Forecasting the Future Climate – Part 2
“The news from this Midwestern farm is not good. The past four years of heavy rains and flash flooding here in southern Minnesota have left me worried about the future of agriculture in America’s grain belt. For some time computer models of climate change have been predicting just these kinds of weather patterns, but seeing them unfold on our farm has been harrowing nonetheless.” Jack Hedin, Minnesota farmer, NYT Op/ed November 27, 2010 
Jack Hedin continues “Climate change, I believe, may eventually pose an existential threat to my way of life.” Let’s be clear. Any existential threat to American farming is an existential threat to America. Maybe Rush Limbaugh can get by on Oxycontin, but the rest of us have to eat.
Last week, we showed that even the lowest estimate, the Rutledge forecast , for remaining recoverable fossil fuels may lead to a major extinction event because of rising atmospheric carbon dioxide and rapidly increasing ocean acidification. The rate of ocean acidification is ten times larger than the rate during the Paleocene-Eocene Thermal Maximum, 55 million years ago (Pelejero ). The lowest credible estimate results in a peak production of all fossil fuels in 2024, just 14 years from now. Therefore, in this scenario and without proactive effort, it is reasonable to assume we will cut down every tree on the planet to keep warm and cook our food. Thus a loss of all forests and corals suggests a major extinction event will occur even with the lowest credible estimates for remaining fossil fuels. Both extirpations are already underway. All other estimates are much worse in terms of species extinction.
Table 1 shows the present and pre-industry CO2, temperature and sea level. According to Hansen , there is between 0.6 and 1.4 degrees C, warming in the pipeline. This agrees with what happened during the last interglacial period, the Eemian, 125,000 years ago [5 and 6]. The notation kya means thousands of years ago. Note that with only 300 ppmV (parts per million by volume) the Earth surface temperature was 1.9 degrees C higher than the pre-industrial climate and 1.1 degrees higher than today’s climate. The frightening thing is that sea levels, from Greenland and West Antarctica ice sheet melting, were between 6 and 9 meters or 18 and 28 feet higher than today.
In order to melt ice sheets takes energy delivered over time into the Earth system. The current radiation imbalance of the Earth is about 1.6 Watts/meter squared . A Watt is a measure of energy flow, a Joule per second, where a Joule is a measure of energy. Over time, this energy heats the oceans and evaporates water, and heats the glaciers melting them in addition to heating the Earth surface. Melting glaciers is a wet process which takes considerably less time than building the glaciers in the first place. How fast the glaciers melt is a controversial subject. People generally speak of sea level rise within this century, as if sea levels will not continue to rise after that. This adds unnecessary confusion and considerably to the name calling. We see that Al Gore is in fact correct in his movie, An Inconvenient Truth, as sea levels during the Eemian inform us that 6 meters of sea level rise is not at all an unreasonable expectation and may already be unavoidable. We also know that sea levels can rise fast because that is what they did. Between 14,000 and 16,000 years ago, as the Earth emerged from the last glacial maximum, sea levels rose between 5 and 6 meters per century for some time. Also between 8,260 and 7,680 years ago sea levels increased an average of 5 meters per century over 600 years. Both estimates are from Ward . Our predicament is, in fact, much worse.
During the Pliocene, 2 to 5 million years ago [9, 10, 11 and 12], atmospheric carbon dioxide was between 300 and 425 ppmV. Surface temperatures were 2 to 4 degrees higher than pre-industrial values and the sea level was 25 meters (75 feet) higher than today. Note that we are at the upper end of the Pliocene atmospheric carbon range. Recall from last week that we will be well above the Pliocene upper limit for hundreds of years. As the radiation imbalance persists, energy accumulates which continues to melt the polar ice. During the Miocene, 15 million years ago , atmospheric carbon dioxide was above 450 ppmV, which is where we are headed, and sea levels were between 25 and 40 meters above today’s levels.
If atmospheric carbon dioxide reaches 750 ppmV, all of the great ice sheets may melt resulting in 66 meters of sea level rise .
What if Rogner is correct  and we burn all of that fossil fuel? We know how to compute the increase in Carbon Dixoide within a first order using the equations we derived in . We simply divide 5000 Giga tonnes carbon by 4.2 to estimate atmospheric carbon dioxide increase to be about 1200 ppmV. Add this to the existing 400 ppmV and we are well into Eocene conditions, 1600 ppmV. In this case, we will have changed the Earth’s climate within a few hundred years to an extent which took Mother Nature tens of million of years to accomplish. If we manage to put this much fossil carbon in the atmosphere this fast, we can assume with high probability that we will succeed in melting all of the polar permafrost [16-17] adding another 1500 Giga tonnes of carbon and we will likely initiate a methane hydrate burp (there is some evidence we already are doing this ) which will increase atmospheric carbon by several thousand billion tonnes . Much of the release from these two sources will be in the form of methane rather than carbon dioxide which is about 33 times more powerful a green house gas. If Rogner is correct and we indeed burn it all up, we should assume with non-zero probability that we will cause our own self extinction.
Is all lost? Certainly not from an engineering perspective, in the next article, I will outline the technical solutions.
Hedin concludes: “The country must get serious about climate-change legislation and making real changes in our daily lives to reduce carbon emissions. The future of our nation’s food supply hangs in the balance.”
Actually, considerably more than that hangs in the balance but Hedin’s advice is well worth heeding.
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