Re: Paleoclimate and CO2
- --- In email@example.com, lasallia <no_reply@...> wrote:
>From the RealClimate website:Ok, but how do they know that the 5,000 year warming that follows ice
>"The reason has to do with the fact that the warmings
>take about 5000 years to be complete.
>The lag is only 800 years.
>All that the lag shows is that CO2 did not cause
>the first 800 years of warming, out of the 5000 year trend.
>The other 4200 years of warming
>could in fact have been caused by CO2,
>as far as we can tell from this ice core data."
ages isn't all, or nearly all, due to the same factors that caused
the first 800 years of the warming? (Earth receiving more direct
sunlight via orbital changes/Milankovitch effect) After all, it is a
100,000 year cycle we're talking about. They say CO2 'could' have
been the cause after 800 years of warming. But why would one assume
or suspect that a warming that occurs with a periodicity of ~100,000
years take only 800 or so to complete? Wouldn't it seem much more
plausible that a warm up related to something as monumental as
changes in the planet's orbit take several thousand years? Why should
CO2 be the suspect when there really isn't any evidence to support
the suspicion? Total CO2 concentrations, both natural and man-made,
only amount to about 0.035% of the atmosphere here on Earth. On Venus
I can understand, as Venus' atmosphere is something like 97% CO2.
Quite a big difference from 0.035.
or, if the long url above breaks apart:
--- In firstname.lastname@example.org, lasallia <no_reply@...> wrote:
From the RealClimate website:
This is an issue that is often misunderstood in the public sphere and
media, so it is worth spending some time to explain it and clarify
it. At least three careful ice core studies have shown that CO2
starts to rise about 800 years (600-1000 years) after Antarctic
temperature during glacial terminations. These terminations are
pronounced warming periods that mark the ends of the ice ages that
happen every 100,000 years or so.
Does this prove that CO2 doesn't cause global warming? The answer is
The reason has to do with the fact that the warmings take about 5000
years to be complete. The lag is only 800 years. All that the lag
shows is that CO2 did not cause the first 800 years of warming, out
of the 5000 year trend. The other 4200 years of warming could in fact
have been caused by CO2, as far as we can tell from this ice core
The 4200 years of warming make up about 5/6 of the total warming. So
CO2 could have caused the last 5/6 of the warming, but could not have
caused the first 1/6 of the warming.
It comes as no surprise that other factors besides CO2 affect
climate. Changes in the amount of summer sunshine, due to changes in
the Earth's orbit around the sun that happen every 21,000 years, have
long been known to affect the comings and goings of ice ages.
Atlantic ocean circulation slowdowns are thought to warm Antarctica,
From studying all the available data (not just ice cores), the
probable sequence of events at a termination goes something like
this. Some (currently unknown) process causes Antarctica and the
surrounding ocean to warm. This process also causes CO2 to start
rising, about 800 years later. Then CO2 further warms the whole
planet, because of its heat-trapping properties. This leads to even
further CO2 release. So CO2 during ice ages should be thought of as
a "feedback", much like the feedback that results from putting a
microphone too near to a loudspeaker.
In other words, CO2 does not initiate the warmings, but acts as an
amplifier once they are underway. From model estimates, CO2 (along
with other greenhouse gases CH4 and N2O) causes about half of the
full glacial-to-interglacial warming.
So, in summary, the lag of CO2 behind temperature doesn't tell us
much about global warming. [But it may give us a very interesting
clue about why CO2 rises at the ends of ice ages. The 800-year lag is
about the amount of time required to flush out the deep ocean through
natural ocean currents. So CO2 might be stored in the deep ocean
during ice ages, and then get released when the climate warms.]
To read more about CO2 and ice cores, see Caillon et al., 2003,
Guest Contributor: Jeff Severinghaus
Professor of Geosciences
Scripps Institution of Oceanography
University of California, San Diego.
From the RealClimate website:
- Why should CO2 be the suspect when there really isn't any evidence to
support the suspicion? Total CO2 concentrations, both natural and man-
made, only amount to about 0.035% of the atmosphere here on Earth. On
Venus I can understand, as Venus' atmosphere is something like 97% CO2.
> Quite a big difference from 0.035.Carbon dioxide is the suspect because we know it's properties. I think
you'll find there is an equally big temperature difference between
Earth and Venus too. (By equally, I do not mean to imply correlation.)