Judith Curry Advocates Against Action on Climate Change

by Michael Mann, Huffington Post, October 17, 2014

Georgia Tech's Judith Curry has authored an op-ed in the Wall Street Journal claiming that "there is less urgency to phase out greenhouse gas emissions now" than in the past. This could not be further from the truth.

She ties her argument to a new study she has co-authored, as well as the global warming speed bump (or faux pause). Neither offers a compelling reason to avoid reducing emissions. Her study looks at recent temperatures and uses them to try and determine how much the atmosphere will warm from our CO2 emissions.

The result is a figure low enough for contrarians to trumpet, but still not really that far from the official figures provided by the UN's IPCC, the gold standard of climate science. This is why the new study (and the others very similar to it) have elicited only a collective yawn from serious academia.

So the piece repeats the same tired claims about lowered sensitivity, using the "pause" meme and her own study as justification for delaying action. According to her (and of course the contrarians) a limited set of studies using a single incomplete methodology are reason enough to put off getting serious about climate change. One of us (Dr. Mann) addressed this misguided claim about climate sensitivity to CO2 earlier this year in a detailed piece in Scientific American.

To summarize the article, it turns out that even if one assumes these recent studies are correct, this buys us only a decade of extra time before crossing the internationally agreed-upon limit of 2 °C of warming. This means that even if Curry's correct, it may just be the difference between bad and terrible consequences of our inability to get emissions under control.

This understanding is shared by all the mainstream climate scientists who have examined the breadth of the scientific literature. For example, Oxford University professor and IPCC author Dr. Myles Allen told Carbon Brief that a reduction in climate sensitivity as presented by Curry and others "is hardly a game-changer" because it "would mean the changes we expect between now and 2050 might take until the early 2060s instead."

In a response from the Union of Concerned Scientists, Peter Frumhoff describes it even more eloquently, saying that Curry's call for delay "is like refusing to treat a patient because you can't tell if their fever is 103 or 104 degrees."

Esoteric and academic arguments about the response of the atmosphere to a doubling of CO2 may be interesting for those steeped in the peer-reviewed literature, but for the public and policy makers the important and unfortunate fact is that climate change is continuing unabated. This was the hottest September on record, after the hottest August on record (yielding the hottest summer on record), and the oceans continue to warm rapidly. In fact, some parts of the ocean have been shown to be warming even more rapidly than we thought.

In the end, Curry's claims fly in the face of what we know. Quite literally, according to the largest scientific organization in the world and publisher of the journal Science. The American Association for the Advancement of Science (AAAS) released this year a report titled "What We Know" that shows that taking action now reduces both the cost and the risks associated with our warmed world.

Regardless of whether Curry is right about the climate being slightly less sensitive to CO2 (something that hundreds of thousands of years of paleoclimate records suggest is false) the fact remains that the sooner we reduce emissions, the less damage we will endure. And interestingly, Curry admits that the only substantial worry is from a high emissions scenario. But if we listen to her argument for inaction, that high emissions scenario is exactly what we'll get.

Ultimately, we all wish that Curry is right, and climate change won't be as costly as the mountain of evidence suggests. Unfortunately, the science so far shows that if anything, we've been underestimating the scale of the impacts. The Wall Street Journal does its audience a disservice by portraying a ten-year reprieve (at best) as though it was a full pardon.

Signed,

Professor John Abraham, University of St. Thomas
Dr. Peter Gleick, MacArthur Fellow, hydro climatologist
Professor Scott Mandia, Suffolk County Community College
Professor Michael Mann, Pennsylvania State University
Professor Richard C.J. Somerville, University of California, San Diego

http://www.huffingtonpost.com/michael-e-mann/judith-curry-climate-change_b_6000636.html

Climate science tells us the alarm bells are ringing

by Michael Oppenheimer and Kevin Trenberth, op-ed, The Washington Post, June 7, 2013

Michael Oppenheimer is a professor of geosciences and international affairs at Princeton University. Kevin Trenberth is a distinguished senior scientist at the National Center for Atmospheric Research.

In a recent op-ed for The Post, Rep. Lamar Smith (R-Tex.) offered up a reheated stew of isolated factoids and sweeping generalizations about climate science to defend the destructive status quo. We agree with the chairman of the House Committee on Science, Space and Technology that policy should be based on sound science. But Smith presented political talking points, and none of his implied conclusions is accurate.

