It’s increasingly likely that the planet will reach 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, of warming, probably within the next two decades. But while that level of warming comes with a variety of dangerous effects, it’s not a point of no return, scientists say, and it doesn’t mean “we’re done,” as President Joe Biden has claimed.
Carbon dioxide and other gasses that trap heat, known as greenhouse gases, emitted by human activity have “unequivocally caused global warming,” according to the United Nations’ Intergovernmental Panel on Climate Change. The average global temperature has already increased by 1.1 C, or 2 F, since 1850-1900, the latest IPCC report published in March says. And even in a very low greenhouse gas emission scenario “global warming is more likely than not” to reach 1.5 C between now and 2040, the report says.
Every increment of global warming intensifies the adverse impacts of climate change. Effective climate action, however, can limit and reduce losses and damages, scientists agree. Warming also “could gradually be reduced again by achieving and sustaining net negative global CO2 emissions,” the IPCC report says.
But in urging people to support his climate policies, Biden has been overly pessimistic. In an interview with “The Daily Show” that aired on March 13, for example, Biden said crossing the 1.5 C threshold would mean that a “whole generation is damned. I mean, that’s not hyperbole.”
That same day, in remarks at a Democratic National Committee reception, he said if global warming goes above 1.5 C “we’re done; there’s no way to turn it around, according to the scientists that tell us.”
The White House did not explain what he meant by an entire generation being “damned” after 1.5 C of warming, nor did it give us any indication of which studies suggest “we’re done.”
“I think passing 1.5 C means social and economic ‘chaos,’ but ‘done’ sounds like nothing we do afterwards matters,” Stanford University climate scientist Rob Jackson told us in an email. “That’s wrong. Every tenth of a degree matters, before and after 1.5 C,” he wrote.
Climate scientist Michael Mann said Biden’s statements contribute to the climate “doomerism” narrative, which he has said could be dangerous and paralyzing, since it implies that it’s already too late to cut back on emissions.
“Biden said ‘we lose it all’ if we warm beyond 1.5C,” Mann, a professor and director of the Penn Center for Science, Sustainability and the Media at the University of Pennsylvania, said on Twitter, referring to language Biden used in July. “Unhelpful rhetoric, unsupported by the science. It’s a continuum not a cliff. We’ve lost much already, and lose more with each fraction of a degree. If we miss the 1.5C exit ramp, we still go for 1.6C exit rather than give up,” Mann said.
The president also has been overly confident at times when talking about American progress in limiting warming to 1.5 C. While the White House typically refers to the U.S. goal in reducing emissions as “within reach,” Biden sometimes says the country is “on track” to achieving the goal.
“With these actions, the United States is on track to achieve a 1.5 degree-aligned goal cutting emissions 50 to 52% by 2030,” he said on April 20, while referring to the Inflation Reduction Act and other actions.
But studies have found that although the IRA — which includes investments in clean energy and is projected to lower emissions 40% below 2005 levels by 2030 — will make significant progress toward achieving the goal, it’s not enough, even with other existing policies.
“Based on Congressional action and currently finalized regulations, we are not on track to meet 50-52% below 2005 by 2030,” Jesse Jenkins, who leads the Princeton Zero carbon Energy systems Research and Optimization Laboratory, told us in an email. It’s possible, Jenkins said, that once certain rules are finalized and others are proposed, that “the gap could be closed,” but it’s premature to say so now.
Why 1.5 Degrees Celsius
The idea of limiting warming to 1.5 C first emerged in climate talks in 2010. Prior to that time, the goal was to keep global warming below 2 C (3.6 F) above pre-industrial levels to meet the United Nations Framework Convention on Climate Change’s objective to “prevent dangerous human interference with the climate system.” But in 2010, experts gathered at the conference decided it was necessary to review “the adequacy” of that target and to consider “strengthening” the goal to 1.5 C.
The IPCC defines global warming as the estimated increase in global mean surface temperature, which is the average temperature of the air near the surface of land and ocean, averaged over a 30-year period, relative to pre-industrial levels.
Over the next several years, the language around the goal shifted, with the recognition that particularly for vulnerable regions, going past 1.5 C could be very risky, and that the 2 C goal should not be thought of as a “guardrail” under which all would be safe.
“While science on the 1.5 °C warming limit is less robust, efforts should be made to push the defence line as low as possible,” a 2015 report concluded.
The guidance was then considered in the Paris Agreement, the landmark climate agreement adopted by 196 member parties in December 2015. The agreement set the overarching goal of “holding the increase in the global average temperature to well below 2°C above pre-industrial levels,” but also said members of the agreement should pursue “efforts to limit the temperature increase to 1.5°C above pre-industrial levels.”
