Posted by: bmeverett | July 23, 2013

Havin’ a Heat Wave


It’s been really hot in Boston this summer. It’s been hot before, of course, but this time I hear friends, neighbors and people on the street blaming global warming. I fully expect that when I get back to class at Fletcher this fall, I’ll hear again how only the stupidest people could question climate change after the horrible summer we just had. This is the same argument we heard after Hurricane Sandy.

As I discussed in previous posts, this argument is just plain false. Hurricane Sandy was a terrible storm, bringing a lot of damage and suffering. It was caused by a relatively small late-season hurricane getting wrapped up with a Nor’easter. This happens several times each century. The infamous “Perfect Storm” of October, 1991 was a similar event. Sandy differed from The Perfect Storm only because it veered to the west and hit the New York/New Jersey area rather than staying out to sea.

So what conclusions can we draw about our hot summer? If we define a Boston heat wave as 6 or more consecutive days above 90º F, we could say that heat waves have become more common in Boston over the years. We’ve had 7 such heat waves in the last 50 years while we had only two in the preceding 50 years. Sounds like it’s getting hotter. On the other hand, let’s look at the problem a different way. Consider July temperatures for Boston since 1920. The mean July temperature over this period was 73.3º. So far the 2010s have been pretty darn hot, with July temperatures averaging 77º. If, on the other hand, the mean July temperature in Boston correlates with atmospheric carbon, we ought to see a trend over time. In fact, there is no trend. Before the 2010s, the warmest decadal average for July was the 1980s, followed by the 1950s, the 1970s, the 1990s, the 1940s, the 2000s, the 1960s, the 1930s and the 1920s.

How about July in New York? Would we get the same result? Hardly. The 2010s have been hot in New York as well, but the history is very different. The New York decades, in order of decreasing average July temperatures were the 2010s, the 1950s, the 1970s, the 2000s, the 1990s, the 1960s, the 1930s, the 1940s, the 1980s and the 1920s. The temperature data for individual cities don’t disprove the climate change hypothesis, but they don’t support it either. Picking a hot year or a hot decade or a hot location means absolutely nothing.

Furthermore, the term “global warming” has two components. It’s not only “warming” but “global”. In fact, we have a global temperature data series, and the data were developed by climate change advocates at NASA. This data series, which you can find at http://data.giss.nasa.gov/gistemp/graphs_v3/Fig.A2.txt, shows that global temperatures increased until 1998 and have leveled off since. What does this summer’s Boston heat wave mean in that context?

To maintain its credibility, the Climate Community needs to stop pointing to random anecdotes and start offering some real science. As discussed in previous posts, science involves stating a hypothesis (e.g., increasing human greenhouse gas emissions will accelerate global temperatures bringing catastrophic results) and then making predictions to see whether they support the hypothesis or not. The key issue here is that the hypothesis must be falsifiable. In other words, the prediction must provide information as to whether the hypothesis is correct or not.

It seems rather obvious that the use of individual data points or anecdotes tells us nothing about broader trends, but that’s exactly what the Climate Community continues to do. Extreme weather events, such as hurricanes or heat waves may seem compelling but people do not carry around in their heads a sufficiently long or complete data series to calculate meaningful trends. For example, my Fletcher students average about 28 years of age. That means they were adults when Hurricane Sandy hit, but only 6 years old when The Perfect Storm struck in 1991. Sandy was thus their only experience with storms of this type. Those students who grew up in Boston have experienced only two heat waves as adults and perhaps one as a teenager. That may suggest to them that heat waves are a rare and recent phenomenon. People in their 80s, on the other hand, may have experienced 8 or 9 heat waves and may thus conclude that they occur routinely. Intuitive judgments are of limited value. Only a proper review of all the available data offers real insight.

Let’s take an example and hypothesize that human beings are getting taller over time. How would we test that hypothesis to see if it’s true? You might structure a survey of people carefully selected by age, geography, racial/ethnic background, nutrition, etc, calculate their average height and then calculate the average height of a similar group a generation later. There would be lots of methodological arguments about how to conduct such a survey, and the results might be controversial, but the approach is theoretically correct. Nobody would accept the statement “Bill is seven feet tall” as support for the hypothesis.

The Climate Community shies away from making predictions, perhaps out of fear that the predictions may not come true, thereby undermining their political position. Their preference seems to be to wait to see the millions of weather data points generated annually and then point out the ones that are anomalous as proof of the “weird weather” that the Climate Community sees all around us. The problem with this approach is that weather has huge short-term variability. There have been 203 days so far in 2013. Each day has a recorded high and low temperature, giving us 406 temperature data points for the year to date. Meteorologists can also tell us the “normal” or historical average temperature for each day. Only 20 of the actual temperatures readings so far in 2013 matched their historical “normal” values. The other 183 high and low temperatures were “abnormal”. This is always true, and a long string of “abnormal” weather says nothing at all about Climate Change.

Rather than just complain about the Climate Community, let me offer an example of real science: Einstein’s general theory of relativity. Einstein’s hypothesis was that gravity is not a force, but rather a curvature space-time, caused by the presence of matter. Einstein, as a true scientist, did not argue that his hypothesis was correct because he was smarter than everyone else or because it was supported by a committee of other scientists. He didn’t try to demonize people who disagreed with him or to convince politicians to declare his hypothesis legally correct. In fact, Einstein proposed three tests that would either prove or disprove his hypothesis, and he was quite honest about the process, stating, “If a single one of the conclusions drawn from it [the general theory of relativity] proves wrong, it must be given up”.

The first test was the change in the orbit of the planet Mercury. All other things being equal, Mercury’s orbit around the Sun should be an ellipse with the Sun at one focus, and that orbit should not change over time. Scientists had recognized since the 1850s that Mercury’s orbit in fact changes slightly over time and were able to explain 92% of the observed changes in terms of the gravitational pull of the other planets and the fact that the Sun is not a perfect sphere. The remaining 8% was unexplained. Einstein argued that the general theory of relativity should produce a more precise estimate of Mercury’s orbital change because it added a third factor: the curvature of space-time due to gravity. Einstein’s calculations predict almost 100% of the observed orbital change, and the more precise the observations have become over time, the better the fit. Unlike the Climate Community, Einstein put his hypothesis on the line. This is true science.

The other two tests of general relativity produced comparable results. Newtonian physics predicted that the Sun’s gravity would bend starlight, but could account for only half the observed result. General relativity predicted close to 100% of the observed bending. The third test was the gravitational red shift of light, a test which could not be made until the late 1950s when sufficiently sensitive instruments had been developed. Again, Einstein’s predictions matched the observations very well.

It’s worth noting that general relativity cannot be tested against an individual person’s life experiences and observations. People can see Mercury, and have been able to make broadly correct predictions of its movement for at least a few thousand years. More precise predictions, however, require sophisticated instruments and careful observations of Mercury’s movements over centuries – well beyond the perceptual or chronological capabilities of an individual. No scientist worth his salt would have proposed testing the general theory of relativity by asking people to have a look at Mercury over the next few days and see what happens. Furthermore, we could not have tested the validity of general relativity unless we had a proper theoretical understanding of the other factors (gravitational pull from the other planets and the shape of the Sun) so we could isolate the impact of space-time curvature. That is how you do science.

Heat waves come and go. We need science not ideology to explain how and why.

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