The two of us have spent, in total, more than seven decades studying Earth’s climate, and we have joined hundreds of top climate scientists to summarize the state of knowledge for the Intergovernmental Panel on Climate Change (IPCC), the World Climate Research Program and other science-based bodies. We believe that our views are representative of the97 percent of climate scientists who agree that global warming is caused by humans. Legions of studies support the view that, left unabated, this warming will produce dangerous effects. (This commentary, like so much of our work, was a collaborative process, with input from leading climate scientists Julia Cole, Robert W. Corell, Jennifer Francis, Michael E. Mann, Jonathan Overpeck, Alan Robock, Richard C.J. Somerville and Ben Santer.)

Man-made heat-trapping gases are warming our planet and leading to increases in extreme weather events. Droughts are becoming longer and deeper in many areas. The risk of wildfires is increasing. The year 2012, the hottest on record for the United States, illustrated this risk with severe, widespread drought accompanied byextensive wildfires.

Last month, levels of carbon dioxide in the atmosphere exceeded 400 parts per million, approaching the halfway mark between preindustrial amounts and a doubling of those levels. This doubling is expected to cause a warming this century of four to seven degrees Fahrenheit. The last time atmospheric carbon dioxide reached this level was more than 3 million years ago, when Arctic lands were covered with forests. The unprecedented rate of increase has been driven entirely by human-produced emissions.

Projections from an array of scientific analyses summarized by the National Academy of Sciences and most of the world’s major scientific organizations indicate that by the end of this century, people will be experiencing higher temperatures than any known during human civilization — temperatures that our societies, crops and ecosystems are not adapted to.

Computer model projections from at least 27 groups at universities and other research institutes in nine countries have proved solid. In many cases, they have been too conservative, underestimating over the past 20 years the amounts of recent sea-level rise and Arctic sea ice melt.

Much has been made of a short-term reduction in the rate of atmospheric warming. But “global” warming requires looking at the entire planet. While the increase in atmospheric temperature has slowed, ocean warming rose dramatically after 2000. Excess heat is being trapped in Earth’s climate system, and observations of the Global Climate Observing System and others are increasingly able to locate it. Simplistic interpretations of cherry-picked data hide the realities.

In recent years, our understanding of the relationship between climate and extreme weather has sharpened, along with our appreciation of the vast damages such events cause.

Contrary to Smith’s assertions, there is conclusive evidence that climate change worsened the damage caused by Superstorm Sandy. Sea levels in New York City harbors have risen by more than a foot since the beginning of the 20th century. Had the storm surge not been riding on higher seas, there would have been less flooding and less damage. Warmer air also allows storms such as Sandy to hold more moisture and dump more rainfall, exacerbating flooding.

Smith referred to the IPCC’s special report on extremes but did not mention that the report connects several types of extreme weather to climate change, including heat waves, extreme precipitation and, in some regions, drought. Furthermore, the last major IPCC report, in 2007, stated unequivocally that Earth is warming.

While we are addressing science here, one broad policy implication is clear: Humans must reduce their greenhouse gas emissions. Since John Tyndall discovered in 1859 that carbon dioxide and other greenhouse gases cause warming, science has made great strides toward establishing the scope of that warming and its impact.

The combined impetus of observed trends in climate and weather extremes, and continuing discoveries in climate science, lay bare how ludicrous Smith’s suggestion is that since we know nothing, we should do nothing.

We know a lot, more than enough to recognize that the alarm bells are ringing.

Increases in heat waves and record high temperatures; record lows in Arctic sea ice; more severe rainstorms, droughts and wildfires; and coastal communities threatened by rising seas all offer a preview of the new normal in a warmer world. Smith’s policy plan amounts to “wait and see.” But the longer we wait — effectively, like him, closing our eyes to science — the more difficult and expensive the solutions become, and the more irreversible the damage will be.

http://www.washingtonpost.com/opinions/climate-science-tells-us-the-alarm-bells-are-ringing/2013/06/07/ca81cb84-cef6-11e2-8845-d970ccb04497_story.html

Nation’s Top Climate Scientists Urge President Obama to Reject Keystone XL Pipeline

For immediate release, January 15, 2013, 350.org

OAKLAND CA -- Eighteen of the nation’s top climate scientists released a letter to President Obama today urging him to say no to the Keystone XL tar sands pipeline. 

