In addition to the effects from temperature increases, Caldeira discusses how the chemistry of the oceans would be altered. Carbon dioxide dissolves in water to produce carbonic acid—a corrosive agent that would eat away shells and skeletal materials of marine organisms. This ocean acidity could kill off entire species, including those vital to the bottom of the planet's food chain. Caldeira emphasizes that "to find comparable events in Earth history, we need to look back tens of millions of years to rare catastrophic events."
A story that appears in the September 16 issue of Science seems to support this prediction of more catastrophic weather to come. It shows that the number of Category 4 and 5 hurricanes worldwide has nearly doubled over the past 35 years, even though the total number of hurricanes has dropped since the 1990s. The shift occurred as global sea surface temperatures have increased over the same period.
Photo from: Weather Services International
Peter Webster, professor at Georgia Tech's School of Earth and Atmospheric Sciences, along with NCAR's Greg Holland and Georgia Tech's Judith Curry and Hai-Ru Chang, studied the number, duration, and intensity of hurricanes (also known as typhoons or tropical cyclones) that have occurred worldwide from 1970 to 2004. The study was supported by the National Science Foundation (NSF), NCAR's primary sponsor.
"What we found was rather astonishing," said Webster. "In the 1970s, there was an average of about 10 Category 4 and 5 hurricanes per year globally. Since 1990, the number of Category 4 and 5 hurricanes has almost doubled, averaging 18 per year globally."
Category 4 hurricanes have sustained winds from 131 to 155 miles per Hour. Category 5 systems, such as Hurricane Katrina at its peak over the Gulf of Mexico, feature winds of 156 mph or more. "Category 4 and 5 storms are also making up a larger share of the total number of hurricanes," said Curry, chair of the School of Earth and Atmospheric Sciences at Georgia Tech and coauthor of the study. "Category 4 and 5 hurricanes made up about 20% of all hurricanes in the 1970s, but over the last decade they accounted for about 35% of these storms." The largest increases in the number of intense hurricanes occurred in the North Pacific, Southwest Pacific, and the North and South Indian Oceans, with slightly smaller increases in the North Atlantic Ocean. All this is happening as sea surface temperatures have risen across the globe anywhere from around one-half to 1 degree Fahrenheit, depending on the region, for hurricane seasons since the 1970s.