...The early decades of the 20th century showed a distinct warming trend, peaking in the 1930s. However, from the 1940s through to the early 1970s, temperatures fell - sufficiently for commentators to raise the spectre of global cooling as we slid into the next ice age. A sudden jump in the mid-1970s heralded the return of a warming trend and led to the current concern about global warming.But peak temperatures were recorded in 1998; since then, we have had eight years with no warming. In the meantime, CO2 levels have risen inexorably.
Since we cannot experiment to test the effect of this on climate, scientists rely on observation and, in parallel, produce mathematical models of how the climate system operates. These models - fed with a range of assumptions about how population and energy use may change - are run on the world's most powerful supercomputers to give projections for future climate changes. It is these on which tales of future catastrophe are based.
But the climate over the past century has not behaved as simple models predict. Scientists have tweaked the models to reproduce the stop/start pattern, by adding in the effect of volcanic eruptions and man-made sulphate aerosols. Because they can be made to simulate the actual pattern of 20th-century temperature change, the assumption is that they provide a good model of future changes.
What the modellers do not explain are documented changes to the climate during recorded history. During the Roman Warm Period, England was a significant wine producer, a thousand years later Greenland was settled and farmed during the Medieval Warm Period, and harvests failed and ice fairs were held on the frozen Thames in the Little Ice Age of the 17th and 18th centuries. None of it was a result of man-made CO2 emissions.
The answer may lie in the ultimate source of warmth and life on Earth: the sun. Solar activity varies in a cyclic way, with sunspots being an obvious sign of changes. The more spots, the more active the sun. On a simple level, we know that the Little Ice Age coincided with a very low level of solar activity. We also know that the sun is currently in a particularly active phase...
...To shut down debate is unscientific. Science progresses by observation and deduction, by setting up hypotheses and testing them. Allowing one view to be pushed forward with no dissent sets a precedent that will stifle innovative thinking. Whatever Al Gore may believe, there is an even more inconvenient truth: he could be wrong.
Martin Livermore has a calm, thoughtful and truly scientific article about global warming over at the Telegraph (U.K.)
