My greener friends are increasingly troubled by the lack of a rise in recent global surface temperatures. Using monthly data measured as the departure from long-term averages, there's been no significant warming trend since the fall of 1996. In other words, we are now in our 17th year of flat temperatures.
Since 1900, the world has seen one other period of similar temperature stagnation (actually a slight cooling) that lasted for 30 years and ended around 1976. The current one is happening with much more putative warming "pressure," because the atmosphere's carbon-dioxide content is much higher than it was in mid-century.
From the Industrial Revolution to 1950, atmospheric carbon-dioxide concentrations rose by about 15 percent. Today, the increase is up to 41 percent, making long periods without warming either 1) increasingly unlikely, or 2) the natural result of simply overestimating how "sensitive" surface temperature is to carbon dioxide. My money is on the latter.
Now, just for fun, let's assume that on Jan. 1, another warming trend began, at the same rate that was observed in the last such period, from 1977 through 1998, or 0.17 C per decade.
Running a large experimental sample reveals that, on average, the rate of warming will have to continue through 2020 before a statistically significant trend emerges in the post-1996 data. (Remember that a "trend" that does not meet the normal grounds for significance is one that cannot scientifically be distinguished from "no trend.")
In other words, it's a pretty good bet that we are going to go nearly a quarter of a century without warming.
In response, the climate establishment is becoming increasingly polarized, with a growing number of researchers calculating less warming this century, while the apocalyptics, such as NASA's James Hansen, simply edge out further on increasingly thin limbs.
This is quite a change. In 2002, I published a paper, "Revised 21st Century Temperature Projections," which used a variety of independent sources and generally predicted a range of 21st century warming of 1.0 to 3.0 C. In response, the 2009 "Climategate" emails revealed a number of surreptitious attempts and schemes to either get the paper removed, get the esteemed geographer who was the relevant editor of the journal Climate Research fired from his University of Auckland professorship, or, if all else failed, destroy the journal itself.
Formally, the "climate sensitivity" is the total amount of warming projected for a doubling in atmospheric carbon dioxide. In their last climate compendium, published in 2007, the United Nations Intergovernmental Panel on Climate Change gave a "likely" range for the sensitivity of "2 C to 4.5 C with a best estimate of about 3.0 C." Since then, it appears that a new "consensus" is lowering the forecast. The reason I'm betting that the sensitivity of temperature to dreaded carbon dioxide has been overestimated is the number of recent publications saying just that. Here's a partial list:
Richard Lindzen gives a range of 0.6 to 1.0 C (Asia-Pacific Journal of Atmospheric Sciences, 2011); Andreas Schmittner, 1.4 to 2.8 C (Science, 2011); James Annan, using two techniques, 1.2 to 3.6 C and 1.3 to 4.2 C (Climatic Change, 2011); J.H. van Hateren, 1.5 to 2.5 C (Climate Dynamics, 2012); Michael Ring, 1.5 to 2.0 C (Atmospheric and Climate Sciences, 2012); and Julia Hargreaves, including cooling from dust, 0.2 to 4.0 C and 0.8 to 3.6 C (Geophysical Research Letters, 2012). Each of these has lower and higher limits below those of the Intergovernmental Panel on Climate Change.
What commonly occurs when weather forecasts begin to go bad? As every child knows, if the forecast starts out calling for a foot of snow, and then is cut to six inches, that usually results in about three.
Similarly, as projections for warming are lowered, don't be surprised if planetary temperature finally settles in the bottom half of the newly predicted ranges.
Science historians have repeatedly documented that we are particularly reluctant to abandon widely held views, or scientific paradigms. When professional advancement (i.e., research money) is particularly dependent upon a certain view (we wouldn't spend billions on climate research unless it was important, right?), it's even harder to let go, but that is what we may be seeing.
People are beginning, cautiously, to dial back 21st century warming because there has been none. Because dreaded sea-level rise is also proportional, those estimates are going to have to come down, too.
One of these years, the upcoming end of the world from global warming is going to be officially canceled, to be replaced by a new apocalypse, which I predict will be called "acid oceans," or something like that.