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Dr. James White: Atmos. CO2 changes from 180–280 ppm between glacials & interglacials. We just hit 380 ppm [2009]. Last time we had 380 was 3M years ago—arctic was ice free, sea level was 75 ft higher (“bye bye to Florida for the most part”). [Fact Checking]

April 26, 2014 11:27 pm1 comment

Summary of initial comments (paraphrases and quotes):

Dr. Andreas Schmittner: “J.White is absolutely right [that] on long time scales higher CO2 means a warmer climate, less ice and higher sea level. […] I think the 380-400 ppm is a good estimate… [although] 75 ft seems a little too high.”

Dr. Stephanie Thomas: Recent data posted by Mauna Loa shows just over 400 ppm for the weeks of 3/30/14, 4/6/14, and 4/13/14. The 20 ppm increase since 2009 shows how quickly CO2 is rising. 

Dr. Andrew Dessler: “I don’t see anything I would consider to be wrong.” Will add one note: 380 ppm may certainly raise sea level by tens of feet, but it takes “a very long time (many centuries/millennia) […] to melt that much ice.”

Dr. Mauri Pelto: Will just point out some recent research “indicating soils that have been buried continuously beneath the Greenland Ice Sheet  for the last 3 million years. (Check it out here). This indicates the Pilocene…”

Dr. Scott Denning:  “J.White’s basic assertion is that sea levels will behave in the future as they have done in the past… This is not controversial… It may take many centuries or even millennia… The response will be slow, but the costs are astronomical.” 

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Dr. James White in “Colorado and a Warming Planet“, produced by Colorado University Outreach in 2009:

(00:57 -2:35)

As a climate scientist I do my work in Greenland and in Antarctica because that is where the big ice sheets are. [It’s] where we make measurements to look at climate change.  We use ice cores to look roughly 800,000 to a million years in the past to look at levels of greenhouse gases in the atmosphere. At times the earth has cooled off enough that huge glaciers have formed covering all of Canada and covering all of Scandinavia.

The amount of carbon dioxide change between an inter-glacial period to a glacial period is 100 parts per million (ppm). It has gone from 180 to 280 ppm. This year we hit 380 ppm of CO2 [note: video was filmed in July 2009]. [Looking at the Mauna Loa data posted by the NOAA, the weekly average for the weeks of March 30th, April 6th, and April 13th was just over 400 ppm. — Dr. Thomas]  I can look in the past and say, ok, when was the last time we had 380 ppm in the atmosphere. The climate at that time — about 3 million years ago was when we had 380 ppm — was a completely ice free arctic, probably a little bit of an ice sheet in Greenland, but there were trees growing up to the edge of the arctic circle. [I would simply point out the research reported from this week in Greenland indicating soils that have been buried continuously beneath the Greenland Ice Sheet for the last 3 million years. Check it out here (link). This indicates the Pliocene as the last period without a substantial ice sheet. — Dr. Pelto] Sea level was 75 feet higher. 75 feet is bye bye to Florida for the most part.

[Dr. SchmittnerJim White is absolutely right. On long time scales higher CO2 means a warmer climate, less ice and higher sea level. In fact, it is very likely that we will pass the 400 ppm CO2 mark (as measured at Mauna Loa) very soon (in the coming months). Reliable ice core CO2 data go back only ~800,000 years, so for the time before that estimates are indirect and have larger errors. But I think 380 or 400 ppm is a good estimate for 3 million years ago.

I’m not so sure about his sea level estimate. The latest IPCC report states in chapter that global mean sea level (GMSL) “during these middle Pliocene warm periods was higher than today, but low agreement on how high it reached” and  “assessment by Chapter 5 suggests that GMSL was above present, but that it did not exceed 20 m above present …”. So, 75 feet seems a little too high.]

[Dr. ThomasI second Dr. Schmittner’s comments on the challenges of reconstructing atmospheric CO2 in deeper time; and yet, most paleoclimate proxy reconstructions that I know of for that time period indicate atmospheric CO2 concentrations at or above 380 ppm.]

We have increased carbon dioxide in the atmosphere by the same amount that was accompanying a huge climate shift. We are not stopping our burning of fossil fuels anytime soon, so we will reach 400 ppm. We will probably reach 400 and something ppm. I hope we don’t reach 500 ppm, but this is entirely possible. These are big changes that are going to have profound impacts.

[Dr. SchmittnerJim’s concerns here echo Maureen Raymo’s recent comments, which are shared by many of my paleoclimate colleagues (including myself). Sea level will continue to rise for a long time. We don’t know how fast and how much. But we do know that both, speed and final level, will depend on future greenhouse gas emissions. The more we emit the faster and higher sea level will be rising.]

[Dr. DesslerI don’t see anything in here that I would consider to be wrong. The one thing I would add to this is the idea of timescale. It certainly may be the case that 380 ppm is sufficient to raise sea level by tens of feet. If so, that’s going to take a very long time (many centuries/millennia). Even under the most aggressive emission scenarios, we are unlikely to see the earth transform into that of the Pliocene this century — it takes a very long time to melt that much ice.]

Dr.James White

Source: Learn More About Climate, Office for University Outreach, University of Colorado Boulder.

“Colorado and a Warming Planet” was co-produced by the Office of University Outreach at the University of Colorado Boulder, Sovereign Pictures, and Landlocked Films. See the full video here at CU-Boulder’s ‘Learn More About Climate’ website. Republished under fair use for educational commentary.

Administrator’s Note: The first post had some formatting issues that weren’t conducive to sharing on social media. Took it down and replaced it with this one. Unfortunately, this deleted one comment in the Public Comment Thread. Apologies to Mike Johnson. Also added Dr. Scott Denning’s initial comment to the top on 4/29/14.


  • Jim White’s basic assertion here is that sea levels will behave in the future as they have done in the past: that the geologic record provides a huge data set of seas rising when CO2 and temperatures rise, then falling when CO2 and temperatures fall. This is not controversial and in fact must be the case over sufficiently long time periods. But the timing of ice sheet growth and melting is slow relative to human history, so Jim White makes no prediction of how fast these changes will occur. It may take many centuries or even millennia for ice sheets to adjust.

    Of course it’s not just Florida that is at risk. If sea levels rise 75 feet most of the world’s coastal cities will be lost: New York, London, Shanghai, Tokyo. Something like 60% of the world’s population lives in this zone. The response will be slow, but the costs are astronomical. As a thought experiment, compare the total value of all the real estate in coastal cities,plus all the goods and services produced there, with the marginal cost of renewable vs fossil energy. Climate mitigation is far cheaper!

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