SINGAPORE — What will happen if global production and consumption remain largely unconstrained by controls to minimize the impact on the Earth’s complex climate system?
Prospects for concluding an effective international accord in Mexico in less than two months time remain clouded. Modest progress at the latest round of U.N. climate talks that ended in Tianjin on Oct. 9 was overshadowed by continuing deadlock between China and United States, the world’s two biggest greenhouse gas polluters.
Yet policymakers running economies and corporate executives want greater clarity from scientists about the future implications of the rise in temperature near the surface of the land and sea.
Some aspects of climate change are well established. Measurements show that the average temperature has increased by about 0.8 degree Celsius since 1850. In the same period, concentrations of global warming gases in the atmosphere have risen sharply.
The Intergovernmental Panel on Climate Change, the group of international scientists and officials advising the United Nations and member states on global warming and its likely effects, focuses on a small group of well-known greenhouse gases including carbon dioxide, methane, nitrous oxide, ozone and several types of industrial fluorinated gases. The IPCC concluded in 2007 that most of the temperature increase since the mid-20th century was “very likely” due to higher global warming gas concentrations from human activity, mainly burning fossil fuels and clearing forests for agriculture.
The IPCC estimated that if current patterns of energy-intensive economic growth continued, the temperature would rise 2.5 to 4.7 degrees C by 2100 over pre-industrial levels. As a result, it predicted a series of mainly adverse consequences as the world became hotter.
While there is no retreat among mainstream climate scientists from the major IPCC findings, there is a new emphasis on the uncertainties involved. This is partly due to recent criticism of the IPCC, which shared the Nobel Peace Prize in 2007 with former U.S. Vice President Al Gore for their efforts to spread knowledge about man-made climate change.
However, a handful of mistakes in the IPCC’s 2007 report of over 3,000 pages have come to light in the past year, following the leak of e-mails from some scientists associated with its work that suggested there may have been manipulation to create greater certainty than warranted by the evidence.
From the start of the IPCC’s assessment work in the 1980s, it has had to strike a balance between conveying complexity and providing decision-makers and the public with clear analysis and conclusions.
A critical review in August by the council representing a group of national academies of science noted that the IPCC’s 2007 report tended to “emphasize the negative impacts of climate change,” many of which were “not supported sufficiently in the literature, not put into perspective or not expressed clearly.”
Climate science has advanced markedly over the past 20 years. There are many reasons for this. They include improved measurements, especially from satellites and from ice cores that contain climate history stretching back at least 800,000 years. Increased computer power is being used to simulate past climate and project future changes.
Yet the more scientists learn about the climate and how it behaves, the more surprises and uncertainties they discover. In a paper published the week before last, researchers reached the counter-intuitive conclusion that the sun may warm the Earth more during waning solar cycles and that this could help to explain recent cold winters in Europe and North America even as the average global temperature increased.
This does not undermine the case for man-made global warming. Some skeptics argue that solar activity is heating the Earth. The average amount of radiation from the sun has risen slightly in the past 150 years. But climate scientists say that the increase is only about one-tenth of the warming effect of greenhouse gas emissions.
Still, Kevin Trenberth, head of climate analysis at the U.S. National Center for Atmospheric Research, wrote in January that although “our knowledge of certain factors (responsible for climate change) does increase, so does our understanding of factors we previously did not account for or even recognize.”
Among these is the role of clouds. Solar radiation and clouds strongly influence both short-term weather and longer-term climate. For example, low, thick clouds reflect the sun’s rays back into space, causing cooling. High clouds, especially thin cirrus, trap outgoing infrared radiation, producing the greenhouse effect.
Yet science has so far been unable to say whether temperature rise will alter cloud formation in a way that amplifies or moderates warming, and by how much. There is similar uncertainty about the role of tiny but prolific aerosol particles in the atmosphere. Aerosols, including black carbon, come from both human activities (mainly incomplete burning of fossil fuels, wood and other vegetation) and natural sources (mainly dust storms).
Aerosols absorb and emit heat, reflect light and, depending on their properties, can either cool or warm the atmosphere. They also have the potential to determine the properties of clouds. The Royal Society, Britain’s national academy of science, says that current understanding of the aerosol effect on climate is poor.
There are also major gaps in knowledge about the behavior of ice sheets in Greenland and Antarctica, ocean circulation, and the way carbon dioxide and organic carbon move between the atmosphere, land and sea.
The next IPCC report is due in 2013. Will it be less definitive than the controversial 2007 report?
The Royal Society’s short guide to the science of climate change, published last month, notes that researchers are focused on remaining uncertainties and that some may start to be resolved. But “others are unlikely ever to be significantly reduced” and there “remains the possibility that hitherto unknown aspects of the climate and climate change could emerge and lead to significant modifications in our understanding.”
This will not be welcome news for those who want clarity from climate science. Of course, uncertainty can work both ways, since the changes and their impacts may be either smaller or larger than those currently projected by the IPCC. Like many important decisions, it seems that policy choices about climate change must continue to be made on the basis of incomplete information.
Michael Richardson is a visiting senior research fellow at the Institute of South East Asian Studies in Singapore.