Wednesday, December 16, 2015

The Reddest Herring

Ted Cruz, Republican senator and candidate for the Republican presidential nomination, says the earth hasn't warmed for eighteen years. Cruz, a climate change denier, chaired a hearing of the Senate Subcommittee on Space, Science, and Competitiveness that mostly featured witnesses who deny climate change, even as talks were underway in Paris to negotiate a worldwide response to global warming.

"According to the satellite data," Cruz said in his opening remarks, "there has been no significant global warming for the past 18 years. Those are the data. The global warming alarmists don't like these data, they are inconvenient to their narrative. But facts and evidence matters."

Cruz's claim highlights the danger of taking scientific instruction from a slick demagogic opportunistic ideologue who is not himself a scientist. Cruz has called climate change "pseudoscience," even though the greater scientific enterprise broadly, and by every imaginable measure, accepts the reality of anthropogenic (human caused) climate change. Tens of thousands of scientists worldwide, in a multitude of disciplines and specialties, are involved in climate related research. All the world's top scientific academies and societies concur. My post from two and a half years ago is still a good overall introduction to the overwhelming scientific consensus, and both consensus and certainty have increased in the intervening time. Prominent during these last couple of years was the release of a the IPCC's Fifth Assessment Report (AR5) in September 2013, and the record-setting warmth of 2014.

So what about that satellite data that show, according to Cruz, that the earth has not been warming? Golly, if we're using satellites to measure the earth's temperature, we ought to have a good picture of what is going on, right? Well, it isn't that simple.

Satellite global warming measurements of the kind described here are actually one of the most fraught and difficult specialties in climate science. The first thing you should understand is that the satellites being discussed don't measure the earth's surface temperature; they "measure" the temperature of a particular part of the atmosphere called the mid-troposphere, and somewhat indirectly. The troposphere is the lower layer of the atmosphere, between the Earth's surface and the upper atmosphere, which is called the stratosphere. Climate change models predict tropospheric warming and stratospheric cooling in a climate that's warming overall, and most scientists say that's what we're observing. This is apart from what we're observing at ground level, which is unambiguous warming.

The satellites specifically examine the troposphere over tropical latitudes—not the entire planet—because climate models predict disproportionately greater warming (called "tropospheric amplification") in this region of the atmosphere as the planet warms. A few scientists say they're not seeing enough mid-tropospheric warming, and climate change deniers and skeptics line up behind those particular scientists. One of them, Dr. John Christy, was a witness at Cruz's hearing.

The contention by some of insufficient tropospheric amplification since 1998 is where Cruz's bald "no significant global warming for the past 18 years" assertion comes from. Note that Cruz doesn't explain when he makes his claim that he's ignoring the more direct and straightforward ways that surface (not tropospheric) temperature is measured, and the broad agreement of warming among the several independent agencies that do that measuring. Presenting as conclusive only "facts"—contested facts, at that—that misleadingly advance your position before an uninformed public, while ignoring context, caveats, and stronger contradictory evidence, is dishonest and dishonorable, at least outside of debate tournaments where you have to argue whatever side you're assigned. The silver-tongued Cruz was a star debater in high school and college, and listening to him you constantly get the impression he's craftily and disingenuously pulling one over on you while arguing his assigned side.

With respect to temperature inferences of the troposphere, I placed scare quotes around the word "measure" above because satellite readings don't involve taking the troposphere's temperature with actual thermometers. This gets technical really fast, but the polar orbiting satellites use microwave sounding units to measure "the intensity of upwelling microwave radiation from atmospheric oxygen, which is related to the temperature of broad vertical layers of the atmosphere." [Quotation found here.]

Some of the difficulties in these measurements involve calibration of the equipment, warm-target bias, deterioration of the sensors, reconciling the measurement record over successive iterations of equipment, diurnal variation, and so forth. For example:

The satellite time series is not homogeneous. It is constructed from a series of satellites with similar but not identical sensors. The sensors also deteriorate over time, and corrections are necessary for orbital drift and decay. Particularly large differences between reconstructed temperature series occur at the few times when there is little temporal overlap between successive satellites, making intercalibration difficult.

Corrections are constantly applied to the resulting datasets to accommodate these difficulties, especially as they become better understood. Read more about all of this in the "Trends from the record" section of the quoted article.

