Kevin
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 Posted: Sun Oct 02, 2005 2:09 pm Post subject: U.S. EPA Reports Large Increase in Strong Hurricances, etc. |
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As reported by EPA at:
http://yosemite.epa.gov/oar/globalwarming.nsf/content/newsandeventsScienceandPolicyNews.html
Study Finds Large Increase in Strong Hurricanes
The number of Category 4 and 5 hurricanes has increased by 80 percent worldwide during the past 35 years, according to a study in the 16 September 2005 issue of Science (vol. 309, pp. 1844-1846). Hurricanes in these two highest storm categories, with winds of 135 miles per hour or greater, now account for roughly 35 percent of all hurricanes, up from around 20 percent in the 1970s.
The trend toward more-frequent strong hurricanes occurred during a period when sea-surface temperatures rose globally, with increases ranging from 0.5 to 1 degree Fahrenheit during the hurricane season. But the researchers found no global long-term trend in the overall number of hurricanes, and the total number of hurricanes per year has actually declined in most of the world since the 1990s, at a time when sea-surface temperatures have risen the most. Furthermore there was no increase in the intensity of Category 4 and 5 hurricanes, just an increase in their number.
The relationship between sea-surface temperatures and hurricane behavior is complex, and the authors note that attributing the trends to global warming would require “a longer global data record and, especially, a deeper understanding of the role of hurricanes” in the climate system.
Researchers Find Evidence of Human-Produced Warming in Oceans
A new study has found a “compelling agreement” between observed changes in ocean temperatures since 1960 and the changes simulated by two climate models under rising atmospheric concentrations of greenhouse gases. In all of the world’s ocean basins, the warming predicted by the models for the upper 700 meters (2,300 feet) of the ocean corresponded to actual measurements obtained at sea, with confidence exceeding 95 percent.
“The immediate conclusion is that human influences are largely responsible for the warming signal,” the authors write. “The statistical significance of these results is far too strong to be merely dismissed, and should wipe out much of the uncertainty about the reality of global warming,” said lead author Tim Barnett of the Scripps Institution of Oceanography.
Barnett and his colleagues used one of the models to explore whether the climate’s own natural variability could account for the warming oceans, or whether the warming could be explained by other natural factors such as solar variability and volcanic eruptions. In neither case could the model replicate the warming that has been observed in the real world. The changes were simply too strong to be explained by natural causes.
The authors argue that since these two climate models have been shown to simulate past changes accurately, their predictions for future changes, at least out to the next 20-30 years, “are apt to be reasonably good.” The study was published in the June 2, 2005 online version of the journal Science.
Energy Imbalance Said to Confirm Greenhouse Gases’ Contribution to Warming
Precise measurements of temperature within the ocean confirm that the Earth is absorbing more energy from sunlight than it emits back to space, providing perhaps the strongest evidence to date that rising concentrations of greenhouse gases and other pollutants are the primary cause of the current global warming trend. The findings are reported in the April 28, 2005 issue of the journal Science.
“The magnitude of the imbalance agrees with what we calculated using known climate forcing agents, which are dominated by increasing human-made greenhouse gases,” said lead author James Hansen, director of the NASA Goddard Institute for Space Studies.
The average energy imbalance amounts to 0.85 + 0.15 Watts per square meter, largely reflecting the amount of heat soaked up and stored by the world’s oceans. The imbalance implies that the global temperature takes decades to fully respond to changes in greenhouse gases, because the ocean’s thermal inertia acts as a brake on warming. It also implies that the Earth would warm by about 1 degree Fahrenheit over the course of the current century even if greenhouse gas concentrations were held constant at today’s levels, because the oceans will continue to absorb energy, increase in temperature, and warm the atmosphere until the energy coming in from the sun and the energy emitted out to space are in balance. In addition, the new findings imply that sea level rise and the disintegration of ice sheets are likely to increase.
The authors note that the increasing heat storage in the ocean cannot be explained by natural fluctuations. Under natural conditions, the ocean would release its heat more slowly only if its surface cools (if, for example, cool water from the ocean depths rose to the surface). But the ocean’s surface has been warming, suggesting that the warming climate is the more viable explanation for the phenomenon.
Climate May Be More Sensitive Than Previously Thought
Doubling the concentration of carbon dioxide in the atmosphere could cause the Earth to warm by less than 2ºC (3.6ºF) or more than 11ºC (19.8ºF), according to a new study based on more than 2,500 climate model simulations carried out on thousands of personal computers. The study, by a team of British scientists, aimed to determine the full range of the climate’s sensitivity (the amount by which the global temperature changes in response to a given increase in greenhouse gases) by testing multiple versions of the same climate model. Each version differed from the others in several ways, allowing the researchers to explore the effects of a range of uncertainties in how the model represents the atmosphere.
The sensitivities in the different versions ranged from less than 2ºC to more than 11ºC, more than twice the 2-5ºC range estimated by the Intergovernmental Panel on Climate Change in its most recent assessments. Both the low end and the high end of the new range should be considered plausible, the researchers say, because the model versions that produced those sensitivities also produced realistic simulations of past climate.
The new findings come from the world’s largest climate modeling experiment, climateprediction.net , which runs models on thousands of personal computers. More than 95,000 people from 150 countries participate in the project, including more than 24,000 in the United States. The software incorporating the climate model runs in the background when the computer is idle.
The results of the study are published in the 27 January 2005 issue of Nature (vol. 433, pp. 403-406). |
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