“Eighteen months ago some of us wrote you about the proposed Keystone XL tar sands pipeline, explaining why in our opinion its construction ran counter to both national and planetary interests,"  wrote the scientists. "Nothing that has happened since has changed that evaluation; indeed, the year of review that you asked for on the project made it clear exactly how pressing the climate issue really is."

Indeed the past year has shown that climate change is here. A few months after Superstorm Sandy flooded parts of the Northeast, NOAA announced last week that the average temperature for 2012 was 55.3 degrees Fahrenheit, 3.2 degrees above normal and a full degree higher than the previous warmest year recorded -- 1988. 

The State Department is expected to soon release its supplemental environmental impact statement (SEIS) required for the northern leg of the Keystone XL pipeline. The department’s previous pipeline EIS downplayed climate risks by arguing that the tar sands would be developed with or without Keystone XL and therefore the project had no responsibility for the additional greenhouse gas emissions that come from burning tar sands oil. 

But two of Canada's largest banks, TD Economics and CIBC, have recently said that without added capacity, "Canada's oil industry is facing a serious challenge to its long-term growth" and that “Canada needs pipe — and lots of it — to avoid the opportunity cost of stranding over a million barrels a day of potential crude oil growth.”

The Obama Administrations has promised action on climate change but if KXL is approved, the Administration would be actively supporting and encouraging the growth of an industry which has demonstrably serious effects on climate.

Thousands of concerned citizens will come to Washington, DC on February 17th, President's Day weekend, to oppose the Keystone XL pipeline. Rally information is at www.350.org/presidentsday.

### 

1. Full text of the letter: 

Dear Mr. President,

You take office for the second time at a critical moment. As you may know, the U.S. has just recorded the hottest year in its history, beating the old mark by a full degree; the same year that saw the deep Midwest drought, and the fury of Hurricane Sandy, also witnessed the rapid and unprecedented melt of the Arctic ice pack. 

If we are to restrain the rise in the planet's temperature, it will require strong action from, among others, the planet's sole superpower. Some of that work will be difficult, requiring the cooperation of Congress. But other steps are relatively easy.

Eighteen months ago some of us wrote you about the proposed Keystone XL tar sands pipeline, explaining why in our opinion its construction ran counter to both national and planetary interests. Nothing that has happened since has changed that evaluation; indeed, the year of review that you asked for on the project made it clear exactly how pressing the climate issue really is. 

We hope, as scientists, that you will demonstrate the seriousness of your climate convictions by refusing to permit Keystone XL; to do otherwise would be to undermine your legacy.

Thank you,

James Hansen, Research Scientist, The International Research Institute for Climate and Society, The Earth Institute, Columbia University

Ralph Keeling, Director, Scripps CO2 Program Scripps Institution of Oceanography

John Harte, Professor of Ecosystem Sciences, University of California

Jason E. Box, Professor, Byrd Polar Research Center

John Abraham, Associate Professor, School of Engineering, University of St. Thomas

Ken Caldeira, Senior Scientist. Department of Global Ecology, Carnegie Institution

Michael MacCracken, Chief Scientist for Climate Change Programs, Climate Institute

Michael E. Mann, Professor of Meteorology, Director, Earth System Science Center, The Pennsylvania State University

James McCarthy, Alexander Agassiz Professor of Biological Oceanography, Harvard University

Michael Oppenheimer, Albert G. Milbank Professor of Geosciences and International Affairs, Woodrow Wilson School and Department of Geosciences, Princeton University

Raymond T. Pierrehumbert, Louis Block Professor in the Geophysical Sciences, The University of Chicago

Richard Somerville, Distinguished Professor Emeritus and Research Professor, Scripps Institution of Oceanography

George M. Woodwell, Founder, Director Emeritus, and Senior Scientist, Woods Hole Research Center

Mauri Pelto, Department of Environmental Science, Nichols College

David Archer, Professor, Department of Geophysical Sciences, The University of Chicago

Dr. Ted Scambos, Lead Scientist, National Snow and Ice Data Center, University of Colorado at Boulder

