There has recently been much huffing and puffing about an apparent slowdown in the rate of global warming, with a recent article in The Economist on the matter getting lots of attention, http://www.economist.com/news/science-and-technology/21574461-climate-may-be-heating-up-less-response-greenhouse-gas-emissions . The supposed "reduced climate sensitivity" (to CO2 concentration changes) has gotten all the usual suspects very excited, from longtime more or less respectable scientific "skeptics" (most of whom accept that there is warming but just say it is not as great as most others say) through literate innumerates such as George Will who recently asserted that there had not been a year warmer than 1998 since then (2010 was and is currently the record-holder), on through to the completely irresponsible political hacks ranting about hoaxes such as Sen. Inhofe (Lunatic-OK) and Virginia AG Ken Cuccinelli, now running for Governor of my state, who sued the University of Virginia to get ahold of the emails of climatologist Michael Mann where surely he would find the smoking gun to show the hoaxing conspiracy (!!!). In any case, there does appear to have been some slowing of the rate of increase in average global temperature in the last few years, with this spring being the coldest in the US since 1975 punctuating the point, even though "weather is not climate." So, what is up?
According to recent research by Balmaseda et al appearing in Geophysical Research Letters and some other outlets, as linked to at Real Climate, http://www.realclimate.org/index.php/archives/2013/04/the-answer-is-blowing-in-the-wind-the-warming-went-into-the-deep-end/ , indeed the answer is blowing in ocean winds that have reduced the warming effect in the atmosphere in the near term. However, while the air may not have gotten as much warmer as the main models predicted, the planet is still warming. The main recent locus of this warming has been in the ocean at depths greater than 700 meters, "the deep end." This fulfills a warning made by many that indeed the global climate is very hard to model, with lots of nonlinear dynamics and complexities and sub-parts that react and interact with all kinds of thresholds. A piece of this is that at some point down the road the warming will again move towards the surface and back into the atmosphere, so we could get a rather sharp and sudden increase down the road at some point (and also El Nino and some other such phenomena are playing roles). I have a few further observations.
One is to anyone who wants to argue that the claim that global warming may have slowed down (or possibly even reversed slightly) cannot be right because the glaciers are still retreating and the Arctic ice sheet reached an all time minimum in late 2012. I note that once the average global temperature gets above a certain point, the glaciers can retreat and the Arctic ice can continue to shrink at a constant level of temperature without any further increases happening. So, these real phenomena do not prove that the average global temperature is continuing to increase.
Also, there is the fact that there are substantial regional variations in temperature trends. This was used by some skeptics to argue against global warming some years ago when it was noted that certain parts of the globe were indeed cooling. However, in connection with the last paragraph, the part of the world that has seen the most warming all along has been the Arctic zone, something I had forecast to me decades ago by Patrick Michaels, a prominent warming skeptic (although one of those who says that warming is happening). So, it could well be that there continues to be a rising temperature in the Arctic zone, even if the global average were to be falling slightly, or at least constant.
A more general point is one that many people are unaware of, that the probability distribution of likely outcomes is almost certainly highly kurtotic, quite likely a Paretian power law, with fat tails, and very unlikely to be Gaussian normal. As it is most of the IPCC reports have plugged in assumptions of the latter, but Martin Weitzman has in several places argued that the power law outcome is much likelier, with the ubiquity of nonlinear positive feedback effects of various sorts in the system responsible for this (albedo, methane in Siberia, etc.). This means that the probability both of a seriously catastrophic increase in temperature and also of a reversal and decline in temperature are much higher if Weitzmann is right and the IPCC is wrong. By his calculation, if the distribution is Paretian power law, the probability of a seriously catastrophic 12 degrees C temperature increase could be as high as 1% ("Fat-Tailed Uncertainty in the Economics of Climate Change," Review of Environmental Economics and Policy, 2011, vol. 5, pp. 275-292).
Regarding the possibility of a temporary stallout or reversal of global temperature, it should be kept in mind that between about 1940 and 1975 global average temperature in fact declined somewhat, even as CO2 concentrations were mounting. It remains both unmodeled and unclear why that happened, and indeed in the early 1970s there were more climatologists than is now admitted who were forecasting either a new ice age or at least an unclear outcome between warming and cooling tendencies (that had flipped around to a mostly pro-warming stance by 1975). A possible candidate for cooling was higher rates of emissions of sulfur-laden aerosols from coal burning, which came under regulation in the leading industrial countries starting in the early 1970s. Indeed, the only letter I ever had published in the Washington Post was on precisely this issue back in 1977 (yes, I have been involved with climate modeling off and on for 40 years). And while the dates are propitious and telling, this matter is not really resolved even now.
In any case, it does look like global warming is still proceeding, but at somewhat deep levels in the oceans (yes, there is data supporting this, not just modeling), which at some point will surface to become more clearly manifest. The hacks and innumerates should be more careful about their spoutings, although I have no doubt that this will not slow them down or quiet them.
Barkley Rosser
PS, Addendum: For anybody wanting to look at the global temperature average series by month and half year since 1880, please see http://data.giss.nasa.gov/gistemp/tabledata_v3/GLB.Ts+dSST.txt .
11 comments:
In the meantime, the most recent report is that CO^2 concentrations are approaching 400 ppm much sooner than previously expected.
Climate change is one of those cases, Barkley, when I think the burden of empirical evidence is on those who think that warming (in some meaningful sense) isn't taking place. The reason is that the basic physics and chemistry all point to the likelihood that it should be. It's as if you showed me a green plant and said, I don't think it is employing photosynthesis. Maybe not, but you'd have to demonstrate it. The default assumption is that it obeys the general laws that green plants obey.
