A new scientific study led by the US National Oceanic and Atmospheric Administration reaches a powerful conclusion about the climate change caused by future increases of carbon dioxide: to a large extent, there’s no going back.
The pioneering study, led byNOAA senior scientist Susan Solomon, shows 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. The findings appear during the week of January 26 in the Proceedings of the National Academy of Sciences.
“Our study convinced us that current choices regarding carbon dioxide emissions will have legacies that will irreversibly change the planet,” said Solomon, who is based at NOAA’s Earth System Research Laboratory in Boulder, Colo.
“It has long been known that some of the carbon dioxide emitted by human activities stays in the atmosphere for thousands of years,” Solomon said. “But the new study advances the understanding of how this affects the climate system.”
The study examines 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.
If CO2 is allowed to peak at 450-600 parts per million, the results would include persistent decreases in dry-season rainfall that are comparable to the 1930s North American Dust Bowl in zones including southern Europe, northern Africa, southwestern North America, southern Africa and western Australia.
The study notes that decreases in rainfall that last not just for a few decades but over centuries are expected to have a range of impacts that differ by region. Such regional impacts include decreasing human water supplies, increased fire frequency, ecosystem change and expanded deserts. Dry-season wheat and maize agriculture in regions of rain-fed farming, such as Africa, would also be affected.
Climate impacts were less severe at lower peak levels. But at all levels added carbon dioxide and its climate effects linger because of the ocean.
“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.
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.
“Additional contributions to sea level rise from the melting of glaciers and polar ice sheets are too uncertain to quantify in the same way,” said Solomon. “They could be even larger but we just don’t have the same level of knowledge about those terms. We presented the minimum sea level rise that we can expect from well-understood physics, and we were 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.
Geoengineering to remove carbon dioxide from the atmosphere was not considered in the study. “Ideas about taking the carbon dioxide away after the world puts it in have been proposed, but right now those are very speculative,” said Solomon.
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 (Swiss Federal Institute of Technology), Switzerland, and Pierre Friedlingstein of Institut Pierre Simon Laplace, Gif-Sur-Yvette, France.
This week, in Ireland Green Party leader and Minister for the Environment John Gormley abandoned plans to ban traditional incandescent light-bulbs. Gormley said Ireland will accept the EU plan, which dates from 2006, for a phased withdrawal from the market.
Labour Party environment spokesman Joanna Tuffy, said the decision to wait for an EU-wide ban made sense because an Irish-only ban could have damaged Irish retailers.
"If he was to jump the gun, people would buy their incandescent lightbulbs in Newry rather than change their light-fittings," she said.
NOAA: 2008 Global Temperature Ties as Eighth Warmest on Record
The year 2008 tied with 2001 as the eighth warmest year on record for the Earth, based on the combined average of worldwide land and ocean surface temperatures through December, according to a preliminary analysis by NOAA’s National Climatic Data Center in Asheville, North Carolina. For December alone, the month also ranked as the eighth warmest globally, for the combined land and ocean surface temperature. The assessment is based on records dating back to 1880.
The analyses in NCDC’s global reports are based on preliminary data, which are subject to revision. Additional quality control is applied to the data when late reports are received several weeks after the end of the month and as increased scientific methods improve NCDC’s processing algorithms.
NCDC’s ranking of 2008 as the eighth warmest year compares to a ranking of ninth warmest based on an analysis by NASA’s Goddard Institute for Space Studies. The NOAA and NASA analyses differ slightly in methodology, but both use data from NOAA's National Climatic Data Center – the federal government's official source for climate data.
Global Temperature Highlights – 2008
The combined global land and ocean surface temperature from January-December was 0.88 degree F (0.49 degree C) above the 20th Century average of 57.0 degrees F (13.9 degrees C). Since 1880, the annual combined global land and ocean surface temperature has increased at a rate of 0.09 degree F (0.05 degree C) per decade. This rate has increased to 0.29 degree F (0.16 degree C) per decade over the past 30 years.
Separately, the global land surface temperature for 2008, through December, was sixth warmest, with an average temperature 1.46 degrees F (0.81 degree C) above the 20th Century average of 47.3 degrees F (8.5 degrees C).
Also separately, the global ocean surface temperature for 2008, through December, was 0.67 degree F (0.37 degree C) above the 20th Century average of 60.9 degrees F (16.1 degrees C) and ranked tenth warmest.
Global Temperature Highlights – December 2008
The December combined global land and ocean surface temperature was 0.86 degree F (0.48 degree C) above the 20th Century average of 54.0 degrees F (12.2 degrees C).
Separately, the December 2008 global land surface temperature was 1.22 degrees F (0.68 degree C) above the 20th Century average of 38.7 degrees F (3.7 degrees C) and ranked 14th warmest.
For December, the global ocean surface temperature was 0.74 degree F (0.41 degree C) above the 20th Century average of 60.4 degrees F (15.7 degrees C) and tied with December 2001 and December 2005 as sixth warmest.
Other Global Highlights for 2008
The United States recorded a preliminary total of 1,690 tornadoes during 2008, which is well above the 10-year average of 1,270 and ranks as the second highest annual total since reliable records began in 1953. The high number of tornado-related fatalities during the first half of the year made 2008 the 10th deadliest with a 2008 total of 125 deaths.
Northern Hemisphere snow cover extent in December was 16.95 million square miles (43.91 million square kilometers). This was 0.17 million square miles (0.43 million square kilometers) above the 1966-2008 December average. Northern Hemisphere snow cover extent was below average for most of 2008.
Arctic sea ice extent in 2008 reached its second lowest melt season extent on record in September. The minimum of 1.80 million square miles (4.67 million square kilometers) was 0.80 million square miles (2.09 million square kilometers) below the 1979-2000 average minimum extent.