Quantcast
Climate

New Climate Study: Most Severe Warming Projections Are Now the Most Likely

By Tim Radford

Global warming, under the notorious "business-as-usual scenario" in which humans go on burning fossil fuels to power economic growth, could by 2100 be at least 15 percent warmer than the worst UN projections so far. And the spread of uncertainty in such gloomy forecasts has been narrowed as well.

Climate scientists had worked on the assumption that there was a 62 percent chance that the world would have warmed on average by more than 4°C if no action was taken to reduce greenhouse gas emissions.


But a new study has not only raised the stakes, it has narrowed the uncertainty. There is now a 93 percent chance that global warming will—once again, under the business-as-usual scenario—exceed 4°C by 2100.

And since the world's nations met in Paris in 2015 and agreed to keep overall global warming to "well below" 2°C, even that figure represents "dangerous" global warming. One degree higher would count as "catastrophic." And a rise of beyond 5°C would deliver the world into an unknown and unpredictable period of change.

Two U.S. scientists reported in the journal Nature that they went back to the climate models used as the basis for forecasts made by the UN's Intergovernmental Panel on Climate Change and then matched the reasoning against observations.

In particular, they looked again at seasonal and monthly variability in climate and the latest thinking about energy use, and carbon dioxide emissions, and their impact on temperatures.

There has always been an argument about the long-term accuracy of climate models and what they can usefully predict about the real world by the century's end. If anything, the new results suggest that tomorrow's reality could be even worse.

"Our results suggest that it doesn't make sense to dismiss the most-severe global warming projections based on the fact that climate models are imperfect in their simulation of the current climate," said Patrick Brown, of the Carnegie Institution at Stanford University in California.

Deeper cuts

"On the contrary, we are showing that model shortcomings can be used to dismiss the least severe predictions."

And, the authors warned: "Our results suggest that achieving any given global temperature stabilization target will require steeper greenhouse gas emissions reduction than previously calculated."

Climate models are only as good as the climate data on which they are based, and one source of uncertainty has been the effect of warming on cloud formation: a warmer world means more evaporation, which could mean more warmth is trapped in the atmosphere—or it could mean more clouds, which reflect more solar radiation back into space.

For decades, researchers have tried to calculate with precision the links between ratios of greenhouse gases released from the combustion of coal, natural gas and oil, and shifts in average planetary temperature.

Simpler evidence

One of the Carnegie authors, Ken Caldeira of the Institution's global ecology lab, has so far calculated the rate at which carbon dioxide sets about warming the atmosphere, and the capacity of greenhouse gases to go on warming the world for millennia.

The latest conclusions have been based on simpler evidence: the accuracy with which their forecast models can "predict" the recent past.

"It makes sense that the models that do the best job at simulating today's observations might be the models with the most reliable predictions," professor Caldeira said.

"Our study indicates that if emissions follow a commonly-used business-as-usual scenario, there is a 93% chance that global warming will exceed 4°C by the end of this century. Previous studies have put this likelihood at 62%."

Reposted with permission from our media associate Climate News Network.

Show Comments ()

EcoWatch Daily Newsletter

Sponsored
Popular
Kodachrome25 / Getty Images

Roof-to-Garden: How to Irrigate with Rainwater

By Brian Barth

The average American household uses about 320 gallons of water per day, a third for irrigation and other outdoor uses. Collecting the water flowing down your downspouts in rainstorms so you can use it to irrigate in dry periods is often touted as a simple way to cut back. But setting up a functional rainwater irrigation system—beyond the ubiquitous 55-gallon barrels under the downspout, which won't irrigate much more than a flower bed or two—is a fairly complicated DIY project.

Keep reading... Show less
Health
A family wears face masks as they walk through the smoke filled streets after the Thomas wildfire swept through Ventura, California on Dec. 6, 2017. MARK RALSTON / AFP / Getty Images

How to Protect Your Children From Wildfire Smoke

By Cecilia Sierra-Heredia

We're very careful about what our kids eat, but what about the air they breathe?

Keep reading... Show less
Health
Hero Images / Getty Images

Study: Children Have Better Nutrition When They Live Near Forests

Spending time in nature is known to boost mental and emotional health. Now, a new global study has found that children in 27 developing nations tend to have more diverse diets and better nutrition when they live near forests.

The paper, published Wednesday in Science Advances, provides evidence that forest conservation can be an important tool in promoting better nutrition in developing countries, rather than clear-cutting forests for more farmland.

Keep reading... Show less
Health
Navy torpedo bomber spraying DDT just above the trees in Goldendale, WA in 1962. USDA Forest Service

Maternal DDT Exposure Linked to Increased Autism Risk

A study published in the American Journal of Psychiatry Thursday found that mothers exposed to the banned pesticide DDT were nearly one-third more likely to have children who developed autism, Environmental Health News reported.

Keep reading... Show less
Sponsored
GMO
Significant cupping of leaves from dicamba drift on non-Xtend soybeans planted next to Xtend beans in research plots at the Ashland Bottoms farm near Manhattan, KS. Dallas Peterson, K-State Research and Extension / CC BY 2.0

Top Seed Companies Urge EPA to Limit Dicamba

Two of the nation's largest independent seed sellers, Beck's Hybrids and Stine Seed, are urging the U.S. Environmental Protection Agency (EPA) to place limits on the spraying of the drift-prone pesticide dicamba, Reuters reported.

This could potentially hurt Monsanto, which along with DowDupont and BASF SE, makes dicamba formulations to use on Monsanto's Xtend seeds that are genetically engineered to resist applications of the weedkiller. Beck's Hybrids and Stine Seed, as well as other companies, sell those seeds.

Keep reading... Show less
Food
Baby son in high chair feeding father. Getty Images

Baby Food Tests Find 68 Percent Contain 'Worrisome' Levels of Heavy Metals

Testing published by Consumer Reports (CR) Thursday found "concerning levels" of toxic metals in popular U.S. baby and toddler food.

The consumer advocacy group tested 50 nationally-distributed, packaged foods designed for toddlers and babies for mercury, cadmium, arsenic and lead.

Keep reading... Show less
Sponsored
Popular
Interior Secretary Ryan Zinke talks to journalists outside the White House West Wing before attending a Trump cabinet meeting on Aug. 16. Chip Somodevilla / Getty Images

Zinke Announces Plan to Fight Wildfires With More Logging

The Trump administration announced a new plan Thursday to fight ongoing wildfires with more logging, and with no mention of additional funding or climate change.

Keep reading... Show less
Energy
Wangan and Jagalingou cultural leader Adrian Burragubba visits Doongmabulla Springs in Australia. The Wangan and Jagalingou are fighting a proposed coal mine that would likely destroy the springs, which are sacred to the Indigenous Australian group. Wangan and Jagalingou

Indigenous Australians Take Fight Against Giant Coal Mine to the United Nations

By Noni Austin

For tens of thousands of years, the Wangan and Jagalingou people have lived in the flat arid lands of central Queensland, Australia. But now they are fighting for their very existence. Earlier this month, they took their fight to the United Nations after years of Australia's failure to protect their fundamental human rights.

Keep reading... Show less
Sponsored

mail-copy

The best of EcoWatch, right in your inbox. Sign up for our email newsletter!