A senior scientist at the National Oceanic and Atmospheric Administration (NOAA), Susan Solomon, has led a new study which shows how changes in surface temperature, rainfall, and sea level are mostly irreversible for more than 1,000 years after carbon dioxide emissions are completely stopped.

The study shows 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 authors found that the scientific evidence is strong enough to quantify some irreversible climate impacts, including rainfall changes in certain key regions, and global sea level rise.

The results of allowing CO2 to peak at 450-600 parts per million, would include decreases in dry-season rainfall that are similar to the 1930s North American Dust Bowl in zones including southern Europe, northern Africa, southwestern North America, southern Africa and western Australia.

The decreases in rainfall is predicted to last for centuries. The regional impacts are likely to include expanded deserts, decreasing human water supplies, increased fire frequency and ecosystem change. Dry-season wheat and maize agriculture in regions of rain-fed farming, such as Africa, would be affected.

The climate effects last so much longer than previously thought because of the way the oceans work. Susan Solomon said, “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.”

The scientists emphasize that 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 authors find that the irreversible global average sea level rise by the year 3000 would be at least 1.3–3.2 feet (0.4–1.0 meter) if CO2 peaks at 600 parts per million, and double that amount if CO2 peaks at 1,000 parts per million.

The authors of the report did concede that the additional contributions to sea level rise from the melting of glaciers and polar ice sheets are too uncertain to quantify in the same way.  They have presented the minimum sea level rise that they expect from well-understood physics, and they were still surprised that it was so large.

Rising sea levels would cause “…irreversible commitments to future changes in the geography of the Earth, since many coastal and island features would ultimately become submerged,” the authors write.

The authors relied on measurements as well as many different models to support the understanding of their results. They focused on drying of particular regions and on thermal expansion of the ocean because observations suggest that humans are contributing to changes that have already been measured.

Besides Solomon, the study’s authors are Gian-Kasper Plattner and Reto Knutti of ETH Zurich, Switzerland, and Pierre Friedlingstein of Institut Pierre Simon Laplace, Gif-Sur-Yvette, France.

Image is of Lake Hume, NSW Australia at 4% by suburbanbloke on flickr under the Creative Commons license