James Hansen is both a champion and icon of climate activism. A respected scientist (I certainly respect him), he has been tireless in attempting to raise awareness of the possible effects of global warming and the human emissions that contribute to it. Sometimes he has gone overboard–but that’s a bit to be expected in a cause that he sincerely believes to be of utmost importance to us all.
He recently published a very short note acknowledging that temperatures have not risen over the past decade. There’s something in it that we might find of interest: “The 5-year mean global temperature has been flat for a decade, which we interpret as a combination of natural variability and a slowdown in the growth rate of the net climate forcing.”
He explains later, “It should be noted that the “standstill” temperature is at a much higher level than existed at any year in the prior decade except for the single year 1998, which had the strongest El Nino of the century. However, the standstill has led to a widespread assertion that “global warming has stopped”. Examination of this matter requires consideration of the principal climate forcing mechanisms that can drive climate change and the effects of stochastic (unforced) climate variability.
“The largest climate forcing is caused by increasing greenhouse gases, principally CO2 (Fig. 5). The annual increment in the greenhouse gas forcing (Fig. 5) has declined from about 0.05 W/m2 in the 1980s to about 0.035 W/m2 in recent years 8. The decline is primarily a consequence of successful phaseout of ozone-depleting gases and reduction of the growth rate of methane. Also, the airborne fraction of fossil fuel CO2 emissions has declined and the forcing per CO2 increment declines slowly as CO2 increases due to partial saturation of absorption bands, so the CO2 forcing growth rate has been steady despite the rapid growth of fossil fuel emissions.”
As I have written previously, fossil fuel emissions haven’t ‘grown rapidly’–they’ve exploded. According to CDIAC, one third of all human emissions in history have occurred since 1998–right when temperatures stopped rising.
Taking Hansen at his word (and I do and I think you should, too), we get an inkling of something important, but as yet not explicitly said.
Of course CO2 concentrations contribute to warming–that’s basic physics, using the same calculations that make our modern world possible. But they are not the control knob on the dashboard that is the prime mover of temperatures. Hansen himself writes about solar variability, aereosols (which might be increasing as the developing world continues industrialization), the relative proportion of El Nino to La Nina years, and of course the natural variability that is always present even when we cannot define it.
CO2 is one actor. Not the only one and perhaps not even the most important one. With recent stories about black soot being an easier problem to solve, perhaps this is legitimizing language from the climate guru himself–climate change has many causes. Some of them are our responsibility. One is CO2. Another is pollution, another is deforestation, another is other land use changes. Some of the causes of climate change are not human-caused.
This should encourage us to look at what we can do most effectively in the short term.
- Quick phase-out of coal
- Fight against black soot
- Stop deforestation
- Begin replanting
Look–I’m not suggesting that we abandon the fight against CO2 emissions. Nor am I suggesting that global warming has gone away. But here, in an important document written by a highly respected climate scientist, is essentially implicit permission to look at all of the causes and all of the potential solutions.