Unsettled: What Climate Science Tells Us, What It Doesn’t, and Why It Matters

by Steven E. Koonin

As you can see, the numbers of record highs and lows both decline precipitously between 1930 and the present day, with the number of lows declining more rapidly—explaining why the ratio of record highs to record lows is larger in recent years, even as both types of records are becoming much less frequent.

However, in later years, as the bar to a new record increases, the numbers of records become much smaller, and so the ratio fluctuates much more. The upshot is that by using the running records method, the ratio graph is guaranteed to show a long period of values around 1 at the start of the record, followed by dramatic variations toward the end, creating the impression of large changes in recent decades, even if they aren’t present. While it produces a scary visual, this ratio has almost nothing to do with how temperatures are actually changing.

The record highs clearly show the warm 1930s, but there is no significant trend over the 120 years of observations, or even since 1980, when human infl uences on the climate grew strongly. In contrast, the numbers of record daily cold temperatures decline over more than a century, with that trend accelerating after 1985. These two panels together show something that is completely contrary to common perception—that temperature extremes in the contiguous US have become less common and somewhat milder since the late nineteenth century.

But by the CSSR’s own definition, the number of record highs has been falling.

Nowhere in the AP article (except for the figure heading) do they mention that the numbers of both hot and cold records are declining. Incredibly, they even include a quote from a former Weather Channel meteorologist that’s directly contradicted by their own figure: “You are getting more extremes. Your chances for getting more dangerous extremes are going up with time.”

Of course, temperatures getting milder in this way (fewer harsh winters and cold evenings) makes for a very different (and less alarming) story than torrid summers and blazing afternoons becoming more common. As it happens, the evidence of a rise in the coldest temperatures is perfectly consistent with a warming globe—just not a “roasting” one that lends itself to graphics of bursting thermometers.

pattern? And while far from complete, aircraft observations extend back to about 1944. Before then, however, there are only records of those storms that made landfall or, occasionally, reports from ships unlucky enough to have encountered one. Going back even further means relying on historical reports and various proxies (paleotempestology is the wonderful name for that field of study). So to understand trends over more than seventy years (before the onset of significant human influences), we have to correct for imprecise and incomplete observations, unfortunately all too common across climate science.

There has been no significant trend in the global number of tropical cyclones nor has any trend been identified in the number of US land-falling hurricanes.13 Wow! I thought to myself. That’s surprising and pretty important. How come this isn’t up front as a Key Message?

That’s a pretty weak statement for a Key Finding—medium confidence that human activities contributed to variability (by how much?), followed in turn by medium confidence that the variability contributed to “an observed upward trend” (by how much?).

The National Academies’ review of the CSSR doubled down on burying the lede.

The discussion of hurricanes in the 2017 CSSR is a profound violation of Feynman’s Wesson Oil caution, that a scientist must “try to give all of the information to help others to judge the value of your contribution; not just the information that leads to judgment in one particular direction or another.”

Most significantly, the majority of the authors had only low confidence that any other observed tropical cyclone changes were beyond what could be attributed to natural variability.19 I’ve been unable to find any media coverage (or even a press release) of that paper. Instead, the media continues to promulgate unsupported alarm. For example, to herald the publication of a different study, USA Today used the headline “Global warming is making hurricanes stronger, study says.”

So how are tornadoes counted? Today, weather radar can detect even very weak tornadoes from distances of more than 160 km (100 miles). Before radar was widely deployed, however, weak tornadoes didn’t always make it into the record. While strong tornadoes leave an evident trail of destruction, weaker tornadoes can come and go without a trace, particularly in sparsely populated areas.

In other words, as human influences have grown since the middle of the twentieth century, the number of significant tornadoes hasn’t changed much at all, but the strongest storms have become less frequent.

there is no evidence of increase in precipitation at the global scale in response to the observed global warming.

This doesn’t accord with the notion that a warming globe will accelerate the hydrological cycle—more rain, more floods.

But what about those regional increases? Annual precipitation in the US has gone up 0.6 percent per decade since the start of the twentieth century, as shown in Figure 7.3 (average US annual precipitation is 767 mm or 30.21 inches). As you can see, though, a simple trend doesn’t really describe the data here, either: the overall change is small compared to the dramatic year-to-year fluctuations.

