Paul Mayewski's lecture, Abrupt Climate Change and Extreme Events, suggests that the doubling of annual melting days we've seen over the last five years in the Arctic is a sign of an abrupt climate change.
The IPCC report ignored abrupt change and multiple abrupt change in favor of linear change models. Why?
Because the first truly well-defined abrupt climate change event that has occurred in the last 100 years is Arctic warming.
In other words, scientists hadn't had enough time to analyze it.
These are the things that can trigger a fast change
- Greenhouse gases (CO2, CH3, N2O)
- Thermohaline (for example by adding fresh water)
- Ice Dynamics
- Solar variability (which changes ozone level)
Because of Antarctica's lost ozone and because the continent is very high, the westerlies [red curved arrow] are stronger and further south, while closer to the equator the atmosphere has warmed. This traps more cold air, reduces north-south exchange [small blue arrow in lower right] and also drags colder water to the surface in the Southern Ocean.
In effect, the Antarctic ozone hole is helping to protect Antarctica, not the coastal edges but the rest of it. Wind speeds are increasing on the order of 15 to 20% in the southern ocean.
The big news, however, came from a new technique to analyze ice cores at far higher resolution using laser ablation. In the transition from the last ice age to the Holocene they found a doubling in the length of Summer. The abrupt change 11,650 years ago at Holocene onset had a similar abrupt change in Summer, measured as annual melting days, as the last 5 years in the Arctic.
The bottom line is that the magnitude and speed of change that we have just experienced is similar although less aerial extent to the transition from the last ice age into modern climate. [emphasis mine]
About that transition from the ice age comparison....
... the latest study of climate sensitivity to increased atmospheric greenhouse gas levels, which doubled the estimate of global temperatures rise for a doubling of pre-Industrial greenhouse gas concentrations, admitted that climate scientists had erred by calculating the measure previously from the evidence of temperatures rises when coming out of a glaciation. Calculating from the recent Holocene climate regime as the starting-point gave the new, believable, and catastrophic estimates. [emphasis mine]