The sun has been shown to be at least partially responsible for causing some climate change through an increased solar output, writes Dick Ahlstrom.
Research has proven that variability in the sun's energy output is contributing to our warming climate. Yet the changes on Earth are seen on a regional rather than global basis and are small compared to the impact caused by human activity.
The solar contribution to climate change has provided a useful excuse for those attempting to explain away atmospheric warming, something which made it imperative that scientists actually study the truth behind the claims, stated Prof Jo Haigh who this evening delivers a joint Academy Times/Monsignor Pádraig de Brún Memorial Lecture on the issue at NUI Galway.
"There are people now who want to show that all global warming is due to the sun," states Prof Haigh who is professor of atmospheric physics at Imperial College London and head of the space and atmospheric physics research group there. "It is very convenient for the climate sceptics because they could argue we can burn all the coal we like."
The title of her talk tonight in the O'Flaherty Theatre at NUI Galway, is, Solar variability and Climate: conjecture, politics and science.
The issue has in the past been very controversial, although the scientific community is taking it more seriously now, she told The Irish Times prior to the lecture.
The subject had a "very chequered past" because of weak research but also because of unfounded claims being made in the name of science. Before the 1970s or even 1980s it wasn't even considered serious science, she says.
One of the early difficulties was deciding what to measure. "There was no measurement system to show that the sun's energy varied." Yet people were well aware of changes in the sun due to the 11-year sunspot cycle.
Scientists discovered that it was possible to detect changes over periods lasting hundreds of thousands of years, but this was linked to changes in the Earth orbit rather than solar output.
Variability was also noted over several centuries, for example when the mediaeval period experienced general warming and the 18th century marked cooling.
Yet periods of higher sunspot activity were known to be associated with warming, not globally but in certain regions. Warming was most pronounced in the mid to higher latitudes but with little change in the tropics, she says.
This has now been attributed to rising ultraviolet (UV) output associated with the solar maximum. General solar output goes up by just 0.1 per cent at this time, Dr Haigh says.
"But if you look at the UV, the changes are a few per cent and that affects the Earth's stratosphere, 10 to 20km up where the ozone is. You get a definite solar signal in the stratosphere."
The effect can cause a one per cent change in the entire lower atmosphere. Yet it is not the temperature change warming things directly at ground level, it is the altered movement of air masses influenced by a disturbed stratosphere, she says.
The phenomenon is being studied by Nasa's €63 million Solar Radiation and Climate Experiment (Sorce) mission, launched in 2003 to study why variations in the sun affect Earth's atmosphere and climate.
It has shown that during the most recent solar maximum the global mean temperature rise on Earth was only about 0.2 degrees Fahrenheit, but parts of the central US warmed by 0.7 degrees F.
Research in this area is valuable as it allows solar variability to be dismissed as the primary cause of global warming, Prof Haigh believes. "You can't really explain global warming in terms of solar variability. It has a significant effect but it is not global warming."
The free public lecture takes place at 8.30pm in the O'Flaherty Theatre. A limited number of seats will be available on the night