(and also, to some extent, in summer) as would be expected in a warming globe—especially one in which low temperatures are increasing,

while snow cover during the fall and winter has been increasing modestly.

However, a straight-line trend doesn’t really describe the data, since there has been no change in the ten-year average during the thirty years since 1990, even as the globe has warmed 0.5°C (0.9°F). I’m surprised not to have seen that in the CSSR’s Key Finding (or, in fact, anywhere else in the report).

Models project that the Southwest will become steadily drier as the globe warms, but the data shown for the twentieth century are well within the historical context and, as the AR5 notes, the current impact of human influences seems weak in comparison with natural variability.21 A study published in 2020 confirms the notion that a leading cause of multiyear US droughts over the past millennium has been internal variability of the atmosphere.

That kind of long-term perspective makes it difficult to attribute recent droughts solely to human influences. But, oddly, it’s entirely absent from the 2014 National Climate Assessment. The subsequent CSSR of 2017 doesn’t offer any figure like our Figures 7.9 and 7.10, but it does have half a page of text describing the past millennium.25 Alas, it then spends about twice as long discussing the then most recent six-year California drought, which that state’s governor had declared over six months before the CSSR was released.

A striking image of a half-submerged Statue of Liberty filled the cover of the September issue of National Geographic magazine in 2013, touting its lead story: “Rising Seas—how they are changing our coastlines.” Any curious reader could have consulted the record of the tide gauge at The Battery at the tip of Manhattan (less than two miles from the statue) and seen that sea level there has been rising at an average rate of about 30 cm (1 foot) per century since 1855.1

During the last interglacial (low-ice) period 125,000 years ago, known as the “Eemian,” sea levels were some 6 meters (20 feet) higher than they are today!

has been clear for some time that there was a signifi cant increase in the rate of sea level rise in the four oldest records from Northern Europe starting in the early to mid-19th century. The results are consistent and indicate a signifi cant acceleration that started in the early to mid-19th century, although some have argued it may have started in the late 1700s.

That statement was a red flag for me, because it compares the rise over the past twenty years with that over more than a century. The fact that three of the seven inches of rise since the dawn of the twentieth century occurred in the past twenty-five years does indeed seem alarming—but suddenly less so if you know that it also rose almost as much (6 cm, as opposed to 7 cm) in the twenty-five years between 1935 and 1960.

The CSSR, on the other hand, follows the lead of some prominent climate scientists in hiding the large fluctuations in the rate of sea level rise over the past century, presumably because they make the past three decades seem less unusual. The report misleads by omission in not mentioning either the strong decadal variability of sea level rise during the twentieth century or the fact that the then most recent values of the rate were statistically indistinguishable from those during the first half of the twentieth century.

the contribution from Greenland went through a minimum around 1985 and is now no higher than it was in 1935;

But, as I mentioned, graphs of the sea level itself, rather than the rate at which it’s rising, can be deceptive and, in any event, we’ve got to take the long-term view. Figure 8.8, which shows the rate of rise for The Battery sea level over the past century, should calm any sense of alarm.

So it’s reasonable to expect that the rate will decline again during the next few decades. The average rates projected by the IPCC, on the other hand—even the low RCP2.6 rate of 5.5 mm/yr—would be so unusually high that they would fall outside the scale of this chart. The next few decades will tell.

But it failed to mention that the NOAA tide gauge record for Honolulu shows an average rate of 1.5 mm (0.06 inches) of rise per year since 1905, meaning that, absent some very dramatic acceleration, it would take two hundred years to achieve even the lowest mapped rise of 30 cm (one foot).

So Greenstone begins his testimony by taking an unrealistic, extreme scenario as his starting point.

A crucial measure of a model’s credibility is its ability to reproduce the past.

papers to appear claiming that a warming world would also mean a wetter California.28 Perhaps this is just the process of scientific understanding being refined. Less charitably, I get the distinct sense that the science is unsettled enough that any unusual weather can be “attributed” to human influences.

