FloodList: New Scale to Characterize Strength and Impacts of Atmospheric River Storms

A team of researchers led by Scripps Institution of Oceanography at the University of California San Diego has created a scale to characterize the strength and impacts of “atmospheric rivers” - long narrow bands of atmospheric water vapor pushed along by strong winds. They are prevalent over the Pacific Ocean and can deliver to the Western United States much of its precipitation during just a few individual winter storms.

Atmospheric river hits California. Credit: Jesse Allen, NASA Earth Observatory/ VIIRS satellite

They are the source of most of the West Coast’s heaviest rains and floods, and are a main contributor to water supply. For example, roughly, 80 percent of levee breaches in California’s Central Valley are associated with land-falling atmospheric rivers.

The scale, described in the February 2019 Bulletin of the American Meteorological Society, assigns five categories to atmospheric rivers (ARs) using as criteria the amount of water vapor they carry and their duration in a given location. The intention of the scale is to describe a range of scenarios that can prove beneficial or hazardous based on the strength of atmospheric rivers.

The scale was developed by F. Martin Ralph, director of the Center for Western Water and Weather Extremes (CW3E) at Scripps, in collaboration with Jonathan Rutz from the National Weather Service and several other experts. It ranks atmospheric rivers from 1 to 5 and creates the categories “weak,” “moderate,” “strong,” “extreme,” and “exceptional.” It uses amounts of water vapor within an atmospheric river as its basis and a period of 24-48 hours as its standard measurement of duration. When an AR lasts in an area for less than 24 hours, it is demoted by one category, but if it lingers for more than 48 hours, it is promoted. This approach is based on research showing that a combination of strong water vapor transport with long duration over a location, is what causes the greatest impacts. Unlike the hurricane scale, recently criticized for not representing adequately the impacts of slow-moving lower-category hurricanes, the AR scale builds in duration as a fundamental factor.

Key describing atmospheric river intensity categories. Credit: CW3E/Scripps Institution of Oceanography at UC San Diego.

The scale ranks ARs as follows:

• AR Cat 1 (Weak): Primarily beneficial. For example, a February 23, 2017, AR hit California, lasted 24 hours at the coast, and produced modest rainfall.
• AR Cat 2 (Moderate): Mostly beneficial, but also somewhat hazardous. An atmospheric river on November 19-20, 2016, hit Northern California, lasted 42 hours at the coast, and produced several inches of rain that helped replenish low reservoirs after a drought.
• AR Cat 3 (Strong): Balance of beneficial and hazardous. An atmospheric river on October 14-15, 2016, lasted 36 hours at the coast, produced 5-10 inches of rain that helped refill reservoirs after a drought, but also caused some rivers to rise to just below flood stage.
• AR Cat 4 (Extreme): Mostly hazardous, but also beneficial. For example, an atmospheric river on January 8-9, 2017, that persisted for 36 hours produced up to 14 inches of rain in the Sierra Nevada and caused at least a dozen rivers to reach flood stage.
• AR Cat 5 (Exceptional): Primarily hazardous. For example, a Dec. 29 1996 to January 2, 1997, atmospheric river lasted over 100 hours at the Central California coast. The associated heavy precipitation and runoff caused more than $1 billion in damages.

Ralph is considered a leading authority on atmospheric rivers, which were officially defined by the American Meteorological Society in 2017. Researchers have only begun to study atmospheric rivers in depth in the past two decades building on earlier research into extra-tropical cyclone structure and precipitation, especially in the United Kingdom. In that time, they have also come to understand how these events frequently make the difference between flood and drought years in key coastal regions around the world such as California.

All categories of atmospheric river intensity were observed during a 2017 event. Credit: CW3E/Scripps Institution of Oceanography at UC San Diego

Ralph said that the scale could provide a crucial tool to officials with an operational need to assess flood potential in their jurisdictions before storms strike. Unlike other scales that focus primarily on damage potential, such as the Fujita scale for tornadoes or the Saffir-Simpson scale for hurricanes, the atmospheric river scale accounts not only for storms that can prove hazardous, but also for storms that can provide benefits to water supply.

