James Hansen, Director of the NASA Goddard Space institute – the foremost US Government climate modeling agency – gave a presentation at the American Geophysical Union annual meeting in San Francisco last week (16,000 scientists attended the annual festivities). The rate of CO2 change today is 20,000 times higher than at any time in the last 65 million year, since the dinosaurs became extinct. The highest natural forcing of CO2 in the Cenozoic Era (the last 65 million years) was about 100 ppm per million years or 1/10,000 ppm per year. Today’s CO2 change rate is 2 ppm per year – 20,000 times greater… (remember, we cannot directly compare our world today to that world when the dinosaurs were around. The geologic weathering rate, solar forcing and tectonics were entirely different then. That is why that period (Mesozoic) is a different geologic epoch than the one we are in today (Cenzoic).
So the argument that there have been larger changes than what are happening to day is pure fiction. Yes there have been larger changes, but they happened in hundreds of thousands or millions of years. Slow feedback processes like geologic weathering and ocean sequestration take thousands to hundreds of thousands of years to happen.
This is a quote from DR. Hansen’s Bjerknes Presentation at the AGU in December that illustrates the Venus Syndrome analogy: "Given the solar constant that we have today, how large a forcing must be maintained to cause runaway global warming? Our model blows up before the oceans boil, but it suggests that perhaps runaway conditions could occur with added forcing as small as 10-20 W/m2 (Watts per square meter – a 60 watt light bulb provides 3 to 6 times more forcing per unit of area than is required to turn the Earth into a Venus)"
The conversion from W/m2 to degrees is 3/4 degree C per W/m2. Or 1.35 degrees F per W/m2. This is 13.5 to 27 degrees F of global warming. (Updated as per March 2009, the latest climate models show a likely warming of 10 to 13.5 degrees this century, with more in the 22nd century.)
The threat of the Venus syndrome is very real. Runaway, irreversible climate change is a very frightening and factual probability. When the Earth went into its snowball state, the runaway albedo feedback was to blame. Ice reflects 90% of the sun’s heat harmlessly back into space. Earth, rock, vegetation and open water absorb up to 90% of the sun’s heat and changes it into infrared radiation that is trapped on the planet by the greenhouse effect. As the planet warms, the water vapor effect works in the same way in the opposite direction. The difference? When the Earth goes into snowball, carbon dioxide slowly builds up in the atmosphere from volcanoes because there is no ocean, vegetation, earth or rocks to absorbed the CO2. This buildup eventual invokes the greenhouse effect, the planet warms enough to melt the ice. In a runaway heating scenario where the water vapor feedback is invoked, the oceans simply evaporate into space. There is no return. Here’s a quote lifted from the notes of his PowerPoint presentation:
"There may have been times in the Earth’s history when CO2 was as high as 4000 ppm without causing a runaway greenhouse effect {the Mesozoic period – time of the dinosaurs}. But the solar irradiance was less at that time. What is different about the human-made forcing is the rapidity at which we are increasing it, on the time scale of a century or a few centuries. It does not provide enough time for negative feedbacks, such as changes in the weathering rate, to be a major factor. There is also a danger that humans could cause the release of methane hydrates, perhaps more rapidly than in some of the cases in the geologic record. In my opinion, if we burn all the coal, there is a good chance that we will initiate the runaway greenhouse effect. If we also burn the tar sands and tar shale (a.k.a. oil shale), I think it is a dead certainty."
The importance of the venue for these statements can not be under-stated. The AGU is the largest organized body of scientists on the planet and Dr. Hansen is likely the single most important climate modeler on the planet.
I highly recommend a review of Dr. Hansen’s PowerPoint presentation below. This is one of the most concise and broad ranging summaries of the basic climate science concerning the climate crisis I have ever seen.
December 20, 2008 Berknes Lecture http://www.columbia.edu/~jeh1/