A Canadian physicist says his studies have all but completely ruled out the premise that global warming throughout the industrial era has not been merely a natural fluctuation in Earth’s climate, as some have been claiming. The assertion was made after the scientist analyzed temperature data from as far back as 1500.
“This study will be a blow to any remaining climate-change deniers,” said study author Shaun Lovejoy who is also a professor of physics at McGill University in Montreal. “Their two most convincing arguments – that the warming is natural in origin, and that the computer models are wrong – are either directly contradicted by this analysis, or simply do not apply to it.”
Published in a recent edition of the journal Climate Dynamics, the study, based on statistical analysis of historical data rather on complex computer models used in previous studies, provides a new perspective to the question of what is behind global warming trends.
Lovejoy said that his analysis led him to conclude “with confidence levels great than 99%, and most likely greater than 99.9%,” that global warming since 1880 has been mostly caused by man-made emissions from the burning of fossil fuels and long-term temperature variations not caused by nature.
The historical temperature data Lovejoy used for times prior to the industrial era (before 1760) were estimates that were made from “multi-proxy climate reconstructions” that had been developed by scientists in recent years.
The climate reconstructions took into consideration a variety of natural indicators such as information from tree rings, ice cores, and lake sediments.
For his data from the industrial era, Lovejoy used levels of carbon-dioxide produced by the burning of fossil fuels as a representation for all human caused climate changes, since there has been a close relationship between the world’s economic activity and the release of greenhouse gases and particulate pollution.
“This allows the new approach to implicitly include the cooling effects of particulate pollution that are still poorly quantified in computer models,” said Lovejoy.
Lovejoy said that his findings complement those made in a report just released by the UN’s IPCC. He said that his study predicted, with 95% confidence, that doubling the carbon-dioxide levels in the atmosphere would increase global temperatures between 1.9 and 4.2 degrees Celsius. The IPCC’s prediction puts the rise in temperature between 1.5 to 4.5 degrees Celsius if atmospheric carbon-dioxide levels double.
“We’ve had a fluctuation in average temperature that’s just huge since 1880 – on the order of about 0.9 degrees Celsius,” said Lovejoy. “This study shows that the odds of that being caused by natural fluctuations are less than one in a hundred and are likely to be less than one in a thousand.”