Terry L. Root, Senior Fellow, Stanford University

Alan Robock, Professor II, Distinguished Professor, Department of Environmental Sciences, Rutgers University

Affiliations are listed for identification purposes only. 

http://www.350.org/scientists-call-president-reject-keystone-xl-pipeline

Summer of Extremes: Roundup of U.S. Records by Richard Somerville and Jeff Masters

Summer of Extremes: Roundup of U.S. Records

An Update from Climate Communication, September 25, 2012

Expert Reviewers:

• Richard Somerville, Scripps Institution of Oceanography, UC–San Diego
• Jeff Masters, Weather Underground

With oppressive heat waves, devastating droughts, ravaging wildfires, and hard-hitting rainstorms, the summer of 2012 has been one for the record books. Thousands of precipitation and temperature records were broken, plaguing almost all of the contiguous United States this season and underscoring the connection between climate change and increasingly frequent and intense extreme weather. With climate change, we’ve set the stage for precisely this kind of extreme weather, and unfortunately, our changing climate threatens to alter summers to come.

It is important to note that as the planet continues to warm, new high temperature records and some other types of extremes will increasingly occur, but where they occur in a given year will not be predictable due to natural modes of climate variability. Extreme weather pummeled the United States this summer, but the next few years might see the most dramatic extremes occurring elsewhere around the world. Regardless, record-breaking high temperatures, droughts, wildfires, and heavy downpours are all signs of new extreme weather patterns that we can expect to see more of in a warming world, both domestically and abroad.

Here’s a roundup of weather events during the record-breaking summer of 2012:

Heat

• From June to August 2012, nearly 10,000 daily high temperature records were broken compared to just over 1,400 daily low-temperature records throughout the same 3-month period.
• July 2012 was the hottest month in U.S. history.
• June–August 2012 was the 3rd hottest on record for the continental U.S., 2.3 degrees F above the 20th century average.
• Wyoming and Colorado each had their hottest summer on record; Nevada was record hot for August.
• Approximately 6% of the 300 largest U.S. cities set their all-time heat records in 2012. The only year with more all-time heat records than 2012 is 1936, when 20% of U.S. cities set their all-time heat records.
• Remarkably, 50% of the contiguous U.S. had maximum temperatures that were in the highest 10% historically during summer 2012. 
• More than 80 million people—about 10 million more than in 2011—experienced 100°F or higher temperatures. Oklahoma City had 18 straight days where temperatures reached 100° or greater, including three days in a row that were 112 °F, exacerbating wildfires and drought in the state. The only heat wave in Oklahoma history that compares to the August 2012 heat wave occurred during the great Dust Bowl summer of 1936, the hottest summer in U.S. history. Oklahoma City experienced a record streak of 22 straight days with a temperature of 100 °F or hotter that year.
• The unusually hot summer helped January–August be the warmest such period in U.S. history. Even if September–December temperatures rank in the coldest 1/3 of historical temperatures, 2012 will still set a record for the warmest year in U.S. history (since record-keeping began in 1895).

Drought

• More than 2/3 of the country experienced drought throughout the summer of 2012, much of it classified as “severe to extreme.”
• The percentage area of the U.S. experiencing top-10% drought conditions was 36%, which was second only to the summer of 1934 (57%).
• The U.S. Department of Agriculture (USDA) declared a federal disaster area in more than half of all the counties in the U.S., mostly caused by drought. It was the largest disaster declaration ever made by the USDA.
• The nation could face costs of up to $77 billion due to the 2012 drought, making it the 3rd costliest weather-related disaster since 1980, behind Hurricane Katrina and the drought of 1988.
• July 2012 ranked 4th for the greatest percent area of the contiguous U.S. covered by moderate or greater drought and was the worst drought since 1954. Drought records go back to 1895.

