July 31, 2006

Climate Scientist Hansen

Here are a few gleanings from the work of NASA's leading climate scientist James Hansen:

A global tipping point will be reached in 10 years if levels of greenhouse gases like methane and CO2 are not reduced. Global warming at this point becomes unstoppable. He claims that the tipping point (also known as the runaway effect) is upon us, and that if in 10 years the human population is unable to reduce greenhouse gases, that the oceans might rise as much as 10 feet by 2100.

Global warming is 1 to 1.4 °F in the past century, and about 0.5 °F or more in the last 25 years.

Climate sensitivity to CO2 doubling is 5.4 ± 1.8 °F (Under 'business as usual' this will occur by the end of the century).

Some "greenhouse skeptics" subvert the scientific process, ceasing to act as objective scientists, rather presenting only one side, as if they were lawyers hired to defend a particular viewpoint.

In 2000 he authored a paper called Global warming in the twenty-first century: an alternative scenario in which he presents a more optimistic way of dealing with global warming focusing on non-CO2 gases in the short run, giving more time to make reductions in fossil fuel emissions. This is a result both of the fact that CO2 is responsible for a minority of greenhouse gas warming, and because fossil fuels also emit climate-cooling aerosols which offset the effect of CO2. From the paper,

Thus, assuming only that our estimates are approximately correct, we assert that the processes producing the non-CO2 GHGs have been the primary drive for climate change in the past century.

In 2004 he wrote a paper called Defusing the global warming time bomb, containing:

At present, our most accurate knowledge about climate sensitivity is based on data from the earth’s history, and this evidence reveals that small forces, maintained long enough, can cause large climate change.

Human-made forces, especially greenhouse gases, soot and other small particles, now exceed natural forces, and the world has begun to warm at a rate predicted by climate models.

The stability of the great ice sheets on Greenland and Antarctica and the need to preserve global coastlines set a low limit on the global warming that will constitute “dangerous anthropogenic interference” with climate.

Halting global warming requires urgent, unprecedented international cooperation, but the needed actions are feasible and have additional benefits for human health, agriculture and the environment.


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