Coyote Blog

I promise, cross my heart, this is my last post on climate change for a while.  I thought my series of posts last week about the funny math of carbon offsets was the last, but Joe Miller at Catallarchy wrote something that caused me some introspection:

Just one caveat, though: I'm really, seriously, profoundly uninterested
in your skepticism about man-made global warming. Personally, I think
that the debate is just about as fruitful as a discussion of the
relative merits of evolution and Genesis as models of the origins of
the universe. It's called scientific consensus, people. You seem to
like it well enough for every other subject. And even if that
overwhelming scientific consensus turns out to be wrong, it's not like
a debate here is going to help with that. When scientists are wrong,
it's up to, you know, like, other actual scientists to settle
the question. A bunch of non-scientists googling studies that say what
we like them to say isn't accomplishing much, really.

Certainly I have always been in favor of facts and science over hysteria.  I criticized the rampant breast implant litigation in the face of science that showed no real long-term harms.  Ditto vaccinations.  So am I being a Luddite by, as an amateur, being skeptical of the scientific "consensus" on global warming?  Certainly climate change hawks want to paint my positions as "holocaust denial."  I had a few thoughts:

• For what it is worth, I have actually read much of the 2001 IPCC climate report (not the management summary, which is a worthless political document, but the report itself).  Courtesy of JunkScience.com, who has posted some of the 2007 report, I have read key parts of that report as well.  So I have at least informed myself beyond random Google searches.  My original university training was as a scientist, and later an engineer, though neither in climate (physics and mechanical engineering).
• The media has been known to declare a consensus ahead of its actual existence.  One example that comes to mind is a recent letter that a number of economists wrote supporting a Federal minimum wage increase, which much of the media spun into a "consensus" among economists that a minimum wage increase would be desirable and would not reduce employment.  I don't know Mr. Miller, but my bet is that some of the folks at Catallarchy might dispute this particular scientific consensus.
• To even imply that there is a single consensus on something as complex and multi-faceted as anthropomorphic global warming is facile.  I will take the movie "An Inconvenient Truth" as a fair representation of what the media perception of the consensus is  (the IPCC report actually does not agree in full, but we will get there in a minute).  Taking that movie as our straw man, the "consensus" or hypothesis is as follows:

1. The world has been warming for a century, and this warming is beyond any historical cycles we have seen over 1000 years  (ie, the hockey stick)
2. The last century's warming is almost all due to man's burning of fossil fuels and other releases of greenhouse gasses
3. In the next 100 years, CO2 produced by man will cause a lot more warming
4. Positive feedbacks in the climate, like increased humidity, will act to triple the warming from CO2
5. The bad effects of warming greatly outweigh the positive effects, and we are already seeing them today (polar bears dying, glaciers melting, etc)
6. These bad effects, or even a small risk of them, easily justify massive intervention today in reducing economic activity and greenhouse gas production

I believe this is a mostly fair representation of the media reporting of the scientific "consensus", with the exception that the media never really goes into step #4, and assigns all the blame for 6-8 degree temperature rise forecasts to CO2.  But this split between #3 and #4 is important to understand the science at all, and is included in the IPCC report, so I will make it. 

This is a complicated string of logic, with multiple assumptions.  I hope you see why declaring a scientific consensus on all points of this hypothesis is facile.  So where is there a scientific consensus on all of this?  My interpretation from the recent IPCC report and other sources is:

