Researchers have recently reported new scientific findings that have important implications for how we humans respond to climate change.
On April 21, SCIENCE, the journal of the American Association for the Advancement of Science, carried a report which helps people to more readily accept the reality of climate change and to better understand its implications for the future of the planet. The article reports on the findings of several researchers who advise that that the likely rise in global temperatures is now better understood. Whereas previously it was thought that temperatures would rise by as much as 9 or 11 degrees Celsius, now it appears likely that the increase will be restricted to between 1 and 4.5 degrees Celsius.
This is a very important conclusion from these researchers as policy makers around the world can now start to determine what actions need to be taken to mitigate against a likely maximum rise of 4.5 degrees rather than 9 or 11 degrees. At the same time, the probability that the most likely temperature rise will be about 2.5 degrees has doubled as shown in the attached graph.
These findings are important because they provide greater certainty in an field of science that has been subject to great uncertainty and scepticism. One reason why Australia and the US rejected the Kyoto agreement was because of the uncertainty behind the science on which it was based. Now, with a better understanding of what changes will result from climate change, the world can move forward with a global agreement that will result in significant reductions in greenhouse gas emissions.
Below is the text from the article:
Latest Forecast: Stand By for a Warmer, But Not Scorching, World
While newly climate-conscious news reporters seek signs of apocalyptic change in hungry polar bears and pumped-up hurricanes, evidence-oriented researchers are working to nail down some numbers. They are concerned with climate sensitivity: how much a given increase in atmospheric carbon dioxide will warm the world. If it's extremely high, continued emissions of greenhouse gases could ignite a climatic firestorm. If it's very low, they might merely raise the global thermostat a notch or two.
Now two new studies that combine independent lines of evidence agree that climate sensitivity is at least moderately strong moderate enough so that a really scorching warming appears unlikely. Even with the most conservative assumptions, says climate researcher Chris E. Forest of the Massachusetts Institute of Technology in Cambridge, the studies cool the maximum warming. And the reinforced low end of the range, he says, means continued emissions will fuel a substantial warming in this century.
The new studies use a technique called Bayesian statistics to gauge how adding new information improves past estimates of climate sensitivity. Most previous estimates used only a single line of evidence, such as how climate warmed as greenhouse gases increased during the 20th century or how climate cooled right after the debris from a major volcanic eruption £ shaded the planet. Lately, such analyses have tended to support a 25-year-old guess about climate sensitivity: If the concentration of CO2 were to double, as is expected by late in the 21st century, the world would warm between a modest 1.5°C and a hefty 4.5°C (Science, I 13 August 2004, p. 932). The low end of that a range looked fairly firm; the negligible warming claimed by greenhouse contrarians looked
very unlikely. But no one was sure about the high end. Some studies allowed a real chance that doubling CO2 could raise temperatures by 7°C, 9°C, or even 11°C (Science, 28 January 2005, p. 497).
The two new studies rein in those soaring upper limits for climate sensitivity while reinforcing the substantial lower limit. Climate modeler Gabriele Hegerl of Duke University in Durham, North Carolina, and colleagues started with Northern Hemisphere temperatures between 1270 and 1850 extracted from records such as tree rings. In those pre-industrial times, volcanoes, the waxing and waning of the sun, and natural variations in greenhouse gases were changing temperature. Hegerl and her colleagues then combined the pre-industrial temperature response to those climate forcings with the global response in the 20th century to volcanoes, rising greenhouse gases, and thickening pollutant hazes. In this week's issue of Nature, they report a 5% probability that climate sensitivity is less than 1.5°C and a 95% chance that it's less than 6.2°C. That's still pretty high, but a far cry from 9°Cor 11°C.
In a similar study published on 18 March in Geophysical Research Letters, climate modelers James Annan and Julia Hargreaves of the Frontier Research Center for Global Change in Yokohama, Japan, found the same lower limit of 1.5°C and a 95% upper limit of 4.5°C. They combined published 20th century warming data with records of coolings after recent volcanic eruptions and estimates of chilling in the depths of the latest ice age.
"Combining multiple lines of evidence is certainly the way to go," says Forest. An extremely high climate sensitivity "is probably less likely than we thought a year ago," agrees climate researcher Reto Knutti of the National Center for Atmospheric Research in Boulder, Colorado. More importantly, "we start to see a much better agreement on the lower bound," says Knutti. "We can be pretty sure the changes will be substantial" by the end of the century, he says.
-RICHARD A. KERR