“The scale recognizes that weak ARs are often mostly beneficial because they can enhance water supply and snow pack, while stronger ARs can become mostly hazardous, for example if they strike an area with conditions that enhance vulnerability, such as burn scars, or already wet conditions,” say Ralph and co-authors in the paper appearing today in the February 2019 issue of the Bulletin of the American Meteorological Society, “Extended durations can enhance impacts.”

Coauthors of the paper include weather forecasters, such as meteorologist Jon Rutz and Chris Smallcomb of the National Weather Service (NWS).

“The concept of ARs has directly benefited NWS operations in the West through better scientific understanding, more accurate precipitation forecasts, and a better vehicle for communicating impacts to our partners,” said Rutz. “The AR scale is a significant step forward, providing forecasters with a tool to distinguish between primarily beneficial and primarily hazardous storms. I anticipate that this scale will be adopted and highly used.”

Previous analysis has shown that on the West Coast, the Oregon coast receives the most atmospheric rivers in the “extreme” range (AR Cat 4), averaging about one per year. Washington receives extreme atmospheric rivers about every two years, the Bay Area about every three years and Los Angeles every 10 years. The 1996-1997 atmospheric river that caused the largest flood damages in California since 1950 would be categorized as an “exceptional” AR storm. The strongest atmospheric river storms hitting the Southern California coast annually, typically fall in the “moderate” to “strong” range (AR Cat 2-3).

When atmospheric river storms along the West Coast are predicted, the scale rankings will be updated and communicated via the CW3E website and Twitter handle. This new scale will add to data, seasonal outlooks and precipitation forecasts provided by the center as a resource to water managers, weather forecasters, emergency officials, policy makers, and others.

The researchers said that the atmospheric river scale is intended as a tool to increase situational awareness ahead of a major storm in a way that reflects conditions broadly in a region of roughly 50 km size. It is not intended to represent detailed conditions on smaller spatial scales where variable topography, land surface types, and vulnerabilities vary greatly and thus modulate storm impacts.

“This scale enables improved awareness of the potential benefit versus hazard of a forecast AR,” said co-author Michael Anderson of the California Department of Water Resources. “It can serve as a focal point for discussion between water managers, emergency response personnel and the research community as these key water supply and flood inducing storms continue to evolve in a changing climate.”

“Forecasters in the western U.S. have been using the concept of ARs in their forecasting for a few years now, and many have been looking for a way to distinguish beneficial from hazardous AR storms,” said Rutz. “The scale was designed partly to meet this need, and it is anticipated that it will be used extensively.”

Source: University of California – San Diego

http://floodlist.com/america/usa/new-scale-to-characterize-strength-and-impacts-of-atmospheric-river-storms

Bulletin of the American Meteorological Society, 94(4) (April 2013) 499-514; doi: http://dx.doi.org/10.1175/BAMS-D-11-00262.1

Monitoring and Understanding Trends in Extreme Storms: State of Knowledge

Kenneth E. Kunkel, Thomas R. Karl, Harold Brooks, James Kossin, Jay H. Lawrimore, Derek Arndt, Lance Bosart, David Changnon, Susan L. Cutter, Nolan Doesken, Kerry Emanuel, Pavel Ya. Groisman, Richard W. Katz, Thomas Knutson, James O'Brien, Christopher J. Paciorek, Thomas C. Peterson, Kelly Redmond, David Robinson, Jeff Trapp, Russell Vose, Scott Weaver, Michael Wehner, Klaus Wolter and Donald Wuebbles

