The study found that even if countries were to meet their existing pledges, the world has only about a 5 percent chance to limit the Earth’s warming to “well below” 2 degrees Celsius (3.6 Fahrenheit) over preindustrial levels — a key aim of the international agreement.
Raftery and a colleague calculated that global emissions would need to fall steadily — about 1.8 percent each year on average — to put the world on a more sustainable trajectory. While no two countries are alike, that amounts to overall emissions reductions roughly 80 percent more ambitious than those pledged under the Paris agreement, he said.
In many respects, the race to slow the Earth’s warming is a daunting math problem. Emissions have risen about 1.4 percent annually on average over the past decade, not including the abnormal plunge in 2020 driven by the coronavirus pandemic.
In 2019, the world logged the highest emissions ever recorded, at 59 billion tons of carbon dioxide equivalent emissions, a category that includes not only carbon dioxide but also methane and other climate-warming agents. If that trend continues unabated, scientists say, the world could begin to cross troubling climate thresholds within the coming decade.
The architects of the Paris accord and numerous world leaders have long underscored that the pledges made in 2015 were not enough to limit warming to acceptable levels. The expectation was always that nations would grow more ambitious with time, and there is evidence that is happening.
But as global emissions have continued to rise, as countries have failed to hit even modest targets and as the consequences of a warming world have become more tangible, the push for leaders to act more aggressively has become only more urgent.
“Time is running out,” Niklas Höhne, a German climatologist and founding partner of NewClimate Institute, said in an interview. “The longer we wait, the more difficult it will be to turn emissions downward.”
Höhne is also part of the team behind Climate Action Tracker, an effort that tracks what cuts countries have vowed to take and how they are, or aren’t, living up to those promises. He said that with the pledges countries have made, the world is currently on pace to reach 2.6 Celsius (4.7 Fahrenheit) of warming by the end of the century. But based on measures they have actually put into place, the figure is closer to 2.9 Celsius (5.2 Fahrenheit).
At either level, scientists say humans would be forced to grapple with ever more extreme weather events, crippling heat waves and wildfires, and disastrous levels of flooding that could leave some coastal communities uninhabitable.
The level of ambition necessary varies greatly between countries, Raftery said, noting that the United States would need to increase its existing goal by 38 percent to do its part toward achieving the 2C goal. The United Kingdom, which has already made progress on its promises, would need a boost of about 17 percent. Meanwhile, countries such as Brazil, which have seen emissions climb despite promises to scale them back, would need bolder action to make up for lost time.
Kelly Levin, a senior associate at the World Resources Institute, noted that Tuesday’s study did not take into account more recent policies that some large countries have adopted or already begun to implement, and which could put the world on a more hopeful path.
“Given the recent momentum we have seen — for example, from the Biden administration’s recent executive orders, to bans of the internal combustion engine in countries and by companies — their estimates, which are based on recent trends, are likely too conservative,” Levin said in an email.
Still, she said, by any calculation there remains “a wide gulf between where emissions are headed today” and where they need to be to avoid the worst impacts of climate change.
The findings also echo those published late last year by the U.N. Environment Program, which said nations would need to “roughly triple” their current emissions-cutting pledges to limit the Earth’s warming to “well below” 2 degrees Celsius. To reach the loftier goal of holding warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit), that report found, countries would need to increase their targets at least fivefold, a change that would require rapid and profound shifts in how societies travel, produce electricity and eat.
A critical moment will arrive later this year when leaders from around the world assemble in Glasgow for a U.N. climate conference, which was delayed a year because of the pandemic. Presidents and prime ministers worldwide already are facing pressure to show up with more ambitious pledges in hand.
Some of the world’s biggest economies have said they intend to do just that. China, the world’s largest emitter, has promised to reach zero net carbon emissions by 2060. The European Union has said that by the end of the decade, it intends to cut emissions “at least 55 percent” from 1990 levels.
More than 125 countries, representing more than two-thirds of global emissions, have either adopted or are discussing a goal of reaching net zero emissions by the middle of the century, Höhne said.
The United States, which is rejoining the Paris accord after President Donald Trump withdrew from it last year, has not yet formally submitted a new pledge. But President Biden has made clear that he will aim to put the world’s second-biggest emitter on a path to net zero emissions by 2050, while also decarbonizing the electricity sector by 2035.
“President Biden knows that we have to mobilize in unprecedented ways to meet a challenge that is fast accelerating. And he knows we have limited time to get it under control,” U.S. climate envoy John F. Kerry told an online summit last month.
U.N. Secretary General António Guterres has continued to press nations to go further and faster, as the world has already surpassed 1 degree Celsius of warming.
“The drive for net-zero emissions must become the new normal for everyone, everywhere,” Guterres said in a speech Monday. “At the same time, all commitments to net zero must be underpinned by clear and credible plans to achieve them. Words are not enough.”
Raftery said that while the findings of Tuesday’s study might initially seem discouraging, he sees glimmers of optimism. Major countries are promising bold action, markets are moving away from fossil fuels, businesses are paying attention to climate concerns and upcoming stimulus funding could prioritize greener investments.
“I’m a bit surprised in a way to see it’s not as hopeless as I would have felt three years ago,” he said of the changes needed to alter the world’s trajectory. “It’s a heavy lift, but it’s not impossible.”