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A runner in Death Valley National Park.

A runner braves the heat in Death Valley National Park in California as temperatures approach record-breaking highs.

Photograph by David McNew, Getty Images

Ker Than in Pasadena, California

for National Geographic

Published July 1, 2013

The American Southwest is broiling in triple-digit temperatures for the fourth consecutive day as a result of a record-breaking heat wave that is smothering the region.

In Death Valley, California, the temperature reached 128° Fahrenheit (53° Celsius) on Sunday—just a few degrees shy of the July 10, 1913, record of 134° Fahrenheit (57° Celsius).

The heat wave has also been partly blamed for a wildfire that killed 19 firefighters on Sunday in Yarnell Hill, Arizona.

So what's behind the heat wave? Is global warming a factor? And how does it compare with past events? We talked to Martin Tingley, a climatologist at Harvard University, to find out.

In April, Tingley and his colleague Peter Huybers published a study in the journal Nature that concluded that the years 2005, 2007, 2010 and 2011 were warmer than any year going back 600 years, to 1400.

Do scientists know what's behind the current heat wave?

Looking at the meteorological charts, it looks to be a blocking event. That happens when there's a particular configuration of the jet stream that's quite stable. So there's a big high-pressure ridge on the West Coast and a low-pressure trough in the East Coast. That's why it's quite rainy here [in Cambridge, Massachusetts] and very hot on the West Coast.

Have you or other scientists had a chance to analyze this current heat wave and determine how it compares to past years?

No ... because 2013 is not over yet. One very hot week will have some signature on the seasonal average, but how large that signature will be depends on what happens for the rest of the summer.

Also, the study that Peter [Huybers] and I did made use of paleoclimate records—things like tree rings and ice cores. One of the limitations of that study is we can't really think of week-long heat waves like what's going on. We were limited to seasonal averages—hot summers versus cool summers—and we found that recent warm extremes in terms of summer average conditions at the high northern latitudes are unprecedented in the last 600 years.

You reached those conclusions after performing a statistical analysis on the paleoclimate data. Do you have an analogy that helps explain how that analysis works?

One imperfect analogy: Even though you and I have never met, I would bet that I'm taller than you because I'm 6-foot-4-inches (1.9 meters), and that puts me in a high percentile of the distribution of heights. But if I were to walk into a room of 1,000 people, I probably wouldn't be the tallest.

It's the same when we're addressing the question of was 2011 the hottest year in the last 600 years. It's a different statistical question to ask was it warmer than one particular year in the past—that's like me saying I'm taller than you—and it's a much different question to ask whether 2011 was the hottest year amongst all of the past 600 years.

To deal with this, what we do is instead of coming up with a single best estimate ... we use a simple statistical model to simulate 4,000 equally likely realizations of the climate [based on the paleoclimate data]. Then we can ask in how many of these 4,000 possible climate histories was 2011 the warmest year? So instead of having a single best estimate, we have 4,000 possible realizations.

Climate scientists often compare the effects of global warming to loaded dice: Not every roll of a loaded die will come up six—but sixes will occur more often than if the die had not been tampered with. Is that still the thinking?

Can we attribute this particular heat wave to an anthropogenic impact on the climate? The only safe answer is, well, probably not. It's like if I flip one coin and it comes up heads, that doesn't mean the coin is loaded.

But what we're seeing now, there seems to be a trend toward more hot extremes and fewer cold extremes. That's a pattern that's consistent with an anthropogenically-forced increase in temperatures.

What can people expect from future extreme heat waves that are affected by global warming? Will they be anything like the current heat wave affecting the West Coast?

I think that's a really big open question right now: Given rising mean temperatures, how will the extremes change, in both magnitude and frequency? It's actually one of the research projects we are tackling at the moment: How are extremes in temperature on daily timescales changing with respect to the mean temperature?

If the mean temperature goes up by half a degree, do the extremes simply track that half-degree increase? Or are the extremes being amplified in some sense so that they are becoming hotter with respect to the mean?

As a climate scientist, are you doing anything personally to prepare for the hotter summers that will result from global warming?

Well, I like to ski a lot in the winter, and I'm concerned that ski conditions are becoming more variable, especially on the East Coast.

That's not really something that I've done in my life to prepare, but it's something that's given me a lot of pause. Will the slopes have consistent snow cover for the next generation of skiers, and will the tradition of East Coast skiing survive a warming climate?

11 comments
Sally Edelstein
Sally Edelstein

Poor mankind! His triumphant march towards progress is always being blamed for the actions of a fickle Mother Nature whose erratic behavior has recently played havoc with our weather systems.

Panicked cries of global warming by hand wringing environmentalists fault the recent rash of oppressive heat, ferocious fires, dangerous storms on our long dependence on fossil fuels. When it comes to weather, it's not the first time man's triumph over nature has been called into question by alarmists. In the 1950s blaming finger  pointing also turned towards mans industrial might and scientific progress in playing havoc especially when it came to harmless atmospheric bomb testing. To learn more http://envisioningtheamericandream.com/2012/07/11/man-what-a-heat-wave/

Reynold Zhang
Reynold Zhang

In China,it's really hot for me.The worst thing is that we have to study in school for next years' University Entrance Exams.Poor us.

