29 May 2014

Why worry

Andrew Glikson gave us a perfectly good reason to worry. Andrew is an Earth and paleo-climate scientist. He spoke at a public lecture at ANU entitled From the dinosaurs to sapiens : The origin of mass extinctions of species . Now this isn't necessarily happy talk; it's talk of extinctions. I thought there had been 5 mass extinctions (given the book I borrowed called The sixth extinction), but it seems there have been more. Maybe some were mini-mass extinctions. As I explained to Andrew, I am no geologist and some of the earlier talk was reasonably (although not very) concerned with chemistry and geology and the rest and the questions were more so. But I got enough to realise we should worry. Basically he argued this. Following Catastropthism (Couvier) and Uniformitarianism (Hutton, Lyell) we had another paradigm shift, in 1980, when the KT (Cretaceous–Tertiary) Boundary was discovered by father and son team, Luis and Walter Alvarez in rocks near Gubbio in the Apennines. Basically, they found a layer with a high level of iridium (6ppb vs normal 1ppb) but with no plutonium. This means the layer is of extraterrestrial origin but not from a supernova (given no plutonium), thus from an asteroid strike. Subsequent work discovered various craters, mostly hidden by Earth's weathering, especially Chicxulub crater in the Yucatan Peninsula in Mexico. Suffice to say, changed fossil record, 200 finds of the iridium anomalies around the world and a string of other evidence led to this new paradigm being accepted in 2010. Interestingly, Andrew spoke of various impact craters around Australia, including one we've seen, Gosse Bluff, a 24 km diameter crater formed by an asteroid of 5km diameter. He talked of shock morphism and various stony finds, but the essential discussion that followed was on the resulting carbon emissions, interestingly called the carbon winter and subsequent (very lengthy) carbon summer. Think indications of climate change, global warming. The KT impact released ~4,600Gt of carbon, raising atmospheric carbon from ~500ppm to 2,300ppm. Our little experiment in anthropomorphic carbon emissions has released ~560Gt of carbon in the 250 years since the industrial revolution and has raised atmospheric carbon from 280ppm to 401pp. [It's going up ~2.5ppm pa]. Interestingly, it's not primarily the level of carbon but the speed of change that really worried Andrew. The problem is that biology can't compensate; life doesn't evolve so quickly. But the real killer was this diagram above. The X-axis is time: from 20,000BCE through 0 and present to 4,000CE. The Y-axis is temperature, from -4deg to +6deg. Look at this. At 20,000BCE, the temperature is -3deg. Agriculture begins ~8,000BCE, part way along the comfy period when the temperature is 0deg. Average temperature starts cooling, but then the Industrial Revolution comes and the temperature spikes. It's currently ~+0.9deg. For all intents and purposed, the temperature rise is vertical at this scale. A very, very good reason to be worried. Andrew mentioned civilisation collapse in paleo-climatic studies and how they were associated with changes to rivers. He mentioned the IPCC projections of 3-6deg warming by 2100 (yes, Virginia, during the lives of our grandchildren). He highlighted the danger of sudden change and displayed a table of atmospheric carbon and temperature rises in previous mass extinctions (the other graph). Nothing approached 0.9deg in 250 years. His last words were that it's "far more serious than the public has been led to believe". Why worry? Too true, it's probably too late to bother.

Dr Andrew Glikson gave a public lecture at ANU.

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