Studies that examine the effects of atmospheric greenhouse gases often focus on the possible dangers of climate change in the 21st century. However, a new study published on February 10, 2009 by the Proceedings of the National Academy of Sciences indicates that climate change resulting from carbon dioxide (CO2) concentrations is mostly irreversible for at least 1000 years after emissions stop.
The study - "Irreversible climate change due to carbon dioxide emissions" - was conducted by Susan Solomon, Gian-Kaspar Plattner, Reto Knutti, and Pierre Friedling. They report that atmospheric temperature increases "are not expected to decrease significantly even if carbon dioxide emissions were to completely cease." They also report that many regions will experience irreversible dry-season rainfall reductions and that sea levels will continue to rise as a result of thermal expansion.
A Thousand Years of Hotter Temperatures
When atmospheric CO2 increases, so does the average global temperature. Even if human activity were to emit no additional CO2, the temperatures would remain relatively constant through the end of the millennium. This is because of the complex relationship between the atmosphere and the oceans. True, if CO2 emissions were to stop, atmospheric CO2 concentrations would begin to decay, and there would be a decrease of radiative forcing, which is a change in the difference between the incoming radiation energy and the outgoing radiation.
However, although radiative forcing decreases, the ocean's capacity for heat uptake also decreases. In fact, there is a "near balance between the long-term decrease of radiative forcing due to CO2 concentration decay and reduced cooling through heat loss to the ocean." As a result, atmospheric temperatures will not drop significantly for 1000 years after the CO2 emissions have stopped.
Below Average Dry-Season Rainfall for the Next Millennium
When the atmosphere warms, rainfall patterns begin to change, leading to adverse effects on the water supplies for humans, agriculture, and ecosystems worldwide. Indeed, decreases in rainfall have already been observed in large regions such as the Mediterranean, southern Africa, and southwestern North America.
According to the study's authors, "increased temperature causes increased water vapor concentrations, and changes in water vapor transport and the hydrologic cycle can hence be expected." What this means is that a drying pattern could be seen over much of the already-dry subtropics.
In northern Africa, southern Europe, and western Australia, dry-season rainfall could decrease by as much as 20% if the planet were to warm by 2 degrees Celsius. Under the same rise in temperatures, rain in eastern South America, southwestern North America, and southern Africa could drop about 10%, which is about the same amount of rainfall decrease as was seen during the Dust Bowl. And these drying patterns may be here for a thousand years.
Higher Sea Levels for 1000 Years
When the atmosphere grows warmer, the oceans grows warmer, and when the oceans grow warmer, they begin to expand, and when the oceans expand, sea levels rise. Add to this mix the loss of land ice and mountain glaciers, and there will undoubtedly be a significant impact on shorelines around the world.
Because higher atmospheric temperatures are likely to last through the end of the millennium, the ocean will continue to absorb heat and continue to expand for many years to come. "Sea level rise can be expected to affect many coastal regions," and that impact will last for at least a thousand years.
Reaching the Next Millennium
Even if CO2 emissions were to stop today, the impact of what has already been pumped into the atmosphere will be felt to the year 3000 and beyond. But CO2 emissions are not stopping. Indeed, they're projected to grow significantly over the next 20 years. How long, then, will it take to undo the additional damage that has yet to be done?
R.H. Sheldon - A number of years ago, long before I moved to the Northwest, I hitchhiked with a friend across Washington state to northern Idaho. We got ...
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