Evidence that Global Warming Is Due to Nature Continues to Decline

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earthThe argument used to be that global warming existed at all. Now, the debate is more often over whether global warming is the result of natural or manmade activities. A new study is designed to eliminate any argument that warming is caused by nature or that the previous computer models are wrong. The study, published in the science journal Climate Dynamics, takes a new approach in determining whether the cause has been mostly from man-made emissions from fossil fuels. Unlike the computer models that estimate the effects of greenhouse-gas emission, historical data was used to disprove the hypothesis that warming over the past century is due to natural long-term variations in temperature.

Shaun Lovejoy of McGill University analyzed data from 1500, showing that there is virtually no possibility that global warming is the result of a fluctuation in the earth’s climate. The study applied the statistical methodology to look at the probability that global warming since 1880 was the result of natural variability. The conclusion he reaches was that the competing hypothesis could be ruled out “with confidence levels greater than 99% and, most likely, those greater than 99.9%.”

A system to estimate historical temperatures developed in recent years by scientists called “multi-proxy climate reconstructions” was used along with fluctuation-analysis techniques borrowed from nonlinear geophysics. A number of gauges from nature are taken into consideration to determine the temperature variations that have taken place over wide ranges of time scales. While Lovejoy’s findings were not based on the huge computer models scientists typically use in estimating the magnitude of future climate change, they were complementary to those found by the International Panel on Climate Change (IPCC), allowing him to predict with confidence that doubling the levels of carbon-dioxide in the atmosphere would result in an increase in the temperature of the climate by 2.5 and 4.2 degrees C.

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