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Author Topic: Are current pre-industrial CO2 levels lowest in Earth's history?  (Read 4945 times)

Offline Eric A. Taylor

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I have been looking through the geological ages of the Earth. For most of Earth's history carbon dioxide levels in the atmosphere have been much much higher than in the modern era (pre-industrial). Dropping to current levels only a few million years ago in the Neogene. For most of Earth's history CO2 levels have been 6 to 10 times what they are today (post Cambrian). Levels in the Cretaceous were 6 times today's levels. How does this jibe with climate change and humans forced climate change?

Pre-Cambrian levels were even higher but I'm not sure we can count that period as the Earth then was vastly different then than it is today.


 

Offline frethack

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Only the Carboniferous Period had CO2 levels as low as present.
 

Offline Eric A. Taylor

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I thought the Carboniferous had CO2 levels 3 times pre-industrial. O2 levels were 163% of present levels, which begs the question, what were forest fires like then?
 

Offline frethack

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GEOCARB III estimated the Carboniferous at about current levels of CO2...though the study is nearly 10 years old.  When I leave the lab Ill find and post the citation and the main graphs.  Im sure there are newer studies, but nothing that I know of that is as comprehensive.
 

Offline JimBob

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SEE ABOVE

(It is what this guy does at "work")
 

Offline frethack

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Here is a link to a pdf of the paper:

http://earth.geology.yale.edu/~ajs/2001/Feb/qn020100182.pdf

And if you happen to belong to a university library, here is the citation:

Berner, R.A., Kothavala, Z., 2001. GEOCARB III: a revised model of
atmospheric CO2 over Phanerozoic time. Am. J. Sci. 301, 182204.
 

Offline Madidus_Scientia

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Indeed, CO2 has been much higher in the past, but there are more factors than CO2 that determine climate, such as solar variations, aerosols from volcanoes etc. The evidence is that modern global warming is due to increased greenhouse gases, given that no other factors have changed significantly since pre-industrial times. The sun has actually been cooler than it usually is in the last 30 years.

Also the rate at which the CO2 increased is unprecedented, usually it happens slowly over geological timescales, and ocean acidity has a chance to buffer itself by dissolving sediments deep on the sea floor. We have increased the CO2 much too fast for this reaction to happen.
 

Offline frethack

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The evidence is that modern global warming is due to increased greenhouse gases, given that no other factors have changed significantly since pre-industrial times.

The modern warming is partially due to greenhouse gasses.  Other factors have changed significantly since pre-industrial times (increased solar variability, increased gulf stream transport, increase in the AMOC, increased monsoonal intensity, etc.).

The sun has actually been cooler than it usually is in the last 30 years.

Other than the current deep minimum for the past two years, solar cycles 21, 22 and 23 were still large when compared to the past 5000 years, and solar cycles 18 and 19 were giant.  Modern (post industrial) solar activity is higher than it has been since the Holocene Climate Optimum.

Sunspot number since the Little Ice Age:



Holocene sunspot number (from Usoskin et al. 2007):


 

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