While not denying human responsibility, an expert on radiative heat in the atmosphere argues that even small increases in solar radiation could impact on our changing climate, writes Dick Ahlstrom.
The climate change being recorded around the Earth is down to human activity, most scientists accept. But there are other potential contributors to global warming, including the sun.
Even a small increase in solar radiation could have an impact on the rate of warming, suggests the professor of atmospheric physics at Imperial College London, Prof Joanna Haigh.
Haigh comes to NUI Galway later this month to discuss her studies of solar forcing at a joint Academy Times/Monsignor Pádraig de Brún Memorial Lecture.
Solar Variability and Climate Change is the title selected by Prof Haigh for the event.Haigh is an expert in radiative transfer in the Earth's atmosphere. She studies how gases and clouds in the atmosphere absorb and scatter radiation from the sun and also thermal radiation.
"A fundamental understanding of these mechanisms is important because the Earth's climate depends on a balance between incoming solar and outgoing thermal radiation," Haigh writes.
"In order to predict possible changes in the climate we need to assess its response to any imposed radiative imbalance."
She acknowledges that suggesting solar forcing is a possible contributor to global warming often triggers claims that she is a "greenhouse sceptic" and an apologist for the carbon-dioxide lobby.
She does not deny the human contribution to global warming, but argues that we need to look at all elements of the climate-changing mix. "As a scientist I try to remain objective and say what I'm interested in is the physics, the physical processes and how these things all interact with each other," she has commented on Australian radio.
Many studies have shown a link between variations in the 11-year solar cycle and a synchrony with changes in the meteorological readings, but the changes in solar irradiance seem too small to account for the apparent response on Earth.
Prof Haigh conducted research that provides a possible explanation for this apparent incongruity, however. She suggests that variations in solar output of ultraviolet radiation may be amplified by increasing the amount of ozone in the upper atmosphere.
Ozone is a powerful greenhouse gas, and increased amounts could contribute to global warming. She has calculated that ozone production in the stratosphere goes up by about 2 per cent when the solar cycle is at its peak. She predicts that this in turn would heat the lower stratosphere by about half a degree.
Climate models suggest that a warmer stratosphere would expand and tend to push tropical weather systems away from the equator and towards the mid latitudes. This would be disruptive to existing weather patterns, she notes.
Prof Haigh delivers her talk at NUI Galway in O'Flaherty Theatre at 8.30pm on Thurs, Nov 22. The lecture is free but places are strictly limited and must be booked in advance. Reserve your ticket via the Royal Irish Academy's website, www.ria.ie; a limited number of tickets will also be available by phoning the Academy on 01-6762570