Climate warming charging water cycle, producing bigger storms
Has the home planet’s pot begun to boil? Is there turbulence awaiting us in the decades ahead?
The energy so far pumped into the Earth’s atmosphere by climate warming has begun to turbo-charge the global water cycle, raising the specter of a future with more devastating storms, accompanied by longer and more implacable droughts.
The rise of the average global temperature about 1 degree Fahrenheit between 1950 and 2000 intensified the Earth’s natural process of evaporation and precipitation by about 4%, researchers reported in a study in the journal Science.
That’s about double the rate predicted by most current climate models, the authors noted.
"Salinity shifts in the ocean confirm climate and the global water cycle have changed,” said lead author Paul Durack, a post-doctoral fellow at the Lawrence Livermore National Laboratory, in this story. "These changes suggest that arid regions have become drier and high rainfall regions have become wetter in response to observed global warming."
It gets worse. If current trends continue -- possibly triggering another 3-5 degrees F of average global warming over the coming decades -- this water cycle could intensify by another 20% or more.
Fasten your seatbelts, people. It’s going to be a bumpy 21st century.
More rain, deeper snow, longer droughts
“More moisture in the atmosphere means storms can carry more rain to produce more- intense rain events causing flash flooding and damage, . . . posing a risk to life,” the authors explained here.
The new study -- “Ocean Salinities Reveal Strong Global Water Cycle Intensification During 1950 to 2000” — was sponsored by Australian Climate Change Science Program. Lead author Durack is a graduate of the CSIRO-University of Tasmania Quantitative Marine Science program. His co-authors were Susan Wijffels and Richard Matear.
As many people might remember from the elementary school cartoonsadorned with smiling Suns and dancing raindrops, the water cycle is at the crux of the Earth’s weather and climate. Warmed by solar energy, water evaporates from the oceans and lakes into the air, where vapor forms clouds and systems, which then drift across the globe to spill rain and snow on land and sea. Rinse and repeat.
The notion that global warming might accelerate this natural process has long been a major issue under investigation by climate scientists. Results could include faster evaporation from the ocean surface, with warmer air holding ever-more water vapor, spawning storms with bigger volumes of precipitation and more violence.
"The ocean matters to climate -- it stores 97% of the world’s water; receives 80% of the all surface rainfall,” explained co-author Matear, with Australia’s Commonwealth Scientific and Industrial Research Organisation, in this story. “It has absorbed 90% of the Earth's energy increase associated with past atmospheric warming."
Further "warming of the Earth’s surface and lower atmosphere is expected to strengthen the water cycle largely driven by the ability of warmer air to hold and redistribute more moisture," he added.
'Weird' Arctic weather
Other research has found equally disconcerting trends, including bouts of “weird” Arctic weather and more lightning strikes during thunderstorms.
“Among the most important potential impacts of anthropogenic climate warming are changes in extreme weather,” explained Anthony Del Genio in Earthzine and a posting by NASA. “Wet regions will become rainier while arid and semi-arid regions expand and become drier. Equally important are the winds, hail, lightning, and fires that result from storms.”
The trends are not straightforward. People might be most terrified of the prospect of tornadoes or mondo hurricanes. But will these killer storms hit more often? Not necessarily.
For instance, recent evidence suggests that thunderstorms might become less frequent in general, but the storms that do hit could be more severe and deliver more lightning strikes.
With more lightning, this shifting pattern could trigger an increase in wildfires in Alaska and the western United States.
“As climate warms, we might experience fewer storms overall, but more of the strongest storms,” Del Genio said here. “What the public cares about most, though, is storm damage, which depends on more than just changes in the storms themselves. Regardless of whether lightning increases with warming, drying in western North America will likely lead to more fire damage (and) more flooding damage to coastal areas from storm surges.”
In the high Arctic, warming climate has gone beyond tinkering with the water cycle and triggered “weird weather” throughout the Northern Hemisphere, suggested Jennifer Francis, a researcher at the Institute of Marine and Coastal Sciences at Rutgers University, in this story posted in March by Environment 360 at Yale.
A new “Arctic amplification” feeds on itself — melting sea ice, raising air temperatures as much as 9 degrees F and altering the jet stream storm tracks, she said.
“As sea ice retreats, sunshine that would have been reflected back to space by the bright ice is instead absorbed by the ocean, which heats up, melting even more ice,” Francis explained here.
“Extra heat entering the vast expanses of open water that were once covered in ice is released back to the atmosphere in the fall. This has led to an increase in near-surface, autumn air temperatures of (3.6-9 degrees F) over much of the Arctic Ocean during the past decade. All that extra heat being deposited into the atmosphere cannot help but affect the weather, both locally and on a large scale. And there are growing indications that some weather phenomena in recent years — such as prolonged cold spells in Europe, heavy snows in the northeastern U.S. and Alaska, and heat waves in Russia — may be related to Arctic amplification.”
Using salt as a signal about rain
The water cycle research led by Durack cued into how the saltiness, or salinity, observed in vast regions of the global ocean has changed in relation to rising temperatures. In gathering thousands of salinity measurments taken across the globe since 1950, the scientists also drew on the global Argo system of thousands of oceanographic buoys for data since 2000.
New York Times science writer Justin Gillis provided a good explanation of their difficulties in detailing the process and how it has changed in a story published last week:
“The paper is the latest installment in a long-running effort by scientists to solve one of the most vexing puzzles about global warming.
“While basic physics suggests that warming must accelerate the cycle of evaporation and rainfall, it has been difficult to get a handle on how much acceleration has already occurred -- and to project the changes that are likely to result from continued planetary warming.
“The fundamental problem is that measurements of evaporation and precipitation over the ocean — which covers 71% of the earth’s surface, holds 97% of its water and is where most evaporation and precipitation occurs — are spotty at best. To overcome that, scientists are trying to use the changing saltiness of the ocean’s surface as a kind of rain gauge.
“That works because, as rain falls on a patch of the ocean, it freshens the surface water. Conversely, in a region where evaporation exceeds rainfall, the surface becomes saltier.”
In the end, Durack and his colleagues concluded that the water cycle would intensify about 8% for every additional degree Celsius of warming on the Earth’s surface.
The changes won’t be consistent or uniform. Some regions -- especially the arid zones -- will grow even drier. Other places, where rainfall might be plentiful now, will grow even wetter. Large storms may become even more damaging, even if less frequent.
Unforeseen consequences will disrupt the lives of millions.
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