Wildfires

• January–August 2012 broke the year-to-date record for most acreage burned by wildfires (6,888,342).
• A total of 3 million acres burned from mid-July to the end of August 2012.
• Summer 2012 is setting a record pace for Missouri wildfires, with more than 50 fires and more than 4,000 acres of public and private lands burned in the 3-month period. 
• The Whitewater–Baldy Complex wildfire in southwestern New Mexico was the largest in state history. The previous record was set in 2011.
• The Waldo Canyon Fire in Colorado caused the evacuation of more than 32,000 residents during the summer of 2012 and caused more than $352.6 million in damage. It holds the record for most destructive and expensive fire in Colorado state history.
• The 8.5 million acres burned this year already puts 2012 in 5th place for biggest fire year since 1960, according to the National Interagency Fire Center. With over three months left in the year, 2012 will likely end as the 1st or 2nd biggest fire year in U.S. history for total acreage consumed.

Extreme Storms

• In June 2012, Tropical Cyclone Debby produced record-breaking rainfall across Florida, dropping more than 20 inches of rain in 24 hours in some locations. When Tropical Storm Debby formed on June 23, it was the first time since record keeping began in 1851 that 4 tropical storms formed before July.
• During Hurricane Isaac in August 2012, 7.86 inches of rain fell at New Orleans International Airport, setting a daily rainfall record and shattering the 4.5 inch mark established by Hurricane Katrina in 2005. New Orleans averages 5.98 inches of rain in an entire month. It is estimated that Hurricane Isaac could cause up to $2 billion in onshore economic damage to Louisiana and Mississippi.
• Fueled by extreme heat, the derecho event in late June slammed 700 miles of the U.S. with violent winds that left 22 dead and millions without power. Washington, D.C., one of the areas most affected by the derecho, set a June record-high temperature during that time, while Columbia, S.C., broke its all-time temperature record.

West Nile

• More than 2,100 cases of West Nile virus—including 92 deaths—were reported through early September of 2012, setting a record for highest human toll since the disease was first detected in the U.S. in 1999. The cases are projected to continue into the fall.

Summer of Extremes: Roundup of Global Records

Heat

• Summer 2012 was the 3rd hottest summer on record globally, and land temperatures were the hottest on record.
• The last time the world saw a cooler-than-average July was 1976.
• June 2012 was the 4th hottest June, July was the 4th hottest July, and August 2012 was the 4th hottest August ever recorded for the entire planet.
• August 2012 was the 330th consecutive month that the global temperature was above the 20th-century average.

Arctic Sea Ice Melt

• In September 2012, Arctic sea ice reached the lowest level since satellite monitoring began more than 30 years ago. Half of the Arctic sea ice has disappeared, compared to the 1979–2000 average.
• The new record is 18% below the earlier record set in 2007.
• In early August 2012, the Greenland ice sheet melted to a 30-year low.

Climate change has shifted the odds, altered the natural limits, and increased the severity of certain kinds of extreme weather. As a result, we are witnessing an increase in record-breaking extreme weather events.

http://climatecommunication.org/new/articles/summer-of-extremes/overview/

Nation’s Top Scientists Urge State Department to Consider Climate Change in New Review for Keystone XL Pipeline

Press Release: Scientist Letter on Keystone XL -- FOR IMMEDIATE RELEASE

July 17, 2012 

Nation’s Top Scientists Urge State Department to Consider Climate Change in New Review for Keystone XL Pipeline 

WASHINGTON, DC -- Ten of the nation’s top climate scientists released a letter to Secretary Clinton today, urging the State Department to conduct a serious review of the climate change impacts of the Keystone XL pipeline. 

“At the moment, your department is planning to consider the effects of the pipeline on ‘recreation,’ ‘visual resources,’ and ‘noise,’ among other factors,” wrote the scientists. “Those are important—but omitting climate change from the considerations is neither wise nor credible.” 

The State Department is currently accepting comments on the scoping evaluation that will determine what environmental considerations will be included in the supplemental environmental impact statement (SEIS) required for the northern leg of the Keystone XL pipeline.

The department’s previous pipeline EIS downplayed climate risks by arguing that the tar sands would be developed with or without Keystone XL and therefore the project had no responsibility for the additional greenhouse gas emissions that come from burning tar sands oil. 

"Keystone became the biggest environmental cause of Obama's first term--and the reason most of those who marched and went to jail gave for their concern was the climate impact of those vast tar sands," said May Boeve, Executive Director of 350.org. "It would be ironic in the extreme if the State Dept. didn't take the issue seriously in its review."

