What Does the Last Decade Tell Us about Global Warming? (Hint: the ‘skeptics' have the momentum)
“Worldwide temperatures haven’t risen much in the past decade…. If you are a climate-change activist pointing to year after year of mounting climate crises, you might want to rethink your approach.”
- Richard Kerr, Science, May 2, 2008.
There has been a flurry of activity in recent weeks in the discussion as to the significance (scientific, political, social) of the evolution of the global average surface temperature during the past 10 years or so.
For those of you who don’t know, the surface temperature of the globe, as a whole, has not warmed-up by anyone’s calculation since at least the turn of the century (January 2001) and depending on your dataset and statistical technique of choice, perhaps as far back as January 1997. And all of this non-warming occurred over a period of time during which the global emissions of CO2 increased faster than ever before (thanks primarily to China). In fact, anthropogenic greenhouse-gas forcing is about 5 percent greater now than a decade ago (about 16 parts per million).
To many folks who have, for years, been fed a constant course of “the-world-is-heating-up-faster-than-ever-before-and-you-are-the-cause,” 9 to 12 years of no warming at all seems to indicate that something is amiss with this mantra.
This was reflected in a Gallup Poll last spring, which found the highest percentage yet of people who think that “global warming” is being “exaggerated.” And this number has been growing.
IPCC “Consensus” and Unwarming
The growth in climate realism (i.e., a realization that alarmists are overplaying the probable impact of CO2 emissions) has most certainly been sparked by the fact that the rate of the earth’s temperature rise has been slowing rather than accelerating, contrary to general IPCC conclusions. This development, naturally, plays into the political debate about (at the 11th hour if not midnight) “mitigating” potential climate change through carbon dioxide emissions reductions.
While the mainstream press has been slow to embrace the fact that the earth’s temperature rise has ground to a halt, Andy Revkin’s recent article in the New York Times has (belatedly [correction: see comments below]) brought the issue the issue front and center. Already, there had been lively discussions on this subject in the halls of Congress and all across of the web.
For instance, this past winter, the recent lack of warming was a focal point in testimony given by Dr. Patrick Michaels before the House Subcommittee on Energy and Environment.
More recently, this fact was included by Matt Rogers writing for the popular “Capital Weather Gang” blog as among his list of 10 reasons for his “Skeptical Take on Global Warming.”
And the Houston Chronicle’s Eric Berger made a pretty big deal about it in his recent SciGuy blog post, stating “But a funny thing happened on the way to the end of the world: hurricane activity on the global scale is near historical lows. And the Earth seems to have, at least temporarily, stopped warming” (emphasis added).
But the growing popularity of this line of reasoning and it potential to do a lot of public relations damage to the alarmist cause is not going unnoticed, whether at Climate Progress or other ‘alarmist’ bastions.
Pew Center Tries to Quiet Science Concern
In its recent update of its global-warming science material, the Pew Center included a list of climate “misconceptions.” Among them was this one:
The last few years have been cooler, so global warming can’t be real;
Or, Global warming stopped in 1998;
Or, The world has been cooling for the past decade.
Pew reported that “The Reality” was:
The climate is defined by long-term averages in global temperature and other climate metrics, and those are still increasing.
This response basically avoided taking the original contention head-on.
In fact, global warming has stopped.
The question, thus, needs to be: “Since the average global surface temperature has remained relatively unchanged for the past decade or so, what does this mean for our understanding of what drives temperature changes, and what we may expect in the future?”
The answer to this question could be that there is something wrong with our scientific understanding of what makes the climate tick—or at least how this understanding is translated into the computer code of climate models—which of course would have all sorts of implications.
So, instead of going there, the primary effort to-date has been to try to demonstrate that there actually is no problem at all—that this lack of temperature rise is just what you would expect to occur with “global warming,” to go along with other expectations such as increasing sea ice in the Southern Ocean, increased ice accumulation across Antarctica (or should that be decreasing ice accumulation across Antarctica—I guess it all depends on what the latest study shows), more precipitation (or less depending on which is currently making the news), more hurricanes (well, not more in number, but more intense, or if not more intense, then they’ll be bigger in areal extent, or maybe…), cold outbreaks (when they occur, warm outbreaks otherwise), etc.
