Story by NASA
August 3, 2012: This past June more than 170 all-time US heat records were tied or broken--many of them originally set in the historically hotter months of July and August. And with a drought plaguing much of the country, the ground is as dry and crispy as a saltine cracker.
By early July, 56% of the contiguous U.S. was experiencing drought. That's the largest percentage in the 12-year record of the U.S. Drought Monitor. Fires scorched over 1.3 million acres across the US in June, reducing hundreds of homes to ashes in the West.
Just imagining prospects for the rest of the summer is enough to bring sweat to your brow. And last winter is partly to blame.
"799 daytime heat records were broken in the first five days of January in the US," says Jake Crouch, a climate scientist from the NOAA National Climatic Data Center. "Last year's was the fourth warmest winter since 1895. And it was dry, with a dearth of snowfall in many places. During most of this past winter and spring, a positive North Atlantic Oscillation pressure pattern kept the jet stream further north and the US warmer and drier than normal."
With little moisture in the soil to evaporate and dissipate some of the sun's energy, more solar radiation is converted to sensible heat, he says.
Of course global warming is on the tips of many tongues.
"CO2 is up from 280 parts per million in the 19th century atmosphere to 400 parts per million now -- a 43% increase," says NASA climatologist Bill Patzert. "We're emitting six times more carbon from fossil fuel use now than we did 50 years ago. Atmospheric CO2 hasn't been this high in 400,000 years."
Greenhouse gasses like CO2 and methane have higher heat capacities than many other gasses, causing the atmosphere to retain more heat.
"The atmosphere becomes a heat source itself, radiating heat back onto the Earth. 85 to 90% of that heat is absorbed by the oceans, because water has a high heat capacity. So the oceans expand and rise. Global sea levels have risen 8 inches over the past 130 years, and the average surface temperature of the entire earth (land surface temperatures plus ocean temperatures) has increased 1.6 °F. These facts," he asserts, "are unequivocal proof of global warming."
But is the record-setting summer 2012 evidence of climate change?
"Not necessarily," says Patzert. "We've always had extreme weather. US history is written in great natural calamities -- tornadoes, hurricanes, heat waves, droughts, floods. Global warming is happening, but it would be irresponsible to say that this heat wave and all these broken records are due to global warming from human causes. It's just not that simple."
John Christy, a scientist from the University of Alabama in Huntsville, agrees: "Heat waves are a natural part of the climate system, and while the recent heat wave was remarkable, it was not as intense as others in the past."
He offers a few examples of past heat waves and droughts.
"The central US suffered several heat waves in the 1930s -- the dust bowl years -- when more statewide, all-time record high temperatures were set than in any other decade. And the western US experienced decades-long droughts in the 12th century. So dry were mountain areas that we can still see near-hundred-year-old trees standing upright in the bottom of alpine lakes where they grew on dry ground 900 years ago.1 This shows that in the 12th century it was so dry and hot that the lakes dried up and allowed trees to grow over a significant period before moisture finally returned."
Patzert and Christy are on opposite sides of the global warming debate. Patzert firmly believes that Earth is warming up and humans are the main reason why. Christy, on the other hand, argues that natural climate variations are almost solely to blame. Yet they both agree that the summer 2012 weather might be just that – weather. They also both believe that improvement is needed in models indicating effects of human and other factors on weather and climate.
"Today's climate models are extremely sophisticated, constantly improving, and will be crucial to charting our future -- but they aren't perfect," says Patzert.
One component that needs improvement: clouds.
"Clouds play a key role in climate because they affect the amount of sunlight reflected and absorbed," says Christy. "We need higher resolution models to portray them more accurately. The distance between grid measurement points in current models is too great to capture meter to meter variations in clouds, land cover, and other variables that affect climate."
One more point of agreement: the summer of 2012 is too hot to handle.
What Happened to All the Snow? --Science@NASA
Europe Hammered by Winter; Is North America Next? -- Science@NASA
More from Crouch: "Another driver could be the La Nina which ended a few months ago. When there is a La Nina, most of the nation tends to be warmer and drier than average, with the exception of the Pacific Northwest. Although La Nina is officially over, there is a lag in the atmosphere and La Nina like conditions are still possible in the atmosphere. We provide an overview of what other atmospheric drivers were likely in play for the warm June that we just experienced at this website."Footnote: (1) For an article on some of these trees, see http://www.nvwra.org/storage/newsletters/jnwra_2_article3_kleppe.pdf .
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