COHERENT AND CONVERGENT EVIDENCE
In my class at Michigan I talk about coherent and convergent evidence of global warming. Observations are at the forefront of this argument. There is evidence in the physical climate system; there is evidence in ecosystems. If you take a single set of observations and examine them in isolation, then normally there are several possibilities of how the observations can be explained. However, if you have numerous sets of independent observations, then it is possible to examine patterns of behavior between them. These patterns are useful in determining cause and effect-- identifying links.
The direct measurements of global warming are, of course, temperature. As widely reported, 2006 was another warm year in a series of warm years. The National Climatic Data Center reports on the state of the climate
each year . The figure below from--The Climate of 2006 "Annual Report" shows the difference, the anomaly, between the annual averaged temperature in 2006 and an average calculated from 1961 to 1990. Figure 1.
2006 Annual Temperature Anomaly.
Most striking is that 2006 is warmer over virtually the entire planet. This has been true year after year for the last decade. If this warming was due to dynamic variability, then intuition would suggest more of a balance between warmer and cooler areas.
"Climate Change 2007" reports that the signal of warming can be found not only at the surface, but in the middle troposphere, the ocean, and changes of snow cover, glaciers, sea ice and ice sheets. All of this is consistent with a warming planet. The National Oceanographic Data Center
provides reports of the warming ocean. A favorite paper of mine by Tim Barnett and co-workers in the July 8, 2005 "Science"
convincingly attributes the oceanic warming to greenhouse gas increases--to humans. They show how scientists define fingerprints
based on patterns of behavior. Fingerprinting
and identification of the warming signals in several independently measured parameters are at the foundation of the coherent and convergent determination of global warming.