[asa] Oceans and the history of global climate

One of the symposia I was able to attend at the AAAS meeting was on the study of the ocean for insight into historical patterns of global climate. The two papers I heard were by Jim Zachos from U. Cal-Santa Cruz and Mark Pagani from Yale.
Here are a few tidbits I gleaned that I thought were interesting.

1. Ocean surface concentrations of the isotopic ratio C-13/C-12 can be reconstructed historically from corals and forams. The data obtained in this way correlate well with atmospheric data reconstructed from trees. The data over the past millenium show a constant ratio until the mid 19th century at which point the ratio drops rapidly to its present level. That reduction can be traced to the release of carbon from fossil fuels which have approximately 60% lower C-13/C-12 ratio than current atmospheric levels. In other words, the carbon-13 ratio provides conclusive evidence that the rise in atmospheric carbon dioxide concentration since the mid-19th century is due to anthropogenic burning of fossil fuels.

2. The symposium focused on detailed analyses of the climate over the last 65 million years as deduced from oceanic data. The time from now to 35Mya is dubbed the icehouse era while 35-65Mya is the hothouse era. The carbon levels were also much higher in that hothouse era.

  In the hothouse era there is a fascinating dip in temperature at the Paleocene-Eocene transition at 55Mya. The global temperature peaked at 52Mya at around 8C warmer than today. But at the 55Mya mark there is a sharp dip and recovery of around 3C. A very careful study of fossils around that time frame allowed them to correlate the carbon concentration and the temperature. The rate of the transition is definitely less than 4,000 years and could be less than 1,000 years. More study of this dip and recovery would be of considerable interest in understanding how fast the earth responds.

  At the peak temperature at 52Mya, there was no freezing temperature at the North Pole and that's when the swamps and vegetation thrived in that area, ultimately becoming the oil fields now of interest. There was no ice on the earth (in marked contrast to around 600 Mya or so when it was all ice!). The Antarctica ice formation happened at the hothouse/icehouse transition at 35 Mya. Pagani reported that a very thorough study had cleared up discrepancies in the carbon data and that the resulting data showed a steep gradient of carbon concentration that matched the temperature change very well at that transition.

  Although I couldn't follow all the details, they also stated that during this "icehouse" period, there had been a lot of bewilderment about how the temperatures and carbon levels correlated but that these were now better understood and consistent with a 3C/doubling of carbon concentration.

 Finally, they noted that around 5 Mya there was a period when the atmospheric carbon dioxide concentration was around 400--about what it is now. At that time the global temperature was 3C higher than today and the sealevel was 25 meters higher. Although some parameters may be different, this is a reasonably good estimate of what the equilibrium temperature and sealevel might be for today's carbon concentration. In fact, we might say that this much temperature rise is baked into the system. We just don't know how long it will take to get there. That is a critical parameter since the urgency and the impact depend very much on the rate of transition.

 Several of you have commented that your remaining hesitance about global warming has been the uncertainty of the global climate computer modeling. In this analysis from the oceans, no such complex models are used. The C-13 data clearly nails the origin of the carbon increase and the historical data give good indication of the equilibrium temperature and sealevels. What remains is the time scale for reaching equilibrium. The models are focused on doing that. The fossil records in the oceans do indicate, especially at the Paleocene-Eocene transition--that the response of the earth can be quite rapid, though precision cannot get into the range of a hundred years.

Randy

To unsubscribe, send a message to majordomo@calvin.edu with
"unsubscribe asa" (no quotes) as the body of the message.
Received on Sun Feb 17 21:40:59 2008