Tuesday, September 11, 2012

2012 U.S. drought and Arctic ice melting: Is this from human impacts on climate systems?

by Rob Elmore, @RobElmore on Twitter – September 2012

For the non-climate-scientist reader (and written by one of the same), this posting aims to highlight input from science writers regarding the 2012 U.S. drought and extensive melting of ice in the Arctic. By presenting these quotes, the posting is intended to help the reader sort through whether the 2012 news stories on these topics should or should not be regarded as clear indications of human impacts on climate systems in wide-ranging parts of the Earth.

(Note: Numbered links below are spelled out as complete web citations at the end of this posting.)

It’s useful to start with quotes from this (1) recent “Information Statement” by the American Meteorological Society, which outlines for scientists and non-scientists alike some key patterns that weather and climate scientists have determined regarding drought and Arctic ice conditions. It includes these quotes:

“Climate models simulate the important aspects of climate and climate change based on fundamental physical laws of motion, thermodynamics, and radiative transfer.”

“...climate models have demonstrated skill in reproducing past climates, and they agree on the broad direction of future climate.”

“Arctic sea ice extent and volume have been decreasing for the past several decades.”

“The model projections show that the largest warming will occur in northern polar regions, over land areas, and in the winter season, consistent with observed trends.”

“For many areas [around the globe], model simulations suggest there will be a tendency towards more intense rain and snow events separated by longer periods without precipitation.”

“...model simulations suggest that precipitation will increase in the far northern parts of North America, and decrease in the southwest and south-central United States where more droughts will occur.”

“For the longer term, paleoclimatic observations suggest that droughts lasting decades are possible and that these prolonged droughts could occur with little warning.”

“Drier conditions in summer, such as those anticipated for the southern United States and southern Europe, are expected to contribute to more severe episodes of extreme heat.”

“There is unequivocal evidence that Earth’s...snow cover, mountain glaciers, and Arctic sea ice are shrinking.”

“Technological, economic, and policy choices in the near future will determine the extent of future impacts of climate change. Science-based decisions are seldom made in a context of absolute certainty.”


Appearing in the Washington Post, this (2) article is by James E. Hansen, who directs the NASA Goddard Institute for Space Studies, and includes these quotes:

“...a stunning increase in the frequency of extremely hot summers...

“Our analysis shows that it is no longer enough to say that global warming will increase the likelihood of extreme weather and to repeat the caveat that no individual weather event can be directly linked to climate change. To the contrary, our analysis shows that, for the extreme hot weather of the recent past, there is virtually no explanation other than climate change.”

“The deadly European heat wave of 2003, the fiery Russian heat wave of 2010 and catastrophic droughts in Texas and Oklahoma last year can each be attributed to climate change.”

“Even with climate change, you will occasionally see cooler-than-normal summers or a typically cold winter. Don’t let that fool you.”

“When we plotted the world’s changing temperatures on a bell curve, the extremes of unusually cool and, even more, the extremes of unusually hot are being altered so they are becoming both more common and more severe.”

"There is still time to act and avoid a worsening climate, but we are wasting precious time."

This (3) article published by CBC News (Canadian Broadcasting Corporation) notes:

“This summer, record-breaking temperatures threw an estimated 62 per cent of America's farms into moderate drought or worse, according to the U.S. Department of Agriculture.”

"We typically don't see drought intensify like we did this year."

“...a study published this month in the journal Nature Climate Change predicts the U.S. will suffer a series of severe droughts in the next two decades...”

This (4) article in Wired includes:

‘ “In any single event, it’s hard to really know if you’re just seeing a natural variation or climate change,” cautioned climatologist Chris Funk of the University of California, Santa Barbara. With that caveat, Funk said when asked if human activity exacerbated the drought, “Tentatively, the answer is yes. To some extent, it is.” ... Funk’s specialty is the dynamics of sea surface temperatures in the Indian Ocean and western Pacific Ocean. Over the last century, and in particular the last two decades, these rose by an average of 1.25 degrees Fahrenheit. Ocean temperature trends can be tricky to interpret, but there’s little scientific disagreement about Indian Ocean warming: It’s almost certainly man-made, a result of greenhouse gases trapping heat in Earth’s atmosphere.‘

‘Bin Guan, a drought specialist at the California Institute of Technology, struck a cautionary note on early interpretations. “Drought development is a long, complicated process,” he said. “Its response to greenhouse gases is more complicated than temperature alone because it’s a combination of temperature, precipitation, evaporation, soil moisture, and other conditions.” Whether the current drought’s severity is linked to greenhouse gas pollution is “difficult to say with certainty,” Guan said. “It could be a combination of both natural forces and human impact, but we can’t be sure, at least for now.” ‘

This (5) transcript of a “Science Friday” interview on NPR (National Public Radio) includes the following quotes:

“Reporting in the Bulletin of the American Meteorological Society, researchers write that extreme heat waves, such as the one last year in Texas, are 20 times more likely today than they were in the 1960s.”

“Tom Peterson is principal scientist at NOAA's National Climatic Data Center in Asheville, North Carolina.”

