Megan McArdle

Matt may be right that I haven't harangued people about climate change
recently, so here goes: dude, if you're still a climate change skeptic, it's
time for a rethink. When the science correspondent for Reason magazine
comes over to the reality of anthropogenic global warming, it's safe to say that
the skeptics have lost the debate. Not only the vast majority of the scientific
community, but even most of the hard-core skeptics at conservative magazines,
have abandonned the hope that we are not warming up the climate.

There's still debate about the effects of the warming, and what we should do
about it. But there's not much question that it's happening.

Duh.  The vision of the skeptic community denying that the world is
warming at all is a straw man created by the climate catastrophists to avoid
arguing about the much more important point in her second paragraph.  What I
can't understand is McArdle's, and many intelligent people I meet, seeming
unintrest in the degree of man-made impact.

The chief debate really boils down to those of us who think that
climate sensitivity to CO2 is closer to 1C (ie the degrees the world will warm
with a doubling of CO2 concentrations from pre-industrial levels) and those who
think that the sensitivity is 3-5C or more.  The lower sensitivity implies a
warming over the next century of about a half degree C, or about what we saw in
the last century.  The higher numbers represesent an order of magnitude more
warming in the next century.  The lower numbers imply a sea level rise measured
in inches.  The higher numbers imply a rise of 1-2 feet  (No one really know
where Al Gore gets his 20 foot prediction in his movie).  The lower numbers we
might not even notice.  The higher numbers will certainly cause problems.

The other debate is whether the cost of CO2 abatement should even be
considered.  I have talked to many people who say the costs are irrelevant -
Gaia must come first.  But steps to make any kind of dent in CO2 production with
current technologies will have a staggering impact on the world economy.  For
example, there are a billion Asians poised to finally to enter the middle class
who we will likely consign back to poverty with an aggressive CO2 reduction
program.  With such staggering abatement costs, it matters how bad the
effects of man-made global warming will be. 

There are many reasons a 1.0 climate sensivity is far more defensible
than the higher sensitivities used by catastrophists.  My
argument a lower climate sensitivity and therefore a less aggresive posture on
CO2 is here
.  Cross-posted at Climate Skeptic.

Update: Sure, we skeptics debate the degree of past warming, but it really can't be denied the earth is warmer than 100 years ago.  The problem catastrophists have with defending their higher climate sensitivities is that these sensitivities imply that we should have seen much more warming over the past 100 years, as much as 1.5C or more instead of about 0.6C.  These scientists have a tendency to try to restate historical numbers to back their future forecast accuracy.  We skeptics fight them on this, but it does not mean we are trying to deny warming at all, just make sure the science is good as to the magnitude.

One other thought - everyone should keep two words in mind vis a vis CO2 and its effect on temperature:  Diminishing Return.  Each new molecule of CO2 has less impact on temperature than the last one.  Only by positing a lot of weird, unlikely, and unstable positive feedbacks in the climate can scientists reach these higher sensitivity numbers (more here).  A good economist would laugh if they understood the assumptions that were being made in the catastrophic forecasts that are being used to influence government action.


  1. napablogger:

    Coyote, I agree with you about AGW. One point though, you mention that you don't know where Gore got his 20 feet level, but in another post you said that James Hansen was the one predicting that. The only one in fact. I am wondering how you arrived at the one to two foot level.

    Not trying to be a wise guy, but I write for the local paper and intend to write about this.

  2. morgan:

    one aspect i feel ought to be injected into this debate: timescale has an enormous impact on temperature trends. "warmest in a hundred years" sound impressive, but in climate time, that's like saying the hottest half a second of this minute. it is not particularly warm right now. in fact, it's quite cold.

    a great deal of the warming trend currently debated has to do with the choice of the starting point around 1850. this choice has more to do with the spread of reliable thermometers than with and good scientific rationale. it also happened to coincide with the deep part of the so called "little ice age" which was the coldest period in the last 9000 years. is using that point to anchor a mere 150 years of data reasonable? probably not. it skews the results significantly.

    we are now approximately 1 degree below the levels of medieval times, a generally prosperous time when civilization progressed rapidly due, at least in part, to agricultural plenty and a stable climate. the same was true of the roman warming of 200bc to 600ad, which had similar temperatures. neither one attained the high temperatures of the Holocene maximum (when the arctic was 5 degrees C warmer than currently), which persisted for 3000 years.

    there is conspicuous evidence that the “unprecedented shrinkage of glaciers” on Greenland and in Europe has ample precedent within fairly recent periods. how else can one explain the ruins of Viking villages emerging from beneath the Greenland ice sheets as they pull back around the edges of the landmass? surely no one is arguing that the Vikings built churches in ice caves… there are many analogous finds in Europe where farms and mines have been emerging from the ice around the edges of some retreating glaciers.

    if we go back further, the downtrend in temperature becomes more pronounced. 5 million year temperature is in a clear downtrend. the same is true of 65 million year temperature. paleoclimatologists speak of a "gradually intensifying ice age". the antarctic reglaciated about 13 million years ago. ice at the poles deepens ice ages. so the ice age deepens.

    looked at in a truly long timeframe of 550 million years, we are currently experience temperatures within the lowest 5% of all those experienced since the emergence of multi-cellular life on earth.

    and we are worried about it getting too hot?

    we are at a temperature cooler than that experienced by the medieval kings and roman emperors. it is much cooler than the 3000 year climate optimum that saw the emergence of civilization as we think of it. many historians have argued that the higher temperatures were what allowed this to happen.

    many of those proclaiming the urgency of the need to address current warming seem to believe that climate never changed before we started messing with it 150 years ago. nothing unusually is going on here. climate is constantly in flux. we are well within historical patterns here. wine was grown in london. northern greenland was covered in boreal forest.

    surely, we must have something more important to worry about.

  3. Allen:

    Another way of putting it is that too many approach the debate as if it's black and white. Either their is warming or their isn't; either you're willing to buy into the most unlikely of scenarios or you're in complete denial; etc. The problem is that there are good things and bad things. Like Lomborg points out. There were something like 3-6k (whatever it was) deaths in Britain last summer from the heat. But what doesn't get headlines are the 30,000 (or whatever it was; IIRC these are about the right proportion) deaths from COLD every winter. It makes sense. Britain a wet, cold miserable place in the winter. Surely you'd think they'd be all for the earth getting a little warmer. Not only less deaths but an overall more pleasant climate for them.

    Good point about the Vikings in Greenland.

  4. markm:

    Morgan: "a great deal of the warming trend currently debated has to do with the choice of the starting point around 1850. this choice has more to do with the spread of reliable thermometers than with and good scientific rationale."

    Besides that, I've often seen AGW cheerleaders citing studies with starting points in the 1970's - when the same types of alarmists were worried about an impending ice age. It certainly wasn't as cold as the 1850's, but the winter of 1977-78 had several of the worst snowstorms I've seen in my life - which includes about 33 years in Minnesota and northern Michigan. Now, when it's satellite infrared temperature readings, you've got to start in the 1970's because the first satellites were launched then, and when it's ground-level thermometer readings, you can't go back further than the Little Ice Age because that's when thermometers were invented, but I've also seen especially cold starting years picked for no apparent reason.

    Aside from the obvious one, that is...