A coalition of environmental groups including 350.org, Center for Biological Diversity, CREDO, the Natural Resources Defense Council, the National Wildlife Federation, and Sierra Club are collecting hundreds of thousands of comments on the SEIS scoping evaluation that will be delivered to the State Department before the July 30 comment deadline. 

1. Full text of the letter: 

July 17, 2012 

Dear Secretary Clinton,

We are writing to ask that the State Department conduct, as part of its evaluation of the Keystone XL pipeline proposal, a serious review of the effect of helping open Canada’s tar sands on the planet’s climate.

At the moment, your department is planning to consider the effects of the pipeline on “recreation,” “visual resources,” and “noise,” among other factors. Those are important—but omitting climate change from the considerations is neither wise nor credible. The vast volumes of carbon in the tar sands ensure that they will play an important role in whether or not climate change gets out of hand; understanding the role this largescale new pipeline will play in that process is clearly crucial.

We were pleased that President Obama saw fit to review this project more carefully; it would be a shame if that review did not manage to comprehensively cover the most important questions at issue.

Sincerely,

John Abraham

Associate Professor, School of Engineering

University of St. Thomas

Ken Caldeira

Senior Scientist

Department of Global Ecology

Carnegie Institution

James Hansen

Research Scientist

The International Research Institute for Climate and Society

The Earth Institute, Columbia University

Michael MacCracken

Chief Scientist for Climate Change Programs

Climate Institute

Michael E. Mann

Professor of Meteorology

Director, Earth System Science Center

The Pennsylvania State University

James McCarthy

Alexander Agassiz Professor of Biological Oceanography

Harvard University

Michael Oppenheimer

Albert G. Milbank Professor of Geosciences and International Affairs

Woodrow Wilson School and Department of Geosciences

Princeton University

Raymond T. Pierrehumbert

Louis Block Professor in the Geophysical Sciences

The University of Chicago

Richard Somerville

Distinguished Professor Emeritus and Research Professor

Scripps Institution of Oceanography

George M. Woodwell

Founder, Director Emeritus, and Senior Scientist

Woods Hole Research Center

Affiliations are listed for identification purposes only.

http://www.350.org/en/press-release-scientist-letter-keystone-xl

Heat Waves and Climate Change. A Science Update from Climate Communication – June 28, 2012. Expert Reviewers: Kevin Trenberth and Jerry Meehl (NCAR), Jeff Masters (Weather Underground), and Richard Somerville (Scripps Inst. of Oceanography)

Heat Waves and Climate Change

A Science Update from Climate Communication – June 28, 2012

Expert Reviewers:

• Kevin Trenberth, National Center for Atmospheric Research
• Jerry Meehl, National Center for Atmospheric Research
• Jeff Masters, Weather Underground
• Richard Somerville, Scripps Institution of Oceanography, University of California, San Diego

There has been a remarkable run of record-shattering heat waves in recent years, from the Russian heat wave of 2010 that set forests ablaze to the historic heat wave in Texas in 2011 and the “Summer in March” in the U.S. Midwest in 2012. These events typify the on-going trend driven by climate change.

This report, Heat Waves and Climate Change, summarizes our current scientific understanding of the connection between climate change and the recent increase in extreme temperatures, as reported in peer-reviewed research articles published through May 2012.

Overview

Climate change is already affecting extreme weather. The National Academy of Sciences reports that the hottest days are now hotter.¹  And the fingerprint of global warming behind this change has been firmly identified.^2 3 4

Since 1950 the number of heat waves worldwide has increased, and heat waves have become longer.⁵  The hottest days and nights have become hotter and more frequent.^6 7    In the past several years, the global area hit by extremely unusual hot summertime temperatures has increased 50-fold.⁸  Over the contiguous United States, new record high temperatures over the past decade have consistently outnumbered new record lows by a ratio of 2:1.⁹   In 2012, the ratio for the year through June 18 stands at nearly 10:1.¹⁰  Though this ratio is not expected to remain at that level for the rest of the year, it illustrates how unusual 2012 has been and how these types of extremes are becoming more likely.

