A new study shows the recent "pause" in global warming is most likely linked to an interaction between Atlantic and Pacific climate oscillations.
According to the researchers, the findings suggest there is not actually a slowdown in global warming, as has been previously considered, Penn State University reported.
"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," said Michael Mann, distinguished professor of meteorology at Penn State. "The North Atlantic and North Pacific oceans appear to be drivers of substantial natural, internal climate variability on timescales of decades."
The research team analyzed a combination of "real-world observational data and state-of-the-art climate model simulations" from the Intergovernmental Panel on Climate Change to gain a better understanding of what causes climate variability in the Northern Hemisphere.
The study looked at the influences of the Atlantic Multidecadal Oscillation (AMO) (oscillations in North Atlantic sea-surface temperatures over periods of 50 to 70 years) and Pacific Decadal Oscillation (PDO) (which varies over broader timescales). Using climate simulations, the researchers showed the AMO and PMO are not significantly correlated, and the Northern Hemisphere is most likely warming more slowly because of a downward-trending PMO.
The study concluded the downward-trending PMO and perceived "pause" in climate warming are linked to heat beneath the Tropical Pacific as well as La Niña type conditions; the most likely explanations for these phenomena is "random excursions" of the AMO. Based on historical trends of AMO and PMO, the researchers believe this trend will most likely reverse itself in the future and add to human-caused warming.
"Our findings have strong implications for the attribution of recent climate changes," Mann said. "Internal multidecadal variability in Northern Hemisphere temperatures likely offset anthropogenic warming over the past decade."
The findings were published in a recent edition of the journal Science.
