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Annual Public Lectures Series > Ruth Curry
Scientists and Journalists:
Getting the Point Across
June 11-15, 2007
Ocean Circulation and Climate Change: A Chilling Combination?
Ruth Curry, Research Specialist, Woods Hole Oceanographic Institution
Summary of comments from June 11
There is no longer a question about whether the Earth is warming, said Ruth Curry, research specialist at Woods Hole Oceanographic Institution. "It is a fact."
In Curry's public lecture, "Ocean Circulation and Climate Change: A Chilling Combination?" on Monday, June 11, 2007, she noted that scientists have reliable measurements of the Earth's climate from 140 years of direct temperature readings; tree rings that chronicle climatic changes over the last thousand years; and ice cores that reveal the climate of hundreds of thousands of years ago.
The lecture was the first in Metcalf Institute's annual public lecture series at the URI Graduate School of Oceanography.
Curry explained that these climate records show that climate changes have occurred in the past on about a 100,000 cycle, due to wobbles in the Earth's orbit around the Sun and a resulting increase in solar radiation reaching the Earth. In contrast, instruments in space have not recorded an increase in solar radiation that could account for the current warming. Instead, greenhouse gases, especially carbon dioxide, have caused the Earth to retain more of the energy delivered by solar radiation.
The ocean "conveyer belt," which pushes warm water poleward along the ocean's surface and pushes cold water toward the Equator along the ocean floor, regulates the world's climate to a great degree. For instance, Western Europe's warm winters relative to its latitude are due to air absorbing heat from the warm currents flowing northward in the area. However, because of warming temperatures – one degree Celsius in the last century – ice at the poles has been shrinking and thinning.
Ice reflects solar radiation back to outer space, while land absorbs and is warmed by solar radiation; therefore, the melting of ice actually accelerates global warming. This feedback cycle, in which one change triggers another change that amplifies the overall trend, has occurred before. Curry noted that scientists are especially concerned about climate change because they have not observed natural systems "putting on the brakes," or developing a moderating response that neutralizes global warming.
The rate of sea level rise is poorly understood and not really predictable, Curry said. Conservative estimates put sea level rise at about 3 feet within the next century. However, scientists have observed floating ice shelves, like those around Greenland, disintegrating and becoming unstable. It is not known whether these ice sheets and shelves will melt incrementally or in dramatic events, and Curry believes that ice response could be the most likely candidate to cause rapid climate change. The Greenland Ice Sheet, Curry said, is so vast that its complete melting could cause sea level in the entire world to rise by 7 meters – and the Antarctic Ice Sheet is even larger than that.
Species that depend on ice, like the polar bear, are not able to adapt to their changing environment. In the oceans – which absorb more solar radiation than the land and therefore are even more than 1 degree Celsius warmer – ecosystems are also unable to keep pace with the changing temperature. Corals are unable to support the symbiotic organism zooxanthellae in warm temperatures, and die without their presence. Even where zooxanthellae are still able to survive, the changing chemistry of the oceans – with more carbon dioxide absorbed and increasing acidity – dissolves the calcium carbonate with which corals build themselves. When thinking of this reaction, Curry suggested, think about the interaction of baking soda, or sodium bicarbonate, and vinegar, an acid.
Freshwater resources will become scarcer, hurricanes will become more intense, and the sea level will rise quickly as a result of climate change, Curry said. Changing our sources of energy from carbon-burning ones to alternative energies is necessary to stem climate change, and even small commitments are important. "We might not be able to get a 20-percent reduction in greenhouse gas emissions by 2010," she said, "but a five percent reduction still helps." She said she had noticed both examples of clear, un-hyped reporting and exaggerated, sensational writing, but felt that when scientists and journalists "team up," the public experiences an epiphany about climate change.
Curry took questions from the more-than-full house, including one from Chelsea Wald, a fellow in the Annual Workshop for Journalists program, run by the Metcalf Institute for Marine and Environmental Reporting. Wald noted that she experiences people localizing the climate change phenomenon to a great degree, saying, for instance, "It sure was a warm winter! Global warming must be here." Wald wondered whether this localizing or small-scaling of climate change could send the wrong message; for instance, an especially cold winter could cause people to believe that warming is no longer a problem. Curry responded that "weather is not climate," and that it is important to remind people of the larger picture, both geographically and historically. Scientists look for climate change not in local weather events, but in long-term, geographically-broad data sets.
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December 4, 2007