Re: [asa] Serious scientists getting closer to the cosmic connection to climate

On 1/16/07, PvM <pvm.pandas@gmail.com> wrote:
>
> Even if we accept a statistical correlation, and the data are
> certainly not clear, the effect of such correlation need to be shown.
> As data have shown, the solar contributions are much smaller than the
> anthropogenic component.

The following commentary from NOAA puts this in perpective, noting the 5X
greater effect of GHG vs irradiance forcing:

http://www.ncdc.noaa.gov/oa/climate/globalwarming.html#Q4

Since our entire climate system is fundamentally driven by energy from the
sun, it stands to reason that if the sun's energy output were to change,
then so would the climate. Since the advent of space-borne measurements in
the late 1970s, solar output has indeed been shown to vary. There appears to
be confirmation of earlier suggestions of an 11 (and 22) year cycle of
irradiance. With only 20 years of reliable measurements however, it is
difficult to deduce a trend. But, from the short record we have so far, the
trend in solar irradiance is estimated at ~0.09 W/m2 compared to 0.4
W/m2from well-mixed greenhouse gases. There are many indications that
the sun
also has a longer-term variation which has potentially contributed to the
century-scale forcing to a greater degree. There is though, a great deal of
uncertainty in estimates of solar irradiance beyond what can be measured by
satellites, and still the contribution of direct solar irradiance forcing is
small compared to the greenhouse gas component. However, our understanding
of the indirect effects of changes in solar output and feedbacks in the
climate system is minimal. There is much need to refine our understanding of
key natural forcing mechanisms of the climate, including solar irradiance
changes, in order to reduce uncertainty in our projections of future climate
change.

In addition to changes in energy from the sun itself, the Earth's position
and orientation relative to the sun (our orbit) also varies slightly,
thereby bringing us closer and further away from the sun in predictable
cycles (called Milankovitch cycles). Variations in these cycles are believed
to be the cause of Earth's ice-ages (glacials). Particularly important for
the development of glacials is the radiation receipt at high northern
latitudes. Diminishing radiation at these latitudes during the summer months
would have enabled winter snow and ice cover to persist throughout the year,
eventually leading to a permanent snow- or icepack. While Milankovitch
cycles have tremendous value as a theory to explain ice-ages and long-term
changes in the climate, they are unlikely to have very much impact on the
decade-century timescale. Over several centuries, it may be possible to
observe the effect of these orbital parameters, however for the prediction
of climate change in the 21st century, these changes will be far less
important than radiative forcing from greenhouse gases.

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Received on Wed Jan 17 11:21:56 2007