The science is definite: People are dramatically overhauling Earth’s climate. That’s the conclusion of a major new analysis. The impacts of climate change, it found, are visible across the globe. And they are intensifying quickly. The window to reverse some of these effects is closing rapidly, too, the report says.
That August 9 report comes from the IPCC. That’s short for the United Nations’ Intergovernmental Panel on Climate Change.
“There is no room for doubt any longer” about humans’ role in climate change, says Kim Cobb. She’s a climate scientist at Georgia Tech in Atlanta. She also was part of team that wrote the report’s first chapter. “Now we can say quite definitely,” she notes, “that a whole class of extreme [events]” is linked to human-caused climate change.
To make those claims, scientists reviewed new studies from a relatively new branch of research. It’s known as attribution science. Those studies show that climate change is having big impacts everywhere on Earth. The altered climate is unleashing drought and fire conditions in the U.S. West, triggering heat waves in Europe and behind massive flooding in Asia.
In all, the new report found, each of the past four decades has been the warmest since 1750 and the start of the industrial revolution.
The new study also looks at several different scenarios of what our future climate might look like. These include perhaps the most hopeful scenarios. One of them looked at what might happen if, by 2050, the world achieves “net zero” emissions of greenhouse gases. That would be where emitted gases are balanced by processes that can take those gases out of the atmosphere.
Baylor Fox-Kemper sees “hints of light” late in our century if the world can get down to net-zero emissions by mid-century. Fox-Kemper is an oceanographer at Brown University in Providence, R.I. He also was the coordinating lead author of the new report’s chapter on oceans and Earth’s icy regions. If that net-zero path is achieved, he says, the science seems to show that “temperatures come back down a little.” They don’t make it all the way back to conditions typical of the 1750s, he says, “but there’s a little recovery.”
Other changes, Fox-Kemper notes, cannot be reversed within the next century or for quite a while longer. Even for scenarios where mid-century emissions fall to net-zero, “it’s still pretty bad,” he says. Sea levels, for example, will continue to rise until about the year 2300. That’s partly due to Greenland’s melting ice sheet. “We may have already crossed [the] threshold beyond which Greenland’s melting could be stopped,” he says. Still, the report finds, swift and deep cuts in greenhouse-gas releases would significantly slow how high sea levels rise by 2100.
Since 1990, the IPCC has several massive climate assessments. The latest is the sixth of these. For each report, hundreds of scientists from around the world analyzed data from thousands of studies. Based on these data, they formed an agreed-upon picture of how Earth’s climate is changing and what role people appear to have played in triggering those changes.
“The key message [of this report] is still the same as was first published in 1990,” said Petteri Taalas. He spoke at an August 9 event announcing the new report’s release. Taalas is Secretary-General of the World Meteorological Organization in Geneva, Switzerland. The IPCC still finds, he said, that “human-induced emissions of greenhouse gases pose a threat for humans’ well-being and [life on Earth].”
Better data, stronger projections
Researchers understand climate change far better now than in 1990. Over the last 30 years, findings have poured in from tens of thousands more observing stations. Satellites also have been collecting data. Computer models have used those data to make dramatically better projections of our future climate.
The IPCC’s fifth assessment, released in several parts during 2013 and 2014, was itself a game-changer. It stated for the first time that greenhouse gases released by human activities are driving climate change. That conclusion set the stage for 195 nations in 2015 to sign an agreement in Paris. In it, they pledged to curb releases of greenhouse gases.
That Paris Accord set a target of limiting the global average rise in temps to just 2º Celsius (3.4° Fahrenheit) above 1750 levels. But nations most threatened by climate change feared that this target wasn’t tough enough. So the United Nations did something novel. It commissioned the IPCC to compare what a future Earth might look like if warming were instead limited to just 1.5 ºC.
That special report came out in 2018. It revealed how just half a degree of extra warming by 2100 could still greatly alter the world. It would up the chance of heat waves and higher seas, for instance. The one-two punch of this report’s findings and the scorching temperatures in 2019 grabbed the world’s attention.
Scientists were surprised by how forcefully the 1.5 ºC report landed.
Ko Barrett is the vice-chairman of the IPCC. She’s also a senior advisor for climate at the U.S. National Oceanic and Atmospheric Administration. It’s in Silver Spring, Md. “Even for me, a person who has dedicated my entire professional career to addressing climate change, the 2019 report caused me to rethink my personal contribution to the climate problem,” Barrett says. “Climate change was not some distant temperature target,” she says. “It was now.”
The IPCC’s new report emphasizes local and regional effects climate change can unleash. Its authors hope the new report will have a similar impact to their 2018 one. And its timing is important. Beginning October 31, world leaders are scheduled to meet in Glasgow, Scotland. There they will discuss updated — and potentially far stronger— plans to reduce greenhouse gases and meet targets of the 2015 Paris Accord.
With previous reports, “the world listened, but it didn’t hear. Or the world listened, but it didn’t act strongly enough,” said Inger Andersen. She’s the executive director of the U.N. Environment Program, based in Nairobi, Kenya. “We certainly urge [the world] … to listen to the facts on the table now,” she said at the Aug. 9 event for the report’s release.