Roy Spencer recently posted an article on his blog called “Ten Years After the Warming,” in which he argues that there’s no excuse for a decade without much warming, because the radiative forcing is supposedly higher than it’s ever been. Steve Milloy has also reposted the article on his aptly titled blog, JunkScience.com. (In case you don’t remember, Steve Milloy is a Fox News commentator who goes about labeling as “junk science” any environmental issues that might precipitate some government regulation. Yes, that includes links between second-hand smoke and cancer.) Spencer’s main point is this:
You cannot simply say a lack of warming in 10 years is not that unusual, and that there have been previous 10-year periods without warming, too. No, we are supposedly in uncharted territory with a maximum in radiative forcing of the climate system. One cannot compare on an equal basis the last 10 years with any previous decades without warming.
This is the same Roy Spencer who is constantly claiming that he can explain most of the warming trend over the last 100 years by appealing to various modes of natural variation in the climate, e.g., the Pacific Decadal Oscillation and the El Niño Southern Oscillation. These climate oscillations depend on complicated stuff like deep ocean currents that are hard to predict, given that we don’t have that many observations of what the state of the system is like at any given time. (In other words, it’s expensive and hard to measure deep ocean temperatures and currents, so we don’t have that many observations.) Since these kinds of things are hard to predict exactly with a model, climatologists usually talk about long-term trends caused by external “forcing” (by things like CO2 emissions and variations in solar output), overprinted by random “natural variation”. The main difference between Roy Spencer and the rest of the climatologists is that he thinks that natural variation is important over much longer time periods, whereas the others generally think it’s mainly important over about a decade or less. For example, he complained in his book, , The Great Global Warming Blunder,
The IPCC has taken for granted that there are no natural variations in global average temperatures once one gets beyond a time scale of ten years or so. (p. 16)
The United Nations’ Intergovernmental Panel on Climate Change does acknowledge that there is natural climate variability on a year-to-year basis, and maybe even decade-to-decade. After all, we have clear evidence that events like El Niño and La Niña cause some years to be warmer than others. Yet the IPCC refuses to accept that the global warming (or cooling) on time scales of thirty years or more can also be caused by Mother Nature. That, apparently, is humanity’s job. (p. 1)
In this latest article, however, Roy seems to be saying that the temperature should have kept going up pretty steeply because the external forcing from greenhouse gases has continued to rise. The problem is that this is true ONLY if you ignore natural variation that might temporarily offset the external forcing.
Spencer’s newfound suspicion of decadal-scale natural variations is unfounded. Foster and Rahmstorf (2011), for example, statistically removed the effects of El Niño/La Niña cycles, volcanoes, and solar variation, to produce the temperature evolution that WOULD HAVE occurred if these random, natural variations hadn’t happened. Here’s what they got (Fig. 1).
There is still random variation evident in Fig. 1, so we obviously haven’t removed all the noise, but the trend is much more consistently upward, including during the last decade. The fact is that natural variation can EASILY account for a leveling off of the temperature rise for a decade or so, and what’s more, even though climate models aren’t very good at predicting when these natural variations will occur, they do at least predict that they WILL happen (Santer et al., 2011).
The bottom line is that Roy Spencer has been arguing all along that natural variation can cause the temperature to go up or down for a while no matter what the external forcing is doing, and no matter how long the time period, but now he suddenly can’t imagine that this could happen over a single decade!
It’s also funny that Steve Milloy passed on Spencer’s assertions, but then just two days later he was promoting a paper in which Spencer argued that standard climate models are uncertain because “alternative hypotheses for the cause(s) of the warming, such as natural climate cycles or indirect forcing by the sun, have seen relatively little research.” (And of course, Roy cited his book, The Great Global Warming Blunder to support this point.) Milloy likes to label as “junk science” any science that leads to conclusions that might precipitate government regulations, but the fact is that he doesn’t have the expertise to understand the science he pans or the “alternative” science he promotes.