Mann: We Must Heed James Hansen On Global Warming And
Extreme Weather Since He’s Been Right For So Long

NASA’s James Hansen has been accurately warning about the dangers of global warming for more than three decades. In fact, 31 years ago this month, Hansen and six other NASA atmospheric physicists, published a seminal article in Science, ?Climate Impact of Increasing Atmospheric Carbon Dioxide.?

The paper has a number of caveats, as befits a major projection before modern climate models and modern supercomputers were available, before we had decades of verifying observations, and before we knew just how fast greenhouse gas emissions would rise.

Yet the analysis bears up unbelievably well ? any one of us would be delighted if we published something three decades ago that was this prescient:

The global temperature rose 0.2°C between the middle 1960s and 1980, yielding a warming of 0.4°C in the past century. This temperature increase is consistent with the calculated effect due to measured increases of atmospheric carbon dioxide. Variations of volcanic aerosols and possibly solar luminosity appear to be primary causes of observed fluctuations about the mean trend of increasing temperature. It is shown that the anthropogenic carbon dioxide warming should emerge from the noise level of natural climate variability by the end of the century, and there is a high probability of warming in the 1980s. Potential effects on climate in the 21st century include the creation of drought-prone regions in North America and central Asia as part of a shifting of climatic zones, erosion of the West Antarctic ice sheet with a consequent worldwide rise in sea level, and opening of the fabled Northwest Passage.

The 1980s warmed, manmade warming has emerged from the noise, the Northwest passage opened, the drought prone-regions have emerged, and sea level rise is a top worry, in part because of erosion of WAIS (see Nature 2012: Antarctica Is Melting From Below, Which ?May Already Have Triggered A Period of Unstable Glacier Retreat?). That’s five for five.

In 1990, Hansen coauthored a more detailed warning on the future of warming-driven drought  in the Journal of Geophysical Research. It projected that drought would become increasingly common in the ensuing decades — another accurate prediction. The study warned that severe to extreme drought in the United States, then occurring every 20 years or so, could become an every-other-year phenomenon by mid-century. Many recent studies support that conclusion (see “James Hansen Is Correct About Catastrophic Projections For U.S. Drought If We Don?t Act Now“).

Now Hansen has published an analysis of how warming is driving the extreme weather we have been slammed by in recent years, including the off-the-charts heat waves and droughts (see Hansen: ?Climate Change Is Here ? And Worse Than We Thought?). The AP quoted a number of credible independent experts supporting Hansen’s analysis:

The science in Hansen?s study is excellent ?and reframes the question,? said Andrew Weaver, a climate scientist at the University of Victoria in British Columbia?.

Another upcoming study by Kevin Trenberth, climate analysis chief at the National Center for Atmospheric Research, links the 2010 Russian heat wave to global warming by looking at the underlying weather that caused the heat wave. He called Hansen?s paper an important one that helps communicate the problem?.

White House science adviser John Holdren praised the paper?s findings in a statement: … ?This work, which finds that extremely hot summers are over 10 times more common than they used to be, reinforces many other lines of evidence showing that climate change is occurring and that it is harmful.?

? Granger Morgan, head of engineering and public policy at Carnegie Mellon University, called Hansen?s study ?an important next step in what I expect will be a growing set of statistically-based arguments.?

The NY Times article on Hansen’s study also quoted Weaver in support of the analysis, but managed to find some credentialed critics:

Martin P. Hoerling, a researcher with the National Oceanic and Atmospheric Administration who studies the causes of weather extremes, said he shared Dr. Hansen?s general concern about global warming. But he has in the past criticized Dr. Hansen for, in his view, exaggerating the connection between global warming and specific weather extremes. In an interview, he said he felt that Dr. Hansen had done so again.

Dr. Hoerling has published research suggesting that the 2010 Russian heat wave was largely a consequence of natural climate variability, and a forthcoming study he carried out on the Texas drought of 2011 also says natural factors were the main cause.

Dr. Hoerling contended that Dr. Hansen?s new paper confuses drought, caused primarily by a lack of rainfall, with heat waves.

?This isn?t a serious science paper,? Dr. Hoerling said. ?It?s mainly about perception, as indicated by the paper?s title. Perception is not a science.?

Nonsense, literally.

Having reviewed the drought literature (and talked to leading drought experts) for my Nature piece, “The Next Dust Bowl,” I was able to show in May that Hoerling’s attacks on Hansen do not reflect the scientific literature and are incorrect.

Indeed, given that Hansen’s 1990 study was titled, ?Potential evapotranspiration and the likelihood of future drought,? we know that he and the community of drought experts have long understood that drought conditions are driven by more than precipitation changes. The whole point of that paper was to examine the impact of warming-driven evaporation on soil moisture and drought. You can actually worsen droughts in semi-arid regions that don’t see a net precipitation change just from the heat drying out the soils.