There are multiple groups of scientists who produce datasets from these tropospheric satellite measurements, and they don't all agree [see *footnote]. The two most prominent datasets are one called UAH, produced by Dr. John Christy (as I said, one of Ted Cruz's witnesses) and Dr. Roy Spencer, both of the University of Alabama, Huntsville; and another called RSS, produced by Remote Sensing Systems, a private research company that works for NOAA and NASA. Most scientific experts seem to agree that the satellite data shows the expected tropospheric warming, but the UAH group does not. It all comes down to how adjustments are made to the raw satellite data. Adjustments made to the UAH data over time have brought it closer to the RSS data, but differences remain. Both datasets, and indeed the models underlying computer simulations of tropospheric amplification, continue to be revised as additional understanding emerges.

Ted Cruz hangs his hat on the findings of the UAH team—which is arguably a scientific outlier in this particular debate—and proclaims them conclusive. My advice is that unless you have truly mastered the arcane science of satellite tropospheric measurements, and can lay aside your subjective or ideological biases, you should leave this sleeping dog lie. It is highly unlikely that anybody reading my words—me included—will be equipped to reach a conclusion based on solid understanding of the science. As always, we non-experts ought to be guided by what we are equipped to gauge, which is the overwhelming scientific consensus on climate change.

I should add that many—perhaps most—experts do find the expected tropospheric amplification in the satellite record. But even if you conclude this is a contested area of climate science, you should place it in proper perspective. There are so very many concurring lines of evidence all showing anthropogenic warming, which is why the scientific consensus is so strong. Some of them are: direct surface measurements (on land and at sea) with a vast network of actual thermometers; the alarming, accelerating melting of ice sheets in polar regions, and of glaciers worldwide; the concomitant rise in sea levels, along with increased flooding in coastal areas; a temporal change in the onset of the seasons (eg., spring arrives earlier), based on plant bloom times and numerous other data; observed migration of legions of plant and animal species to higher latitudes, far beyond their historical ranges; equatorial fish species found at high latitudes (such as swordfish off Iceland) for the first time ever; invasive species (such as pine bark beetles) exploiting new habitats that were previously too cold.

The list is practically endless. Here's one of my personal favorites: Armadillos, whose native range is the warm, deep south, are now common in my neck of the woods—er, prairie. A couple of decades ago they did not exist here. Now they're numerous, featuring prominently as disgusting roadkill on our highways. Here are some of my own armadillo photos from near my tallgrass prairie restoration.

Ted Cruz's contention that the earth has not warmed for 18 years is egregiously false. Surface temperature measurements made by multiple teams working independently (these include NASA, NOAA, and JMA—the Japan Meteorological Agency) confirm that the ten hottest years ever recorded (since the instrumental record began in the 1800s) all occurred since 1998, in Cruz's 18-year window. Last year, 2014, was the hottest year ever, and 2015 will easily blow through that record.

Cruz is an ideological advocate driven by ambition, not a seeker or elucidator of truth. The senator showed himself to be deeply unserious in an interview with NPR's Steve Inskeep, while talking about his subcommittee hearing, when he said this:

You and I are both old enough to remember 30, 40 years ago, when, at the time, we were being told by liberal politicians and some scientists that the problem was global cooling. That we were facing the threat of an incoming ice age. And their solution to this problem is that we needed massive government control of the economy, the energy sector and every aspect of our lives. But then, as you noted, the data didn't back that up. So then, many of those same liberal politicians and a number of those same scientists switched their theory to global warming.

Yeah, that's it. Forget science; what we have is just a story of  "liberals" looking to control your life. After a false start with cooling, they "switched their theory" and are giddy with joy over how well global warming is working out for their control agenda.

To imply that scientific interest decades ago in cooling trends—whether real, perceived, or theoretical—casts any doubt at all on what science now understands is a nonsensical non sequiter, intended to paint scientists as bumbling and incompetent, or even scheming and manipulative. Cruz apparently doesn't understand that part of science's job is sorting out both opposing and reinforcing factors that influence climate in all directions, and understanding their interplay. That all takes time and effort. It would be unthinkable that we wouldn't know a lot more now than we did four decades ago, particularly given the immensity of the scientific effort in understanding climate over that time.

Anyway, imminent "global cooling" was never widely accepted by the scientific community, nor was it a crisis that demanded government control over "every aspect of our lives." The cyclical (though aperiodic) nature of ice ages has, of course, been long understood. It's been approximately 20,000 years since the last ice age peaked, and we're currently experiencing conditions in the earth's axis and orbit that would normally favor the buildup of ice sheets yet again. But hey, ice ages take time! As in thousands of years to actually get going. They don't come on suddenly or unexpectedly, or catch you off guard.