The UNFCCC asked the IPCC, which is made up of scientists, to prepare a report on the impacts of global warming of 1.5 C compared with 2 C, and on the pathways to get there. The IPCC published that report in 2018.
“What the IPCC 1.5C report told us, and the more recent reports emphasized, is that every half a degree of warming makes things worse,” Natalie M. Mahowald, a climate scientist at Cornell University and one of the authors of the 2018 IPCC Special Report, told us in an email.
The report found a number of significant impacts could be avoided if setting a threshold at 1.5 C compared with 2 C — fewer deaths and illnesses from heat, hunger and infectious diseases; lower risks of flooding, drought and sea level rise; and fewer impacts to ecosystems and biodiversity.
But neither 1.5 C nor 2 C are “magic numbers,” as Katharine Hayhoe, a climate scientist at The Nature Conservancy, puts it. More carbon emissions in the atmosphere will result in more global warming, which will result in a greater risk.
“Trying to put a number on exactly how much global temperature change is dangerous, and how much carbon we can put into the atmosphere before we hit that level, is like trying to put a number on exactly how many cigarettes we can smoke before we develop lung cancer,” she explains in a video from her PBS series “Global Weirding.” “Now, of course we know that the more we smoke, the greater the risk, but we also know there’s no magic number.”
How Close Are We and What Happens If We Reach 1.5 C
According to the last IPCC report published in March, global surface temperature warming reached 1.1 C in the decade of 2011-2020, with a 1.59 C warming over the land and 0.88 C over the ocean. The global temperature has increased faster since 1970 than in any other 50-year period over the last 2,000 years, the report said. Human-made greenhouse gas emissions in 2019 were 12% higher than in 2010, with the largest share coming from fossil fuels combustion and industrial processes, according to the report.
Many adverse impacts, losses and damages related to climate change had already happened, the report said, and every increment of warming will make the risks of more damage intensify. Some future changes are “unavoidable and/or irreversible,” the report said.
“People are already suffering and dying from climate change,” Kristie L. Ebi, professor of global health and environment at the University of Washington and one of the authors of the IPCC 1.5 C report, told us in an email. “The magnitude and pattern of health risks of 1.5C are projected to be larger than current impacts. Each additional unit of warming is projected to further increase the level of risk.”
The estimated remaining carbon budget, or the amount of CO2 that could still be emitted, for a 50% chance of limiting warming to 1.5 C is 380 billion metric tons, according to the latest Global Carbon Project report released in November 2022. At the current rate of emissions, analysts say that would last for about nine years. According to the report, 2022 global carbon emissions remained “at record levels – with no sign of the decrease that is urgently needed to limit warming to 1.5°C.” It projected total global CO2 emissions of 40.6 million metric tons.
Overshooting, or failing to limit warming to 1.5 C by 2100, “will result in irreversible adverse impacts on certain ecosystems with low resilience,” according to the latest IPCC report. Some of these impacts — mass mortality of trees, drying of peatlands and permafrost thawing — could cause additional warming, the report notes, which would in turn make it harder to return to 1.5 C.
According to the IPCC Special Report, some of the impacts of global warming of 1.5 C include:
- Sea level is projected to rise to a range of 10 to 30 inches relative to 1986-2005 levels.
- Out of 105,000 species studied, about 6% of insects, 8% of plants and 4% of vertebrates are projected to lose more than half of their habitats.
- About 70% to 90% of tropical coral reefs would disappear.
- Many marine species would shift their range to higher latitudes, and the amount of damage to marine ecosystems will increase, reducing coastal resources. The global annual catch for marine fisheries will decrease by about 1.5 million metric tons, according to projections of a global fishery model.
- Health risks related to climate, such as heat illnesses and deaths or vector-borne diseases, are projected to increase.
Limiting warming to 1.5 C is still possible but it would require “rapid and deep and, in most cases, immediate greenhouse gas emissions reductions in all sectors this decade,” according to IPCC’s latest report. To achieve that goal, global net carbon dioxide emissions would need to be reduced by about 48% from 2019 levels by 2030, 65% by 2035, 80% by 2040, and reach net-zero emissions, or the balance between emissions produced and removed, around 2050.
But in the big picture, if warming exceeds 1.5 C, it doesn’t mean “we’re done,” as Biden said. Scientists say there’s no reason to give up.
“We have to remember there’s no expiration on climate action,” Twila Moon, deputy lead scientist at the U.S. National Snow and Ice Data Center, told PBS while discussing a study that shows ice sheets in Greenland and Antarctica are melting faster than predicted. “Every tenth of a degree that we prevent warming is worthwhile and will benefit us. And we can continue to strengthen our actions,” she said.