Abstract

The state of knowledge regarding trends and an understanding of their causes is presented for a specific subset of extreme weather and climate types. For severe convective storms (tornadoes, hailstorms, and severe thunderstorms), differences in time and space of practices of collecting reports of events make using the reporting database to detect trends extremely difficult. Overall, changes in the frequency of environments favorable for severe thunderstorms have not been statistically significant. For extreme precipitation, there is strong evidence for a nationally averaged upward trend in the frequency and intensity of events. The causes of the observed trends have not been determined with certainty, although there is evidence that increasing atmospheric water vapor may be one factor. For hurricanes and typhoons, robust detection of trends in Atlantic and western North Pacific tropical cyclone (TC) activity is significantly constrained by data heterogeneity and deficient quantification of internal variability. Attribution of past TC changes is further challenged by a lack of consensus on the physical linkages between climate forcing and TC activity. As a result, attribution of trends to anthropogenic forcing remains controversial. For severe snowstorms and ice storms, the number of severe regional snowstorms that occurred since 1960 was more than twice that of the preceding 60 years. There are no significant multidecadal trends in the areal percentage of the contiguous United States impacted by extreme seasonal snowfall amounts since 1900. There is no distinguishable trend in the frequency of ice storms for the United States as a whole since 1950.

Accepted: May 15, 2012

A supplement to this article is available online (10.1175/BAMS-D-11-00262.2)

 

Correspondence: Kenneth Kunkel, Cooperative Institute for Climate and Satellites, 151 Patton Ave., Asheville, NC 28801. e-mail: ken.kunkel@noaa.gov

http://journals.ametsoc.org/doi/full/10.1175/BAMS-D-11-00262.1

James Hansen et al., Climate Sensitivity, Sea Level, and Atmospheric CO2 [in review]

Climate Sensitivity, Sea Level, and Atmospheric CO₂

James Hansen, Makiko Sato, Gary Russell and Pushker Kharecha

NASA Goddard Institute for Space Studies and Columbia University Earth Institute, New York, NY, U.S.A.

Abstract

Cenozoic temperature, sea level and CO₂ co-variations provide insights into climate sensitivity to external forcings and sea level sensitivity to climate change. Pleistocene climate oscillations imply a fast-feedback climate sensitivity 3 ± 1 °C for 4 W/m² CO₂ forcing for the average of climate states between the Holocene and Last Glacial Maximum (LGM), the error estimate being large and partly subjective because of continuing uncertainty about LGM global surface climate. Slow feedbacks, especially change of ice sheet size and atmospheric CO₂, amplify total Earth system sensitivity. Ice sheet response time is poorly defined, but we suggest that hysteresis and slow response in current ice sheet models are exaggerated. We use a global model, simplified to essential processes, to investigate state-dependence of climate sensitivity, finding a strong increase in sensitivity when global temperature reaches early Cenozoic and higher levels, as increased water vapor eliminates the tropopause. It follows that burning all fossil fuels would create a different planet, one on which humans would find it difficult to survive.

Full paper [in review] here: http://arxiv.org/ftp/arxiv/papers/1211/1211.4846.pdf

Water vapor belches over the North and South Poles

These animations absolutely stunned me the first time I saw them, and truth be told, they still awe me.

The first is an animation of the water vapor cycle over the globe -- notice the way the Earth seems to breathe as the solar equator moves north and south.

At the poles, WV concentrates above the Arctic during December-January, and above Antarctica during June-July.

It is easier to see what occurs at the poles if you look at this animation frame by frame (each month is one frame).

Water Vapor

July 2012July 2002

Download a Quicktime animation of this dataset (5 MB)

http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MYDAL2_M_SKY_WV

Next, we see a mechanism whereby the WV perhaps disappears so quickly after January in the Arctic:

http://eoimages.gsfc.nasa.gov/images/imagerecords/36000/36972/npole_gmao_200901-02.mov

Let this QuickTime file load up and watch the polar vortex being divided in two (animation on the left) while hot air shoots up 30,000 m and temperatures up there go from -88 C to +12 C! (animation on the right).  I call this an atmospheric water vapor belch.

