A Demonstration that Global Warming Predictions are Based More On Faith than On Science

Roy W. Spencer, Ph. D.
Wednesday, January 13, 2009

I’m always searching for better and simpler ways to explain
the reason why I believe climate researchers have overestimated the
sensitivity of our climate system to increasing carbon dioxide
concentrations in the atmosphere.

What follows is a somewhat different take than I’ve used in
the past. In the following cartoon, I’ve illustrated 2 different
ways to interpret a hypothetical (but realistic) set of satellite
observations that indicate (1) warming of 1 degree C in global average
temperature, accompanied by (2) an increase of 1 Watt per sq. meter of
extra radiant energy lost by the Earth to space.

The ‘consensus’ IPCC view, on the left, would be that
the 1 deg. C increase in temperature was the cause of the 1 Watt
increase in the Earth’s cooling rate. If true, that would mean
that a doubling of atmospheric carbon dioxide by late in this century
(a 4 Watt decrease in the Earth’s ability to cool) would
eventually lead to 4 deg. C of global warming. Not good news.

But those who interpret satellite data in this way are being sloppy.
For instance, they never bother to investigate exactly WHY the warming
occurred in the first place. As shown on the right, natural cloud
variations can do the job quite nicely. To get a net 1 Watt of extra
loss you can (for instance) have a gain of 2 Watts of forcing from the
cloud change causing the 1 deg. C of warming, and then a resulting
feedback response to that warming of an extra 3 Watts.

The net result still ends up being a loss of 1 extra Watt, but in
this scenario, a doubling of CO2 would cause little more than 1 deg. C
of warming since the Earth is so much more efficient at cooling itself
in response to a temperature increase.

Of course, you can choose other combinations of forcing and
feedback, and end up deducing just about any amount of future warming
you want. Note that the major uncertainty here is what caused the
warming in the first place. Without knowing that, there is no way to
know how sensitive the climate system is.

And that lack of knowledge has a very interesting consequence. If
there is some forcing you are not aware of, you WILL end up
overestimating climate sensitivity. In this business, the less you know
about how the climate system works, the more fragile the climate system
looks to you. This is why I spend so much time trying to separately
identify cause (forcing) and effect (feedback) in our satellite
measurements of natural climate variability.

As a result of this inherent uncertainty regarding causation,
climate modelers are free to tune their models to produce just about
any amount of global warming they want to. It will be difficult to
prove them wrong, since there is as yet no unambiguous interpretation
of the satellite data in this regard. They can simply assert that there
are no natural causes of climate change, and as a result they will
conclude that our climate system is precariously balanced on a knife
edge. The two go hand-in-hand.

Their science thus enters the realm of faith. Of course, there is
always an element of faith in scientific inquiry. Unfortunately, in the
arena of climate research the level of faith is unusually high, and I
get the impression most researchers are not even aware of its existence.