News Section
Stories from Climate Central's Science Journalists and Content Partners

Hansen Study: Extreme Weather Tied to Climate Change

Extreme weather events, such as the heat waves that have broiled the High Plains and Midwest this summer, smashing thousands of temperature records, are a direct consequence of global warming, according to a new study led by prominent climate scientist, James Hansen of NASA. The study seeks to reframe how people view the links between manmade global warming and extreme weather events, going farther than ever before in making direct ties between the two.

The study by Hansen, who first warned of the consequences of manmade global warming in landmark Senate testimony in 1988, shows that a new category of extremely hot summers has become far more common than would ever have happened without the buildup in heat-trapping greenhouse gases from human activities.

“I don’t want people to be confused by natural variability — the natural changes in weather from day to day and year to year,” Hansen said in a press release. “We now know that the chances these extreme weather events would have happened naturally — without climate change — is negligible.”

The study was published in the journal Proceedings of the National Academy of Sciences, and is based on a statistical analysis that examines how global summertime temperatures have been changing in recent decades. Unlike many other studies of extreme weather events, it does not employ the use of climate computer modeling, and does not look at specific extreme events in isolation, but rather takes a global view.

According to the study, during the period from 1951-1980, extremely hot summers covered just 1 percent of Earth’s land area. This had risen to 10 percent of the Earth’s land area by the period from 1981-2010, and even higher during the 2006-2010 period.

In other words, the study found that the odds of such extreme summers were about 1-in-300 during the 1951-1980 timeframe, but that had increased to nearly 1-in-10 by 1981-2010.

"This is not some scientific theory,” Hansen said to The Associated Press. “We are now experiencing scientific fact.”

James Hansen testifying on global warming before a Senate committee in 1988.
Credit: Wikimedia Commons.

Although the statistical analysis that lies at the heart of the study may not break much new scientific ground — it has long been known that as average temperatures increase, extreme heat events would become much more common — the study argues more forcefully than ever that global warming is tilting the odds so far in favor of certain types of extreme weather events that the standard caveat that global warming cannot be blamed as the sole cause of individual extreme weather events is no longer accurate.

The study finds that manmade global warming caused the Texas heat wave of 2011 and the deadly Russian heat wave of 2010 by dramatically altering the frequency of extremely hot summers.

“ . . . We can say with high confidence that such extreme anomalies would not have occurred in the absence of global warming,” the study says.

Andrew Weaver, a climate scientist at the University of Victoria in British Columbia told the Associated Press that the study successfully "reframes the question" regarding extreme weather and climate events and global warming.  

"Rather than say, 'Is this because of climate change?' That's the wrong question. What you can say is, 'How likely is this to have occurred with the absence of global warming?' It's so extraordinarily unlikely that it has to be due to global warming," Weaver said.

Other recent studies, however, have shown that the same extreme events mentioned in Hansen’s study were the result of a mix of natural climate variability and manmade global warming, and the authors of such studies are reluctant to go as far as Hansen does in claiming that global warming is the “cause” of such events.

Peter Stott of the U.K. Met Office is one of the leaders of an international effort to improve researchers’ abilities to assess the causes of extreme weather and climate events. He co-authored a landmark study on the 2003 European heat wave, which found that global warming dramatically increased the odds that such an event would occur, but that natural variability also played a key role.

He said Hansen’s study is “broadly in line” with previous work showing that extremely hot summers are becoming more common, but his view is that it is not yet possible to attribute extreme events directly to manmade global warming.

“I don’t agree with how Hansen frames his conclusion in terms of the Texas 2011 and Moscow 2010 heat waves having been “caused by global warming,” Stott said via email. “Both of these heat waves were associated with unusual [atmospheric] circulation characteristics and a large part of the explanation for both lies in that.”

Temperature departures from average during early August 2012.
Credit: High Plains Regional Climate Center.

Stott emphasized that the “interplay of variability and climate change” is what counts.

Hansen’s study comes while the U.S. is in the midst of one of its worst droughts since 1956, with high temperatures that have broken records that had stood since the Dust Bowl era of the 1930s. His conclusions are in line with other recent studies showing that record warm temperatures are occurring more frequently than record cold temperatures, and that ratio has been particularly lopsided this year.

During the year-to-date, warm temperature records — including record daily highs and record-warm overnight lows — have been outnumbering cold-temperature records by a ratio of about 7-to-1 in the U.S.

