Posted on 10/30/2006 7:17:14 AM PST by cogitator
The rise of the Appalachian Mountains may have caused a major ice age approximately 450 million years ago, an Ohio State University study has found. The weathering of the mountains pulled carbon dioxide (CO2) from the atmosphere, causing the opposite of a greenhouse effect -- an "icehouse" effect.
Scientists have suspected that our current ice age, which began 40 million years ago, was caused by the rise of the Himalayas. This new study links a much earlier major ice age --one that occurred during the Ordovician period -- to the uplift of the early Appalachians .
It also reinforces the notion that CO2 levels in the atmosphere are a major driver of Earth's climate.
Seth Young, a doctoral student in earth sciences at Ohio State, reported the new study October 25 at the Geological Society of America meeting in Philadelphia.
Because we are currently living in an ice age -- or, more precisely, in a slightly warmer interglacial period within an ice age -- CO2 levels worldwide would ordinarily be low; but scientists believe that humans have raised CO2 levels by burning fossil fuels.
Matthew Saltzman, professor of geological sciences and Young's advisor, looks for evidence of ancient climate change to help scientists gain perspective on the climate change of today. He believes the geologic record can help solve current debates.
One such debate is whether atmospheric carbon dioxide truly drives Earth's climate. The planet has shifted between greenhouse conditions and icehouse conditions throughout its history, and research from Saltzman's team strongly suggests that carbon dioxide levels are a key cause.
"In this study, we're seeing remarkable evidence that suggests atmospheric CO2 levels were in fact dropping at the same time that the planet was getting colder. So this significantly reinforces the idea that CO2 is a major driver of climate," Saltzman said.
This study builds on work the same team published in 2005, when they used quartz sandstone deposits in Nevada and two sites in Europe to determine when the Ordovician ice age began -- approximately 450 million years ago.
They've now analyzed the same set of rock samples in a different way, comparing the ratio of two isotopes of the element strontium, strontium-87 and strontium-86.
They found that, immediately prior to the time that the Ordovician ice age began, the strontium ratio dropped dramatically. The likely cause: a vast amount of volcanic rock was being eroded away, and the resulting sediment was being deposited in the world oceans.
"We observed a major shift in the geochemical record, which tells us something must have changed in the oceans," Young said.
The timing of the strontium ratio decline matches the rise of the Appalachian Mountains . The crustal plate underneath what is now the Atlantic Ocean pushed against the eastern side of North America, lifting ancient volcanic rock up from the seafloor and onto the continent.
This kind of silicate rock weathers quickly, Young explained. It reacts with CO2 and water, and the rock disintegrates. Carbon from the CO2 is trapped in the resulting sediment.
The chemical reaction that weathered away part of the Appalachians would have consumed large amounts of CO2 from the atmosphere -- right around the time that the Ordovician ice age began.
The Ordovician period started out warm, with high sea levels worldwide. It ended cold, with low sea levels as glaciers covered the poles and portions of the continents. According to the Ohio State study, most of the Appalachian weathering took place over 7 or 8 million years -- a very short time, by geological standards -- as the climate moved from one extreme to the next.
The crossover between greenhouse and icehouse conditions set the stage for mass extinctions around the planet at the end of the Ordovician.
"We are seeing a mechanism that changed a greenhouse state to an icehouse state, and it's linked to the weathering of these unique volcanic rocks," Young said.
This kind of rock is often called "island arc" rock, because it forms curved chains of volcanic islands such as Indonesia and Japan.
"Those rocks are around today, where you have ocean crust being subducted under a crustal plate," Young explained. "What's unusual about the Ordovician period is that those island arcs were being uplifted onto a continent. The ones in the Pacific Ocean now are mostly underwater, so they're not weathering away like the Appalachian rock did."
The rise and subsequent weathering of the Himalayas may have caused our current ice age, the one that began 40 million years ago.
"In the Himalayas, the process would have been the same -- silicate rocks are exposed to the atmosphere, weathering sucks CO2 out of the atmosphere and chills the planet," Saltzman said.
"This may be the only effective way to bring CO2 levels down to a threshold that's cool enough for ice to start building up."
Coauthors on the study included Kenneth Foland, a professor, and Jeff Linder, a research associate, both in earth sciences at Ohio State. The National Science Foundation funded this research.
Cloud cover is not a forcing, it's a feedback.
Hmmm, it certainly isn't a feed back to the climate modelling the UN/IPCC uses in their assessments. The assumption in the GCMs is no change in cloud cover.
Change as a consequence of thermal effects are the only factor climate models deal with in the sense of "feedback." In the case of GCMs this tends to be mainly their consideration of water vapor as a feedback mechanism from evaporation and effects of thermal variation on ice flows affecting albedo, as opposed to the water droplets of clouds forming as a consequence of cosmic ray interactions which are not a "thermal" effect.
