Talk:Tipping point (climatology)

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This article misunderstands the meaning of tipping point, at least as its used by Hansen or Lenton. A tipping point is *not* when we get to a CO2 level that causes more CO2 to be emitted. Its something like when we get to a T change from CO2 that we are committed to melting Greenland. In fact the concept is very hard to define exactly (I would argue that no-one has done so: it remains a vague concept more useful for generating scary headlines than anythng else). See-also [1]. Or [2] William M. Connolley (talk) 21:25, 9 April 2008 (UTC)

Agree. Hansen seems to like the "small cap" warm weather sea ice removal temperature. Excerpt:

Early energy balance climate models revealed a “small ice cap instability” at the pole (Budyko, 1969; North, 1984), which implied that, once sea ice retreated to a critical latitude, all remaining ice would be lost rapidly without additional forcing. This instability disappears in climate models with a seasonal cycle of radiation and realistic dynamical energy transports, but a vestige remains: the snow/ice albedo feedback makes sea ice cover in summer and fall sensitive to moderate increase of climate forcings. The Arctic was ice-free in the warm season during the Middle Pliocene when global temperature was only 2-3�C warmer than today (Crowley, 1996; Dowsett et al., 1996). Satellite data indicate a rapid decline, �9%/decade, in perennial Arctic sea ice since 1978 (Comiso, 2002), raising the question of whether the Arctic has reached a “tipping point” leading inevitably to loss of all warm season sea ice (Lindsay and Zhang, 2005). Indeed, some experts suggest that “. . . there seem to be few, if any, processes or feedbacks that are capable of altering the trajectory toward this ‘super interglacial’ state” free of summer sea ice (Overpeck et al., 2005).

from "Dangerous human-made interference with climate: a GISS modelE study" Hansen, et al. --DHeyward (talk) 22:38, 9 April 2008 (UTC)