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 on 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 1.5 degrees Celsius (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 1.5 degrees Celsius. 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 already warmed an average of 1.1 degrees Celsius 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 percent chance of limiting warming to 1.5 degrees Celsius.
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 1.5 degree limit is achievable, but it will take a quantum leap in climate action,” António Guterres, the United Nations secretary general, said. In response to the report, Mr. Guterres called on countries to stop building new coal plants and to stop approving new oil and gas projects.
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A species in danger. Federal officials said that sunflower sea stars, huge starfish that until recently thrived in waters along the west coast of North America and that play a key role in keeping marine ecosystems balanced, are threatened with extinction and should be protected under the Endangered Species Act.
Many scientists have pointed out that surpassing the 1.5 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 1.5 degrees of warming and 2 degrees might mean that tens of millions more people worldwide experience life-threatening heat waves, water shortages and coastal flooding. A 1.5-degree world might still have coral reefs and summer Arctic sea ice, while a 2-degree world most likely would not.
“It’s not that if we go past 1.5 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 1.5 is better than 1.6, which is better than 1.7, and so on. The point is we need to do everything we can to keep warming as low as possible.”
Scientists say that warming will largely halt once humans stop adding heat-trapping gases to the atmosphere, a concept known as “net zero” emissions. How quickly nations reach net zero will determine how hot the planet ultimately becomes. Under the current policies of national governments, Earth is on pace to heat up by 2.1 to 2.9 degrees Celsius this century, analysts have estimated.
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.
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 4 degrees Celsius 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 eight 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.
Nations have made some strides in preparing for the dangers of global warming, the report says, for instance by building coastal barriers against rising oceans or establishing early-warning systems for future storms. But many of those adaptation efforts are “incremental” and lack sufficient funding, particularly in poorer countries, the report finds.
And if temperatures keep rising, many parts of the world may soon face limits in how much they can adapt. Beyond 1.5 degrees Celsius of warming, low-lying island nations and communities that depend on glaciers may face severe freshwater shortages
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 1.5 or 2 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 rare earth 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.
The new report is expected to inform the next round of United Nations climate talks this December in Dubai, where world leaders will gather to assess their progress in tackling global warming. At last year’s climate talks in Sharm el Sheik, language calling for an end to fossil fuels was struck from the final agreement after pressure from several oil-producing nations.
“Without a radical shift away from fossil fuels over the next few years, the world is certain to blow past the 1.5 C goal.” said Ani Dasgupta, president of the World Resources Institute, an environmental group. “The I.P.C.C. makes plain that continuing to build new unabated fossil fuel power plants would seal that fate,” he added, using the abbreviation for the Intergovernmental Panel on Climate Change.
While the next decade is almost certain to be hotter, scientists said the main takeaway from the report should be that nations still have enormous influence over the climate for the rest of the century.
The report “is quite clear that whatever future we end up with is within our control,” said Piers Forster, a climate scientist at the University of Leeds who helped write one of the panel’s earlier reports. “It is up to humanity,” he added, “to determine what we end up with.”
