A new paper by McGill University physics professor Shaun Lovejoy posits that the effects of global warming were not fully felt until now because of "natural cooling fluctuations" from 1998 to 2013 caused by the El Nino effect. Lovejoy's paper said that global warming deniers improperly interpreted the cause of the "pause" in global warming, and used it to diminish or minimize the effect of global warming.
Lovejoy's paper used the same statistical analysis method to study global temperatures that he had developed earlier in the year for an April 2014 article published in the journal Climate Dynamics. The earlier paper was a massive statistical analysis of global temperatures for the past 125 years, before the Industrial Revolution. He found that there were natural periods of cooling in the Earth, but that even with that he was able to rule out with a 99% degree of certainty that the current global temperature rise we are experiencing is natural. He said it was 99% likely that global warming has been caused by man-made carbon dioxide emissions since the Industrial Revolution. Tech Times writer Jim Algar wrote about this study in April: https://www.techtimes.com/articles/5512/20140413/odds-very-much-against-global-warming-being-due-to-natural-factors-scientists-say.htm
In his new paper, Lovejoy addressed the cause of the global warming "pause" from 1998 to 2013. He said that the decrease in global warming in this time period was most likely caused by a period of natural cooling on the Earth, which temporarily masked the effect of global warming. The period showed a consistent pattern with pre-Industrial periods of cooling, Lovejoy's paper said. He thinks that this is a much more realistic explanation for the "pause" on global warming in the past 15 years than to say that global warming did not exist. For any remaining skeptics, Lovejoy's earlier paper proved very conclusively that global warming has made real, permanent changes to the Earth over the past 100 or so years.
About every 20 to 50 years, Lovejoy says, there is a natural cooling of about 0.28 to 0.37 degrees Celcius, which is consistent with the cooling since 1998.
Lovejoy says that the 1998 to 2013 cooling "exactly follows a slightly larger pre-pause warming event, from 1992 to 1998," so that the natural cooling during the "pause" is no more than a return to the longer term natural variability, Lovejoy concludes. "The pause thus has a convincing statistical explanation."
Lovejoy added that "Being based on climate records, this approach avoids any biases that might affect the sophisticated computer models that are commonly used for understanding global warming."
