The natural oscillations in the climate, which resulted in cooler Pacific Ocean waters, were partially behind the controversial global warming "pause", say researchers.
However, this in no way suggests that the planet is now cooling, nor that there is any slowdown in human-caused global warming.
After a period of rapid global warming throughout most of the 20th century, the pace of global temperature rise has slowed greatly over the last 10 to 15 years. This unexpected slowdown has raised questions about the accuracy of climate change forecasts, and sent scientists searching for an explanation.
In a paper published in the journal Science, climate researchers argue that this slowdown is the result of natural and decades-long variations in sea water temperatures in the Pacific and Atlantic oceans.
The Pacific and Atlantic oceans undergo
decades-long natural oscillations that alter their sea surface temperatures. These natural cycles flip-flop between cooler and warmer phases. Over the past 130 years, the tempo of global warming has revved up or slowed down in tune with changing ocean temperatures.
Distinguished Professor of Meteorology at Penn State, Michael Mann, and team explained that the recent halt in global warming has been partly due to the natural fluctuations in the climate, with the pendulum soon going the other way.
These swings represent “variability to the internal climate system,” and in no way suggest that human-induced global warming has stopped. The recent slowdown, such as it was, is certainly no reason not to worry, they stress.
Prof. Mann said: “We know that it is important to distinguish between human-caused and natural climate variability so we can assess the impact of human-caused climate change on a variety of phenomena including drought and weather extremes.”