Manabe, Syukuro (1931-)

Pivotal Model

Smagorinsky and Manabe put into their model details that would be influential for the discovery of global warming. Their model accounted for the way rain fell on the surface and evaporated, how radiation passing through the atmosphere was impeded, not only by water vapor but also by ozone and carbon dioxide gas (CO2), how the air exchanged water and heat with simplified ocean, land, and ice surfaces, and much more. Manabe had always been interested in the effects of CO2, and the impact of CO2 on the future climate. Manabes interest stemmed from the consideration that the gas at its current level was a significant factor in balancing the planet's heat. When Fritz Moller theorized that even mild perturbations and human actions could cause a global catastrophe, Manabe decided to work on a model that might account for how the climate system might change. He came to the conclusion that the entire atmosphere had to be studied as a tightly interacting system. In his model, Manabe took full account of water in all its forms. It included the feedback between the air's temperature and the amount of moisture the air would hold. In particular, Manabe calculated the way rising columns of moisture-laden air conveyed heat from the surface into the upper atmosphere.

In 1967, Manabe used a one-dimensional model to test what would happen if the level of CO2 changed. He targeted the climates “sensitivity,” a feature that would eventually become a central preoccupation of modelers. Together with his group, he set out to calculate how much the variation of incoming and outgoing radiation would alter temperature. The answer they reached was that if the levels of CO2 doubled by the end of the century, as seemed possible, global temperature would rise roughly 3–4 degrees F (around 2 degrees C). This was the first time a greenhouse warming calculation included enough of the essential factors, including the correct estimate for water vapor feedback, to seem reasonable to many scientists. Many of them who were to play an influential role in global warming debates, such as Wallace Broecker, recalled that it was these data that made them embrace research into the phenomenon.

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