A new United Nations–led report from hundreds of climate scientists around the world makes it clear: The human-driven climate crisis is now well under way. Earth is likely hotter now than it has been at any moment since the beginning of the last Ice Age, 125,000 years ago, and the world has warmed 1.1 degrees Celsius, or nearly 2 degrees Fahrenheit, since the Industrial Revolution began—an “unprecedented” and “rapid” change with no parallel in the Common Era. What’s more, the recent spate of horrific heat waves, fire-fueling droughts, and flood-inducing storms that have imperiled the inhabited world are not only typical of global warming, but directly caused by it.
These are the conclusions of the newest assessment report of the Intergovernmental Panel on Climate Change, a UN-sponsored body that has periodically released a synthesis of current climate science since its founding in 1988. The group’s reports tend to punctuate the otherwise slow immiseration of climate change; its previous synthesis report, released in 2013, helped inform international climate policy, including the writing of the Paris Agreement.
This is its sixth report and its most definitive. The group’s findings must be agreed to by 195 countries; this famously makes it more conservative than some scientists believe is prudent. But compared with previous reports, there is little restraint here. In its strongest statement of culpability ever, the IPCC declared that humanity is “unequivocally” responsible for climate change. “In past reports, we’ve had to make that statement more hesitantly. Now it’s a statement of fact,” Gregory Flato, a vice chair of the group that authored the report and a senior research scientist within the Canadian government, told me.
Some of the worst impacts of climate change can still be avoided. “There are still emissions pathways that would lead us to limiting warming to 1.5 degrees, but they require deep, rapid cuts in greenhouse-gas emissions,” Flato said. “That leaves a glimmer of optimism that we could limit warming to levels like that.” But it would require much more expedient action from the United States than is contemplated in, say, the bipartisan infrastructure bill that Congress is currently considering.