Some Climate Change Effects May Be Irreversible, U.N. Panel Says
Report highlights human responsibility for heat waves, droughts, intense storms and other extreme weather events
By Robert Lee Hotz and Timothy Puko Updated Aug. 9, 2021 6:00 pm ET
Rising seas, melting ice caps and other effects of a warming climate may be irreversible for centuries and are unequivocally driven by greenhouse-gas emissions from human activity, a scientific panel working under the auspices of the United Nations said Monday in a new report.
World leaders—especially those from the West and island nations that are especially vulnerable to climate change—deemed the report a call to action ahead of international climate negotiations scheduled for November. Many called for cutbacks in fossil-fuel consumption, which the report identifies as a leading driver of the rise in levels of heat-trapping greenhouse gases in the atmosphere.
“The impacts of the climate crisis, from extreme heat to wildfires to intense rainfall and flooding, will only continue to intensify unless we choose another course for ourselves and generations to come,” said U.S. climate envoy John Kerry. “What the world requires now is real action.”
British Prime Minister Boris Johnson singled out the burning of coal, saying the world should “consign (it) to history.”
Issued by the Intergovernmental Panel on Climate Change, an organization of 195 governments, the new report is drawn from a three-year analysis of 14,000 peer-reviewed scientific studies. It is the first major international assessment of climate-change research since 2013.
The report highlights human responsibility for record heat waves, droughts, more intense storms and other extreme weather events seen around the world in recent years. It also sharpens estimates of how sensitive the climate is to rising atmospheric levels of carbon dioxide and other greenhouse gases—a key metric in forecasting the rise of global temperatures in the years ahead.
“It is unequivocal that human influence has warmed the atmosphere, ocean and land,” the report says in its opening lines. “Human-induced climate change is already affecting many weather and climate extremes in every region across the globe.”
The first of four IPCC reports expected in the next 15 months, the report is likely to be a major force in both geopolitics and business. It sets scientific baselines and offers guidance to negotiators regularly convened by the U.N. under the Paris Climate Agreement, which has become a benchmark for corporate as well as governmental efforts to curb emissions.
The next major climate negotiations, known as COP26 and scheduled to begin in Glasgow on Nov. 1, will bring together representatives from nearly every nation in the world to discuss new, more ambitious commitments for cutting emissions. Mr. Kerry has said the U.S. and other countries must use the talks to speed their efforts because those taken so far are failing to make the progress that scientific research says is necessary within about a decade.
The report ties the types of extreme weather events seen in recent weeks—historic heat waves in the Pacific Northwest, torrential floods in Europe and China, and forest fires in the U.S., Russia and elsewhere—directly to climate change.
“We’ve known for decades that the world is warming, but this report tells us that recent changes in the climate are widespread, rapid and intensifying, unprecedented in thousands of years,” said Ko Barrett, vice chair of the IPCC and the senior adviser for climate at the Office of Oceanic and Atmospheric Research at the National Oceanic and Atmospheric Administration. “Further, it is indisputable that human activities are causing climate change.”
The report “connects the dots in a way we really haven’t seen before,” said climate scientist Michael Mann, director of the Earth System Science Center at Pennsylvania State University, who wasn’t involved with the report. “The message eerily resonates with what we’re seeing this summer in Canada, the U.S. and Europe as extreme weather events play havoc on us and our infrastructure.”
Levels of carbon dioxide released into the air by the burning of fossil fuels, cement production and deforestation and other land-use changes reached a modern seasonal high of 419 parts per million in May. That is higher than at any time in the past 3.6 million years, according to NOAA.
Atmospheric levels of methane, an even more potent greenhouse gas, are now about 2½ times their preindustrial levels and steadily rising, according to the International Energy Agency.
In Glasgow, representatives from almost 200 countries are expected to present updated plans for reducing greenhouse-gas emissions. They are working under a global agreement resulting from the 2015 Paris climate summit that called on nations to take steps to limit future global temperature increases to 1.5 degrees Celsius (2.7 degrees Fahrenheit).
“This report tells us that we probably need even more action by all the major economies to work together to avoid even worse impacts than we’re already seeing now,” said Jane Lubchenco, deputy director for climate and the environment at the White House Office of Science and Technology Policy. She wasn’t involved in the IPCC effort.
Greenhouse-gas emissions from human activity have raised global temperatures by 1.1 degrees Celsius since around 1850, the report said. Without rapid reductions in emissions, global temperatures could rise more than an additional 1.5 degrees Celsius over the next 20 years, the report forecasts.
“We know there is no going back from some changes in the climate system, but some can be slowed or stopped if emissions are reduced,” said NOAA’s Dr. Barrett.
The report reflects new scientific methodologies honed in an era of growing climate disturbances. It draws on a better understanding of the complex dynamics of the changing atmosphere and greater stores of data about climate change dating back millions of years, as well as a more robust set of satellite measurements and more than 50 computer models of climate change.
“We are now much better at integrating all the information,” said Gavin Schmidt, the National Aeronautics and Space Administration’s senior climate adviser and director of the Goddard Institute for Space Sciences in New York, who wasn’t involved with the report.
Last year, global temperatures tied for the warmest on record, capping the warmest decade in modern times. Oceans are warming, and sea level is increasing by 3.7 mm, or about 0.1 inch, a year, the scientists said in the report. Mountain glaciers, sea ice and polar ice sheets are steadily melting. Weather around the world has grown more extreme by many measures, the scientists said, with more frequent heat waves and prolonged droughts in some regions and heavier rainfall and flooding in others.
“When you see what has happened this summer with heat waves in Canada and the heavy precipitation in Germany, I think this is showing that even highly developed countries are not spared,” said Sonia Seneviratne, a senior scientist at ETH Zurich in Switzerland and a lead co-author of the report. “We don’t really have time to adapt anymore because the change is happening so quickly.”
Write to Robert Lee Hotz at sciencejournal@wsj.com and Timothy Puko at tim.puko@wsj.com
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