“The Hansen paper adds to an already strong case that climate change is shifting the odds towards more heat extremes,” said Jerry Meehl, a senior scientist at the National Center for Atmospheric Research in Boulder, Colo., and the lead author of a 2009 study that found that daily record highs have become more common than record daily lows in the U.S. during the past few decades.

According to Hansen’s study, the climate itself is becoming more variable as global warming progresses, and this variability is part of the reason why we’re seeing the emergence of a new category of extremely hot summer temperatures.

Scientists who were not involved in this study, however, were skeptical about this finding, noting that the increase in heat extremes is more consistent with the overall shift toward warmer global average temperatures, rather than a change in climate variability.

“The one stretch in the paper is in the linking of the increase in areal extremes to an increase in climate variability,” said Gavin Schmidt, a scientist who works alongside Hansen at NASA's Goddard Institute for Space Studies, said in an email conversation.

Hansen and his colleagues project that extremely hot summers will only grow hotter and more frequent as global average surface temperatures rise in response to manmade climate change. If emissions remain on a “business-as-usual” trajectory, with no major reductions made, the study projects that the extremely hot summers we’re seeing today will become the norm, with even hotter weather constituting future heat waves.

Comments

By JOH (Hixson tn 37343)
on August 6th, 2012

Hanson’s political activism and previous dire predictions taint his climate science analysis and conclusions.

Reply to this comment

By Al Bore (Detroit)
on August 6th, 2012

Climate change fear mongering of the voter’s children is a vote for a President Romney.

Condemning billions of helpless men, women and children to the greenhouse gas ovens of climate blame crisis was a war crime because not one single IPCC report mentions any climate “crisis” without a “possible” or “likely” to qualify it. My house is possibly on fire maybe?
Climate change was a legal lie and a tragic exaggeration and millions of people in the global scientific community sitting on their hands while the planet dies is proof enough of NO CRISIS. Science lab coats gave us pesticides.

THEY ONLY HAVE CONSENSUS THAT IT IS “REAL AND HAPPENING”, not a real “crisis”.

There is NO consensus that there is any “crisis”, just maybe a crisis and it’s been 26 years of this consultant’s wet dream of climate blame.

Reply to this comment

By JC
on August 7th, 2012

The fastest solution to climate change is to severely reduce methane release into the atmosphere. About 1/2 of human induced warming is attributable to methane. It is 24 times more potent than CO2 and takes only 7 years to cycle out of the atmosphere. CO2 takes around 100 years to come out. Human pursuit of animal protein is the leading cause of methane release. Check the facts and act!

“As environmental science has advanced, it has become apparent that the human appetite for animal flesh is a driving force behind virtually every major category of environmental damage now threatening the human future: deforestation, erosion, fresh water scarcity, air and water pollution, climate change, biodiversity loss, social injustice, the destabilization of communities, and the spread of disease.” Worldwatch Institute, “Is Meat Sustainable?”

“The livestock sector emerges as one of the top contributors to the most serious environmental problems, at every scale from local to global. The findings of this report suggest that it should be a major policy focus when dealing with problems of land degradation, climate change and air pollution, water shortage and water pollution, and loss of biodiversity. Livestock’s contribution to environmental problems is on a massive scale and its potential contribution to their solution is equally large. The impact is so significant that it needs to be addressed with urgency.” UN Food and Agricultural Organization’s report “Livestock’s Long Shadow”

“If every American skipped one meal of chicken per week and substituted vegetables and grains… the carbon dioxide savings would be the same as taking more than half a million cars off of U.S. roads.” Environmental Defense Fund

Why would someone choose to be vegan? To slow global warming for one! Here are two uplifting videos to help everyone understand why so many people are making this life affirming choice: http://www.youtube.com/watch?v=fKr4HZ7ukSE and http://www.veganvideo.org

“Nothing will benefit human health and increase the chances for survival of life on earth as much as the evolution to a vegetarian diet.” ~ Albert Einstein

Reply to this comment

By Dave (Basking Ridge, NJ 07920)
on August 7th, 2012

I think it is very likely that the first two comments are from Republicans, but I admit that there is a small probability that I could be wrong.  However, my confidence level exceeds 3sigma.

Reply to this comment

By robert hardt (los angeles, ca 90045)
on August 7th, 2012

Geoengineering the climate, man made weather manipulation, unintended consequences, Unwanted floods, snow, drought, tornadoes. weather derivatives tied to corporate control of food, air, water,????

