Earth is likely to cross a critical threshold for global warming within the next decade, and nations will need to make an immediate and drastic shift away from fossil fuels to prevent the planet from overheating dangerously beyond that level, according to a major new report released Monday.
The report, by the Intergovernmental Panel on Climate Change, a body of experts convened by the United Nations, offers the most comprehensive understanding to date of ways in which the planet is changing. It says that global average temperatures are estimated to rise 2.7 degrees Fahrenheit above preindustrial levels sometime around "the first half of the 2030s," as humans continue to burn coal, oil and natural gas.
That number holds a special significance in global climate politics: Under the 2015 Paris climate agreement, virtually every nation agreed to "pursue efforts" to hold global warming to 2.7 degrees Fahrenheit. Beyond that point, scientists say, the impacts of catastrophic heat waves, flooding, drought, crop failures and species extinction become significantly harder for humanity to handle.
But Earth has warmed an average of 2 degrees Fahrenheit since the industrial age, and, with global fossil-fuel emissions setting records last year, that goal is quickly slipping out of reach.
There is still one last chance to shift course, the new report says. But it would require industrialized nations to join together immediately to slash greenhouse gases roughly in half by 2030 and then stop adding carbon dioxide to the atmosphere altogether by the early 2050s. If those two steps were taken, the world would have about a 50% chance of limiting warming to 2.7 degrees Fahrenheit.
Delays of even a few years would most likely make that goal unattainable, guaranteeing a hotter, more perilous future.
"The pace and scale of what has been done so far and current plans are insufficient to tackle climate change," said Hoesung Lee, chair of the climate panel. "We are walking when we should be sprinting."
The report comes as the world's two biggest polluters, China and the United States, continue to approve new fossil fuel projects. Last year, China issued permits for 168 coal-fired power plants of various sizes, according to the Centre for Research on Energy and Clean Air in Finland. Last week, the Biden administration approved an enormous oil drilling project known as Willow that will take place on pristine federal land in Alaska.
The report, which was approved by 195 governments, says that existing and currently planned fossil fuel infrastructure -- coal-fired power plants, oil wells, factories, cars and trucks across the globe -- will already produce enough carbon dioxide to warm the planet roughly 2 degrees Celsius this century. To keep warming below that level, many of those projects would need to be canceled, retired early or otherwise cleaned up.
"The [2.7] degree limit is achievable, but it will take a quantum leap in climate action," U.N. Secretary-General Antonio Guterres said. In response to the report, Guterres called on countries to stop building new coal plants and to stop approving new oil and gas projects.
Many scientists have pointed out that surpassing the 2.7-degree threshold will not mean humanity is doomed. But every fraction of a degree of additional warming is expected to increase the severity of dangers that people around the world face, such as water scarcity, malnutrition and deadly heat waves.
The difference between 2.7 degrees of warming and 3.6 degrees might mean that tens of millions more people worldwide experience life-threatening heat waves, water shortages and coastal flooding. A 2.7-degree world might still have coral reefs and summer Arctic sea ice, while a 3.6-degree world most likely would not.
"It's not that if we go past [2.7] degrees everything is lost," said Joeri Rogelj, director of research at the Grantham Institute for Climate Change and the Environment at Imperial College London. "But there's clear evidence that [2.7] is better than [2.9], which is better than [3.1], and so on. The point is we need to do everything we can to keep warming as low as possible."
The new report is a synthesis of six previous landmark reports on climate change issued by the U.N. panel since 2018, each one compiled by hundreds of experts across the globe, approved by 195 countries and based on thousands of scientific studies. Taken together, the reports represent the most comprehensive look to date at the causes of global warming, the impacts that rising temperatures are having on people and ecosystems across the world and the strategies that countries can pursue to halt global warming.
This is likely the last warning the Nobel Peace Prize-winning collection of scientists will be able to make about the 2.7 mark because their next set of reports may well come after Earth has either passed the mark or is locked into exceeding it soon, several scientists, including report authors, told The Associated Press.
