Posts tagged ‘Diminishing Return’


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.