John,
I do not think anybody is questioning the data on CO2 concentrations. The issue is how the climate is responding to the clear increases in those. I am putting the link to the Economist article into the main text and note that it briefly mentions this new finding about the oceans heating up more than expected at below 700 meters depth.
Peter,
The Economist article shows that the five-year rolling average increase has slowed down since 2000 and is now hitting the lower end of what has been projected to be happening based on the CO2 emissions. Ultimately all of this is empirical: what is happening to CO2 emissions and how is temperature changing? As of right now it looks like it is not rising as rapidly as expected in the atmosphere or upper oceans, but more than expected below 700 meters depth in the oceans.
My degrees are in engineering, not climate science or meteorology, so you can take my conjecture for what it's worth. In the late 1960's and 1970's, there was a small episode of "global cooling". Not really cooling either, because global mean temperatures had continued to rise, but a serious slowdown in increases.
It was pretty easy to figure out why--dirty fuel oil and even dirtier coal combustion were pumping out massive amounts of sulfur dioxide and black carbon into the air. Virtually all of it was coming from North America and Europe. Needless to say we cleaned up our act with cheap, creative technology.
Once the emissions were brought down, warming began again in earnest. There was a reprieve in the early/mid nineties thanks to Mt Pinatubo, but that was it.
Since 2000, sulfur dioxide and particulate emissions from Dhina and international shipping China have exploded. Global emissions are nearly back to the previous peak in 1975. Things have gotten to the point in terms of health and local environment in China that change is coming.
All the ocean dynamics and all that are interesting math, but I think the real cause is the same one as before. Since the atmospheric lifetime of sulfur dioxide and particulates is about a week, and the lifetime of CO2 is about 100 years, once emissions scrubbing becomes standard in China and on boats, I'm 95% certain we will return to trend temperature change.
Global Sulfur emissions (peer reviewed):
http://www.see.ed.ac.uk/~shs/Climate%20change/Data%20sources/Stern_Chemosphere_2005.pdf
To follow up on Cameron's point, which seems obvious given the geoengineering solution of pumping sulfur oxides et al in the upper atmosphere to cause global cooling, do the climate models incorporate the cooling/rain effects of sulfur et al pollutants which have gone up and down rather drastically over the past century.
Are the models incorporating pollutants as point sources with regional impact, or point sources with global impact, or global parameters?
While the possibility of a reversal to an ice age regime is not taken too seriously, I discuss the nature of ice ages and the likelihood of the next one at:
http://anamecon.blogspot.com/2011/09/ice-age-in-our-future.html
The important thing is that ice ages are not the result of global cooling. Ice ages are the result of global warming, well, global heat retention, and cause cooling.
So watch your latitude!
For those who want to see the global temperature in detail by month and half year since 1880, see http://data.giss.nasa.gov/gistemp/tabledata_v3/GLB_Ts+dSST.txt . During 1937 through 1944 temps were above the 1950-1980 base, with 44 a peak. The decline hit a bottom in 1965 and 1966, although the last year noticeably below the base, almost as low as them was 1976. Four years since 1998 have been higher than it: 2002, 2005, 2007, and 2010, the highest of them all since 1880, with the last two and into this year lower and not above 98.
It is true that particulates do not stay in the atmosphere all that long. This was the main reason that the near split in the lit in 1971 between the warmers and the coolers tilted sharply to the warmers a few years later as this was realized, particularly in comparison to the longevity of CO2 ambience in the atmosphere, with the late Stephen Schneider the poster boy for the shift in attitude, from an "it's up in the air which will dominate" in a 1971 paper to "warming will dominate" in a 1975 one, even prior to the clear appearance of the warming trend in the data.
Some of the models do attempt to model regional sources and effects, hence the accurate forecasts that the Arctic would warm more than other parts of the world.
I am unaware of any serious models that say that ice ages result from warming rather than cooling. What is curious from the historical record as pieced together from ice cap cores is that the changes in temperature both going into and out of ice ages appear to have been quite short in geological terms, as short as 100 years, which could be due to exogenous shocks, or to reflect the nonlinear positive feedbacks many think are present in the system.
Oooops. Url for temp data off in last message, with an _ between GLB and Ts rather than the . that should be there. See the link I have put in the main message at the end as addendum. That seems to work. Sorry.
There have been two periods since the beginning of the industrial age when temperatures have dropped or plateaued for more than a decade while CO2 levels continued to rise: the late 1890s to the mid 1920s, and the early 1940s through the early 1980s. In both cases the correlation between CO2 levels and global temperatures eventually held firm. Whatever the causes of short-term discrepancies in this correlation, this history of global warming -- glossed over by those who tout the current plateauing as disproving theories of climate change -- makes a mockery of the denialists' claims.
Unknown,
Check out my post before the last one, which is fully supported by the link I have provided in the main post to detailed temperature series from NASA. It is only after 1944 that cooling appears, and it pretty much ends with 1976, after which there is never a year that is cooler than the 1950-80 norm. One cannot argue that the cooling lasted into the early 1980s.
However, your main point is well taken indeed. There have been periods of plateaued or even cooling since 1890, even as CO2 emissions and ambient levels have risen. We do not have data from those earlier episodes to know if what was going on was warming deep in the oceans that then reappeared at the surface as is likely to happen in the future.
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