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
Animals
Two baby Loggerhead turtles. U.S. Air Force / Senior Airman Veronica McMahon

A Record 589 Sea Turtles Killed By Florida's Toxic Red Tide

Florida's longest red tide in more than a decade has killed scores of the state's most iconic marine animals.

The current outbreak, which began in October 2017 off southwest Florida, has been tied to a record 589 sea turtle deaths and 213 manatee deaths, the Herald-Tribune reported, citing figures from the Florida Fish and Wildlife Conservation Commission.

Keep reading... Show less
Animals
Lake Baikal. W0zny / Wikimedia / CC BY-SA 3.0

Wildlife Under Siege at the World’s Oldest Lake

By Marlene Cimons

Lake Baikal is the world's oldest and deepest lake. It's at least 20 million years old, and roughly a mile deep at its lowest point. The Siberian lake contains holds more water than all the North American Great Lakes combined, what amounts to more than one-fifth of all the water found in lakes, swamps and rivers. It was formed by the shifting of tectonic plates, which created a valley that filled with water. That shift continues today at a rate of around 1 to 2 centimeters year, meaning the world's biggest lake is only getting bigger.

Keep reading... Show less
Insights/Opinion
Oil rig operating next to a walk and bike way in the Signal Hill area of Los Angeles. Sarah Craig / Faces of Fracking / CC BY-NC-ND 2.0

U.S. Oil and Gas Industry Is Drilling Us Towards Climate Disaster

By Kelly Trout

As the 116th Congress commences, in the wake of dire reports from climate scientists, the debate over U.S. climate policies has taken a welcome turn towards bold solutions. Spurred on by grassroots pressure from Indigenous communities, the youth-led Sunrise Movement and communities from coast to coast fighting fossil fuel infrastructure, Capitol Hill is alive once again with policy proposals that edge towards the scale required to address the crisis we're in.

Keep reading... Show less
Animals
Bumblebee on goldenrod. Jim Hudgins / USFWS

Half of Michigan's Bumblebee Species in Decline, One Extinct

Honeybees get a lot of attention for their worrisome decline, but many species of bumblebees—which are key pollinators—are also in trouble.

In Michigan, half of its bumblebee species have declined by 50 percent or more, Michigan Radio reported.

Keep reading... Show less
Sponsored
Popular
Bound bales of crushed plastic bottles and containers sit stacked ready to be recycled at a recycling center in the Netherlands. Jasper Juinen / Bloomberg / Getty Images

Toward a Circular Economy: Tackling the Plastics Recycling Problem

By Margaret Sobkowicz

Why has the world continued to increase consumption of plastic materials when at the same time, environmental and human health concerns over their use have grown?

Keep reading... Show less
Oceans
Bleached coral at the Great Barrier Reef. The Ocean Agency / XL Catlin Seaview Survey / Richard Vevers

2018 Was the Hottest Year Ever Recorded for Our Oceans

The year 2018 was the hottest year for the planet's oceans ever since record-keeping began in 1958, according to a worrisome new study from international scientists.

The findings, published Wednesday in the journal Advances in Atmospheric Sciences, noted that the five warmest years for our oceans were the last five years—2018, 2017, 2015, 2016 and 2014 (in order of decreasing ocean heat content).

Keep reading... Show less
Sponsored
EPA Acting Administrator Wheeler / EPA

Senate Shouldn’t Put Wheeler at the Wheel of the EPA

By Ana Unruh Cohen

As the longest government shut down in history drags on, and the experts protecting our air and water remain off the job, the Senate is barreling forward to put Andrew Wheeler at the wheel of the U.S. Environmental Protection Agency (EPA). He is unfit for this public trust.

In his seven-month tenure as the acting administrator at EPA, Wheeler's relentlessly pushed to advance the pro-polluter agenda launched by Scott Pruitt, the worst administrator in the agency's storied 48-year history. Wheeler may lack Pruitt's scandals, but he's no improvement.

Keep reading... Show less
Health
Westend61 / Getty Images

Top 20 Healthy Salad Toppings

By Lizzie Streit, MS, RDN, LD

Salads are typically made by combining lettuce or mixed greens with an assortment of toppings and a dressing.

Keep reading... Show less
Sponsored

mail-copy

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