2018 article written by one of the IPCC’s coordinating lead authors reviewed a further four years of published papers and came to a similar conclusion: . . . the total economic impacts of climate change are negative, but modest on average, and that the severe impacts on less developed countries are caused primarily by poverty.30 The consensus on the minimal overall economic impact of rising temperatures is well known to experts, though it’s an inconvenient one for those wishing to sound the alarm on climate. I was dumbfounded when I asked a prominent environmental policymaker about the UN assessment and the response was: “Yes, it’s unfortunate that the impact numbers are so small.”

Within a few hours of the NCA2018’s release on Black Friday, I had drafted a short Op-Ed saying more or less what I have said here, which the Wall Street Journal published online on Monday.32 The next day, a prominent US energy economist sent an email thanking me for making the point—alas, that person could never express that thanks publicly. The next week, one of the authors of the original 2017 research paper from which the estimates used in the assessment report were drawn expressed dismay at the way their results were portrayed in the media.

The climate science establishment,

mongering. Or perhaps, like the policymaker I mentioned earlier who wished the impact numbers had been greater, it was precisely the coverage they’d been hoping for.

If crucial parts of the science really are unsettled, as we’ve seen over the past chapters, why is the narrative of The Science so different? Can it really be that the multiplicity of stakeholders in climate matters—scientists, scientific institutions, activists and NGOs, the media, politicians—are all contributing to misinformation in the service of persuasion? And why has The Science gained such prominence over science?

The British papers were often overtly partisan, not just in their editorials, but also in their reporting. Although I had read widely among US national newspapers, including the New York Times, the Wall Street Journal, and the Washington Post, it was a revelation to see the stark differences in what was covered, and how it was covered, among the UK’s Guardian, the (London) Times, the Telegraph, and the Financial Times.

In the years since, US media outlets have developed more explicit and more differentiated points of view themselves, and those have likewise seeped from their editorial pieces into their reporting.

Reporting on the scientific reality that there’s been hardly any long-term change in extreme weather doesn’t fit the ethos of If it bleeds it leads.

As I interact with journalists, I realize that, for some, “climate change” has become a cause and a mission—to save the world from destruction by humans—so that packing alarm into whatever the story is becomes the “right” thing to do, even an obligation. This has been compounded by the rise of a new job category: “climate reporters.”

“making the climate threat feel real, immediate, and potentially devastating to the business world,” conspired with some scientists and others to produce a series of reports mischaracterizing the extreme emissions scenario RCP8.5 as “business as usual” (that is, a world without further efforts to rein in emissions).

Trust in scientific institutions underpins our ability—and the ability of the media and politicians as well—to trust what is presented to us as The Science. Yet when it comes to climate, those institutions frequently seem more concerned with making the science fit a narrative than with ensuring the narrative fits the science. We’ve already seen that the institutions that prepare the official assessment reports have a communication problem, often summarizing or describing the data in ways that are actively misleading.

Even given the need for brevity, this is a misleadingly incomplete and imprecise accounting of the state of climate science. It conflates human-caused warming with the changing climate in general, erroneously implying that human influences are solely responsible for these changes. It invokes “certain extreme events” while omitting the fact that most types (including those that pop most readily to mind when one reads the phrase “extreme events,” like hurricanes) show no significant trend at all. And it states that “sea level is rising” in a way that not only suggests that this, too, is solely attributable to human-caused warming, but elides the fact that the rise is nothing new.

an NGO, there is a message to be adhered to. For academics, there is pressure to generate press and to secure funding through grants. There’s also the matter of promotion and tenure. And there is peer pressure: more than a few climate contrarians have suffered public opprobrium and diminished career prospects for publicizing data that doesn’t support the “broken climate” meme.

Scientists not involved with climate research are also to be faulted. While they’re in a unique position to evaluate climate science’s claims, they’re prone to a phenomenon I call “climate simple.” The phrase “blood simple,” first used by Dashiell Hammett in his 1929 novel Red Harvest, describes the deranged mindset of people after a prolonged immersion in violent situations; “climate simple”

is an analogous ailment, in which otherwise rigorous and analytical scientists abandon their critical faculties when discussing climate and energy issues. For example, the diagnosis was climate simple when one of my senior scientific colleagues asked me to stop “the distraction” of pointing out inconvenient sections of an IPCC report. This was an eyes-shut-fingers-in-the-ears position I’ve never heard in any other scientific discussion.

Whatever its cause, climate simple is a problem.