It is impossible nowadays to have an informed discussion of global warming and climate change without understanding the role of the oceans in affecting the key processes of change. A new study led by award-winning NOAA scientist Susan Solomon, examined how changes in surface temperature, rainfall and sea level are largely irreversible for more than 1,000 years after carbon dioxide (CO2) emissions are completely stopped. NOAA issued a press release describing the study, which was itself reported in the Proceedings of the National Academy of Sciences.
According to Solomon, who is based at NOAA’s Earth System Research Laboratory in Boulder, Colorado, “Our study convinced us that current choices regarding carbon dioxide emissions will have legacies that will irreversibly change the planet.” Solomon adds, “It has long been known that some of the carbon dioxide emitted by human activities stays in the atmosphere for thousands of years. . .but the new study advances the understanding of how this affects the climate system.”
The study examined the consequences of allowing CO2 to build up to several different peak levels — beyond present-day concentrations of 385 parts per million, and then completely halting the emissions after the peak. The study authors found that the scientific evidence is strong enough to quantify some irreversible climate impacts, including rainfall changes in certain key regions, and a global sea level rise.
Among the conclusions:
- If CO2 is allowed to peak at 450-600 parts per million, there would be persistent decreases in normal dry-season rainfall that would compare to the 1930s North American Dust Bowl in zones that include southern Europe, northern Africa, southwestern North America, southern Africa and western Australia.
- These decreases in rainfall are expected to last not just for decades but for centuries.
- The increases in CO2 that occur in this century “lock in” sea level rise that would slowly follow in the next 1,000 years.
- Considering just the expansion of warming ocean waters — without melting glaciers and polar ice sheets — the study finds that the irreversible global average seal level rise by the year 2000 would be at least 1.3 – 3.2 feet (-.4 – 1.0 meters), if CO2 peaks at 600 parts per million, but would double if CO2 peaks at 1,000 parts per million.
The ocean link to CO2 levels is well understood. “In the long run, both carbon dioxide loss and heat transfer depend on the same physics of deep-ocean mixing. The two work against each other to keep temperatures almost constant for more than a thousand years, and that makes carbon dioxide unique among the major climate gases,” said Solomon. In simple terms, all the CO2 that humans have recently added to the atmosphere upsets this delicate balancing mechanism.
The study likely represents a relatively optimistic view of potential climate affects because it assumes that CO2 additions can be stopped altogether, and it does not include the likely considerable addition affects of glacial and polar ice cap melting to sea-rise levels. It does not seem much of a stretch to say that coastal and island geography all over Earth is likely to change dramatically before the next millennium.
Copyright © 2009 by Marine Science Today, a publication of OceanLines LLC