Global warming may not be caused by humanity's fossil fuel emissions, but could be due to changes in the Sun.

Research suggests that the magnetic flux from the Sun more than doubled this century. As solar magnetism is closely linked with sunspot activity and the strength of sunlight reaching Earth, the increase could have produced warming in the global climate.

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The evidence for an increasingly energetic Sun comes from a new analysis of the magnetic field between the planets, carried out by scientists at the Rutherford Appleton Laboratory, near Oxford, UK.

Solar Wind

This magnetic field is caused by the Solar Wind, a stream of particles given off by the Sun which fills the solar system.

The Solar Wind brings the Sun's magnetic field into space

The scientists produce evidence that since 1964 the interplanetary magnetic field has increased in strength by 40%.

Evidence from before the space age suggests that the magnetic field is 2.3 times stronger than it was in 1901.

Scientists do not doubt that the increased magnetic field results from a more energetic Sun. Their problem is that the effect of these increases on the Earth is unknown.

Not our fault?

The research is published in Nature and in the same journal Professor Eugene Parker, of the Laboratory for Astrophysics and Space Research, University of Chicago, comments that it could explain global warming.

He notes that the increased solar activity has occurred in parallel with an increase in carbon dioxide in the Earth's atmosphere. And it may not be a coincidence, he says.

Professor Parker suggests that the Sun's increased activity caused the Earth's global temperature to rise and that in turn warmed the oceans.

Warmer oceans absorb less carbon dioxide from the atmosphere. So a warmer Earth has more of the so-called greenhouse gases. Humanity's burning of fossil fuels may therefore not be the cause of global warming.

Perilous plans

Professor Parker adds that that more research must be done about the Sun's role in global warming before drastic action is taken here on Earth.

"It is essential to check to what extent the facts support these conclusions before embarking on drastic, perilous and perhaps misguided plans for global action," he says.

Measurements of the magnetic field are not the only evidence for the Sun's variable influence on the Earth. The planet went through a "little ice age" during the 17th Century, at a time when very few sunspots appeared on the surface of the Sun.