The case of cloud variations due to cosmic ray modulation, is independant of atmospheric thermal factors in the sense of "feedback" used in climate modelling reviewed and incorporated into the conclusions of UN/IPCC folks.
Any variation in clouds inducing a temperature change due to external cosmic ray flux becomes a thermal forcing and the change in heat balance as a consequence would theoretically feedback in the hypothesized atmospheric processes of the climate change models same as any temperature change due to CO2 as a thermal forcing agent.
In short cloud cover changes due to factors outside the atmosphere are very definitely treatable as a forcing just a metorice dust, and aerosols in general are perceived to be in climate models.
The feedback factors of climate models operate on atmospheric and surface thermal changes, not externally induced forcings such as the CR factors operating on cloud cover.
Our assessments differ. I think that analysis of Milankovitch forcing by Berger and Loutre is valid, and therefore there isn't any reason to be concerned about a glacial period that is in the distant future.
Hyping global warming and very ill understood and ill based non-science is hardly conducive to achieving such goals, infact can be quite counter productive in terms of actually turning good science and good policy away for lack of credibility in the "Global Warming" alarmists camp.
Well, our viewpoints on the credibility of the science have always been quite different. But I think that the environmental arguments are less weighty than the energy and security concerns vis-a-vis the nation's energy infrastructure.
that concern I can share and work toward correcting such through utilization of real energy alternatives such as nuclear power taking the place of fossil fuel energy dependence. ... I wholly subscribe to the idea that nuclear energy should have been implemented yesterday, and lacking such having been done, it is all the more important to do so now to relieve our dependancing on foreign sources of fossil fuels which impact both our economy and security in our dependance of foreign souces."
Total agreement here. As you might guess, I also favor development of biofuels -- but to get to a more stable energy system, utilzing tar sands, oil shales, and other sources may be necessary.
Global Warming hype through the UN/IPCC however is not the way to achieve either of the above for the reasons stated
Within a decade -- I hope we'll still be discussing this -- we'll know with considerably more certainty if it's hype or not.
No doubt about that!
I'll check the link; can't reply any more on Halloween.
I think that analysis of Milankovitch forcing by Berger and Loutre is valid,
And I figure the more moderna and best assessment of Muller and others of Milankovitch's choice of eccentricty as opposed to orbital inclination to be the valid assessment. The choice of Milankovitch in chosing eccentricty as a factor appear to be rooted mainly in a coincidental period of operation near 100kyrs as opposed to more likely factors involved in orbital inclination modulating the incidence of meteoric dust and particles distributed about the solar system mean orbit with a much clearer and more consistant period of operation.
Dust answers more for cloud formation and a much larger effect than the small variations of incideant solar radiation due to variations in distance from the sun in changes in eccentricty that are even out of phase with the proported effects not to mention totally inadequate to explain observed correlations with solar activity as opposed to variations in solar irradiance.
Your logical conclusion here is based on an inaccurate starting premise
Which starting premise is that? I base my estimates on the basis of the lack of modelling of significant factors beyond mere thermal feedback factors of indeterminate magnitude or sign.
I don't see any modeling for effects on cloud formation of meteoric dust intercepted due to changes in orbital eccentricity per Muller and others, nor any attempts to model the effects of electron interactions enhancing cloud formation due to decadal and millenial modulations of cosmic ray fluxes.
Remember it doesn't take much variation in cloud formation due to such effects to totally dominate Earth's thermal balance through changes in albedo. A mere 2% change in cloud cover due to such effects since the Maunder Minimum wipes out even the highest upper boundries of thermal variation left from which hypothesize CO2 effects as a consequence of incomplete climate modelling.
Merely assigning solar activity effects to variations in solar brightness simply leaves far to much slack in the models leaving the assessment of direct radiation effects of CO2 impacts wide open to overestimations with the broad range of uncertainty that current climate models leave wide open for specualative assignment to the inappropriate drivers.
As you might guess, I also favor development of biofuels -- but to get to a more stable energy system, utilzing tar sands, oil shales, and other sources may be necessary.
Then I would suggest you would do better to address those issues directly rather than trying to tie your kite on the "Global Warming" string.
In hanging on the Global Warming you only lose credibility due to the extreme tenor of its alarmists in exchange for more solid and acceptable arguments that would lead to substantive change towards your claimed strategic goals of national security and national economic health.
Even biofuels I will agree with you on insofar as such may be derived from cellulose waste products rather than usable food stocks. Dedicating arable acres to biofuels for the sake of such fuels, to the exclusion of that which could be used for food, would not however be too smart.
Remember pushing in the direction of cooling in terms of global climate change end up can reducing arable lands as opposed to increasing such which future generations also need.
can't reply any more on Halloween.
Yep, catching up with me here as well.
Respond with yah when I can. Unfortunately will probably be busy with appointments over the rest of the week as well. So it's pretty much catch as catch can where internet debate is concerned nowadays.
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