From 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 irrelevent – 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 aggresive 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 Coyote Blog.

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.

  • 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” sounds 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 unusual 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.

  • John David Galt

    If Megan McArdle can prove that humans could be causing catastrophic global warming, there’s a $125K prize waiting for her at junkscience.com.

    Meanwhile, scientists of many nations are about to meet and consider the merits of Gregory Benford’s proposal to cool the earth by dumping a bargeful of iron filings in the ocean to stimulate plankton growth — an idea first proposed in Reason.

    Naturally Greenpeace is opposed — because it would prove to everyone that their whole agenda is unnecessary.

    (If this is tried and does work, then in a few years when they’re predicting ice ages again, I sure hope we’ll find some equally quick way to warm the earth!)

    The worst thing about a democratic form of government is that it enables these Chicken Littles to waste everybody’s time.

    The schools ought to be training kids to realize that the media are always going to be saying there’s an emergency — it sells papers and TV ads — and similarly, busybody politicians are always going to be saying there’s an emergency, because emergencies, real or imaginary, are the health of the State.

  • Surely you have seen this by now, but Investors Business Daily has found out that James Hansen


    has received $720,000 from none other than George Soros’s Open Society Institute, under the “politicization of science” (/sarc) project.

    He also championed global cooling in 1973 (I’m sure you knew that)

    “The Post reported that Rasool, writing in Science, argued that in ‘the next 50 years’ fine dust that humans discharge into the atmosphere by burning fossil fuel will screen out so much of the sun’s rays that the Earth’s average temperature could fall by six degrees.

    “Sustained emissions over five to 10 years, Rasool claimed, ‘could be sufficient to trigger an ice age.’

    “Aiding Rasool’s research, the Post reported, was a ‘computer program developed by Dr. James Hansen,’ who was, according to his resume, a Columbia University research associate at the time.”

    So, emissions can either cool or warm us, depending on how Hansen’s model plays out that day. Brilliant.

  • jt

    The argument about diminishing returns may be a little hard for some people to grasp for atmospheric CO2 levels, but it’s easy to see how it applies to real-world “greenhouses”–the ones made of glass. One pane of glass traps a lot of solar heat, a second pane *might* bump the temperature up a bit (that’s the reason we install double-pane windows in our homes), but you don’t get much heat conversion payback beyond that point.

  • Actually we can’t definitively prove that the “globe” has warmed since 100 years ago. Two things are obvious: 1)We’re not very good at measuring surface temps, 2)What meaning does a “global mean temperature” have anyway?

    Some places get cooler, some get warmer. And what we end up with is global warming? Puhleeze!

    IF, and it’s a big if, we believe the surface temp record, then it hasn’t warmed at all since the 1930s, we’re simply returning to that temp level.