ROYAL SOCIETY ISSUES REVISED STATEMENT ON CLIMATE CHANGE

Britain's Royal Society has rewritten its guide to climate change following a complaint in May by 43 members that previous statements had exaggerated the degree of certainty over climate change and that it had refused to accept dissenting views.  A commission headed by physicist John Pethica, Royal Society vice president, has compiled the new report “Climate Change: A Summary of the Science”. The statement is more nuanced that the previous document called Climate Change Controversies – A Simple Guide” published in 2007 which was set out as a point by point rebuttal of climate sceptic claims and was subsequently criticised. 

The publication divides the science into three areas: aspects where there is wide agreement, areas where there is a wide consensus but continuing debate and discussion, and aspects that are not well understood. Pethica said: “Climate change is an important issue affecting everyone. Much of the public debate on climate change is polarised at present, which can make it difficult to get a good overview of the science. This guide explains where the science is clear and established, and also where it is less certain. It is not a simple guide, as this is not a simple issue. This summary has been produced for all who want to understand the full range of the scientific evidence. “

On 28 May, when the Royal Society announced that it was to publish a new guide, Martin Rees, President of the Royal Society said:”Climate change is a hugely important issue but the public debate has all too often been clouded by exaggeration and misleading information. We aim to provide the public with a clear indication of what is known about the climate system, what we think we know about it and, just as importantly, the aspects we still do not understand very well.” When it announced the decision to review its position, the Royal society stated that: “Any public perception that science is somehow fully settled is wholly incorrect — there is always room for new observations, theories, measurements.”

The new document (which can be downloaded from here) states: “There is strong evidence that changes in greenhouse gas concentrations due to human activity are the dominant cause of the global warming that has taken place over the last half century.”

Areas of wide agreement

Widely agreed issues include the following:

• Surface temperatures have warmed by 0.8C since 1850 in two bursts, one between 1910 and 1940 and the other from 1975 to around 2000.
• Global average carbon dioxide concentrations have increased from around 280ppm in the mid-nineteenth century to around 388ppm by the end of 2009; and are higher than any observed in the last 800,000 years.
• The net human climate forcing is around 1.6W/sq.m; this level of forcing will lead to a 0.4C average surface warming.
• The relationship between carbon dioxide levels and the climate is active so that changes in either will affect the other.
• Future climate change forecasts

Areas of consensus and continued debate

Among those aspects of climate change where the Royal Society panel states there is wide consensus but continuing debate and discussion are the following:

• It will take several millenia for carbon dioxide levels to return to pre-industrial levels.
• Other climate drivers include volcanoes, the sun and other human activities.
• Climate sensitivity indicates that a 3C to 4.5C increase will result from a doubling of carbon dioxide levels.
• The impact of climate change on global average temperatures exceeds the effects of natural variability.
• Climate models are unable to replicate recent changes on the basis of natural climate forcings.

Uncertainties

Key areas highlighted as not being well understood include:

• Observations are not yet good enough to quantify, with confidence, some aspects of the evolution of either climate forcing or climate change, or for helping to place tight bounds on the climate sensitivity.
• Observations of temperature prior to 1850 are limited.
• Projections of climate change are sensitive to how clouds are modeled.
• The response of the carbon cycle to climate change is unknown because of uncertainties about carbon processes including the strength of uptake by the land and oceans.
• Insufficient understanding of ice sheet melting makes accurate forecasting of sea level rises difficult.
• Possible changes in the North Atlantic Ocean can not be assessed with confidence.
• Regional climate models are limited.