Mikhail Koninin
Mikhail Koninin

Here in Siberia (In Novosibirsk) it's cold there days (all spring and june). On 1 july they registered temperature as low as 13,4C' - lowest temperature on 1 july ever registered

David Nitshe
David Nitshe

This may be far-fetched, however, has anyone given any thought to Chem-Trails causing this?

Harold Ambler
Harold Ambler

The desert southwest has been far hotter than today, including during the past century. If you wish to take a longer view, check out "megadrought" on Google, or better still Google scholar. If you think the region was cool during the 500-year drought that various scientists have published about, then you need to rethink your understanding of weather and North American geography. 

There is a truly bizarre need among many to believe that the weather they're witnessing in person or on TV or on the Interweb is "special," just as they themselves are presumably "special." 

No weather of the last ten years is unprecedented. None of it. 

Deal with it. 

I learned a lot when I researched my book on the subject of climate change, and the process left me stupefied in the face of the superstition passing as science in American journalism. The book, should you be interested, is here: 

http://www.amazon.com/Dont-Sell-Your-Coat-ebook/dp/B0072VSQFQ/ref=kinw_dp_ke?ie=UTF8&m=AG56TWVU5XWC2

Phillip Noe
Phillip Noe

With the likelihood of the countless unfriendly events and circumstances in our future why haven't our governments moved more quickly to reduce global emissions?  Clearly, vested interests have far too much influence in Washington.  And now the Congressional House and Senate have Republicans that work to obstruct almost anything the President does.  We need to shift to a cleaner economy but our President needs the help of Congress.  Contact your Congressman/women and insist they work harder to pass legislation to curb the more dire effects of climate change.  If they won't, work to have them removed in the next election.  Our future generations are at risk.

John C.
John C.

Yes, it's all the fault of those evil Republicans, as usual.Well, Einstein let's look at the facts. India and China are building one new coal plant a week. What are the dark "vested interests" behind that? Try 2 billion people trying to lift themselves out of subsistance poverty into the middle class. They won't be able to do it with windmills and carrying cloth Whole Foods bags. They want the life you take for granted and really don't care how many ice bergs or polar bears there might be 100 years from now.The Obama economy is still stuck on recession, there's been a 60% loss of middle class jobs and 59% increase in low wage jobs since he took over. So what's his solution? Do everything he can to hobble the energy sector, the one bright spot in the economy, killing jobs and driving up energy costs for everyone. And having zero effect on the climate because...there's only one atmosphere and China and India have no intention of staying poor to please us.Obama is an international laughing stock. He can't even get China, Russia or even Ecuador to turn over Snowden but he's going to convince the developing world to give up coal and oil? Great energy plan - kill American jobs, keep the worst recovery on record going and have no effect whatsoever on climate.What losers liberals are, from the nincompoop at the top to his dummy scientifically illiterate followers at the bottom.

Jack Wolf
Jack Wolf

@John C.

Opps, they cut off my edit.  Here is my edited response:

They'll care when they see the physical dangers and the impacts on their health, or their children's health.  At some point the cost of climate change will be too big to ignore.  Lastly, its hot, and been hot for a while.  I think the ratio of hot temp records to cold records is over 5 to 1.  Just wait for those new records to be broken again, and again. 

And, I think you're off topic,  They are talking climate science, not political science, but maybe you just didn't read it.

Jack Wolf
Jack Wolf

@John C. They'll care when they see the physical danger and the impacts on their health, or their children's health.  And, at some point, the cost of climate change will be too big to ignore and will the thermometer..

John C.
John C.

@Jack Wolf @John C. 

I was responding to the political ad above my post. Climate science has established that global temperatures are increasing in general although the specific factors driving it are still far from exactly quantified, e,g, the 15 year plateau that caught everyone and their climate models by surprise. CO2 production in the U.S. is at its lowest level in 20 years. Not because of top down enviro policy, but because the free market opened up vast resources of cheap natural gas as an alternative to coal. The market will similarly end up being the solution in China and India. Simply because 2 billion people trying to improve their lives are not going to give it all up just to please rich liberal Westerners. Until the market transforms the economics of energy in China and India there is little or nothing politicians can to in the U.S. to affect global CO2 levels. Obama's attempt to "do something" with his new enviro policy is pure political theater, nothing more. For all his "Flat Earth Society" straw man talk, it's certainly not based on science since it will have no practical effect on global climate. Plus, it will definitely have the effect of killing jobs in the energy sector and driving up costs of energy and all products across the board in the economy. In that way, it's worse than useless. To throw out something like this as an energy / climate solution is laughable, it's no more than an ideological gesture for his base leading up to 2014. 

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