Let me also add, separate from any argument that Hansen has made, that there is increasing evidence we are in the midst of a step function or quantum change in the climate because of Arctic warming (see Arctic Warming Favors Extreme, Prolonged Weather Events ?Such As Drought, Flooding, Cold Spells And Heat Waves?). If this research holds up, then all analyses of current droughts based on precipitation trends that predate the massive loss of Arctic ice in the past few years may well ultimately be overturned.

In any case, Hansen has scientific “street cred” because he has been right for so long. I’ve written that we ignore him at our grave peril because Hansen?s mastery of climate science is quite literally what gives him climate prescience.

One of the country’s top climatologists, Michael Mann, makes the same point in a recent Daily Climate piece that I repost below in its entirety:

Opinion: Ignore climate Cassandra at our peril

James Hansen’s latest findings linking extreme weather to climate change is science society cannot afford to ignore.

by Michael Mann, via The Daily Climate

The first scientist to alert Americans to the prospect that human-caused climate change and global warming was already upon us was NASA climatologist James Hansen. In a sweltering Senate hall during the hot, dry summer of 1988, Hansen announced that “it is time to stop waffling…. The evidence is pretty strong that the [human-amplified] greenhouse effect is here.”

At the time, many scientists felt his announcement to be premature. I was among them.

I was a young graduate student researching the importance of natural ? rather than human-caused ? variations in temperature, and I felt that the “signal” of human-caused climate change had not yet emerged from the “noise” of natural, long-term climate variation. As I discuss in my book, The Hockey Stick and the Climate Wars, scientists by their very nature tend to be conservative, even reticent, when it comes to discussing findings and observations that lie at the forefront of our understanding and that aren’t yet part of the “accepted” body of scientific knowledge.

Dire warning

Hansen, it turns out, was right, and the critics were wrong. Rather than being reckless, as some of his critics charged, his announcement to the world proved to be prescient ? and his critics were proven overly cautious.

Given the prescience of Hansen’s science, we would be unwise to ignore his latest, more dire warning.

In a paper published today in the prestigious journal Proceedings of the National Academy of Sciences, Hansen and two colleagues argue convincingly that climate change is now not only upon us, but in fact we are fully immersed in it. Much of the extreme weather we have witnessed in recent years almost certainly contains a human-induced component.

Hansen, in his latest paper, shows that the increase in probability of hot summers due to global warming is such that what was once considered an unusually hot summer has now become typical, and what was once considered typical will soon become a thing of the past ? a summer too improbably cool to anymore expect.

We need to view this summer’s extreme weather in this wider context.

Not random

It is not simply a set of random events occurring in isolation, but part of a broader emerging pattern. We are seeing, in much of the extreme weather we are experiencing, the “loading of the weather dice.” Over the past decade, records for daily maximum high temperatures in the U.S. have been broken at twice the rate we would expect from chance alone. Think of this as rolling double sixes twice as often as you’d expect ? something you would readily notice in a high stakes game of dice. Thus far this year, that ratio is close to 10 to 1.  That’s double sixes coming up ten times as often as you expect.

So the record-breaking heat this summer over so much of the United States, where records that have stood since the Dust Bowl years of the 1930s are now dropping like flies, isn’t just a fluke of nature; it is the loading of the weather dice playing out in real time.

The record heat ? and the dry soils associated with it ? played a role in the unprecedented forest fires that wrought death and destruction in Colorado and New Mexico. It played a role in the hot and bone-dry conditions over the nation’s breadbasket that has decimated U.S. agricultural yields. It played a role in the unprecedented 50 percent of the U.S. finding itself in extreme drought.

Other threats

Climate change is also threatening us in other ways of course, subjecting our coastal cities to increased erosion and inundation from rising sea level, and massive flooding events associated with an atmosphere that has warmed by nearly 2?F, holding roughly 4 percent more water vapor than it used to ? water vapor that is available to feed flooding rains when atmospheric conditions are right.

The state of Oklahoma became the hottest state ever with last summer’s record heat. It is sadly ironic that the state’s senior senator, Republican James Inhofe, has dismissed human-caused climate change as the “greatest hoax ever perpetrated on the American people.” Just last week he insisted that concern over the impacts of climate change has “completely collapsed.” This as Oklahoma City has just seen 18 days in a row over 100?F (with more predicted to follow), Tulsa saw 112?F Sunday, and 11 separate wildfires are burning in the state, with historic Route 66 and other state highways and interstates all closed.

The time for debate about the reality of human-caused climate change has now passed. We can have a good faith debate about how to deal with the problem ? how to reduce future climate change and adapt to what is already upon us to reduce the risks that climate change poses to society. But we can no longer simply bury our heads in the sand.

Michael Mann is a widely renowned and much-vindicated climate scientist at Penn State University. This piece was originally published at The Daily Climate and was reprinted with permission.

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