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Global climate changes as forecast by Goddard Institute for Space Studies three-dimensional model.

Article link

Hansen, J., I. Fung, A. Lacis, D. Rind, S. Lebedeff, R. Ruedy, G. Russell and P. Stone, 1988. Global climate changes as forecast by Goddard Institute for Space Studies three-dimensional model. Journal of Geophysical Research. Vol. 93, pgs. 9341-9364.

Essay about this article

In 1988 Hansen, et al. published the results of their latest three-dimensional climate model, GISS Model II. In an exercise later taken up by the IPCC in its reports, the team calculated the global temperature changes over a one hundred year period beginning in 1958 under three very different emissions scenarios. Scenario A keeps trace gas growth rates at about 1.5 percent of emissions, so the net greenhouse forcing continues to increase exponentially; scenario B decreases growth rates, keeping forcing at its current levels; while scenario C incorporates drastic reductions in trace gas growth rates before the year 2000. The three scenarios are then run in three model configurations, one for CO2 forcing only; a second for CO2 and other trace gases, including H2O, CH4, and CFCs; and a third that also included stratospheric aerosol forcings.

The model results suggested that global greenhouse warming would soon rise above the level of natural climate variability. This would be most detectable as an increase of global mean surface air temperature of about 0.4 oC over several years and would constitute a cause and effect relationship between CO2 and climate, or in the vernacular, a “smoking gun.” The group also predicted that warming would be most noticeable over the interiors of continents, over low-latitude oceans, and in high latitudes, especially over ice caps, with an increase in the frequency of severe storms. Model results indicated that by the year 2000 the “man in the street” should be able to notice increased temperatures resulting from global warming. By the year 2050 an increase in the occurrence of extreme heat waves should be clearly noticeable, with the number of days with temperatures at or above 95 oF increasing dramatically.

Model deficiencies include the coarseness of the grid spacing, uncertainties about equilibrium sensitivity to climate forcing, assumptions regarding heat uptake and transport by the ocean, and the treatment of clouds which could either provide positive or negative feedback effects. Hansen, et al. issued an urgent call for better global measurements and models to meet the needs for improved climate assessment and prediction. Such efforts were cast as important steps to reduce the potential risks and costs of climate change to support a global effort to reduce the human influence on climate.

In 1988, James Hansen’ testimony before the U.S. Senate was featured on the front page of the New York Times. He reported that, at least to his satisfaction, he had seen the "signal" in the climate noise and we were in for an unprecedented global warming, perhaps in the form of a runaway greenhouse effect. Hansen later revised his remarks, but his statement remains the starting point of recent widespread concerns over global warming. The question was no longer whether human agency had contributed to global change. That question has been answered in the affirmative long ago. The more significant questions involved the magnitude and consequences of the global changes being caused by a combination of natural forces and increasing anthropogenic stresses.


Discussion Questions

a. This model results suggested that global greenhouse warming would soon rise above the level of natural climate variability. Has it?


b. How have scientists since this article was written worked to address model deficiencies and uncertainties?


c. This article, Hansen’ testimony before the U.S. Senate, the hot summer of 1988, and a front page story in the New York Times are all interrelated. Discuss how public awareness grew after this.



Reference


Global Warming Has Begun, Expert Tells Senate. New York Times (June 24, 1988), 1.





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