New data show limiting warming to 1.5 degrees Celsius, not 2 degrees, will make a difference
Jason Lee/The Sun News via AP
This is the year we learned that the 2015 Paris Agreement on global warming won’t be enough to forestall significant impacts of climate change. And a new field of research explicitly attributed some extreme weather events to human-caused climate change. This one-two punch made it clear that climate change isn’t just something to worry about in the coming decades. It’s already here.
This looming problem was apparent three years ago when nearly all of the world’s nations agreed to cut greenhouse gas emissions to limit global warming to no more than 2 degrees Celsius over preindustrial times by 2100 (SN: 1/9/16, p. 6). That pact was hard-won, but even then, some scientists sounded a note of caution: That target wouldn’t be stringent enough to prevent major changes.
So the United Nations took an unprecedented step. It commissioned the Intergovernmental Panel on Climate Change to examine how the world might fare if global warming were limited to 1.5 degrees instead of 2 degrees. That report, released in October, confirmed that half a degree can indeed make a world of difference (SN: 10/27/18, p. 7). A half degree less warming means less sea level rise, fewer species lost due to vanished habitats and fewer life-threatening heat, drought and precipitation extremes (SN: 6/9/18, p. 6).
There’s little time to reverse course. The IPCC report notes that the planet’s average temperature has already increased by nearly 1 degree since preindustrial times, and that rise is contributing to extinctions, lower crop yields and more frequent wildfires. At the end of 2017, three attribution studies for the first time determined that certain extreme events, including an extended marine heat wave in the Pacific Ocean known as “the Blob,” would not have happened without human-induced climate change (SN: 1/20/18, p. 6).
Less is more
Capping global warming at 1.5 degrees Celsius above preindustrial levels rather than 2 degrees can soften climate impacts.
|Impact||1.5 degrees||2 degrees|
|Global average sea level rise by 2100|
|Increase in ocean acidity by 2100|
|Probability of an ice-free Arctic Ocean in the summer for any given year|
|Increase in the annual maximum daily temperature|
|Proportion of global population facing at least one severe heat wave every five years|
|Global population exposed to severe drought|
|Global population exposed to flooding in coastal areas by 2095|
million per year
million per year
|Proportion of species losing >50% of range that has a climate they can tolerate|
Source: IPCC 2018
This year, researchers reported that the 2017 Atlantic hurricane season got a boost from warm waters in the tropical Atlantic, fueled by climate change (SN Online: 9/28/18). And a team of scientists determined that climate change was the engine behind September’s intense rainfall from Hurricane Florence in the Mid-Atlantic region of the United States (SN Online: 9/13/18).
A report released November 23 by hundreds of U.S. climate scientists from 13 federal agencies put a price tag on many of the effects for the United States (SN Online: 11/28/18). The report predicts the country’s economy will shrink by as much as 10 percent by 2100 if global warming continues on its current trajectory.
Climate simulations suggest that Earth will reach the 1.5 degree threshold within a decade. And even if countries were to agree to limit warming to that level, the planet would almost certainly surpass it before the warming reversed, due to the realities of how quickly emissions can be reduced. Passing that target will probably lead to some irreversible changes, such as melted glaciers and species losses. To overshoot the mark by only a small amount, or not at all, requires reducing emissions by about 45 percent relative to 2010 levels by the year 2030. The planet would then be able to reach net zero, when the amount of carbon released to the atmosphere is balanced by the amount removed, by around 2050, the IPCC report notes.
To bring warming back down below the 1.5 degree target by the end of the century, the world will need negative emissions technologies to remove large amounts of carbon dioxide from the atmosphere. Such technologies that limit or even reverse warming are less pie-in-the-sky than they sound, says Stephen Pacala, an ecologist at Princeton University. “Although there is a lot of doom and gloom available on the progress of humanity, there isn’t on the technological side.” Pacala chaired a National Academies of Sciences, Engineering and Medicine committee that released a report in October that analyzed the viability of current and emerging negative emissions technologies as well as encouraged large-scale investments in them.
Other negative emissions technologies in development could become game changers, Pacala says. Direct air capture, in which CO2 is removed directly from the atmosphere and converted into synthetic fuel, is a proven technology. But so far, the high cost of direct air capture remains a barrier to commercial-scale development. The National Academies report says that nations should subsidize start-ups to drive competition in this area — after all, that’s what worked for wind and solar power, Pacala notes. Other proposed negative emissions technologies, such as converting atmospheric CO2 into a stable mineral form (SN: 9/15/18, p. 9), show some promise but require large-scale financial investment in their basic science to make them viable, the report states.
Reducing demand for resource-intensive products will also be important to reach the 1.5 degree target, Fuss says. Cities need to move away from fossil fuels, and individuals can do their part by, for example, traveling less (SN: 6/9/18, p. 5), eating less meat (SN: 7/7/18, p. 10) and installing more energy-efficient appliances. Data show that, given the right incentives, people are willing to make such lifestyle changes, says IPCC report coauthor Linda Steg, an environmental psychologist at the University of Groningen in the Netherlands. And those incentives aren’t necessarily financial or based on self-interest, she adds. “People are also motivated by protecting the interests of others, or by the quality of the environment.”
Holding warming to 1.5 degrees “is not impossible,” says Natalie Mahowald, a climate scientist at Cornell University and an IPCC report coauthor. But “it really requires ambitious efforts, and the sooner the better. We have to start cutting emissions now.”
Political will to act varies country by country, but scientists have done what they can to convey the urgency and the scope of the climate change problem, says IPCC report coauthor Heleen de Coninck, an environmental scientist at Radboud University in Nijmegen, Netherlands. Nations “have it in their hands, and they know what they are working with,” de Coninck says. “Now it’s up to them.”
The National Academies of Sciences, Engineering and Medicine. Negative emissions technologies and reliable sequestration: A research agenda. Published online October 24, 2018. doi: 10.17226/25259.
Intergovernmental Panel on Climate Change. IPCC special report on global warming of 1.5º C. Published online October 8, 2018.
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