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

Climate

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.

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A net-casting ogre-faced spider. CBG Photography Group, Centre for Biodiversity Genomics / CC BY-SA 3.0

Just in time for Halloween, scientists at Cornell University have published some frightening research, especially if you're an insect!

The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.

"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."

The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.

They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.

They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.

But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.

"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.

What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.

It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.

To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.

First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.

Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.

University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.

"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."

Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.

Hoy agreed.

"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.

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