This past January, I was able to download a satellite photo of the Arctic that appeared to show this sort of mechanism in action:

Notice all the leads in the sea ice -- that stuff used to be so pristine looking before 2007.

These satellite photos come from the Canadian weather service and are updated every few hours:

http://www.weatheroffice.gc.ca/data/satellite/hrpt_dfo_ir_100.jpg

UPDATE:  A commenter named Peter says that the grey areas at the poles are areas not covered by the satellites in the darkness of winter.  Would anyone else care to comment on this?

1 COMMENT:

Peter said...

You're flat-out wrong. The grey areas showing over the North Pole in (NH) winter and the South pole in (SH) winter are areas with no data coverage. Presumably the satellite used (MODIS) can't get adequate data in the dark.

You can tell it's missing data because it's pure grey rather than a shade of yellow.

August 11, 2012 4:37 PM 

Peter, I am not sure why you think the MODIS satellite was used.  Other researchers have used the Aqua satellite that uses infrared.  Some satellites use radar or microwaves.  See, for example, this article:

Water Vapor Confirmed as Major Player in Climate Change

11.17.08

 

The distribution of atmospheric water vapor, a significant greenhouse gas, varies across the globe. During the summer and fall of 2005, this visualization shows that most vapor collects at tropical latitudes, particularly over south Asia, where monsoon thunderstorms swept the gas some 2 miles above the land.
Credit: NASA
> Watch videoWater vapor is known to be Earth’s most abundant greenhouse gas, but the extent of its contribution to global warming has been debated. Using recent NASA satellite data, researchers have estimated more precisely than ever the heat-trapping effect of water in the air, validating the role of the gas as a critical component of climate change.

Andrew Dessler and colleagues from Texas A&M University in College Station confirmed that the heat-amplifying effect of water vapor is potent enough to double the climate warming caused by increased levels of carbon dioxide in the atmosphere. 

With new observations, the scientists confirmed experimentally what existing climate models had anticipated theoretically. The research team used novel data from the Atmospheric Infrared Sounder (AIRS) on NASA’s Aqua satellite to measure precisely the humidity throughout the lowest 10 miles of the atmosphere. That information was combined with global observations of shifts in temperature, allowing researchers to build a comprehensive picture of the interplay between water vapor, carbon dioxide, and other atmosphere-warming gases. The NASA-funded research was published recently in the American Geophysical Union's Geophysical Research Letters.

"Everyone agrees that if you add carbon dioxide to the atmosphere, then warming will result,” Dessler said. “So the real question is, how much warming?" 

The answer can be found by estimating the magnitude of water vapor feedback. Increasing water vapor leads to warmer temperatures, which causes more water vapor to be absorbed into the air. Warming and water absorption increase in a spiraling cycle. 

Based on climate variations between 2003 and 2008, the energy trapped by water vapor is shown from southern to northern latitudes, peaking near the equator.
Credit: Andrew Dessler
> Larger imageWater vapor feedback can also amplify the warming effect of other greenhouse gases, such that the warming brought about by increased carbon dioxide allows more water vapor to enter the atmosphere.

"The difference in an atmosphere with a strong water vapor feedback and one with a weak feedback is enormous," Dessler said. 

Climate models have estimated the strength of water vapor feedback, but until now the record of water vapor data was not sophisticated enough to provide a comprehensive view of at how water vapor responds to changes in Earth's surface temperature. That's because instruments on the ground and previous space-based could not measure water vapor at all altitudes in Earth's troposphere -- the layer of the atmosphere that extends from Earth's surface to about 10 miles in altitude.

AIRS is the first instrument to distinguish differences in the amount of water vapor at all altitudes within the troposphere. Using data from AIRS, the team observed how atmospheric water vapor reacted to shifts in surface temperatures between 2003 and 2008. By determining how humidity changed with surface temperature, the team could compute the average global strength of the water vapor feedback. 

