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Saturday, January 31, 2015

Extreme Climate Change


A
 satellite image shows the huge snowstorm that blanketed the northeastern United States this week. The blizzard was an example of how storms are getting less common but more intense. (NASA/NOAA/NPP/VIIRS)



Climate scientists have been warning for a while that as the planet heats up, storms will become fewer but stronger. This trend has been seen in a variety of historical data tracking wind speed, rain and snow over the past century or so. Now a team of researchers has figured out why, and the explanation is firmly rooted in atmospheric thermodynamics. Global warming is intensifying the world’s water cycle, and that drains energy from the air circulation that drives stormy weather, say Frederic Laliberté of the University of Toronto and his colleagues.

The researchers “have offered a thermodynamic explanation for what the models have been doing all along,” says Olivier Pauluis of New York University, who wrote an accompanying perspective article on the study.
Earth's atmosphere acts like a gigantic heat engine, working on many of the same principles as your car’s engine. Fuel—in this case, energy from the sun—is used to do work. Because more sunlight hits the tropics than higher latitudes, the planet constantly redistributes heat via air motions. Those air motions are the engine’s work. They also help produce the rainstorms and snowstorms that can ruin your day. The engine isn't 100-percent efficient, though. Some heat is lost to space. And much of the remaining energy is expended in the planet’s water cycle, used in the evaporation and precipitation of water.
In their new study, appearing today in Science, Laliberté and his colleagues wanted to see how climate change is affecting this engine's performance. They compared climate records from 1981 to 2012 with climate simulations that model how Earth will behave from 1982 to 2098. They calculated that about a third of the atmospheric energy budget goes to the water cycle. But due to climate change, more energy is going into that cycle—overall, there’s more evaporation and more precipitation—leaving less energy for atmospheric circulation. The atmosphere still needs to get rid of all that precipitation, but it has to do it in fewer storms, which is why the storms get more intense.
“In a warming climate, there will be more water vapor lying around and therefore more fuel for such a storm, making it deepen even more and dump even more precipitation,” Laliberté says. This week’s big snowstorm in the Northeast “was a prime example of the type of atmospheric motions we describe in this paper. It was large-scale, it contained a lot of water vapor [and] it deepened quickly as it encountered a very cold air mass coming down from Canada.”
But while this week’s storm may be an example of what to expect, the paper does not say whether storms in any one part of the world should become more intense than others. “It remains to be understood how do [these findings] translate in terms of specific systems,” Pauluis says. “For example, should we expect the same reduction across the globe, or should tropical systems be affected more strongly?”
“This study says very little about regional climate change,” Laliberté admits. However, he says, “statements for different regions using the same perspective are in the works.” 
Extreme La Niñas could become more frequent because of global warming, according to a study out this week in the British journal Nature Climate Change.
The La Niña climate pattern — a natural phenomenon — is defined as cooler-than-average surface water in the tropical Pacific Ocean. This cooling can set off a chain reaction of weather events around the world, including more hurricanes in the Atlantic, more droughts in the U.S. Southwest and flooding in western Pacific nations.
"Extreme droughts in California will occur more often" if there are more frequent La Niñas, said the study's lead author, Wenju Cai of Australia's Commonwealth Scientific and Industrial Research Organization.
Because of man-made climate change — from the emissions of greenhouse gases — extreme La Niñas will pop up about every 13 years this century, as opposed to once every 23 years as was the case throughout the 1900s, according to the study.
"An increased frequency in extreme La Niña events, most of which occur in the year after an extreme El Niño, would mean an increase in the occurrence of devastating weather events, with profound socioeconomic consequences," Cai said.
La Niñas are the opposite of the more well-known El Niños, which are defined as warmer-than-average ocean water in the Pacific. What's unsettling, Cai said, is that both La Ninas and El Niños could become more intense and frequent because of climate change, leading to wild extremes of wet and dry weather.
This study was a follow-up to one last year that found El Ninos would also double in frequency.
The studies simulated future climate patterns using computer models, which have limitations, Antonietta Capotondi, a scientist from the National Oceanic and Atmospheric Administration's Earth System Research Laboratory, noted in a commentary in the same issue of Nature Climate Change.
"Despite the uncertainties on the reliability of the model projections, the study of Cai and colleagues establishes a plausible scenario of changes that may have very serious implications for society," he wrote.
Other scientists urged caution about reading too much into the findings.