1. The world has been warming for a century, and this warming is beyond
   any historical cycles we have seen over 1000 years  (ie, the hockey
   stick)   There is a strong consensus on the first half.  We can argue about urban heat island corrections and ground vs. satellite all day, but the earth has pretty clearly warmed for a hundred years or so, after cooling before that.  The second half of the proposition is trickier.  The 2001 report relied on the Mann hockey stick to make the point that the 20th century is not just warmer but uniquely warmer.  I sense the 2007 report backing off this -- the Mann analysis has a lot of problems, and ongoing climate research continues to point to the great variability and cyclicallity of climate over time.  There is too much historical evidence, for example, of a warm middle ages for Mann to dismiss it with a few tree rings.
2. The last century's warming is almost all due to man's burning of fossil fuels and other releases of greenhouse gasses.   The 2001 IPCC report implied about half of the century's warming was man-made.  The new report seems to put more of the blame on man.  My sense is this will move over time back to half and half -- the evidence today of increased solar activity is becoming too strong to ignore as a cause along with man-made CO2.  However, I recognize right now that I am out of step with the IPCC and perhaps the "consensus" on this.
3. In the next 100 years, CO2 produced by man will cause a lot more warming.  CO2 production by man will cause more warming.  How much is the subject of models, which any economist or businessperson can tell you are notoriously flaky.  However, here is one fact that is part of the scientific consensus but you never hear in the media -- the relationship between atmospheric CO2 concentration and warming is a diminishing return.  In other words, the next doubling of CO2 in the atmosphere will have less impact on temperatures than the last doubling.  At some point, the effect of CO2 maxes out, and further increases in CO2 have no effect on temperatures.  My reading of the newest IPCC seems to imply that if the models predict about 6 degrees of warming over the next 100 years, of which about 2 is directly from CO2, while the rest are from positive feedbacks (discussed next)
4. Positive feedbacks in the climate, like increased humidity, will act to triple the warming from CO2.  OK, this strikes me as the key point in the scientific consensus.  Hypothesized positive feedback loops in the climate are what take the IPCC models from results that are warmer but probably manageable to results that appear catastrophically warmer.  Their models assume that as the world warms a bit from CO2, other effects take hold, and the world will warm even more.  For example, they posit that if the world is warmer, more water evaporates into water vapor in the atmosphere, which is a strong greenhouse gas, which accelerates the warming.  I think it is absurd to say there is a consensus on this point, which is adding 2/3 or more of the warming.  The notion of positive feedbacks in nature offends my intuition --  there are just not that many such processes in nature, or else nothing would be stable -- but then again Einstein's intution was offended by quantum mechanics and he was wrong.  However, using the IPCC's own findings (starting in section 8.6 here) the IPCC admits to there not even being a consensus on the sign (ie if it is positive or negative feedback) of what they describe as by far the strongest feedback process (cloud cover)!  I don't know how you can declare a consensus if you admit you don't even know the sign of the largest effect.
5. The bad effects of warming greatly outweigh the positive effects,
   and we are already seeing them today (polar bears dying, glaciers
   melting, etc)  It would be absurd to declare a consensus here because no one has really done much definitive work.   Most folks, including me, presume that since substantial warming would take us beyond the temperature range for which our bodies and our civilization has been adapted, the net effect would be bad.  But there are positive offsets to the negative effects (e.g. oceans rising) that you never really hear about in the press (longer growing season, for one) but which are in the IPCC report.  Climate scientists themselves have admitted there is no consensus on what effects that we are seeing today are due to warming.  Part of Antarctica (about 2%) shown in Al Gore's movie is warming, but most scientists now think that this may be due to cyclical variations in ocean currents, while most of Antarctica has actually been cooling of late.  Greenland is warming, but glaciers may not be receding as fast as once feared.  Polar bear populations, despite reports to the contrary, are increasing.
6. These bad effects, or even a small risk of them, easily justify
   massive intervention today in reducing economic activity and greenhouse
   gas production.  Many climate scientists express an opinion on this, often definitively, but if one argues that I am not qualified to test the consensus as a layman on global warming, then certainly climate scientists are far from qualified in drawing any conclusions on this topic.  The effects of a worldwide rollback on CO2 production at current technologies could be catastrophic, particularly for a billion people in India and China just on the verge of emerging from poverty.  Even in some of the most dire forecasts for warming, it is a very open question with little consensus as to whether a cooler but poorer world is better.  In fact, one can argue that even the pious Kyoto-signing countries are voting with their actions, rather than their words, on this issue, since they have resisted taking the hard economic steps necessary to meet their targets.

OK, that is more than I meant to write.  My point is that the word consensus is an absurd word to apply to the topic of anthropomorphic global warming.  Some things we understand pretty well (the world is warming, in part due to man-made CO2) and some we understand less well (the effect of feedback loops).  And some issues, like whether the harms from climate change are worth the cost of avoiding them, are entirely outside the purview of climate science.

Update: Strata-Sphere has a funny bit of related snark:

Global warming on Neptune's moon Triton as well as Jupiter and Pluto, and now Mars has some scratching their heads over what could possibly be in common with the warming of all these planets....

I still don't know. Could there be something in common with all the
planets in our solar system that might cause them all to warm at the
same time?

On a serious note, he has some nifty graphs of historic earth temperature reconstructions (including Mann) vs. sunspot activity reconstructions (sunspot activity generally being a proxy for solar output).  Short answer:  Sunspot activity at historical highs, at the same time as historical highs in temperature.