New Lines of ’Skeptic’ Research
The first paper in the scientific literature to tackle the issue of just how long a period of no warming should be expected was published a few months ago by David Easterling and Michael Wehner. They showed that a zero or negative trend of a decade in length should occur (according to climate models) about 10% of the time during the first half of the 21st century. Another paper appeared a couple of weeks ago, led by Jeffrey Knight, which also concluded that, according to climate models, a negative (or zero) 10-yr trend should be expected to occur about 10% of the time, and further, that a negative trend couldn’t be statistically ruled out as improbable until after about a 15-yr period.
But, these two studies are not the end all and be all on the topic. They both, to a certain degree, include sources of variability besides just intramodel “natural” variability when determining the distribution of the modeled temperature trends. This intermixing of various noise sources has the probable effect of enhancing the perceived degree of “climate” variability and thus making low trends seem more common they should be.
My colleagues and I are currently working up a few tests of our own to see just how common our current period of no global warming really is—at least from the standpoint of today’s climate models when run with projected changes in anthropogenic emissions (greenhouse gases and aerosols). Our results are indicating that 10-yr periods of no warming are much more infrequent in climate model projections than indicated by either Easterling and Wehner (2009) or Knight et al (2009). Hopefully, our results will make it into the scientific literature at some point in the near future and provide additional information to the debate.
But, regardless of the specific details, everyone who looks at it is finding something generally similar, that is, the current lack of warming is bumping against model expectations for the longest period of time over which natural variations could offset the warming pressure from increasing greenhouse gases.
The longer the lack of warming continues the more evidence builds that climate models don’t have a good handle on the situation of how the earth’s climate behaves—which erodes their usefulness as reliable indicators of future climate.
Climate modelers and other climate change (and emission regulation) hopefuls have been looking to the tropical Pacific for signs of the appearance of a strong El Niño to help right the ship and restart things on their warming way (El Niños tend to produce a rise in the earth’s average surface temperature), but the jury is still out as to what to expect from the developing situation there—there are indications that an El Niño is brewing, but just how strong it may become (and how much it will elevate global temperatures) is still a much debated topic (forecasting El Niño strength is notoriously unreliable).
But even a strong El Niño won’t quell the realists’ attack, for El Niños are temporary events and are typically followed by a couple years of cooler temperatures as La Niña conditions often move in to take their place. So, what everyone will be waiting for (if a big El Niño does develop) will be to see whether post-El Niño temperature settle down to pre-event values, or whether they remain relatively elevated. We won’t know this for at least several more years.
So the issue of a sluggishly warming world and what it means is going to be with us for a long time (several years at the very least), and some studies such as Keenlyside et al. (2008) and Swanson and Tsonis (2009) indicate that it will much longer than that. (Lindzen and Choi  think it will be with us forever.) Its ultimate impact on climate science (and climate/energy policy) will hinge on whether or not (and if so, how severely) our understanding of climate processes will have to be altered in order to explain why it happened.
In the meantime, while all this is being sorted out, here is some good advice, meted out last year by Science magazine writer Richard Kerr:
Worldwide temperatures haven’t risen much in the past decade…. If you are a climate-change activist pointing to year after year of mounting climate crises, you might want to rethink your approach.
Easterling, D.R., Wehner, M. F., 2009. Is the climate warming or cooling? Geophysical Research Letters, 36, L08706, doi:10.1029/2009GL037810.
Keenlyside, N.S., et al., 2008. Advancing decadal-scale climate prediction in the North Atlantic sector. Nature, 453,84-88.
Kerr, Richard. “Mother Nature Cools the Greenhouse, But Hotter Times Still Lie Ahead,” Science, May 2, 2008, p. 595.
Knight, J., et al., 2009. Do global temperature trends over the last decade falsify climate predictions? In: Peterson, T. C., and M. O. Baringer (eds), “State of the Climate in 2008” Special Supplement to the Bulletin of the American Meteorological Society, 90.
Lindzen, R.S., and Y-S., Choi, 2009. On the determination of climate feedbacks from ERBE data. Geophysical Research Letters, 36, L16705, doi:10.1029/2009GL039628.
Swanson, K. L., and A. A. Tsonis, 2009. Has the climate recently shifted? Geophysical Research Letters, 36,L06711, doi:10.1029/2008GL037022.