Climate change and oceans
Climate change and oceans (Encyclopedia of Environmental Issues, Revised Edition)
Many scientists have projected that the earth’s temperature will rise at least 3 degrees Celsius (5.4 degrees Fahrenheit) during the twenty-first century, bringing it to a level near that of the middle Pliocene, three million years ago, when the seas were 15 to 35 meters (50 to 115 feet) higher than at the beginning of the century. The carbon dioxide (CO2) level at that time reached 425 parts per million (ppm); by 2010 the CO2 level was at 390 ppm, increasing at a rate of 2 to 3 ppm per year.
In late March, 2006, a report in the journal Science stated that melting ice, principally from Greenland and the West Antarctic ice sheet, could contribute to a rise in sea levels of several meters within a century—an upward revision of previous estimates. In an article published in the March, 2004, issue of Scientific American, James E. Hansen, director of the National Aeronautics and Space Administration’s Goddard Institute for Space Studies in New York City, warned that if recent growth rates of CO2 emissions and other greenhouse gases continue during the next fifty years, temperature increases could provoke large rises in sea levels, with potentially catastrophic effects. According to Hansen, a temperature increase of 2 to 3 degrees Celsius (3.6 to 5.4 degrees Fahrenheit) could provoke rises in sea level of about 25 meters (82 feet) within a few centuries.
(The entire section is 214 words.)
Rising Acidity in the Oceans (Encyclopedia of Environmental Issues, Revised Edition)
In 2003 scientists Ken Caldeira and Michael E. Wickett noted in the journal Nature that CO2 levels were rising in the oceans more rapidly than at any time since the age of the dinosaurs. As the oceans absorb more CO2 and become more acidic, their capacity to hold more CO2 in the future is strongly reduced.
Concerns about rising acidity of the oceans were reinforced in January, 2009, when 155 scientists from twenty-six nations, organized by several international groups under the aegis of the United Nations, issued the Monaco Declaration, warning of severe damage to the oceans by rising acidity. In June, 2009, seventy science academies around the world called for the inclusion of ocean acidity on the agenda of international climate change studies, noting that the oceans already had become more acidic than at any time during the past 800,000 years.
Carbon dioxide is being injected into the oceans much more quickly than nature can neutralize it. Seawater is usually alkaline, about 8.2 pH. The pH scale is logarithmic, so a 0.1 decrease in pH, the change since the beginning of the Industrial Revolution, indicates a 30 percent increase in the concentration of hydrogen ions.
Scientists have investigated what continued ocean acidification might do to animals with calcium shells. One study investigated 328 colonies of massive Porites corals on the Great Barrier Reef off Australia; these...
(The entire section is 255 words.)
The Ocean Food Web (Encyclopedia of Environmental Issues, Revised Edition)
Warming sea surface temperatures may interfere with phytoplankton production, with impacts rippling through the food web. Cooler, upwelling ocean water breaks through warm surface waters less frequently, reducing the nutrients available for plants and animals living in the oceans. By the 1990’s, such decreases in productivity were detected near the California coast, where scientists have documented a measurable decrease in the abundance of zooplankton, the second level in the food web. By the 1990’s, the abundance of zooplankton was 70 percent lower than it had been during the 1950’s.
Scientists also have documented decreased reproduction and increased mortality in seabirds and marine mammal populations in warming water. A 1999 report published by the World Wide Fund for Nature and the Marine Conservation Biology Institute noted that the population of the sooty shearwater, a seabird, off the California coast declined 90 percent during the late 1980’s and early 1990’s, and the population of the Cassin’s auklet declined 50 percent. Zooplankton populations declined markedly at the same time. In Alaska, a severe decline in shearwaters from 1997 to 1998 “was clearly due to starvation,” according to the report.
(The entire section is 181 words.)
Further Reading (Encyclopedia of Environmental Issues, Revised Edition)
Alley, Richard B., et al. “Ice-Sheet and Sea-Level Changes.” Science 310 (October 21, 2005): 456-460.
Caldeira, Ken, and Michael E. Wickett. “Oceanography: Anthropogenic Carbon and Ocean pH.” Nature 425 (September 25, 2003): 365.
Hansen, James. “Defusing the Global Warming Time Bomb.” Scientific American, March, 2004, 68-77.
Holland, Jennifer S. “Acid Threat.” National Geographic, November, 2001, 110-111.
Lynas, Mark. Six Degrees: Our Future on a Hotter Planet. New York: HarperCollins, 2008.
Mathews-Amos, Amy, and Ewann A. Berntson. Turning Up the Heat: How Global Warming Threatens Life in the Sea. Gland, Switzerland: World Wide Fund for Nature/Marine Conservation Biology Institute, 1999.
(The entire section is 89 words.)