Study sheds new light on how the Sun affects the Earth's climate

New study reveals that Sun's activity has recently affected the Earth's atmosphere and climate in unexpected ways</em> - News Release</em>

Imperial College London News Release

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Wednesday 6 October 2010

The Sun's activity has recently affected the Earth's atmosphere and climate in unexpected ways, according to a new study published today in the journal Nature. The study, by researchers from Imperial College London and the University of Colorado, shows that a decline in the Sun's activity does not always mean that the Earth becomes cooler.

It is well established that the Sun's activity waxes and wanes over an 11-year cycle and that as its activity wanes, the overall amount of radiation reaching the Earth decreases. Today's study looked at the Sun's activity over the period 2004-2007, when it was in a declining part of its 11-year activity cycle.

Although the Sun's activity declined over this period, the new research shows that it may have actually caused the Earth to become warmer. Contrary to expectations, the amount of energy reaching the Earth at visible wavelengths increased rather than decreased as the Sun's activity declined, causing this warming effect.

Following this surprising finding, the researchers behind the study believe it is possible that the inverse is also true and that in periods when the Sun's activity increases, it tends to cool, rather than warm, the Earth. This is based on what is already known about the relationship between the Sun's activity and its total energy output.

Although the Sun's activity declined between 2004-2007, the new research shows that it may have actually caused the Earth to become warmer

Overall solar activity has been increasing over the past century, so the researchers believe it is possible that during this period, the Sun has been contributing a small cooling effect, rather than a small warming effect as had previously been thought.

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."

Professor Sir Brian Hoskins, the Director of the Grantham Institute for Climate Change at Imperial College London, added: "We know that the Earth's climate is affected both by human activity and by natural forces and today's study improves our understanding of how the Sun influences our climate. Studies like this are vital for helping us to create a clear picture of how our climate is changing and through this, to work out how we can best protect our planet."

The researchers used satellite data and computer modelling to analyse how the spectrum of radiation and the amount of energy from the Sun has been changing since 2004. Instruments on the SORCE satellite have been measuring the Sun's energy output at many different wavelengths. The researchers fed the data from SORCE into an existing computer model of the Earth's atmosphere and compared their results with the results obtained using earlier, less comprehensive, data on the solar spectrum.

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Notes to editors:

1. "An influence of solar spectral variations on radiative forcing of climate" Nature, 7 October 2010

Corresponding author: J.D. Haigh, Imperial College London.

For full list of authors please see paper.

2. The SORCE satellite (Solar Radiation and Climate Experiment) is a NASA-sponsored satellite that is measuring incoming x-ray, ultraviolet, visible, near-infrared, and total solar radiation. The measurements from SORCE's instruments will help us address long-term climate change, natural climate variability, enhanced climate prediction, atmospheric ozone and UV-B radiation. Stratosphere/mesosphere. The stratosphere is a layer in the atmosphere that begins about 6-8km above the Earth's surface and extends to an altitude of 50km. The mesosphere lies above the stratosphere and extends to an altitude of 95-120km.

3. The University of Colorado was founded in 1876 in Boulder and is nested in the foothills of the Rocky Mountains. CU-Boulder is a national public research institution with an enrollment of more than 30,000 students, both undergraduates and graduates. The student population comes from all 50 American states and from more than 100 foreign countries.

4. About the Grantham Institute for Climate Change at Imperial College London

The Grantham Institute for Climate Change is committed to driving climate change related research and translating it into real world impact. Established in February 2007 with a £12.8 million donation over ten years from the Grantham Foundation for the Protection of the Environment, the Institute's researchers are developing both the fundamental scientific understanding of climate change, and the mitigation and adaptation responses to it.

The Institute intends that this work should be directly relevant to policy and decision makers. The Grantham Institute is unique among climate change research centres because it is situated at the heart of Imperial College London, one of the world's leading science, technology and medicine universities. The policy and outreach work that the Institute carries out is based on, and backed up by, the leading edge research of the College's academic staff.

5. About Imperial College London

Consistently rated amongst the world's best universities, Imperial College London is a science-based institution with a reputation for excellence in teaching and research that attracts 14,000 students and 6,000 staff of the highest international quality. Innovative research at the College explores the interface between science, medicine, engineering and business, delivering practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

Since its foundation in 1907, Imperial's contributions to society have included the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of research for the benefit of all continues today, with current focuses including interdisciplinary collaborations to improve global health, tackle climate change, develop sustainable sources of energy and address security challenges.

In 2007, Imperial College London and Imperial College Healthcare NHS Trust formed the UK's first Academic Health Science Centre. This unique partners hip aims to improve the quality of life of patients and populations by taking new discoveries and translating them into new therapies as quickly as possible. Website: www.imperial.ac.uk