Now that Ted Cruz is a presidential candidate, his views on science are, naturally, getting a lot of scrutiny. That’s particularly the case in that while he does seem to acknowledge the reality of at least some amount of climate change, he nonetheless seems a skeptic of the idea that human-caused climate change is happening right now, or has been happening lately.
This has caused some in the media, like press critic Jay Rosen, to wonder how journalists will handle candidates who challenge an important aspect of modern science.
Here’s one journalistic approach: Parsing out what Cruz has said about what he actually thinks, whether it’s accurate, and whether the scientists that Cruz himself seems to rely on would agree with how he characterizes things. So let’s do that.
In a much cited episode on “Late Night with Seth Meyers,” Cruz recently said the following about climate change:
My view actually is simple. Debates on this should follow science and should follow data. And many of the alarmists on global warming, they’ve got a problem cause the science doesn’t back them up. And in particular, satellite data demonstrate for the last 17 years, there’s been zero warming. None whatsoever. It’s why — you remember how it used to be called ‘global warming’ and then magically the theory changed to ‘climate change’? The reason is it wasn’t warming, but the computer models still say it is, except the satellites show it’s not.
The key phrase here is “satellite data demonstrate for the last 17 years, there’s been zero warming. None whatsoever.” And it’s noteworthy, because it shows that Cruz has done some homework and found a particular type of data that would appear to support his claim.
But interestingly, Cruz doesn’t say why we should trust satellite data over, say, ground-based weather station data, or sea-based buoy data. Based on such surface temperature measurements, NASA and NOAA both called last year the warmest on record, followed by 2010, followed by 2005, and then only maybe followed by 1998 — which is presumably the year Cruz considers to have been the hottest, given that it was 17 years ago.
Such is the current ranking of hottest years — and that ranking, on its face, would seem to undermine Cruz’s claim. But actually, that’s not the only or even necessarily the best way of looking at matters.
Individual years can vary in temperature, but decades tell you more about trends. Using this approach, the World Meteorological Organization has ably demonstrated that the decade of the 2000s was warmer globally than the 1990s, which was in turn warmer than the 1980s. So while 1998 may have been one of the top four or five hottest years on record, that hardly means the globe hasn’t been warming in the past 17 years.
Granted, the rate of warming may have been slower of late — according to the U.N.’s Intergovernmental Panel on Climate Change, the rate of warming from 1998 to 2012 was “smaller than the rate calculated from 1951.” But that’s hardly the same as “zero warming.” Moreover, the IPCC warned that “Owing to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends.”
So how can Cruz claim that there’s been no warming in 17 years? First, he’s selectively using one type of data over others. Second, he’s starting his analysis with a single warm temperature year — 1998 — rather looking at the aggregate temperatures of multiple years (or decades).
But moreover, it turns out that even when you look at the data Cruz is citing, his interpretation is questionable.
When PolitiFact investigated Cruz’s “17 years” claim, it reported that Cruz spokesman Phil Novack supported the claim by referring to a blog item by Carl Mears, a physicist and senior scientist at Remote Sensing Systems. In response to a query, Novack sent me the entire response to PolitiFact, which cited Mears as well as another satellite data temperature set to support the idea that “there has been a pause or hiatus in warming during the twenty-first century.”
These datasets use satellites to measure temperatures in the lower troposphere of the planet — basically, the part of the atmosphere where weather occurs. And in Mears’s dataset, for this particular part of the planet, it does look like 1998 was the year with the warmest temperature anomaly.
But if you look at Mears’s blog post, while he agrees there has been a slowdown in the “rate of warming” — which, again, is not at all the same thing as “zero warming” — he disagrees that this undermines global warming concerns. “Does this slow-down in the warming mean that the idea of anthropogenic global warming is no longer valid?” Mears asks. “The short answer is ‘no.’”
Indeed, Mears uses the term “denialists” to refer to climate skeptics in his post.
To explore Mears’s views further, I did one thing journalists can do when covering the climate views of presidential candidates — I contacted the researcher. And his response was quite critical of Cruz’s approach to the evidence on this issue:
Mr. Cruz (and others who seek to minimize the threat posed by climate change) likes to cite statistics about the last 17 years because 17 years ago, the Earth was experiencing a large ENSO [El Nino-Southern Oscillation] event and the observed temperatures were substantially above normal, and above any long-term trend line a reasonable person would draw. When one starts their analysis on an extraordinarily warm year, the resulting trend is below the true long term trend. It’s like a pro baseball player deciding he’s having a batting slump three weeks after a game when he hit three homers because he’s only considering those three weeks instead of the whole season.
Mears went further, explaining that while he studies satellite data, we probably shouldn’t rely on those data more than we rely on the temperatures that NASA and NOAA are using:
My particular dataset (RSS tropospheric temperatures from MSU/AMSU satellites) show less warming than would be expected when compared to the surface temperatures. All datasets contain errors. In this case, I would trust the surface data a little more because the difference between the long term trends in the various surface datasets (NOAA, NASA GISS, HADCRUT, Berkeley etc) are closer to each other than the long term trends from the different satellite datasets. This suggests that the satellite datasets contain more “structural uncertainty” than the surface dataset.
Structural uncertainty, explains Mears, refers to situations in which scientists are “getting different results when different, but scientifically reasonable, methods are used.”
So in sum: In claiming the globe hasn’t warmed in 17 years, Cruz selectively highlighted satellite temperature data, rather than other data (which NASA and NOAA recently used to call 2014 the hottest year on record). He also selectively focused on one year (1998), rather than examining the aggregate temperatures of many years or decades. And finally, a key scientist who studies this type of satellite data, and whose work was cited by Cruz’s spokesman (as backup), criticizes Cruz’s approach and conclusions.
Speaking of conclusions — at this point, feel free to draw your own.