There had also been conjecture decades ago (and there's ongoing study now) about the amount of cooling we could expect from human-emitted reflective particulates in the atmosphere, which have the effect of blocking sunlight. But Ted Cruz's "30, 40 years ago" climate science was truly in its infancy compared to now. Even then, cooling was little more than an interesting idea to ponder, even if it did get some attention in the national media. And if the "data didn't back that up," well, following the data is what science does.

What's missed in this dodge is that even decades ago, from the time of Cruz's distant memory, the notion of anthropogenic global warming was starting to get traction in the scientific community. I suppose that shouldn't be surprising, because the underlying physics is so compelling. Indeed, at a basic level, the physics behind the so-called "greenhouse effect" caused by concentrations of certain gasses in the atmosphere has been well understood for at least two centuries, and is utterly uncontroversial. The thing that had to be worked out was how to quantify the influence of feedbacks, which is where much of the action occurs in climate change. It's worth noting that even Exxon's own scientists were warning, as far back as the 1970s, about the dangers of global warming. Scientific understanding and certainty has increased many-fold since that time.

So Cruz's suggestion of scientists bouncing from one thing to another, casting about for a crisis, was never correct. The notion that hapless scientists can't make up their minds—cooling? warming? which is it?—is a flagrant red herring, wrong in fact, and even worse in intent. Cruz's implicit ridicule notwithstanding, the real takeaway message of these past several decades is how science, when engaged, is able to figure things out and reach overwhelming consensus.

Setting aside Ted Cruz's glib chortling about climate science, it's interesting to ponder the interplay of natural and man-made phenomena that are both driving the climate, potentially in opposite directions. It apparently is indeed the case that, absent human activity, the Earth would now be in the very early stages of descent—culminating thousands of years hence—into a full blown ice age. But human activity is no longer off the table as a driver of climate. In fact, human activity increasingly and amazingly predominates over natural factors.

Don't allow your personal incredulity get in the way of grasping this astonishing fact. Noted climate scientist James Hansen, formerly director of NASA's Goddard Institute For Space Studies, has written persuasively that Earth will never again experience another ice age so long as humans are around to stop it! It turns out that ice ages, seemingly so colossal and inexorable, are no match for a little anthropogenic warming. And I do mean "little." Hansen says it is trivially easy to short circuit ice ages. You can read Hansen's authoritative explanation in his book Storms of My Grandchildren (which I highly recommend), or a passable explanation in my Of Ice Ages and Men.

*Footnote: I wrote above that "there are multiple groups of scientists who produce datasets from these tropospheric satellite measurements, and they don't all agree." Though true, these words make me uncomfortable, because they could be used out of their very specific context to play into the mistaken assumption among poorly informed laymen that climate science and scientists are inherently conflicted about the reality of anthropogenic climate change. They aren't.

Scientists can and do argue among themselves about certain particulars, but the broad picture that emerges from the greater scientific enterprise is one of overwhelming consensus on the reality of anthropogenic climate change. Political and media forces on the right work to paint a false picture of scientific uncertainty, much as tobacco companies tried to do regarding the dangers of cigarette smoking decades ago. This is what climate scientist Michael E. Mann calls "sowing doubt and confusion." Unfortunately, it works.

Think about the consensus this way. If, as is commonly said, 97 percent of scientists with subject matter expertise accept the reality of anthropogenic climate change, then as a matter of simple arithmetic 3 percent do not. And 3 percent, though very small, is not zero. We can presume—in fact we know—that not all of that 3 percent are cranks, charlatans, and shills; some really are highly credentialed, expert scientists. When you see a credentialed scientist persuasively denying the reality of climate change, always remember that he's outnumbered by 32 equally competent and credentialed scientists who take the opposite position. It's really all you can do.

Because most of us aren't experts on the science, we are in no position to evaluate individual claims on their scientific merits. It's important that we not just resort to picking the "side" that aligns with our prejudices by lining up behind a scientist who persuasively tells us what we want to hear. Fortunately we are, even as non-experts, competent to gauge where the greater scientific enterprise stands, and it's pretty easy to see that the scientific consensus on climate change is overwhelming. You can get a quick overview of that consensus here.

Copyright (C) 2015 James Michael Brennan, All Rights Reserved

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