By Michael Richardson, For The Straits Times
THE United Nations climate talks that ended in Tianjin, China, last Saturday reported modest progress, but this was overshadowed by continuing deadlock between China and the United States, the world's two biggest greenhouse gas polluters. The next major meeting on climate change, which begins in Mexico on Nov 29, may not result in an international accord either.
Economic policymakers and company executives want greater clarity from scientists about the future implications of the rise in temperature near the surface of land and sea.
Some aspects of climate change are well established. Measurements show that the average temperature has increased by about 0.8 deg C since 1850. In the same period, concentrations of carbon dioxide and methane in the atmosphere have risen sharply.
The Intergovernmental Panel on Climate Change (IPCC), the group of international scientists and officials advising the United Nations and member states on global warming and its likely effects, 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 energy-intensive economic growth continued, the temperature would be between 2.5 deg C and 4.7 deg C higher by 2100, compared with pre-industrial levels. 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. Mistakes in its 2007 Nobel Prize-winning report have been highlighted, following the leak of e-mail from some scientists associated with its work suggesting manipulation to create greater certainty than warranted by the evidence.
In August, a critical review by the council representing many national academies of science noted that the IPCC's 2007 report tended to 'emphasise the negative impacts of climate change', many of which were 'not supported sufficiently in the literature, not put into perspective, or not expressed clearly'.
Since its work in the 1980s, the IPCC has had to strike a balance between conveying complexity and having clarity in conclusions.
Climate science has advanced markedly since, thanks to improved measurements, especially from satellites and ice cores that contain climate history stretching back at least 800,000 years. Increased computer power helps 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 last week, 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 sceptics 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 the increase is only about one-tenth of the warming effect of greenhouse gas emissions.
As Dr Kevin Trenberth, head of climate analysis at the US National Centre for Atmospheric Research, wrote in January, 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 recognise'.
Among these is the role of clouds. Solar radiation and clouds strongly influence short-term weather and longer-term climate. 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 cannot work out whether temperature rise will alter cloud formation in a way that amplifies or moderates warming, and by how much.
There are also gaps in knowledge about the behaviour 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. By then, some uncertainties may start to be resolved. But as the Royal Society's short guide to the science of climate change published recently notes: 'Others are unlikely ever to be significantly reduced', while it was possible 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. But like many important decisions, policy choices about climate change must continue to be made on the basis of incomplete information.
The writer is a visiting senior research fellow at the Institute of Southeast Asian Studies.