Voorpagina Hansen 1981 (Science)
Voorpagina Hansen 1981 (Science)
They got 10 pages in Science, which is a lot, but in it they cover radiation balance, 1D and 3D modelling, climate sensitivity, the main feedbacks (water vapour, lapse rate, clouds, ice- and vegetation albedo); solar and volcanic forcing; the uncertainties of aerosol forcings; and ocean heat uptake. Obviously climate science was a mature field even then: the concepts and conclusions have not changed all that much. Hansen et al clearly indicate what was well known (all of which still stands today) and what was uncertain.

Next they attribute global mean temperature trend 1880-1980 to CO2, volcanic and solar forcing. Most interestingly, Fig.6 (below) gives a projection for the global mean temperature up to 2100. At a time when the northern hemisphere was cooling and the global mean temperature still below the values of the early 1940s, they confidently predicted a rise in temperature due to increasing CO2 emissions. They assume that no action will be taken before the global warming signal will be significant in the late 1990s, so the different energy-use scenarios only start diverging after that.
Fig.6 of Hansen et al, Science, 1981 giving projections of the global mean temperature compared to 1951-1980 under different energy use scenarios using the climate models available at the time. The observations are based on land stations only and smoothed with a 5-yr running mean.
Fig.6 of Hansen et al, Science, 1981 giving projections of the global mean temperature compared to 1951-1980 under different energy use scenarios using the climate models available at the time. The observations are based on land stations only and smoothed with a 5-yr running mean.

The first 31 years of this projection are thus relatively well-defined and can now be compared to the observations. We used the GISS Land-Ocean Index that uses SST over the oceans (the original one interpolated from island stations) and overlaid the graph from the KNMI Climate Explorer on the lower left-hand corner of their Fig.6.
Detail of Fig.6 (a bit vague due to the magnification) overlaid with the observed global mean temperature anomalies from GISS, using SST over the oceans. The purple line denotes a 10-yr running mean.
Detail of Fig.6 (a bit vague due to the magnification) overlaid with the observed global mean temperature anomalies from GISS, using SST over the oceans. The purple line denotes a 10-yr running mean.

Given the many uncertainties at the time, notably the role of aerosols, the agreement is very good indeed. They only underestimated the observed trend by about 30%, similar or better in magnitude than the CMIP5 models over the same period (although these tend to overestimate the trend, still mainly due to problems related to aerosols).

To conclude, a projection from 1981 for rising temperatures in a major science journal, at a time that the temperature rise was not yet obvious in the observations, has been found to agree well with the observations since then, underestimating the observed trend by about 30%, and easily beating naive predictions of no-change or a linear continuation of trends. It is also a nice example of a statement based on theory that could be falsified and up to now has withstood the test. The “global warming hypothesis” has been developed according to the principles of sound science.

References
J. Hansen, D. Johnson, A. Lacis, S. Lebedeff, P. Lee, D. Rind, and G. Russell, "Climate Impact of Increasing Atmospheric Carbon Dioxide", Science, vol. 213, 1981, pp. 957-966. DOI.

This article was published originally on RealClimate on 2 April 2012.