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David Bradley ISSUE #32
July 2003

Climate Models

Sallie Baliunas of the Harvard-Smithsonian Center for Astrophysics claims to have exposed a fundamental flaw in our models of global climate change. Speaking at a one-day conference organised by the UK's Scientific Alliance entitled 2020 Vision - Powering the UK's Future, Baliunas described research that could have serious implications for our understanding of the problem of global warming and what we do to tackle it.

Contrary to popular belief, Baliunas asserts, the surface temperature of the earth during the twentieth century was not closely linked to the release of greenhouse gases into the atmosphere by humans. Baliunas explained that although such 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.

Underpinning Baliunas' argument is whether or not the nineteenth and the twentieth century were indeed abnormal or normal. She pointed out that climate change works, in fact, on a much longer timescale than our short-term view suggests and that a period of a mere two centuries is just too short to know for certain whether temperature trends have changed because of human activity. We simply cannot disentangle the natural changes from such effects.

Sallie BaliunasBaliunas has looked deeper into the past; the period 1659-2002 in particular shows that the steepest warming actually occurred between 1690 and 1740 - well before the Industrial Revolution and the rise in anthropogenic greenhouse emissions. 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 many other data sources, suggest that the period 800-1200 AD was a time of global warming, while 1300-1900 was a period of global cooling. Indeed, the latter period is described as the "little-Ice Age", the coldest period since the most recent glaciation ended 12,000 years ago. Such data begs the question, how can we understand the present-day warming on the basis of industrialisation?

adapted from http://csep10.phys.utk.edu/astr161/lect/earth/atmosphere.gifBaliunas believes that tracking the temperature of the troposphere (the lower 5 kilometres of the earth's atmosphere) provides a much clearer picture. 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. However, there is one factor that stands out from the crowd - there is a strong correlation, she explained, between the earth's temperature and the sun's strength. Records for at least the last 200 years support this view. Where records are available for the sun's brightness, there is a direct correlation between global temperature and solar energy reaching the earth. Perhaps, Baliunas suggested, recent warming is due to the different rate at which the sun emits energy over time, rather than anthropogenic causes. As such, she believes a cautionary approach is needed to climate change. By 2020, the climate will certainly be changing, but in what ways we do not know.

The views expressed in this item are those of Baliunus and are not necessarily held by D Bradley.