The significant increase in heat extremes we have witnessed associated with a small shift in the global average temperature is consistent with climate change. The percentage change in the number of very hot days can be quite large.¹¹  Global warming boosts the probability of very extreme events, like the recent “Summer in March” episode in the U.S. in which thousands of new record highs were set, far more than it changes the likelihood of more moderate events.¹²

Higher spring and summer temperatures, along with an earlier spring melt, are also the primary factors driving the increasing frequency of large wildfires and lengthening the fire season in the western U.S. over recent decades.¹³   The record-breaking fires this year in the Southwest and Rocky Mountain Region are consistent with these trends.

The impact of these changes can be devastating. The drought, heat wave, and associated record wildfires that hit Texas and the Southern plains in the summer of 2011 cost $12 billion.¹⁴

Figure 1.  Summer in March. The colors show the difference from average temperatures from March 13-19, 2012, in degrees C. The dark red areas were 15 °C (27 °F) above average for this period. Source: NASA.

Looking Forward

Figure 2: Projected Frequency of Extreme Heat: 1-in-20 Year Events. Source: U.S. Global Change Research Program.

Confidence has risen in computer model projections of future changes in hot extremes because recent observations are consistent with the results of past model predictions.¹

Models predict that the same summertime temperatures that ranked among the top 5% in 1950–1979 will occur at least 70% of the time by 2035–2064 in the U.S. if global emissions of greenhouse gases grow at a moderate rate (as modeled under the IPCC SRES A2 scenario). Such a growth rate would require a decline from the current high rate of growth.²

The South, Southwest, and Northeast may be especially prone to large increases in unusually hot summers.³ Parts of the South that currently have about 60 days per year with temperatures over 90 degrees are projected to experience 150 or more days a year above 90 degrees by the end of this century.⁴

By the end of this century, a once-every-20-year heat wave is projected to occur every other year.⁵

Heat Waves: The Details

A heat wave is generally defined as a period of several days to weeks of abnormally hot weather.

In the past 3-4 decades, there has been an increasing trend in high-humidity heat waves, which are characterized by the persistence of extremely high night-time temperatures.¹ The combination of high humidity and high night-time temperature can make for a deadly pairing, offering no relief and posing a particular threat for the elderly. Extreme heat events are responsible for more deaths annually than hurricanes, lightning, tornadoes, floods, and earthquakes combined.²

At the same time, low-humidity heat waves associated with droughts and fueled in part by climate change contribute to the dry conditions that are driving wild fires.^3 4

Numerous studies have documented that human-induced climate change has increased the frequency and severity of heat waves across the globe.^{5 6 7 8 9}

For instance, a thorough statistical analysis of the Russian heat wave suggests that there was an approximate 80% probability that the 2010 July Russian heat record would not have occurred without climate warming, or alternatively the probability increased by a factor of five.^10 11

Globally, extremely warm nights that used to come once in 20 years now occur every 10 years.¹² And extremely hot summers, those more than three standard deviations above the historic average, are now observed in about 10% of the global land area, compared to 0.1-0.2% for the period 1951-1980.¹³

These trends cannot be explained by natural variation alone. Only with the inclusion of human influences can computer models of the climate reproduce the observed changes. These changes include an increase in the number of warm nights, unusually hot days, and heat waves, as well as warming of the warmest night of the year, warming of the coldest nights and days of the year, and warming of the hottest day of the year.^{14 15 16 17 18 19}

Figure 3. The ratio of record daily temperature highs to record daily lows observed at about 1,800 weather stations in the 48 contiguous United States from January 1950 through September 2009. Source: Meehl et al. 2009.

While natural variability continues to play a key role in extreme weather, climate change has shifted the odds and changed the natural limits, making heat waves more frequent and more intense. In an unchanging climate both new record highs and new record lows are set regularly, even while the total number of new records set each year may decrease as time goes on. However, the new records would be, on average, evenly balanced between record highs and record lows. In contrast, the balance shifts in a warming climate, and on average more new records highs than new record lows are set over any time period. It is worth noting that even in a warming climate new record lows are still set, though fewer in number, due to natural variation even as the climate warms.

Sixty years ago in the continental United States, the number of new record high temperatures recorded around the country each year was roughly equal to the number of new record lows. Over the past decade, however, the number of new record highs recorded each year has been twice the number of new record lows, a signature of a warming climate, and a clear example of its impact on extreme weather.²⁰ (See Figure 3.)

