I am introducing a discussion with the purpose of exploring our belief in the potential of climate change to effect our planet. What will each of us be mindful of as we take action?
To do so I am going to quote from a chapter of a recent book by James Hansen. We would all be familiar with the mainstream discussion- maybe up to a metre of sea level rise in a century and maybe a warming of two degrees. We are familiar with the potential for disaster if the temperature warms beyond four degrees. I remember James Lovelock describing how the last time we had a similar amount of carbon in the atmosphere as today was around 3 million years back and that the sea level was 25 metres higher than the current level. And we are told that if all the ice melted the sea level would be 75 metres higher. With this would be catastrophic storms and droughts.
So to the book. Dr. James Hansen is regarded by many people as the world’s foremost climate scientist. He is adjunct professor in the department of earth and environment sciences at Columbia University and director of the NASA Goddard Institute for Space Studies. He frequently gives expert opinion to Goverments, including the US congress. His 2009 book is titled “Storms of my grandchildren, the truth about the coming climate catastrophe and our last chance to save humanity."
Now I will quote from the book-
Venus has so much carbon dioxide in its atmosphere that it has a greenhouse warming of several hundred degrees, with the surface at 450 degrees Celsius, hot enough to melt lead.
Venus is almost as big as earth. Venus and Earth, having condensed from the same interstellar gas and dust during the formation of the solar system, must have begun with similar atmospheric conditions. As the sun brightened, the surface of Venus became hotter, water evaporated and the strong greenhouse effect of water vapour amplified the warming. Eventually a runaway greenhouse effect occurred, with the ocean boiling or evaporating into the atmosphere. The surface became so hot that all the carbon dioxide in the crust was baked out into the atmosphere. The atmosphere of Venus is now almost 97 percent carbon dioxide and the surface pressure on Venus is 90 times greater than the surface pressure on Earth- that's about 1,300 pounds per square inch, which would crush any human visitors, if they were not fried first.
So Venus had a runaway greenhouse effect. Could earth? Of course we know that it could. The question is, rather, how much must carbon dioxide (or some other climate forcing) increase before a runaway effect occurs?
The paleoclimate record does not provide a case with a climate forcing of the magnitude and speed that will occur if fossil fuels are all burned. Models are nowhere near the stage at which they can predict reliably when major ice sheet disintegration will begin. Nor can we say how close we are to methane hydrate instability. But these are questions of when, not if. If we burn all the fossil fuels, the ice sheets almost surely will melt entirely, with the final sea level rise about 75 metre, with most of that possibly occurring within a time scale of centuries. Methane hydrates are likely to be more extensive and vulnerable now than they were in the early Cenozoic. It is difficult to imagine how the methane hydrates could survive, once the ocean has had time to warm up. In that event a PETM- Paleocene-Eocene Thermal Maximum- like warming could be added on top of the fossil fuel warming.
After the ice is gone, would Earth proceed to the Venus syndrome, a runaway greenhouse effect that would destroy all life on the planet, perhaps permanently? I've come to conclude that if we burn all reserves of oil, gas and coal, there is a substantial chance we will initiate the runaway greenhouse. If we also burn the tar sands and tar shale, I believe the Venus syndrome is a dead certainty.