[Tom  Peterson:] “You know, are you asking about the temperature, how warm it got, or are you asking about the probability of warm temperatures reoccurring? And those can wind up having different answers, so you have to be very cautious about the communication. And that's really some of the questions that have been raised by other scientists is exactly, you know, are we communicating this as precisely, accurately as we should be? And if you get really precisely accurate, sometimes people can't really understand you with all the different caveats.”

“...when you have drought, you have less water able to be evaporated or evapotranspirated from plants, and so more of the energy goes into sensible heat of warming the soil. So droughts can cause heat waves. At the same time, a really intense heat wave can cause a drought, because it fosters so much more evapotranspiration and evaporation of the water off the soil.”

“...climate prediction is much more akin to understanding the change of seasonal cycles and the forces that are affecting that, because now we're seeing - for example, we're seeing spring coming earlier.”

Arctic Ice

This (6) article from Huffington Post notes:

“Each year around March, Arctic sea ice begins its yearly melting period until the extent and volume of ice reach their annual minimums, usually sometime in mid-September. After that point, new ice forms until an annual maximum is reached, typically in March of the following year.”

“...the National Snow and Ice Data Center has reported that from 1979 to 2011, the monthly sea ice extent for September -- the month of the seasonal minimum -- has fallen at a rate of 12 percent per decade.”

“Less summer ice is not only a consequence of climate change, but it will also cause further warming: As the summer ice melts, the light colored ice which reflects the sun's rays back to space is replaced with dark water which absorbs more heat and warms the oceans further. 

This (7) story in Forbes includes these quotes:

“As Arctic Ice Reaches Record Low, Meteorologists Name Humans 'Dominant' Cause Of Climate Change”

“Today, the National Snow and Ice Data Center [NSIDC], in conjunction with NASA, announced today that Arctic sea ice has reached a record low since the previous record-breaking low in 2007.”

‘ “...in the context of what’s happened in the last several years and throughout the satellite record, it’s an indication that the Arctic sea ice cover is fundamentally changing,” NSIDC scientist Walt Meier said in a press release. “The Arctic used to be dominated by multiyear ice, or ice that stayed around for several years,” Meier continued. “Now it’s becoming more of a seasonal ice cover and large areas are now prone to melting out in summer.” ’

This (8) from the Washington Post states:

“The Arctic Ocean’s vast, frozen expanse of ice is rapidly vanishing.”

“The amount of Arctic sea ice is shrinking each year — and will soon disappear altogether in the summer months if the planet keeps warming. Since the 1980s, agencies around the world have deployed satellites to measure the extent of Arctic sea ice...

“Over the past three decades, the summer Arctic sea ice extent has declined roughly 40 percent, and the ice has lost significant volume...”

“A new study in this month’s Environmental Research Letters concludes that between 70 and 95 percent of the Arctic melt since 1979 has been caused by human activity. Man-made global warming has rapidly heated up the Arctic — the region has been warming about twice as fast as the global average. (See here for a good explanation of why.)”

“In the past, scientists have underestimated the pace at which Arctic sea ice would disappear. In 2007, the Intergovernmental Panel on Climate Change (IPCC) figured we wouldn’t see ice-free summers in the Arctic until the end of the century or so. But later observations suggested that sea-ice extent is shrinking far more quickly than the IPCC had forecast. It appears that earlier climate models underestimated certain “feedback” effects.”

This (9) article from the Wall Street Journal notes:

“The Northern Hemisphere's largest expanses of ice have thawed faster and more extensively this year than scientists have previously recorded. And the summer isn't over.

“Studies suggest that more of the massive Greenland ice cap has melted than at any time since satellite monitoring began 33 years ago, while the Arctic sea's ice is shrinking to its smallest size in modern times.

“ "This year's melting season is a Goliath," said geophysicist Marco Tedesco, director of the Cryospheric Processes Laboratory at City University of New York. "The ice is being lost at a very strong pace." ”

Finally, this (10) from AFP (Agence France Presse) by way of the New Zealand Herald includes the following:

“The sea ice in the Arctic Ocean has melted to its smallest point ever in a milestone that may show that worst-case forecasts on climate change are coming true, US scientists said today.”

“The extent of ice observed at the weekend broke a record set in 2007 and will likely melt further with several weeks of summer still to come, according to data from the National Snow and Ice Data Center and the Nasa space agency. The government-backed ice center, based at the University of Colorado at Boulder, said in a statement that the decline in summer Arctic sea ice "is considered a strong signal of long-term climate warming." “

“Michael E. Mann, a lead author of a major UN report in 2001 on climate change, said the latest data reflected that scientists who were criticised as alarmists may have shown "perhaps too great a degree of reticence." "I think, unfortunately, this is an example that points more to the worst-case scenario side of things," said Mann, director of the Earth System Science Center at Penn State University. "There are a number of areas where in fact climate change seems to be proceeding faster and with a greater magnitude than what the models predicted," Mann told AFP. "The sea ice decline is perhaps the most profound of those cautionary tales because the models have basically predicted that we shouldn't see what we're seeing now for several decades," he added.”


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