After 2.7 degrees "the risks are starting to pile on," said report co-author Francis X. Johnson, a climate, land and policy scientist at the Stockholm Environment Institute. The report mentions "tipping points" around that temperature of species extinction, including coral reefs, irreversible melting of ice sheets and sea level rise of several yards.
"[2.7] is a critical critical limit, particularly for small islands and mountain [communities] which depend on glaciers," said report co-author and water scientist Aditi Mukherji.
"The window is closing if emissions are not reduced as quickly as possible," Johnson said in an interview. "Scientists are rather alarmed."
Many scientists, including at least three co-authors, said hitting 2.7 degrees is inevitable.
"We are pretty much locked into [2.7]," said report co-author Malte Meinshausen, a climate scientist at the University of Melbourne in Australia. "There's very little way we will be able to avoid crossing [2.7 F] sometime in the 2030s, " but the big issue is whether the temperature keeps rising from there or stabilizes.
The report makes clear that humanity's actions today have the potential to fundamentally reshape the planet for thousands of years.
Many of the most dire climate scenarios once feared by scientists, such as those forecasting warming of 7.2 degrees Fahrenheit or more, now look unlikely, as nations have invested more heavily in clean energy. At least 18 countries, including the United States, have managed to reduce their emissions for more than a decade, the report finds, while the costs of solar panels, wind turbines and lithium-ion batteries for electric vehicles have plummeted.
At the same time, even relatively modest increases in global temperature are now expected to be more disruptive than previously thought, the report concludes.
At current levels of warming, for instance, food production is starting to come under strain. The world is still producing more food each year, thanks to improvements in farming and crop technology, but climate change has slowed the rate of growth, the report says. It's an ominous trend that puts food security at risk as the world's population soars past 8 billion people.
Today, the world is seeing record-shattering storms in California and catastrophic drought in places like East Africa. But by the 2030s, as temperatures rise, climate hazards are expected to increase all over the globe as different countries face more crippling heat waves, worsening coastal flooding and crop failures, the report says. At the same time, mosquitoes carrying diseases like malaria and dengue will spread into new areas, it adds.
To stave off a chaotic future, the report recommends that nations move away from the fossil fuels that have underpinned economies for more than 180 years.
Governments and companies would need to invest three to six times the roughly $600 billion they now spend annually on encouraging clean energy in order to hold global warming at 2.7 or 3.6 degrees, the report says. While there is currently enough global capital to do so, much of it is difficult for developing countries to acquire. The question of what wealthy, industrialized nations owe to poor, developing countries has been divisive at global climate negotiations.
A wide array of strategies are available for reducing fossil-fuel emissions, such as scaling up wind and solar power, shifting to electric vehicles and electric heat pumps in buildings, curbing methane emissions from oil and gas operations, and protecting forests.
But that may not be enough: Countries may also have to remove billions of tons of carbon dioxide from the atmosphere each year, relying on technology that barely exists today.
The report acknowledges the enormous challenges ahead. Winding down coal, oil and gas projects would mean job losses and economic dislocation. Some climate solutions come with difficult trade-offs: Protecting forests, for instance, means less land for agriculture; manufacturing electric vehicles requires mining metals for use in their batteries.
And because nations have waited so long to cut emissions, they will have to spend hundreds of billions of dollars to adapt to climate risks that are now unavoidable.
IPCC chief Lee said the panel doesn't tell countries what to do to limit worse warming, adding "it's up to each government to find the best solution."
"The solutions are at hand," U.S. Vice President Kamala Harris said in a conference call about wildfires. "So let that be an alarm that lets us know that we must act with haste."
"How many reports that chill us to the bone do we need to read before we make the changes required?" asked Tina Stege, climate envoy for Marshall Islands, which are vulnerable to rising seas. "These changes will require some sacrifice -- but aren't they worth it when a liveable future on this planet is what is at stake?"
Information for this article was contributed by Brad Plumer of The New York Times and by Seth Borenstein, Frank Jordans and Fabiano Maisonnave of The Associated Press.