(3BL Media/Justmeans) - James Hansen came to Rochester, NY to give the keynote address at the Sierra Club’s Annual Forum. The title of his talk was “Climate Change and Energy: How Can Young People Take Ownership of Their Future?” It was the culmination of several talks he had given while in town.
Not surprisingly, Hansen began by talking about how last year was the warmest on record and how based on the data recorded so far, this year is well on its way to being warmer. He described the many sources of data corroborating the phenomenon like GRACE satellite data that shows Greenland and Antarctica rapidly losing mass, and the 3,200 Argo floats that have been sampling temperatures in the top 2 km of the ocean. These show the increase in ocean temperature. Though we have had a “pause,” for about a decade, in which the rate of cooling had declined, the recent data shows the resumption of the earlier trend. The pause has been explained by Drew Shindell (a former colleague of Hansen’s) as being due to the short term impact of aerosols, among the explanations that have been put forward.
Hansen’s biggest concerns going forward are two irreversible trends. The first is the extinction of species, the rate of which is estimated to take out anywhere from 25 to 50 per cent of all species living on Earth today, by the end of the century. While climate change is not the only factor driving these extinctions, it exacerbates many of the other stresses, such as loss of habitat and chemical pollutions, which are also primarily human induced.
The second concern is disintegration of the great ice sheets. New satellite data confirms that the ice sheets of Greenland and Antarctica are losing mass at an accelerating pace. In the case of Western Antarctica, that rate of ice loss has been increasing by 25 billion tons per year per year.
He described a newly discovered positive feedback loop to add to the albedo loss, and the release of methane from melting permafrost. This one has to do with the circumpolar circulation of water in the ocean. As the glaciers melt and discharge large amounts of fresh water into the ocean it cause the cold water to sink more slowly which has the effect of causing sea ice to expand. This, in turn, releases heat that is melting the ice shelves that act as buttresses to the great ice sheets. Should the ice sheets disintegrate, ocean levels will rise by huge amounts. Even if temperatures are maintained at the 2 degrees C mark that the IPCC is currently targeting, we could still see sea levels 5-9 meters above their current levels, enough to wipe out virtually all coastal cities.