Re: [asa] AGW discussion

From: Rich Blinne <rich.blinne@gmail.com>
Date: Tue Dec 01 2009 - 11:55:53 EST

On Tue, Dec 1, 2009 at 8:18 AM, Bill Powers <wjp@swcp.com> wrote:

> Randy:
>
> The various data sets that you refer to coherently indicate that something
> like global warming is occuring, i.e., we have some understanding of what
> global warming would look like and we find that those expectations are
> indicated.
>
> However, it seems to me that the data you refer to says little about
> causation. At best, it is associative, e.g., higher atmospheric CO2 is
> associated with global warming.
>
> Am I wrong? Timing would be important here, but not conclusive. For
> example, it could be that cause X is not recorded in the historical data,
> but that rising CO2 precedes, receding glaciers. In this case, X may be the
> "real" cause of global warming and the CO2 precedes the glacial melt just
> because the time scale for glacial effects are longer than CO2 changes.
>
> In any case, I had thought the main issue unde discussion was not whether
> global warming is taking place, but rather the mechanism. Is this correct?
>
> thanks,
>
> bill
>
>
>

We've known causation for quite some time. Back in 1898 Svante Arrhenius
published a paper on how temperature went up logarithmically with CO2
concentrations. Based on the Stephan-Boltzman Law Arrhenius came up with "*if
the quantity of carbonic acid increases in geometric progression, the
augmentation of the temperature will increase nearly in arithmetic
progression". *He was the first person to predict that emissions of carbon
dioxide from the burning of fossil fuels and other combustion processes
would cause global warming. In fact, Arrhenius believed this effect was so
strong that it would forestall the next Ice Age.

The physics of the greenhouse gas progressed with understanding of
absorption spectra pioneered by Knut Angstrom who did the first infrared
spectra of CO2 in 1900 where he found two absorption bands. How this causes
the greenhouse effects is that the gases are transparent at some frequencies
but absorb in others and thus can cause the lower parts of the atmosphere to
warm. The contours of these absorption spectra determine how intense this
effect is. As I stated earlier for CO2 and water vapor the effect is
logarithmic, for methane it's roughly a square root relationship, and for
halocarbons such as CFCs it's a linear relationship. Spectral analysis is a
key tool used by Astronomy so when satellites were put into orbit in the
late 50s and early 60s one thing that was done is to look at the heat
"signature" of the Earth. The reason why this was done was even back then
scientists were noting that the Earth was warming and knowing the physics of
the greenhouse gases they wanted to see whether it was water vapor or CO2
that was causing this warming. Water vapor was acquitted but CO2 was
convicted by this analysis. At roughly the same time direct CO2 measurements
were being made near Mauna Lau in Hawaii. Since then the CO2 concentration
has been increasing roughly linearly with a small annual variation as the
planet "breathes". What Arrenhius couldn't have anticipated was the rate at
which we were burning fossil fuels and what he thought we would burn in
millennia we burned in decades.

One thing to note about finding causation you should look for the same kind
of cause for the same kind of effect. If global average temperature of the
last twelve years is the warmest of the last 150 then we need to look for a
"cause" that is monotonically increasing or decreasing and not cyclical.
Solar forcing and ENSO which are cyclical are not a good candidate. The
other thing is the rate of change needs to match. Orbital forcing which is
the dominant force for paleoclimate change is too slow. Solar variation with
a 11-year cycle is too fast since we went through multiple cycles since 1980
when the more pronounced warming has occurred. Same with ENSO, which has 3-4
year cycles and JMO which is sub-annual. The baby bear in all this is CO2.
It's also a baby bear in the extent of the effect. CO2 is a well-mixed gas
with the concentration being roughly even throughout the planet. It's also
long-lived. During the mid-20th Century aerosols masked the global warming
signature but they have local effects and are not long-lived. Clean ups of
these aerosols via the successful cap and trade regime initiated by the
George HW Bush Administration have now unmasked the CO2 signature and the
effects from them are for the most part gone now. (At least the sulfate
aerosols that cool. So-called black carbon aerosols which are the result of
burning biomass are still a big problem and they cause local warming, not
cooling.)

Unfortunately dropping CO2 emissions to zero will not make the problem go
away since as I said the gas stays in the atmosphere for decades to
centuries. Currently we are feeling the effects of the CO2 concentrations of
20-30 years ago because of the heat storing capacity of the oceans. This
beneficial effect however has a downside with the increased acidification of
the oceans and the decreased thermohaline circulation caused by the fresh
water concentration of melting ice caps. The waaaay overstated Day After
Tomorrow showed a *reductio ad absurdam* of what would happen if the Gulf
Stream stopped -- it won't. Still, a more subtle effect is happening where
global warming can paradoxically cause local cooling.

What we have is the classic Fram oil filter scenario. Pay me now, or pay me
later. Once the CO2 is up in the atmosphere it cannot be undone except by
some really crazy ideas with who knows what unintended effects. All that is
up for debate is how fast this all happens and we are getting a better
handle on this with time. From a geological perspective it's crazy fast,
though. The current rate of increase in CO2 is three order of magnitudes
faster than any time in the planet's history and the absolute amount is
higher than any time during the current icehouse regime. If we aren't
careful we're heading for the hothouse that Arrenhius predicted over a
century ago. And it's the rate of change and not the absolute temperature
which is significant. God designed life to adapt but within limits and we
have no idea whether we are going to blow out those limits. When we have had
rapid change (where "rapid" was slower than the current change) in the past
the result was mass extinctions. So far, the differences between the current
situation and the predicted are close enough for computer models to work
reasonably well. We are getting awfully close to making it not be the case
and entering a different planet and a very risky and dangerous experiment.
The "cliff" is probably somewhere 3 - 6 degrees Celsius from the current
temperatures. (See the book Six Degrees published by the National Geographic
Society) Do we turn around or do we play chicken and risk driving off the
cliff. It's our choice. Remember, the breaks are busted on our car so when
we see the cliff it will be too late.

Rich Blinne
Member ASA

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Received on Tue Dec 1 11:56:04 2009

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