Category Archives: Global Warming

Why SO hot?

You’re an olympic athlete in the javelin throw. You’ve trained hard most of your life, and kept careful records of your distances for some 2,000 practice throws during the last year. It turns out that your distances follow the normal distribution with a mean of 78.82 meters and standard deviation 3.07 meters.

Competition is tough and you’re desperate to win, so you give in to temptation. You start taking a new kind of steroid which improves performance and can’t be detected by the olympic committee’s drug tests. You continue to keep careful records of your practice throws, discovering that the steroids have increased your mean distance by 4 meters.

Come competition time, you’re at your best. You trained hard, got plenty of sleep, ate right, and you were just plain “in the groove.” You’re wearing a new kind of shoe with special cleats designed to give you perfect traction without slowing you down or interfering with your rhythm. Even the weather cooperates, reducing atmospheric friction to a minimum. Everything comes together, all the “natural variation” factors conspire to give you the best performance of your life. Oh happy day! Near day’s end you’re standing on the podium listening to the national anthem, because you won the gold medal with a throw of 89.60 meters — fully 4.2 meters ahead of the 2nd-place throw.

You didn’t just win the gold, you broke the world record (89.58 meters by Jan Železný in 1996; javelins with serrated tails were outlawed in 1991). You’re heralded as a national hero and approached by a well-known breakfast cereal enticing you to sign an endorsement deal for one helluva lot of money. After all, extremes which are that extreme are a big big deal.

That night a sports journalist asks “Why was is so long a throw?” You talk about hard work, proper technique, new training shoes, good weather, and how everything came together at just the right moment. All of which is true.

But the next day the drug tests arrive from the lab. It turns out that the olympic committee has kept pace with the latest in steroid innovations, and the new performance-enhacing drug is detected, no doubt about it. In subsequent investigation, statisticians analyze your careful records of practice throws and demonstrate the surprising increase in your numbers, inexplicable except by cheating. The olympic committee announces that your are stripped of your gold medal and world record, and that you are banned from competition for the next five years.

One of your biggest fans protests that the stats show your drug use only increased your mean distance by 4.00 meters but you beat the 2nd-place throw by 4.2. “He would have won anyway! Give him back his gold! His winning throw wasn’t because of steroids, it was because of a great performance!!!”

There are two things wrong with that claim. First, when we ask “Why was it so long?” we have to include steroids in the list of reasons. Second, it’s downright disingenuous to suggest that there’s some single cause. Yes it was a perfect day, yes those new shoes really did help, yes the weather cooperated, yes you gave a great performance. If you hadn’t worked so hard and so diligently, you wouldn’t even have made it to the olympics in the first place. But steroids increased your chances of throwing the javelin so far, far enough to break the world record, by a factor of more than 60. The fact is that without steroids your throw wouldn’t have been so far.

These days, it’s the weather that’s on steroids. Because of man-made climate change. Cliff Mass’s blog post asks “Why is the Northwest so warm?” Part of the reason — the part that Cliff Mass is desperate to dispute — is global warming.

Uncritical Mass

Cliff Mass is at it again, trying to tell us that the recent extreme heat in the northwest is unrelated to man-made global warming. What’s surprising is that he actually had this to say in a recent blog post:

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Actually …

People requested that I look at the relationship between the change in mean temperature and the change in the frequency of extreme heat, not using temperature at the 850 hPa level (about 1.5 km altitude), not using a reanalysis data set which doesn’t incorporate any actual temperature measurements, not using anomaly data, and not restricting analysis to Dec-Jan-Feb (winter months in the northern hemisphere).

Let’s try to do this right. Let’s use actual temperature data from actual thermometers. Let’s look at temperature at earth’s surface, where we actually live. Let’s use temperature rather than temperature anomaly, since that’s what actally defines what a region would experience as extreme heat. Since I’ll be looking at northern hemisphere locations, let’s use data from Jun-Jul-Aug, actual summer months.

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Somethin’ ain’t right

I retrieved data myself, temperature at the 850 hPa level (about 1.5 km altitude) from 20th-century reanalysis, from ECMWF. I’ve looked at two locations on the equator, at longitude 45E and 60E, selected because they’re two places for which Sardeshmukh shows an increase in mean temperature but not in the probability of extreme temperature, defining “extreme” as more than 2 standard deviations above the mean. Here’s his graph of how the mean temperature has changed (in units of standard deviations):


When I analyzed the data, I got a different result than he got. A very different result. Somethin’ ain’t right, and I really want to know what’s goin’ on.

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Judith Curry responds … sort of (v2)

Sardeshmukh has weighed in on Curry’s blog:

The critic of our study is mistaken on all counts.

1) Contrary to his suspicion, we did correctly define the temperature extremes with respect to the same fixed temperature threshold in both periods at each geographical point. The formula in the math slide, which is for shape preserving changes of the distribution, is also for exceedances beyond a fixed threshold.

2) As already noted at the bottom of the math slide, “the situation gets even more complicated for non-Gaussian distributiions whose changes are not shape preserving”. And indeed they are not shape preserving for daily temperature. There were changes from 1901-1925 to 1981-2005 in both the skewness and kurtosis (a measure of tail heaviness) at most points on the globe, including the Indian ocean point discussed by the critic. I had mentioned these changes in my talk, but not shown them to save time, as the main point of the slide showing the change in daily temperature extremes from 1901-1925 to 1981-2005 had already been made. This was that the global pattern of the change in extremes does not look anything like that of the mean shift, and this is not surprising given the fractional changes in standard deviation. The point of this slide was not that one could deduce the numerical value of the change in the extremes from only the changes in the mean and standard deviation, but that the changes in standard deviation were clearly important, and opposed the changes in the mean in many regions.

I replied on Curry’s blog with this:

If what you say is true, then I have made a grave mistake. But perhaps you can understand my skepticism that an increase in mean by a full standard deviation, combined with an increase in standard deviation, would accompany no change in the probability of exceeding a fixed temperature threshold.

If you will share with me the data you used for that grid point in the Indian Ocean, I can confirm your results with my own eyes. Upon doing so, I will publish on my blog a prominent, unambiguous admission of my error. But until I see it with my own eyes, I remain skeptical.

I look forward to seeing the data

End Update

Well, Judith Curry has “responded” to my last blog post … sort of. Here’s what she has to say about it:

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What’s wrong with this picture?

In her recent blog post Judith Curry gave her reasons for not believing that global warming is exacerbating heat waves. Her conclusion was summarized thus:

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Let them eat curry

It has often been rumored that when Marie Antoinette was told that the people of France faced starvation because they had no bread, she replied “Let them eat cake.”

The story isn’t true, but it does encapsulate the kind of cavalier, thoughtless, arrogant thinking that makes people want to cut your head off.

If the people of India and Pakistan were facing starvation, what would we recommend? “Let them eat curry”? Fortunately, they aren’t presently facing terrible food shortages. But thousands of those people — human beings — died as a result of recent killer heat waves. What advice does Judith Curry offer? This:

Looks like they need more air conditioning in Spain and France and also South Asia.

Does it make more sense to provide air conditioning or to limit CO2 emissions. I vote for more air conditioning in these susceptible regions.

Let them buy air conditioners! Never mind that they’re poor and can’t afford it. Ignore the fact that the energy use would make global warming worse. And be sure to paint it as an “either/or” proposition whether it is or not. Just don’t make us do anything like limit CO2 emissions.