Reply to this comment

By Constance Lever-Tracy (Adelaide South Australia 5050)
on September 12th, 2012

Methane emissions caused by meat production originate in the digestive systems of ruminant animals, mainly cattle and sheep (not fowl). Beef, lamb and milk products are the problem, not chicken. A useful slogan might be:

‘Roast turkey for Sunday dinners and roast beef as a treat at christmas’.

Reply to this comment

By Copie
on March 18th, 2013

James Hansen is disgraceful, continuing to claim that record cold weather is really global warming is disgusting. Get a real job where you don’t have to lie to support your discredited theories!

Reply to this comment

By peter w chilstrom (fennville michigan 48408)
on June 28th, 2013

Jim Hansen and his fellow climate watchers are un appreciated Gaian heroes

the proof in the pudding for climate change is the melting arctic ice and permafrost in the gaian punch bowl
no other proof is needed
the cat few want to bell is   global population growth compounded by a high entropy life style
by a growing number both east and west
i am a non reproducing monastic and my footprint is relatively small compared with other first world consumers
  but living in usa mine is still high and entropic at the global level
at risk of being an object of scorn to the near sighted i submit that we must revivify the sayings found in all religions
the kingdom of heaven is in you
this once elitist mystical statement has profound   non elitist practical value now
this is because there is   very insufficient kingdom of heaven outside for
the 8 billion soon to be living on a very finite earth
a space ship like earth has a seating capacity
we are way over limit already right now and the brakes will fail on the mountain
swami tapasananda aka peter w chilstrom

Reply to this comment

By Walter (Philadelphia Pa 19107)
on July 14th, 2013

OK, lets say that, maybe there is a planetary body in our midst that, could , and has altered the behavior of of our planet, and as it gets closer to earth it’s electric magnetic pull is have great effects on our planets atmosphere including the debris from the surrounding particles accompanying it.

Or get ready for this one (what is written in the holy scriptures is coming to pas, and GOD’s words has not, and will not fail his promise of dismissing this disobedient human race; why is that so hard to except.

Reply to this comment

By Jim Grabill (Portland, OR 97219)
on July 29th, 2013

Dr. Hansen’s book Storms of My Grandchildren explains how he switched from studying Venus to analyzing the climate of Earth, how by simply trying to share scientific findings he ran into continued roadblocks and obfuscation, why the tipping point of 450 ppm of CO2 became 350 ppm, how positive feedback effects greatly exacerbate the overall process, how forces of obstruction actually red-penned scientific reports in the first eight years of this century, and how Dr. Hansen switched from being apolitical, or independent, to realizing he needed to take a stand on this issue, which he and many other leading scientists around the world think is a problem that supersedes others in terms of potential long-term harm to everyone.

Anyone who would like the insight story would want to read this book. Anyone who flippantly criticizes Dr. Hansen for now taking a stand against the development of tar sands fossil fuel needs to read this book. Anyone who thinks that science should be left to scientists and that citizens do not have enough information to have a valid understanding of climate disruption needs to read this book. And of course anyone who “feels” climate change “is the greatest hoax ever perpetrated against the American people” (Senator Inhoff) needs to read this book.

Climate change isn’t a matter best left to “market forces” and top scientists in the world’s largest peer-reviewed study of peer-reviewed science, the IPCC, regularly present the best scientific assessment for citizens and of course policy-makers. Scientific organizations have renamed this era the Anthropogene, acknowledging that we are in a new age when the seven-plus billion people on this planet do affect the rest of the genome, whatever we might believe. Willful ignorance of all this (and of the Stern Review that clearly proves mitigation now is much less costly than trying to adapt later) is not a virtue but an insult to life itself. The continued “misinformation” campaigns of corporations and certain individuals (documented in Our Choice, Al Gore’s excellent book which collects pertinent information and new ideas from a series of over three dozen global summits of experts) are not only unethical but right up there with some of the more egregious crimes we could think of (since lives are at stake, since money is being made today by putting the future in danger).

To everyone who cares about reality, Storms of My Grandfather by James Hansen, and Plan B by Lester Brown, if you haven’t. These are not books written to defend political positions but to share state-of-the-art information and understanding.

