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Statistics and Climate Science: Roger Pielke Missed the Mark

03/27/2014 11:25 am ET | Updated May 27, 2014
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Did Roger Pielke fumble, trip, or score an own-goal?

In his inaugural post on Nate Silver's FiveThirtyEight website, Roger Pielke Jr. put forth a number of arguments suggesting that many changes to extreme weather are not occurring as our climate changes. Pielke offers:

When you read that the cost of disasters is increasing, it's tempting to think that it must be because more storms are happening. They're not. All the apocalyptic 'climate porn' in your Facebook feed is solely a function of perception.

A review of the evidence shows that his view is not supported by much of the scientific literature.

The Pielke post has received a very large and negative reaction from scientists here and here for example, and from comments at the FiveThirtyEight blog. I wrote to Nate Silver last week. Mr. Silver responded by kindly inviting me to write a response to be posted on the FiveThirtyEight website. I submitted this piece which went through editing with the FiveThirtyEight staff. Unfortunately, late in the game, they decided not to run my post. Therefore, I'm publishing it here. I will also state the editorial staff at FiveThirtyEight took great pains with my article and I believe they are committed to appropriately responding to the criticisms of Roger Pielke.

Why has there been such a buzz about FiveThirtyEight and Roger Pielke Jr.? Likely because Pielke has a history of climate claims which have been criticized by scientists -- not the type of hire many of us expected by the FiveThirtyEight team. Dr. Pielke, a political scientist (not a climate scientist), was recently called out by Dr. John Holdren for statements he made to congress on droughts.

The central theme to Pielke's post is that extreme weather costs are increasing but not because of climate change. They are increasing because we are wealthier; we have more to lose. He also writes that increasing storms are not occurring and the extreme weather which is attributable to climate change is not a significant cause of damage. Unfortunately, Roger Pielke's views are at odds with many peer-reviewed studies that look at this, and they are at odds with some of the studies he cites in his article.

In his FiveThirtyEight post, Pielke references the IPCC reports to support his central claims. When I shared a draft of this piece with him, he again referenced the IPCC, highlighting its statement that there is "medium evidence and high agreement that long-term trends in normalized losses have not been attributed to natural or anthropogenic climate change." But the panel, which is referring to an "absence of an attributable climate change signal," has set a high scientific bar for itself. Detecting climate signals in normalized economic losses remains deeply contested, but trends in extreme weather itself can be studied directly, a field around which there is much consensus. Pielke has taken the IPCC's caution at drawing an attributable conclusion and inserted his own counter-claim into the vacuum. But a closer reading of those IPCC reports tells a different story than Pielke's. For temperature extremes, heat waves, and warm spells, the report says:

It is very likely that both maximum and minimum temperature extremes have warmed over most land areas since the mid-20th century. These changes are well simulated by current climate models and it is very likely that anthropogenic (human) forcing has affected the frequency of these extremes and virtually certain that further changes will occur.

The report also states that:

It is likely that the number of heavy precipitation events over land has increased in more regions than it has decreased since the mid-20th century and there is medium confidence that anthropogenic (human) forcing has contributed to this increase.

Third, the report states that "over the satellite era, increases in the frequency and intensity of the strongest storms in the North Atlantic are robust." Pielke does concede that there have been more heat waves and intense precipitation events, "but these phenomena are not significant drivers of disaster costs," he claims. Heat waves and heavy rains are not drivers of disaster costs? Just don't tell that to sufferers of floods from Irene, in Colorado, Duluth, Europe, or in the U.K., to name a few. Also, don't tell residents of France in 2003, Russia in 2010, Oklahoma and Texas in 2011, California this year, Australia, or just about any U.S. citizen in 2012.

What about droughts? The subject is not simple because increasing temperatures cause two competing phenomena. First, some areas get drier because evaporation is strengthened. At the same time, precipitation can increase because there is often more water in warmer air. In many parts of the globe, the "drying" wins out whereas in others areas, things get wetter. But averaging these competing factors on a global scale hides what is happening locally. Take the United States as an example; the first part of 2013 had extraordinary precipitation in the north-central part of the country but exceptionally dry conditions in the West. On "average," you might conclude that this was just a normal spring but in reality, it was two offsetting disasters.

A drought in California continues today and is exacerbated by the increasing temperatures there. You don't have to take my word for it, go look here yourself. Pielke, in his response to me, cited the IPCC's statement that "there is not enough evidence at present to suggest more than low confidence in a global-scale observed trend in drought or dryness (lack of rainfall) since the middle of the 20th century." But he skips the next line, which states:

... due to lack of observation, geographical inconsistencies in the trends, and dependences of inferred trends on index choice... It is likely that the frequency of drought has increased in the Mediterranean and West Africa and decreased in central North America and north-west Australia since 1950.

In other words, we don't have enough data yet, but we do see regional trends that are making some areas drier and some wetter.

But the evidence gets even stronger. Many publications attest to the observable change in extreme weather. A 2012 paper on heat waves reports:

Recent examples of summer temperature anomalies exceeding +3σ include the heat wave and drought in Oklahoma, Texas, and Mexico in 2011 and a larger region encompassing much of the Middle East, Western Asia, and Eastern Europe, including Moscow, in 2010.

Or how about this paper which found "an approximate 80 percent probability that the 2010 (Moscow) July heat record would not have occurred without climate warming." Maybe this 2014 article which states that "when droughts occur they are likely to set in quicker and be more intense." The list goes on and on and on and... well I think we see the point.

And storms? Try this study which shows the impact of increased ocean temperatures on storms like Katina, Ivan and Sandy. Or this 2012 study which finds, "Katrina-magnitude events have been twice as frequent in warm years compared with cold years". Or this very recent paper which concluded that the warm waters caused an increase in the intensity of Superstorm Sandy.

And it isn't just what we've observed. It is what we expect in the coming years and decades that concerns scientists. This study states, "continued increases in greenhouse forcing are likely to increase severe thunderstorm occurrence, thereby increasing the risk of thunderstorm-related damage." As this 2013 paper by Dr. Kerry Emanuel which shows, not only will cyclones become more powerful, they will become more numerous. It is clear that for many types of extreme weather, yes humans are having an impact.

I'll close by commenting on Roger Pielke's writing which leads to potential misunderstanding. His post uses phrases like "there's little evidence of a spike" in floods, droughts and hurricanes. A "spike" is not quantifiable. Statisticians don't calculate "spikes." He also claims that "Today's climate models suggest that future changes in extremes that cause the most damage won't be detectable in the statistics of weather (or damage) for many decades." Yet Pielke cites only his own paper on U.S. hurricane losses which doesn't even account for changes to sea level and increases in rainfall. And last, Pielke spends much time discussing earthquakes, tsunamis and volcanoes in an article that is otherwise focused on extreme weather. These inexact phrases, extensions of his own work beyond their application, and inclusion of non-weather-related disasters are some of the reasons his conclusions are not taken seriously by myself and other climate scientists.

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