The IPCC (the UN Intergovernmental Panel on Climate Change) has been studying climate change since 1990. Its fourth assessment is being published in 2007, and Chapter 1 is available.¹² It calls the evidence of climate warming "unequivocal" and is 90 percent confident that human activity is causing it – in effect strengthening earlier IPCC assessments. It confirms a continuing rise in CO2 and methane emissions, and in their concentration in the atmosphere. It offers different scenarios leading to global surface temperature warming of 1.1 degrees C to 6.4 degrees C (2 to 11.5 degrees F) in this century, with larger increases in the Arctic.

Recent sea level rise works out to about 0.31 meters (12 inches) a century, and the scenarios lead to a rise of 0.18 to 0.59 meters (7 to 23 inches) by 2100, though the IPCC cannot exclude a "substantially higher" rise, because the panel has not had time to absorb the new information about the movement of the great ice sheets.

Some scientists are talking of a one meter rise in world sea levels in this century, accelerating later. This reflects the new discoveries about the ice sheets and the realization that past climate changes have occurred much more swiftly than we had thought. There is a respectable theory that there was an immense flood out the Gulf of St. Lawrence in the early Holocene when the ice dams from the melting Laurentian ice shield gave way and released the stored water. This is said to tie in with evidence of a sudden freshening of the North Atlantic, which affected ocean circulation patterns.

The IPCC focuses on this century, and it is a conservative consensus forum. It notes that "... anthropogenic warming and sea level rise would continue for centuries... even if greenhouse gas concentrations were to be stabilized." We must plan both for the long term and for the likelihood - which is getting likelier - that things will happen faster than the IPCC predictions.

12. IPCC, Climate Change 2007: The Physical Science Basis. "Summary for Policymakers." (2-2-07) www.ipcc.ch/SPM2feb07.pdf.

The above is taken from a forthcoming NPG Forum paper by Lindsey Grant titled, "The Age of Overshoot."