Sincerely, Jim Grabill
Instructor, “Pathways to Sustainability” in Portland, OR

 

Reply to this comment

By Jim Grabill (Portland, OR 97219)
on July 29th, 2013

Corrected : 

re Hansen Study: Extreme Weather Tied to Climate Change

Dr. Hansen’s book Storms of My Grandchildren explains how he switched from studying Venus to analyzing the climate of Earth, how by simply trying to share scientific findings he ran into continued roadblocks and obfuscation, why the tipping point of 450 ppm of CO2 became 350 ppm, how positive feedback effects greatly exacerbate the overall process, how forces of obstruction actually red-penned scientific reports in the first eight years of this century, and how Dr. Hansen switched from being apolitical, or independent, to realizing he needed to take a stand on this issue, which he and many other leading scientists around the world think is a problem that supersedes others in terms of potential long-term harm to everyone.

Anyone who would like the inside story would want to read this book. Anyone who flippantly criticizes Dr. Hansen for now taking a stand against the development of tar sands fossil fuel needs to read this book. Anyone who thinks that science should be left to scientists and that citizens do not have enough information to have a valid understanding of climate disruption needs to read this book. And of course anyone who “feels” climate change “is the greatest hoax ever perpetrated against the American people” (Senator Inhofe) needs to read this book.

Climate change isn’t a matter best left to “market forces” and top scientists in the world’s largest peer-reviewed study of peer-reviewed science, the IPCC, regularly present the best scientific assessment for citizens and of course policy-makers. Scientific organizations have renamed this era the Anthropocene, acknowledging that we are in a new age when the seven-plus billion people on this planet do affect the rest of the genome, whatever we might believe. Willful ignorance of all this (and of the Stern Review that clearly proves mitigation now is much less costly than trying to adapt later) is not a virtue but an insult to life itself. The continued “misinformation” campaigns of corporations and certain individuals (documented in Our Choice, Al Gore’s excellent book which collects pertinent information and new ideas from a series of over three dozen global summits of experts) are not only unethical but right up there with some of the more egregious crimes we could think of (since lives are at stake, since money is being made today by putting the future in danger).

To everyone who cares about reality, Storms of My Grandfather by James Hansen, and Plan B by Lester Brown, if you haven’t. These are not books written to defend political positions but to share state-of-the-art information and understanding.

Sincerely, Jim Grabill
Instructor, “Pathways to Sustainability” in Portland, OR

Reply to this comment

By John Cunningham (Niagara Falls N.y. 14304)
on August 7th, 2013

I do not deny CLIMATE CHANGE, what I think has changed the worlds weather in the past couple of years is the fact that the EARTHS Currents are slowing and STOPPED (Check out the stoppage of the GULF Current in the Atlantic) The EARTHS Currents Engine. NOAA. and NASA have inferred info that there is 240,000,000.689 BARRUALS of heavy OIL in the Gulf trough Stopping the Current.
    The Atlantic, North Atlantic, Baltic and more have stopped, and the Earth’s Currents control the Jet Streams and the Jet Streams control the weather pattern around the WORLD.  and who has
    Gee I wonder where all that heavy oil cloud have come from, lets use a little common sense and who has had a loss of that kind of OIL in the last several years.  Go to Gulf Current Stoppage and see for your self.      THANX   jc

Reply to this comment

By Yoron
on August 25th, 2014

Well, we’re already passed by 400 ppm (parts Co2 per million). Hansen’s book define 350 ppm as the divider between a treatable climate, versus a catastrophic development of the same. He’s right of course, but he misses out on several points of relevance. For example, we’re humans and we have our interests. Those are defined from week to week, some month to month, with a few taking up a lifetime. Our kids for example, but they are all generated from self interests. Another part of our lives is money, we all need it to survive, and those that have always seem to need more. Self interests again, and not benevolent ones either.

Combine that with our ability to lie, to ourselves and so subsequently to others, and one will find a real good explanation to why nothing will change. And the end result of this lying do not fall inside your lifetime, neither your kids. It will take a century before the real impact will be making themselves heard, even though I think Hansen is correct in predicting very variable local weather, aka floods, droughts, heat waves, heavy snow falls, etc etc in the mean time.

And there is no politician on Earth, as far as I know, worrying about what his voters will think of him, ignoring what will happen a century later, is there?

We are too short sighted, and this time I doubt our ability of adaption will persevere. So yeah, he’s most probably correct, but it doesn’t matter. We’ve passed 400 ppm on good way to 450. We also produced around six of the seven billion people existing on this planet in less that one hundred and twenty years. Combine it and use your mind.

Reply to this comment

Name (required):
Email (required):
City/State/Zip:
Enter the word "climate" in the box below:

[+] View our comment guidelines.

Please note: Comment moderation is enabled. Your comment will not appear until reviewed by Climate Central staff. Thank you for your patience.