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Data gathered with the latest technology by the European and American space agencies gives an idea of the complex array of factors involved in determining the cause of changes in climate By Jerome Simpson While the climate change debate rages, data published on websites of both the European and American space agencies have recently shown that it's not just carbon dioxide, or even greenhouse gas emissions, that are contributing to global warming. Even though a worldwide panel of more than 100 scientists working for the United Nations has noted that mounting evidence strongly indicates climate change is caused by human activity, science cannot deliver an unqualified, unanimous verdict on the issue. The task of measuring and projecting climate patterns is too cumbersome to allow for complete certainty, and the number of variables that must be considered is huge. Take the sun's brightness and magnetism, for instance. Three hundred years ago, when the sun was unusually inactive, Europe was known to be a chilly place. Many experts suppose that solar radiation has intensified since then, and recent estimates conclude that the average visible light increased by 0.2 percent since 1700 and ultraviolet rays by 0.7 percent. Increased solar activity can also cause increased magnetism. The Ulysses spacecraft, jointly operated by the European Space Agency (ESA) and the American National Aeronautics and Space Administration (NASA), has found data indicating that the sun's magnetic field in the Earth's vicinity has doubled in strength during the 20th century. The more intense magnetic field has also reduced the number of cosmic rays reaching the earth from the galaxy. These cosmic rays have been shown to contribute to the formation of the kind of sulphuric acid particles on which cloud particles form. It appears that the shortage of cosmic rays has reduced the overall cloudiness of the planet, thus increasing the amount of sunshine and warmth the world absorbs. Fast forward to the more recent past, and NASA-funded research suggests that it is indeed human activity - and not just natural changes - that seems to be causing climate change in the last few decades. Black carbon particles (soot), for instance, which are generated by the burning of coal and diesel, causes a semi-direct reduction of cloud cover. Clouds reflect 40-90 percent of the sun's radiation, so getting rid of clouds will increase the temperature. Research shows that, since 1950, the rate of greenhouse gas heating caused by methane and CFCs has increased even faster than the heating caused by carbon dioxide (CO2). The growth rate of CO2 in the atmosphere doubled between 1950 and 1970, but levelled off from the late 1970s to the late 1990s. Meanwhile, global surface temperatures have increased by about 0.9 degrees Fahrenheit since 1975. But it would be a simplification to only blame human activity for climate conditions. In one instance, after NASA noted a decline in the thickness of Greenland's ice sheet between 1993 and 1999, together with a loss of 51 cubic kilometres of volume, newspaper headlines decried the change as another sign of human-caused global warming. The headlines overlooked a host of other plausible explanations. For example, ice cores taken as part of another NASA-funded study suggested that natural variation in snowfall may be partly to blame. Another possible cause might be the flux of warm water into the North Atlantic, brought on by the 1990-1996 positive phase of the slow moving North Atlantic oscillation (a 20-30 year cycle). Using a variety of methods, scientists can develop a climate record that goes back as far as 1,000 years. But this is still a mere snapshot in terms of cosmological time - ice ages typically occur once every 100,000 years. So it can be difficult for scientists to try to draw conclusions based on this data. If there's one lesson to be learned from a scientific approach to climate change, it's that things are usually much more complex than they first appear. Although climate models have improved, it's theoretically impossible to create a "perfect" model that includes all the details of the real system. And no single scientific result based on real-life data ever deserves absolute confidence. In the end, the best we can expect is a scientific consensus based on a preponderance of evidence. And the evidence indicating that human activity increases climate change is mounting. The report by the scientists working for the UN's Intergovernmental Panel on Climate Change projected an increase in globally averaged surface temperatures of 5.8 degrees Celsius between 1990 and 2100 - the kind of figure that is usually associated with temperature variations over the course of hundreds of thousands of years. This sort of evidence about the threat to our planet is hard to ignore. |
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