Archives for May 6, 2006

The IPCC is intending to release its Fourth Assessment Report (AR4) in three parts next year. Part 1 is likely to be launched in early 2007 and focus on the physical basis for climate change. Part 2 is likely to be released mid year and focus on impacts of global warming while Part 3 will be released later in the year and focus on how to mitigate climate change.

In this week’s journal Nature (Vol 441, 6-7, 4 May 2006) there is information about the climate change predictions in the current draft of Part 1, including:

“The current draft, which represents the message that the scientific authors want to present to policy-makers, contains few statements that will surprise climate researchers, but its tone is much more confident than that of its predecessor, published in 2001. And that, say researchers, will make it harder for sceptical politicians and lobbyists to attack climate predictions.

“People won’t be punching holes in the science,” says Jay Gulledge, a senior research fellow at the Pew Center on Global Climate Change in Arlington, Virginia. Emily Shuckburgh, a climate researcher at the University of Cambridge, UK, agrees: “If you’re a sceptic, it’s difficult to see where to attack on the modelling side.”

One critical number in previous reports has been the sensitivity of the climate to increases in greenhouse-gas levels. In 2001, scientists estimated that a doubling of carbon dioxide levels would cause an increase of 1.5–4.5 °C, but acknowledged that this range was little more than a best guess. The draft 2007 WGI report describes how new models and data sets allow the range to be properly quantified. It estimates the effect of doubling carbon dioxide as a rise of 2.0–4.5 °C and, for the first time, suggests a single most likely figure: 3 °C. This estimate is already widely accepted by climate scientists.

Another set of predictions that have become much more robust are those about ‘commitment’ — the ongoing climatic changes that would be expected even if greenhouse-gas levels could be stabilized. The existence of commitment was acknowledged in the last WGI report, but no number was given in the policy-makers’ summary. In contrast, the 2007 summary stresses that even if greenhouse gases level off now, warming will continue at about the current rate for several decades.

The error bars have also shrunk substantially on one of the biggest uncertainties in 2001 — the role of aerosols such as soot from fires, which exert a cooling effect by reflecting sunlight. In addition, certainty over politically important statements about whether climate change has already been observed has increased. Data on twentieth-century changes in precipitation and sea-level rise are now more precise, and the risk of ocean acidification is detailed for the first time. Such assertions are likely to be seized on by environmental groups if they appear in the final document.”

If you have a password, you can access the draft here: http://www.climatescience.gov/Library/ipcc/wg14ar-review.htm .