Occasionally a piece of news comes along to which you can point and say “Now that’s science.” Here’s one: Scientists at Imperial College London (UK) and the University of Colorado (USA), publishing in Nature [October 7, 2010: An influence of solar spectral variations on radiative forcing of climate] have examined the Sun’s radiation data for the years 2004-2007 and have come to the conclusion that a diminishing total output of radiation from the Sun does not mean a decline in the Earth’s temperature.

As soon as you see the words ‘decline in the Earth’s temperature’ a little tingle in the brain should tell you there’s ‘climate change’ involved. That means this isn’t just science; there are quasi-political reverberations.

However, as science, the results of the study appear to reveal a classic mistake – a fallacy of composition. The accepted notion about the effect of the Sun’s radiation on the Earth is a simple dynamic: More radiation from the Sun, higher temperatures on Earth. Less radiation from the Sun, lower Earth temperatures. That’s an intuitive sort of dynamics, and quite possibly wrong. The problem arises from thinking only of the Sun’s radiation as a total amount of radiation, rather than considering that the Sun emits many kinds of radiation (visible light, infrared, ultraviolet, x-ray, gamma-ray, and so forth).

The radiation from the Sun is known to have a roughly 11-year cycle with higher and lower amounts of total radiation reaching the Earth. The study looked at the data from a declining period of the cycle and found, somewhat surprisingly, that the decline in radiation did not correlate with a decline in Earth’s temperature. What they discovered is that during this period, while the total amount of radiation declined, the amount of visible radiation (energy in the wavelengths of visible light) increased. Since visible light has the most heating effect on Earth’s atmosphere, oceans, and landmass, its increase could explain warmer temperatures.

In science, as in many fields, upsetting established ideas provides something of a rush but comes with risks. In this case, the conclusions of the study run into the study’s own limitations, a problem with alternate explanations, and ultimately the grand question of what, really, is the impact of the solar radiation cycle in Earth’s climate – is it even significant?

As scientists should, the authors of the study point out some of its limitations:

Professor Joanna Haigh, the lead author of the study who is Head of the Department of Physics and member of the Grantham Institute for Climate Change at Imperial College London, said: “These results are challenging what we thought we knew about the Sun’s effect on our climate. However, they only show us a snapshot of the Sun’s activity and its behaviour over the three years of our study could be an anomaly.

“We cannot jump to any conclusions based on what we have found during this comparatively short period and we need to carry out further studies to explore the Sun’s activity, and the patterns that we have uncovered, on longer timescales. However, if further studies find the same pattern over a longer period of time, this could suggest that we may have overestimated the Sun’s role in warming the planet, rather than underestimating it.”

[Source: EurekAlert]

While it is ‘obvious’ that solar radiation has some effect on Earth’s climate, it’s a pretty big assumption to state that the solar cycle has a significant correlation with climate change. Even this study, which might be changing some of the ground rules, doesn’t provide a measure of the strength of correlation between solar radiation and climate change. There are other factors at work: Human activity (such as carbon dioxide production), changes in Earth’s axis, volcanoes, ocean currents and more. Scientists can and will debate the relative impact of these factors. When it comes to the science of big, complex natural occurrences such as climate change, the quest for an accurate as possible evaluation of factors is a hallmark of science.

Those whose bent is toward climate change denial will probably seize upon the ‘controversy’ stirred by this study and point out how scientists are often wrong, or at best can hardly agree among themselves. In this case, it suits their argument that scientist are wrong about their evaluation of the factors affecting climate change. If this is wrong – then what else is wrong? This is actually another form of the fallacy of composition – condemning the whole for an error in a portion. Not that anybody gives a fig about the fallacy. In this particular PR game, it’s the innuendo and impression of suspicion that count.

Meanwhile, the business of science will go on. More studies will be conducted and eventually use a longer time series of data. Alternative theories, many based on climate models different than the one used in the study will be presented. At some point, perhaps, there will be consensus on the relative importance of the Sun’s radiation cycle on Earth’s climate. It will be one more piece of the incomplete mosaic known as our knowledge of climate change.