Michael Crichton’s State of Confusion

Crichton next raises the apparently unrecognised (by the lawyer character at least) fact that the interior of Antarctica is cooling (p196), an issue discussed in another post (Antarctica cooling, global warming?). This is more or less correct (given the obvious uncertainties in long term data from the continental interior), but analogously to the example above, local cooling does not contradict global warming.

Next, and slightly more troubling, we have some rather misleading and selective recollection regarding Jim Hansen’s testimony to congress in 1988. “Dr. Hansen overestimated [global warming] by 300 percent” (p247). Hansen’s testimony did indeed lead to a big increase in awareness of global warming as a issue, but not because he exaggerated the problem by 300%. In a paper published soon after that testimony, Hansen et al, 1988 presented three model simulations for different scenarios for the growth in trace gases and other forcings (see figure). Scenario A had exponentially increasing CO2, Scenario B had a more modest Business-as-usual assumption, and Scenario C had no further increases in CO2 after the year 2000. Both scenarios B and C assumed a large volcanic eruption in 1995. Rightly, the authors did not assume that they knew what path the carbon dioxide emissions would take, and so presented a spectrum of results. The scenario that ended up being closest to the real path of forcings growth was scenario B, with the difference that Mt. Pinatubo erupted in 1991, not 1995. The temperature change for the decade under this scenario was very close to the actual 0.11 C/decade observed (as can be seen in the figure). So given a good estimate of the forcings, the model did a reasonable job. In fact in his testimony, Hansen ONLY showed results from scenario B, and stated clearly that it was the most probable scenario. The ‘300 percent’ error claim comes from noted climate skeptic Patrick Michaels who in testimony in congress in 1998 deleted the bottom two curves in order to give the impression that the models were unreliable.

Dr Hansen is further quoted (a little out-of-context) saying: “The forcings that drive long term climate change are not known with an accuracy sufficient to define future climate change”. Given the discussion above it is clear that without good estimates of the actual forcings, the differences in the model projections can be large. It is widely accepted that exact prediction of what will happen to climate in 50 or 100 years is impossible. Much of the future is of course unknowable. A new energy source could replace fossil fuels, governments could control emissions, or maybe a series of huge volcanoes will erupt. Therefore it is much more sensible to ask, what would climate be like if you doubled CO2? or if this or that scenario occurred. These are much better defined questions. Hansen’s quote is often taken to imply that models are so unreliable they are useless in helping assess the issue. In fact it is the opposite – Hansen is actually claiming that the uncertainty in models (for instance, in the climate sensitivity) is now less than the uncertainty in the emissions scenarios (i.e. it is the uncertainty in the forcings, that drives the uncertainty in the projections).

Continuing to p315, it is claimed that “in the 1970’s all the climate scientists believed an ice age was coming” (and, as described on p563, the MIT academic apparently still thinks so). However, this is not an accurate statement and William Connolley’s pages on the subject are an illuminating read for those wanting more details.

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