Climate Science – Room 101

A warmer atmosphere can hold more moisture and – as atmospheric physicists have been warning us for over 50 years now – this will result in more frequent and more extreme weather events of all kinds. A recent opinion poll in the USA suggested that people who were skeptical of scientists are being convinced by the evidence of their own eyes. About time too, people; welcome to reality! From 350.org: A big (possibly historic) winter storm just hit the Northeast of the United States — and climate change played a role in making it stronger. Unusually warm ocean surface temperatures put more energy and more moisture in the storm, making a mess of roads and power grids. This graph shows how climate change is making big storms more likely. Still not convinced? How about this from James Hansen (et al) last July [PDF]: The greatest barrier to public recognition of human-made climate change is probably the natural variability of local climate. How can a person discern long-term climate change, given the notorious variability of local weather and climate from day to day and year to year?…

Hansen et al (2012) Figure 2

We illustrate variability of seasonal temperature in units of standard deviation (σ), including comparison with the normal distribution (“bell curve”) that the lay public may appreciate. The probability distribution (frequency of occurrence) of local summer-mean temperature anomalies was close to the normal distribution in the 1950s, 1960s and 1970s in both hemispheres (Fig. 2). However, in each subsequent decade the distribution shifted toward more positive anomalies, with the positive tail (hot outliers) of the distribution shifting the most. Figure 2. Temperature anomaly distribution: The frequency of occurrence (vertical axis) of local temperature anomalies (relative to 1951-1980 mean) in units of local standard deviation (horizontal axis). Area under each curve is unity. Image credit: NASA/GISS… Yet the distribution of seasonal temperature anomalies (Fig. 2) also reveals that a significant portion (about 15 percent) of the anomalies are still negative, corresponding to summer-mean temperatures cooler than the average 1951-1980 climate. Thus people should not be surprised by the occasional season that is unusually cool. Cool anomalies as extreme as -2σ still occur, because the anomaly distribution has broadened as well as moved to the right. In other words, our climate now encompasses greater extremes. What then should we learn from all this analysis of historical weather data? We should not be surprised by the storm that has just hit the NE of the USA.

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