roughly 0.45 degrees. To stay under the 2-degree threshold, we have about 900 billion tons of carbon left in the budget. In 2019, emissions reached about 37 billion tons — so if that rate continues and no carbon gets removed from the atmosphere, we'd have about 25 years remaining.
There's still time to mitigate extreme heatwaves, drought, and floods
A difference of half a degree may sound minor, but avoiding that increase would make the difference between extreme and deadly heatwaves, droughts, and floods and milder, less frequent versions of these events.
At 2 degrees of warming, extreme temperature changes could be twice as pronounced as they would be at 1.5 degrees, the IPCC report found. Globally, the chance of at least three months of drought per year would rise from about 20% at a 1.5-degree temperature rise to 35% at 2 degrees.
The Atlantic Meridional Overturning Circulation (AMOC), meanwhile, could lose nearly 30% of its pre-industrial strength if global temperatures rise anywhere between 1.5 and 2 degrees Celsius. This system of ocean currents moves warm water from the equatorial tropics up to Europe and the north Atlantic. The influx of warmer water contributes to western Europe's mild, temperate climate, so if the current gets weaker, it could result in more intense winters in some places and more frequent heatwaves and droughts in others.
Higher temperatures will also shrink the planet's ice sheets, snow cover, glaciers, and permafrost — a layer of soil that used to stay frozen year-round. As permafrost thaws, it releases carbon, which traps heat and contributes to additional warming. With each degree of warming, the top 3 meters of permafrost could lose 20-30% of its volume, the IPCC found.
Even if humanity doesn't wind up avoiding all of these disasters, the report at least tells policymakers what's in store.
"Having that information today allows us to begin the actions that will make us ready a decade from now, mid-century, and at the end of the century," Alex Ruane, one of the report's lead authors, told Insider.
"This provides a kind of roadmap, or at least a forewarning, of the types of changes that we have to be prepared for," Ruane said, adding, "This is where my optimism lies."