"I would say that is it certainly possible that both El Niño and La Niñas could grow more extreme, but there is still much work to be done to explore and test this idea," said meteorologist Michelle L'Heureux of the Climate Prediction Center. "The ideas in this paper are plausible, but are they proven? Not at this point."
Climate analysis chief Kevin Trenberth of the National Center for Atmospheric Research said he was surprised at the level of confidence expressed in the paper because of how inaccurate model simulations can be.
"Not too many, if any, models are really realistic," he said.
New research published this week reveals that vast stretches of the ocean interior abruptly lost oxygen during the transition out of the last ice age that occurred 17,000–10,000 years ago. This event was the most recent example of large-scale global warming, and was caused primarily by changes in Earth’s orbit around the sun
Past climate events provide informative case studies for understanding what is currently happening to the modern climate system. For this research, marine sediment core records across the Pacific Ocean were used to reconstruct the subsurface “footprint” of dissolved oxygen loss during abrupt global climate warming. 
Like most of the life on the planet, the large majority of marine organisms need oxygen to live. Most marine life, from salmon, crabs, to shellfish, respires oxygen and many forms are intolerant of low oxygen seawater. Low oxygen zones have been incorrectly referred to as “dead zones.” In reality, they are host to bizarre ecosystems of extremophiles: worms, bacteria, and specialized urchins and bivalves colonize these harsh environments. 
But, importantly, few commercially significant species of fish or shellfish can live within the low oxygen zones. So, if you are a microbial biologist you might be very excited to find a low oxygen zone, but if you are a commercial fisherperson, that low oxygen zone represents a no-go environment for fishing.
I asked Dr Tessa Hill, associate professor in the Department of Earth of Planetary Sciences at the University of California at Davis, and one of my coauthors on this research, to reflect on motivation behind this project. She said,
This study provides an excellent example of utilizing past periods environmental change to understand and predict the consequences of human-induced climate change, and where we may be headed in the future.
The new research, which I led, found that entire ocean basins can abruptly lose dissolved oxygen in sync with other global-scale climate change indicators: temperature rise, atmospheric carbon concentration increases, and sea level rise.
From the Subarctic Pacific to the Chilean margin in the Southern Hemisphere, we found evidence of extreme oxygen loss stretching from the shallow upper ocean to about 3,000 meters deep in some regions. The transition from the last ice age to today’s warmer climate substantially reduced the oxygenated habitat of the global ocean and reorganized the distribution of marine life.
Low oxygen zones were not found in the upper ocean in the glacial world; once the deglaciation (ie the shedding of massive glaciers, the rise of global temperatures) was underway, ocean systems dramatically responded. Upper ocean ecosystems, which are those that are connected to the surface ocean and have high concentrations of dissolved oxygen, were compressed towards the ocean surface. Below these oxygenated ecosystems, vast and inhospitable low oxygen zones developed.
Major changes in the distribution of oxygen are already underway in the modern ocean. Modern losses of dissolved oxygen have been detected in every ocean basin by oceanographers and modern instrumentation. I asked Dr Lisa A Levin, Distinguished Professor at the Scripps Institution of Oceanography, University of California at San Diego for her perspective on climate-influenced oxygen changes. She told me,
It is important that oxygen appears on our ‘radar screen’ as we look into the future, for oxygen loss in the ocean exerts critical control on the numbers, types and distributions of fish and shellfish that we harvest. By understanding the coupling in the past between the global climate system and oxygen in the ocean we are better prepared to adapt human activities to future changes in oxygenation.
Oceanographers can anticipate that subsurface low oxygen zones have the capacity to rapidly expand to states that the Earth hasn’t seen in 14,000 years. How do we manage and conserve an ocean that is moving towards a physical state that has never been observed in human history
These are real and critical issues that modern fisheries, conservation and resource management will have to grapple with in the coming decades. The immense risk of ocean oxygen loss in a future of climate change essentially dwarfs the existing modern paradigms of ecosystem-level conservation and management action.
To reframe this information, not as a scientist, but as a citizen, a SCUBA diver and salmon eater: we really have a lot to lose in the face of climate change. We need a living, breathing ocean to sustain us, and to sustain the balance of our ocean’s biodiversity, in the future. 
It is my hope that this research can illustrate the risks to our living planet and our food system, which go hand-in-hand with of the need for political solutions to human-caused climate change that are thus far lacking.

New research reveals extreme oxygen loss in oceans during past climate change Sarah Moffitt 29 January 2015 

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