Later On

A blog written for those whose interests more or less match mine.

CO2 in the past

with 6 comments

Very good post at Skeptical Science. From the post:

… So we see that comparisons of present day climate to periods 500 million years ago need to take into account the fact that the sun was 4% less active than now. What about times closer to home? The most recent period when CO2 levels were as high as today was around 15 million years ago, during the Middle Miocene. CO2 levels were at about 400 ppm. What was the climate like at the time? Global temperatures were 5 to 10 degrees Fahrenheit higher than they are today. Sea level was approximately 75 to 120 feet higher. There was no permanent sea ice cap in the Arctic and very little ice on Antarctica and Greenland. The close coupling between CO2 and climate led the author to conclude that "geological observations that we now have for the last 20 million years lend strong support to the idea that carbon dioxide is an important agent for driving climate change throughout Earth’s history."  (Tripati 2009).

To sum up, Dana Royer says it best: "the geologic record contains a treasure trove of ‘alternative Earths’ that allow scientists to study how the various components of the Earth system respond to a range of climatic forcings." Past periods of higher CO2 do not contradict the notion that CO2 warms global temperatures. On the contrary, they confirm the close coupling between CO2 and climate.

Written by LeisureGuy

30 October 2009 at 11:09 am

6 Responses

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  1. What do CO2 levels/global temps that happened 15 million years ago have anything to do with CO2 levels/global temps that happened 500 million years ago?


    30 October 2009 at 2:31 pm

  2. They don’t, in fact. 500 million years ago was a totally different world—and sun. 15 million years ago the earth and sun were more similar to present-day values—and 15 million years ago the CO2 levels were what they were today, and once sustained, the globe became considerably hotter. We, of course, are pushing CO2 into the atmosphere at a phenomenal rate, and it has only reached that level and looks as though the CO2 levels today will continue to rise.

    The particular interest in 15 million years ago is, of course, that that is the most recent time that CO2 levels were as high as they are today.


    30 October 2009 at 2:44 pm

  3. 8000 CO2 ppm is a lot. How much can the Sun affect global temperatures that a CO2 amount THAT HIGH has no effect, if CO2 raises global temperatures?


    30 October 2009 at 5:34 pm

  4. I don’t know the answer to that question. However, there is absolutely no dispute about the proposition that CO2 is a greenhouse gas (traps heat), that the amount in the atmosphere is increasing, and that direct measurements of radiative heat show that it is indeed trapping heat and responsible for the global warming. None of those facts is disputed, and if any is, there is ample direct empirical measurement to prove it.


    30 October 2009 at 5:45 pm

  5. Yes and the greenhouse effect is needed for Earth to support life. It’s not a completely bad thing.


    30 October 2009 at 8:26 pm

  6. Agreed. Fire is another example: it can burn you to death, but it is also useful. See also water: drinking too much too fast is lethal, yet we require it to live. And so on and on.

    The problem is when the CO2 levels reach a point that drastically changes the earth’s climate.


    30 October 2009 at 9:54 pm

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