NOAA’s National Climatic Data Center reports that from January 1 to June 18 of 2012 new high temperature records outnumbered cold records across the United States by nearly 10:1. As noted above, this ratio cannot be expected to remain at that level for the rest of the year, but it illustrates how unusual 2012 has been and how these types of extremes are becoming more likely.

For the U.S., the rise in heat-trapping gases in the atmosphere has increased the probability of record-breaking temperatures 15-fold.²¹ In Europe, global warming is now responsible for an estimated 29% of the new record highs set each year.²²

 Figure 4. Ratios of Record High Temperatures to Record Low Temperatures.

Figure 5. IPCC (2001) graph illustrating how a shift and/or widening of a probability distribution of temperatures affects the probability of extremes.

Figure 4 illustrates that during the 1950s in the U.S. about as many new record highs were recorded as new record lows, roughly consistent with expectations of an unchanging climate. However, in 2009, 2010, and 2011, roughly twice as many new record highs were recorded compared to record lows, qualitatively consistent with a warming climate. The data for the year-to-date in 2012 reflect a very high ratio, much more than 2 to 1, and that highlights the fact that in any given year, a region as small as the U.S. can have very large departures from the global average. Atmospheric circulation variability, El Niños and La Niñas, and many other phenomena are involved in determining which regions will experience extremes in any given year.

A small change in average global temperature leads to a dramatic change in the frequency of extreme events.^23 24 25 The following graphs (Figures 5 and 6) help to illustrate this point. In a normal climate the probability for extreme events can be visualized like a traditional bell curve, as illustrated in Figure 6.

Moderate weather events are much more common than extreme events. So a small shift in temperature has an outsized effect on the frequency of extreme events due to relative impact of this shift.²⁶

Climate change shifts the curve to the hotter side, moving the average over. Climate change also flattens the curve, providing for a greater spread of events, an increase in variability. The combination provides for a dramatic increase in record hot weather.²⁷ Here “variance” is a measure of the spread of temperatures around the “mean” or average temperature.

The graph below (Figure 6) plots historical temperature data from the Northern Hemisphere, with each colored line representing a different decade. A “positive temperature anomaly” means temperatures are higher than the long-term average, while a “negative temperature anomaly” means they are lower. Thus, the graph illustrates both the shift and the flattening of the curve representing the distribution of unusual temperatures.²⁸ The overall effect corresponds with graph (c) in Figure 5 above.

Figure 6. Frequency of summer temperature anomalies (how often they deviated from the historical normal of 1951-1980) over the summer months in the northern hemisphere. Source: NASA/ Hansen et al. (2012).

Heat Waves and Wildfires

For many heat waves, there are also important feedbacks that come into play that amplify drought and heat and set the stage for wildfires. There is a direct local contribution to the drying and high temperatures in the absence of evaporative cooling.¹ While heat waves with high humidity are oppressive and give no relief at night, heat waves often form in association with drought. In these cases, the prevailing dry conditions set the stage for the heat since the land is dried out, the vegetation is wilted, and all of the heat from the sun goes into raising temperatures, whereas ordinarily, in the process of evaporative cooling, surface water or wetness acts as an evaporative cooler (swamp cooler) of sorts.

Some extreme examples have occurred in recent years in south Australia in January 2009, in Russia in summer 2010, and in Texas and Oklahoma in summer 2011. The record high temperatures in each case, along with the tinder dry conditions, led to extensive wildfires that were extremely costly in terms of lives, structures, human dislocations, and costs.^2 3 The exceptionally warm March in the U. S. is but part of record warmth for the first five months of the year (see Figure 8 below) and, along with an absence of snow, the rapid snow melt has left the Rocky Mountains almost without snow by June 1, 2012. The very hot and dry conditions throughout the Southwest and Rocky Mountain Region have led to exceptionally high risk of wildfire. Multiple wildfires have already occurred, and several in Colorado and Utah have expanded into huge burn areas, resulting in loss of life and structures.

As emissions of heat-trapping gases continue to rise, and global average temperatures continue to increase, we can expect even more of the of extreme heat and related impacts we’ve been witnessing in recent years.

Figure 7. Difference from average temperature over the contiguous U.S., January–May 2012. Source: NCDC/NOAA.

(Full List of References)

http://climatecommunication.org/new/articles/heat-waves-and-climate-change/overview/