Would it surprise you to learn the greatest global two-year cooling event of the last century just occurred? From February 2016 to February 2018 (the latest month available) global average temperatures dropped 0.56°C.
You have to go back to 1982-84 for the next biggest two-year drop, 0.47°C—also during the global warming era. All the data in this essay come from GISTEMP Team, 2018: GISS Surface Temperature Analysis (GISTEMP). NASA Goddard Institute for Space Studies (dataset accessed 2018-04-11 at https://data.giss.nasa.gov/gistemp/). This is the standard source used in most journalistic reporting of global average temperatures.
The 2016-18 Big Chill was composed of two Little Chills, the biggest five month drop ever (February to June 2016) and the fourth biggest (February to June 2017). A similar event from February to June 2018 would bring global average temperatures below the 1980s average. February 2018 was colder than February 1998. If someone is tempted to argue that the reason for recent record cooling periods is that global temperatures are getting more volatile, it’s not true. The volatility of monthly global average temperatures since 2000 is only two-thirds what it was from 1880 to 1999.
None of this argues against global warming. The 1950s was the last decade cooler than the previous decade, the next five decades were all warmer on average than the decade before. Two year cooling cycles, even if they set records, are statistical noise compared to the long-term trend. Moreover, the case for global warming does not rely primarily on observed warming; it has models, historical studies and other science behind it. Another point is both February 1998 and February 2016 were peak El Niño months so the record declines are starting from high peaks—but it’s also true that there have been many other peak El Niño months in the past century and none were followed by such dramatic cooling.
My point is that statistical cooling outliers garner no media attention. The global average temperature numbers come out monthly. If they show a new hottest year on record, that’s a big story. If they show a big increase over the previous month, or the same month in the previous year, that’s a story. If they represent a sequence of warming months or years, that’s a story. When they show cooling of any sort—and there have been more cooling months than warming months since anthropogenic warming began—there’s no story.
The public and media case for global warming, unlike the scientific case, depends heavily on short-term observation of actual temperatures. Biased reporting suggests warming is much steadier than it is. If the global temperature really showed half a century of uninterrupted warming—with only warming records, no cooling records—then people with nuanced views of plausible future temperatures could be dismissed as deniers. Annual atmospheric CO2 levels have gone up in pretty much a straight line since 1960, if temperatures did the same thing, the link to CO2 would be direct and obvious. In fact, it is real but complex, and those complexities are important for analyzing policy choices. […]
How should the global average temperature data be reported? There should be equal attention on warming and cooling records. Coverage should be based on how unusual the event is, not whether or not it increases support for favored policies. Ordinary events that have happened many times in the past, before global warming, should not be treated as evidence supporting global warming. Mildly unusual events, in the 2 to 3 standard deviation range, should be reported with strong qualifiers that they have little meaning compared to the overall weight of evidence for global warming. Very unusual events, 3 standard deviations and more, deserve investigation, even if that means burdening the reader with somewhat technical material.
Temperatures may climb from here, so these unusual cooling events need not make mainstream news. But unless that happens soon—and remember that would be bad news—climate reporters will have to discuss cooling, which will mean presenting a more complex story than has been typical in the past. I hope they are up to that task.