The latest analysis of temperature anomalies by James Hansen and his associates at NASA’s Goddard Institute for Space Studies is an important read for those preparing lectures on climate science for fall classes. Among the key take-aways from the analysis:
- Global temperature in the past decade was about 0.8°C warmer than at the beginning of the 20th century (1880-1920 mean). Two-thirds of the warming has occurred since 1975;
- 2010 is likely to be the warmest year in the period of recorded instrumental data, or at least in a statistical dead heat with 2005;
- Because of the underlying warming trend (separated from factors e.g. ENSO), 2012-2014 will probably bring a new record temperature;
- Monthly temperature anomalies are typically 1.5 to 2 times greater than seasonal anomalies, and daily weather fluctuations are even much larger than global mean warming. As Hansen, et al. suggests, given the fact that the public’s perceptions of climate change are affected by recent weather anomalies, it’s not surprising that anomalies such as the unusually cold weather snap this winter in North America, would substantially impact those perceptions. Incidentally, increasing carbon dioxide causes the stratosphere to cool, in turn causing on average a stronger polar jet stream and thus a tendency for a more positive Arctic Oscillation, the primary factor explaining the cold anomaly this winter in North America, though its saliency was stronger than this factor alone;
- Temperature trends are particularly noteworthy because they are taking place at a time of minimum solar irradiance;
- The assertion of climate change denialists that temperatures haven’t increased since 1998, or were essentially flat during the 1990s is contradicted by the data. “There has been no reduction in the global warming trend of 0.15-0.20°C/decade that began in the late 1970s.”
Hansen’s careful analysis also includes some excellent graphs for use in Power Point presentations, as well as a very extensive discussion of how to adjust for factors e.g. ENSO and the urban heat island effect. It also includes an excellent bibliography of additional readings for students wishing to absorb themselves further in the science.