“This new data set shows that as surface temperature increases, so does atmospheric humidity,” Dessler said. “Dumping greenhouse gases into the atmosphere makes the atmosphere more humid. And since water vapor is itself a greenhouse gas, the increase in humidity amplifies the warming from carbon dioxide."

Specifically, the team found that if Earth warms 1.8 degrees Fahrenheit, the associated increase in water vapor will trap an extra 2 Watts of energy per square meter (about 11 square feet).

"That number may not sound like much, but add up all of that energy over the entire Earth surface and you find that water vapor is trapping a lot of energy," Dessler said. "We now think the water vapor feedback is extraordinarily strong, capable of doubling the warming due to carbon dioxide alone."

Because the new precise observations agree with existing assessments of water vapor's impact, researchers are more confident than ever in model predictions that Earth's leading greenhouse gas will contribute to a temperature rise of a few degrees by the end of the century. 

"This study confirms that what was predicted by the models is really happening in the atmosphere," said Eric Fetzer, an atmospheric scientist who works with AIRS data at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Water vapor is the big player in the atmosphere as far as climate is concerned." 

"UV Dosage Levels in Summer: Increased Risk of Ozone Loss from Convectively Injected Water Vapor," by James G. Anderson*, David M. Wilmouth, Jessica B. Smith and David S. Sayres, Science, DOI: 10.1126/science.1222978

Science DOI: 10.1126/science.1222978

• REPORT

UV Dosage Levels in Summer: Increased Risk of Ozone Loss from Convectively Injected Water Vapor

1. James G. Anderson*, 
2. David M. Wilmouth, 
3. Jessica B. Smith and 
4. David S. Sayres

1. ¹Department of Chemistry and Chemical Biology, Department of Earth and Planetary Sciences and School of Engineering and Applied Sciences, Harvard University, Cambridge, MA.

1. ↵*Correspondence: anderson@huarp.harvard.edu.

ABSTRACT

The observed presence of water vapor convectively injected deep into the stratosphere over the United States fundamentally changes the catalytic chlorine/bromine free radical chemistry of the lower stratosphere by shifting total available inorganic chlorine into the catalytically active free-radical form, ClO. This chemical shift markedly affects total ozone loss rates and makes the catalytic system extraordinarily sensitive to convective injection into the mid-latitude lower stratosphere in summer. Were the intensity and frequency of convective injection to increase as a result of climate forcing by the continued addition of CO₂ and CH₄ to the atmosphere, increased risk of ozone loss and associated increases in UV dosage would follow.

http://www.sciencemag.org/content/early/2012/07/25/science.1222978

SELECTED TEXT FROM THE FULL PAPER:

Because the binary sulfate-water aerosols are ubiquitous in the lower stratosphere, if the necessary temperature and water conditions are met, then heterogeneous conversion of inorganic chlorine to free radical form can occur anywhere, not just in the polar regions. While the Arctic lower stratosphere is marginally colder than the mid-latitude lower stratosphere over the US in summer, what matters is the combination of water vapor concentration and temperature.

The in situ observations of H₂O obtained from both the high altitude NASA ER-2 and WB-57 aircraft extending over a number of recent missions are summarized in Fig. 1B. The data shown were retrieved during flights originally selected to observe the outflow from typical convective storms over the US in summer. What proved surprising is the remarkable altitude to which large concentrations of water vapor are observed to penetrate. The convective injection of water into the stratosphere was also observed with surprising frequency, occurring in approximately 50% of the summertime flights over the US. The convective origin of this water vapor is established by simultaneous in situ observations of H₂O and the HDO isotopologue (19, 20), the concentration of which differentiates between direct convective injection and other pathways linking the troposphere and stratosphere (19, 21–23). The observed presence of water vapor enhancements reaching and occasionally exceeding 12 ppmv at temperatures in the vicinity of 200 K in the altitude region between 15 and 20 km, as displayed in Fig. 1B, has significant consequences.

