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Annual Public Lectures Series > Thomas Delworth

Scientists and Journalists:
Getting the Point Across
June 12-16, 2006

Climate Change and the Ocean's Role in the Future of the Planet
Thomas Delworth, Climate Dynamics and Prediction Group Leader, Princeton University/NOAA
Summary of comments from June 15

Thomas L. Delworth, group leader for the Climate Dynamics and Prediction Group of the Geophysical Fluid Dynamics Laboratory/NOAA in Princeton, New Jersey, lectured at the University of Rhode Island's Graduate School of Oceanography on the important role of the ocean as it relates to global climate change on June 15, 2006. By building computer-generated models of the Earth's climate system, Delworth and his fellow group members attempt to improve future climate predictions and understand climate change trends.

After creating global climate computer models, there are several areas the group focuses on. The most significant of these focus points are El Niño and its role in global climate, global climate change, development of ocean models, and the development of hurricane models.

Delworth explained that the ocean's reactions to increasing greenhouse gases and aerosols will play a major role in the earth's future global climate. The ocean consumes 70 percent of the planet's surface and essentially creates a massive reservoir of heat. The inherent thermal characteristics of the ocean mean that it warms and cools very slowly when compared to air temperature. According to models created by Delworth and his group, the ocean will take hundreds of years to fully absorb temperature increases taking place today.

Three characteristics of the ocean are important to consider when evaluating the role it will play in global climate change. First, the ocean has what Delworth refers to as "a mind of its own." The natural inconsistency of the ocean can have a major impact on climate. Oceanic temperature changes occur on a yearly basis. In the Pacific, these changes have the potential to cause droughts in North America, while Atlantic changes result in an increased likelihood of hurricanes.

There is ongoing controversy surrounding the recent upswing in hurricanes which, Delworth stated, cannot be resolved for years. While some scientists argue that the increase is solely a product of the natural variability of the ocean, others suggest that it is a direct response to global warming. The models generated up to this point are not yet sophisticated enough to determine the answer. If global warming is eventually determined to be the dominant factor behind the increase in hurricanes, Delworth said, "the implications would be enormous."

The second of these characteristics is the "buffer" concept. By absorbing heat, the ocean slows the rate of atmospheric warming. Although the atmosphere responds very quickly to radiation increases produced by humans, it also must respond to the ocean and its absorption, which slows down the atmosphere's process. Changes in the ocean occur much more slowly than in the atmosphere, mostly due to large thermal inertia and relatively slow movement. While this is considered a positive aspect in some ways, there is also a down side.

In the last 100 years, the temperature of the atmosphere has increased a relative two degrees. The surface temperature of the ocean has increased one degree while the deep ocean has gone up only one-tenth of a degree. Models generated by the group show that it will take the deep ocean thousands of years to fully equilibrate with surface temperatures.

The third important factor to consider when discussing the ocean's role in global warming is the response it has to human-induced temperature increases. Significant potential changes produced by the group's models in large-scale ocean circulation have resulted in three theories: an Atlantic conveyer belt theory weakening; Pacific tropical circulation; and changes in the southern ocean circulation. Thermal changes predicted will result in the reduction of sea ice and a rise in sea levels. The impact of a conveyor belt weakening, if realized, will cause moderate regional warming and Pacific tropical circulation will be a crucial factor concerning the possibility of North American droughts. Potential changes in southern ocean circulation will be also important factors regarding the uptake of heat and carbon dioxide.

In closing, Delworth explained that the ocean's natural variability really is key in the role it will play in global warming. It also has a crucial role in how the planet responds to increasing greenhouse gases and rate at which temperatures increase and decrease. The response of the ocean to altered climate change will also play a vital role. Delworth also stated that all three of these factors are closely intertwined with each other.

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December 4, 2007