Re: [asa] Physical Model for Climate

On 2/22/07, Rich Blinne <rich.blinne@gmail.com> wrote:
>
>
> On Feb 22, 2007, at 5:14 AM, Dave Wallace wrote:
>
> The March 2007 edition of Scientific American page 71 shows a picture of
> a "RIVER MODEL at the National Center for Earth Dynamics". The
> constructed model is being used to study how sediments move in rivers. I
> seem to recall that other such physical models of rivers have been
> constructed. At first thought it would seem improbable that any
> reasonably sized scale model of a river could result in useful data. I
> suspect they also use digital models to aid their understanding of sediment
> flows.
>
>
> Have any physical models been attempted for climate? If so what results?
>
>
>
> Yes and this is the fundamental reason why we are very confident of the
> amount of forcing by GHG. The forcings by the greenhouse gases have little
> uncertainty because their concentrations are accurately measured in the
> atmosphere, and their infrared absorption properties are very accurately
> measured in the laboratory (your physical model). The two are put together
> using highly accurate numerical methods that have little error.
>
>
>
>

Another thing. Spectra are a powerful tool for discovering things. Take the
following from today's Nature:
 A spectrum of an extrasolar planet
>
> Of the over 200 known extrasolar planets, 14 exhibit transits in front of
> their parent stars as seen from Earth. Spectroscopic observations of the
> transiting planets can probe the physical conditions of their atmospheres1,
> <http://www.nature.com/nature/journal/v445/n7130/full/nature05636.html#B1>
> 2<http://www.nature.com/nature/journal/v445/n7130/full/nature05636.html#B2>.
> One such technique3,
> <http://www.nature.com/nature/journal/v445/n7130/full/nature05636.html#B3>
> 4<http://www.nature.com/nature/journal/v445/n7130/full/nature05636.html#B4>can be used to derive the planetary spectrum by subtracting the stellar
> spectrum measured during eclipse (planet hidden behind star) from the
> combined-light spectrum measured outside eclipse (star + planet). Although
> several attempts have been made from Earth-based observatories, no spectrum
> has yet been measured for any of the established extrasolar planets. Here we
> report a measurement of the infrared spectrum (7.5–13.2 [image: micro]m)
> of the transiting extrasolar planet HD 209458b. Our observations reveal a
> hot thermal continuum for the planetary spectrum, with an approximately
> constant ratio to the stellar flux over this wavelength range. Superposed on
> this continuum is a broad emission peak centred near 9.65 [image: micro]m
> that we attribute to emission by silicate clouds. We also find a narrow,
> unidentified emission feature at 7.78 [image: micro]m. Models of these
> 'hot Jupiter'5<http://www.nature.com/nature/journal/v445/n7130/full/nature05636.html#B5>planets predict a flux peak6,
> <http://www.nature.com/nature/journal/v445/n7130/full/nature05636.html#B6>7,
> <http://www.nature.com/nature/journal/v445/n7130/full/nature05636.html#B7>8,
> <http://www.nature.com/nature/journal/v445/n7130/full/nature05636.html#B8>
> 9<http://www.nature.com/nature/journal/v445/n7130/full/nature05636.html#B9>near 10 [image:
> micro]m, where thermal emission from the deep atmosphere emerges
> relatively unimpeded by water absorption, but models dominated by water fit
> the observed spectrum poorly.
>
Various models including models that looked at the spectral signature of
water and the spectra observed above excluded it for this extrasolar planet.
What does this have to do with climate change? Since we have measured
experimentally what wavelengths of light get absorbed by CO2, the same
spectral analysis can be done from space on our own planet and directly
answer the question of whether we are experiencing anthropogenic climate
change. This is not a hypothetical experiment. It has already been done.
Note the following from Fred Pearce in "With Speed and Violence: Why
Scientists Fear Tipping Points in Climate Change", p. 11:

> The effect [CO2] has on the planet's radiation balance is now measurable.
> In 2001, Helen Brindley, an atmospheric physicist at Imperial College
> Longon, examined satellite data over almost three decades to plot changes in
> the amount of infrared radiation escaping from the atmosphere into space.
> Because what does not escape must remain, heating Earth, this is effectively
> a measure of how much heat is being trapped by greenhouse gases -- the
> greenhouse effect. In the part of the infrared spectrum trapped by carbon
> dioxide -- wavelengths between 13 and 19 micrometers -- she found that less
> and less radiation is escaping. The results for the other greenhouse gases
> were similar.
>

Here's the paper that Fred Pearce referred to:
http://www.nature.com/nature/journal/v410/n6826/abs/410355a0.html

 Increases in greenhouse forcing inferred from the outgoing longwave
radiation spectra of the Earth in 1970 and 1997
>
> The evolution of the Earth's climate has been extensively studied1,
> <http://www.nature.com/nature/journal/v410/n6826/full/410355a0.html#B1>2<http://www.nature.com/nature/journal/v410/n6826/full/410355a0.html#B2>,
> and a strong link between increases in surface temperatures and greenhouse
> gases has been established3,
> <http://www.nature.com/nature/journal/v410/n6826/full/410355a0.html#B3>4<http://www.nature.com/nature/journal/v410/n6826/full/410355a0.html#B4>.
> But this relationship is complicated by several feedback processes—most
> importantly the hydrological cycle—that are not well understood5,
> <http://www.nature.com/nature/journal/v410/n6826/full/410355a0.html#B5>6,
> <http://www.nature.com/nature/journal/v410/n6826/full/410355a0.html#B6>7<http://www.nature.com/nature/journal/v410/n6826/full/410355a0.html#B7>.
> Changes in the Earth's greenhouse effect can be detected from variations in
> the spectrum of outgoing longwave radiation8,
> <http://www.nature.com/nature/journal/v410/n6826/full/410355a0.html#B8>9,
> <http://www.nature.com/nature/journal/v410/n6826/full/410355a0.html#B9>10<http://www.nature.com/nature/journal/v410/n6826/full/410355a0.html#B10>,
> which is a measure of how the Earth cools to space and carries the imprint
> of the gases that are responsible for the greenhouse effect11,
> <http://www.nature.com/nature/journal/v410/n6826/full/410355a0.html#B11>12,
> <http://www.nature.com/nature/journal/v410/n6826/full/410355a0.html#B12>13<http://www.nature.com/nature/journal/v410/n6826/full/410355a0.html#B13>.
> Here we analyse the difference between the spectra of the outgoing longwave
> radiation of the Earth as measured by orbiting spacecraft in 1970 and 1997.
> We find differences in the spectra that point to long-term changes in
> atmospheric CH4, CO2 and O3 as well as CFC-11 and CFC-12. Our results
> provide direct experimental evidence for a significant increase in the
> Earth's greenhouse effect that is consistent with concerns over radiative
> forcing of climate

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Received on Thu Feb 22 10:55:45 2007