The initiation of fundamental changes in the photochemistry of the lower stratosphere in summer is captured in Fig. 1C, that superimposes on the threshold plot for chlorine activation over the range of 2–10 μm²/cm³ for reactive surface area, the observed in situ H₂O mixing ratios and temperatures at 90 ± 10 mb pressure. It is clear that, at observed water vapor concentrations and temperatures, the threshold for chlorine activation converting inorganic chlorine to free radical form is routinely crossed in the summertime. The result is that ClO can become a major component of the available inorganic chlorine budget within regions of high water vapor. Convective injection of water vapor to heights reported here can occur in storm systems that are ~50 km across, with smaller domains of high altitude injection embedded within them at their origin (24). The elevated concentrations of water can spread to 100 km or more in horizontal extent within a few days (19, 25), and remain at the elevated levels reported here over a period of days. This phenomenon has been analyzed by Newman et al. (26) using high altitude (70–100 mb) observations of rocket plume dispersion that defines the rate of horizontal spreading from a point source. Additionally, the circular flow pattern of air in the lower stratosphere over the US resulting from the North American summer monsoon provides the potential for repeated convective injection events into the summer lower stratosphere over the US.

***************

There are a number of important considerations associated with the issue of convective injection of water vapor inducing chlorine activation and catalytic removal of ozone over mid-latitudes of the NH in summer. First is the fact that a remarkably dry stratosphere characterizes the current climate state. However, the paleorecord holds evidence that the stratosphere, under conditions of high CO₂ concentrations, was characterized by significantly higher water vapor concentrations than is the case today (43, 44). If currently increasing concentrations of CO₂, CH₄ and other infrared active gasses force the stratospheric system to a state of increasing water vapor concentrations, the impact on ozone is of significant concern given the concentrations of chlorine and bromine in the stratosphere today.

Second, the loss of ice from the Arctic Ocean opens the possibility for significant increases in CO₂ and CH₄ release from melt zones in the Arctic. A release of just 0.5% per year of the carbon tied up in the soils of Siberia and Northern Alaska alone will double the carbon added to the atmosphere each year from the combustion of fossil fuels world-wide (45). This release of carbon from clathrates and permafrost will accelerate the forcing of the climate that is potentially linked to the intensity and frequency of convective injection of water into the stratosphere.

Third, engineering the climate by the addition of sulfates to increase reflective aerosol concentrations and thereby reduce climate forcing by reflecting sunlight back to space (46, 47) would significantly increase reactive surface area which would accelerate the processing of chlorine to free radical form (Fig. 1, A and C), thereby decreasing ozone concentrations. In the same vein, the convective injection of water vapor into the stratosphere increases the sensitivity of ozone loss to volcanic injection of sulfates into a stratosphere with current loading of chlorine and bromine. Evidence for this was presented for the eruption, in 1991, of Mt. Pinatubo by Salawitch et al. (35).

Fourth, from the perspective of human health, a primary concern is that decreasing ozone concentrations, particularly in summer over populated areas, results in increased UV dosage levels. Sustained increases in UV dosage levels are in turn associated with the increased incidence of skin cancer (48, 49), which is currently 1 million new cases a year in the US (49).

Lastly we emphasize that, because chlorine activation depends exponentially on water vapor and temperature, and in turn that the forcing of climate may well control the convective injection of water into the lower stratosphere, the idea that ozone “recovery” is in sight because we have controlled CFC and halon release is a potentially significant misjudgment.                

Doug O'Harra: Climate warming charging water cycle, producing bigger storms, according to study lead by Paul Durack

Climate warming charging water cycle, producing bigger storms

by Doug O'Harra, Alaska Dispatch, May 4, 2012

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.

http://www.alaskadispatch.com/article/climate-warming-charging-water-cycle-producing-bigger-storms