The Current Wisdom only comments on science appearing in the refereed, peer‐reviewed literature, or that has been peer‐screened prior to presentation at a scientific congress.
It seems like everyone, from exalted climate scientists to late‐night amateur tweeters, can get a bit over‐excited about short‐term fluctuations, reading into them deep cosmic and political meaning, when they are likely the statistical hiccups of our mathematically surly atmosphere.
There’s been some major errors in forecasts of recent trends. Perhaps the most famous were made by NASA’s James Hansen in 1988, who overestimated warming between then and now by a whopping 40% or so.
But it is easy to get snookered by short‐term fluctuations. As shown in Figure 1, it is quite obvious that there has been virtually no net change in temperature since 1997, allowing for the fact that measurement errors in global average surface temperature are easily a tenth of a degree or more. (The magnitude of those errors will be considered in a future Current Wisdom).
Figure 1. Annual global average surface temperature anomaly (°C), 1997–2010 (data source: Hadley Center).
Some who are concerned about environmental regulation without good science have seized upon this 13‐year stretch as “proof” that there is no such thing as global warming driven by carbon dioxide. More on that at the end of this Wisdom.
Similarly, periods of seemingly rapid warming can prompt scientists to see changes where there aren’t any.
Consider a landmark paper published in 2000 in Geophysical Research Letters by Tom Karl, a prominent researcher who is the head of our National Climatic Data Center (NCDC) and who just finished a stint as President of the American Meteorological Society. He couldn’t resist the climatic blip that was occurred prior to the current stagnation of warming, namely the very warm episode of the late 1990s.
Cooler heads at the time noted that it was an artifact of the great El Nino of 1997–98, a periodic warming of the tropical Pacific that has been coming and going for millions of years.
Nonetheless, the paper was published and accompanied by a flashy press release titled “Global warming may be accelerating.”
What Karl did was to examine the 16 consecutive months of record‐high temperatures (beginning in May, 1997) and to calculate the chance that this could happen, given the fairly pokey warming rate — approximately 0.17°C (0.31°F) per decade, that was occurring. He concluded there was less than a five percent probability, unless the warming rate had suddenly increased.
From the press release: