The statistical slight of hand in reporting global temperature data

Has anyone noticed that you almost never hear about global temperature trends over time anymore? For years all we heard from the news media are statements like, “over the last x number of years temperatures have risen by y amount.” Suddenly over the past few years the reporting has changed. Now when new temperature data is released, typically from NASA or some other government agency, what we hear is that the most recent year was the 2nd, 4th, 8th, or whatever warmest on record.

This switch in what is reported, the position of the most recent year, or any particular year to the history of temperature records, actually tells us nothing about global warming and whether or not the planet is in fact warming or cooling. Global warming is a story about global temperature trends over time not a story about a particular data points in time. The switch to the latter represents a statistical slight of hand that has been invoked by global warming alarmists because there has been no statistically significant warming for at least the last ten years, and according to some data records, the last 15 years.

Here is the slight of hand that is being invoked. Temperature records have been kept for about the last 110 years. Since the late 1800s, when these records were begun, there has been a reasonably steady climb in temperatures with two big spurts from the early part of the century to the 1940s and then from the mid 1970s to the late 1990s. This makes complete sense in that during that period the global climate has been coming out of what was called the little ice age, which ended in the mid 1800s. Since the late 1990s, the last 15 or so years, the trend has plateaued. On average there has been no warming or cooling detected. Along this plateau global average temperatures go up and down year to year, just as they did as they were climbing during the years leading up to the plateau.

So what’s going on?  Along the plateau, the average temperature is generally higher than for the years leading up to that plateau. The same is true for the year-to-year variations, i.e., peaks and troughs, in temperature that are occurring along the plateau. In other words, it only makes sense, and one would expect, that the average global temperature in any year along the plateau, whether higher or lower than the year before, would be higher than the vast majority of the hundred years or so years leading up to the last 15 years. This is why pointing to this year or last year or the year before and saying that it is the 5th, 4th, 2nd, or even the warmest year on record is completely non responsive to the question: is global warming occurring? It is in fact an irrelevant response meant to take the average person’s eye off the ball. That ball being average temperature trends over time.

To put this explanation in terms that most of us living in North Carolina have actually experienced, imagine making the drive from the Triad northwest on route 421 into the mountains. As you drive the route the elevation continues to climb as you head toward Boone. At Boone you begin to head south along the Blue Ridge Parkway. As you travel along the parkway you are clearly in the mountains. As you drive along the mountains you go up long hills and down long hills. In other words, all along the parkway and through the mountain range the elevation goes up and down, but one thing is going to be true, the elevation along the Blue Ridge Parkway is higher than at the vast majority of the points along route 421 as you were making the climb toward Boone. Most of us realize that it would say nothing about the average elevation along the Blue Ridge Parkway or the trend in the average elevation along the Parkway to continuously point that out. Yet, this is exactly what is going on when people compare the average temperature in a recent year to the total temperature record for the past 110 years.

Roy Cordato / Senior Economist and Resident Scholar

Roy Cordato is Senior Economist and Resident Scholar at the John Locke Foundation. From January 2001 to March 2017, he held the position of Vice President for Research at the ...

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