Climatic prediction

By: David Bradley

Sallie Baliunas of the Harvard-Smithsonian Center for Astrophysics and TechCentralStation has pointed out a fundamental flaw in the current models of climate change that could have serious implications for our understanding of this problem and how to tackle it.

Contrary to popular belief, says Baliunas, twentieth century surface temperature trends were not closely linked to the anthropogenic (human-caused) rise in greenhouse gas emissions. She suggests that although emissions certainly rose because of human activity in the latter part of the twentieth century and the average temperature was higher than in the nineteenth century, the temperature changes observed do not fit the pattern of greenhouse gas increases.

Baliunas questioned whether the nineteenth and the twentieth century were abnormal or normal, pointing out that climate change works on a much longer timescale and that this period is just too short to know for certain. We simply cannot disentangle the natural changes from the putative effects of human activity.

Looking further into the past, the period 1659-2002 shows that the steepest warming occurred between 1690 and 1740 - before the Industrial Revolution. Going back further still, Baliunas and colleague Willie Soon have studied proxies of climate change, such as geological and biological reservoirs, ice-cores, tree rings and pollen in sediments. Such records and other sources suggest that 800-1200 AD was a period of warming, while 1300-1900 was a period of cooling. Indeed, the latter period is described as the "little-Ice Age", the coldest period since the most recent glaciation ended 12000 years ago. So, how can we answer the question of whether the current warming has been caused by industrialisation?

Baliunas believes that tracking the temperature of the troposphere (the lower 5 kilometres of the earth's atmosphere) clarifies the story of global temperature change. Satellite and weather balloon records show that this region of the atmosphere has not been subject to warming over recent decades. This is in sharp contrast to the assumptions made in the climate change models that imply that a warmer surface derives from a warmer troposphere. The conclusion that Baliunas draws from this is that climate models have greatly exaggerated the temperature rise we might see in the future.

She suggested that there are many factors involved in climate change, among them known unknowns such as water vapour and ice crystals in the atmosphere, but that one strong correlation between temperature and a single factor lies with the sun's output going back at least 200 years. Where records are available for the sun's brightness there is a direct correlation between global temperature and solar energy reaching the earth, and this stands true for at least twenty years of data. Perhaps recent warming is due to the different rate at which the sun emits energy over time, rather than anthropogenic causes.

Baliunas suggests a cautionary approach. By 2020, the climate will certainly be changing, but in what ways we do not know.

This summary was written for the Scientific Alliance as part of a reportage on its meeting 2020 Vision - Powering the UK's Future. Read my full report at http://www.scientific-alliance.org/events_items/past_events/2020vision.htm

 

Also in Issue 74:
Accidents will happen - human reactions to chemicals and biological reagents can end a career
Predicting climate change - As carbon dioxide levels double, what will really happen the day after tomorrow?

Previously in Elemental Discoveries, Issue 73, September 2004:

Green silicon production - making the microelectronics industry favoite element
P2P for scientists - peer mentoring, helping students help each other
Women in science - smashing the glass ceiling
Academic poaching of researchers - plugging the brain drain
Permanent implantable contact lenses - does what it says on the tin
Profile of ETH Zurich - a profile of...
Paradoxical ozone - the paradox of ozone