They warn that the relief is temporary and climate warming which they believe has been caused by human activities will not slow down. Michael Mann (Distinguished Professor of Meteorology at Penn State) and his colleagues explain that global warming has been slowing down partly due to natural climate oscillations. These oscillations are “variability in the internal climate system” and don’t indicate that global warming caused by humans is slowing down. The “warm phase” of the Pacific Decadal Oscillation. Image: Wikipedia. Prof. Mann stated that “we know it’s important to differentiate between natural and human-caused climate variability so we are able to assess the effect of climate change on a range of phenomena, including droughts and extreme weather events.” Mann and Byron A. Steinman (president of geological sciences at Penn State), analyzed a mixture of observational data from real world and climate models simulations of climate to better understand the factors that contributed to the climate variability in Northern Hemisphere over the historical era. The journal Science published their findings (citation below). AMO (Atlantic Multidecadal Oscillation), describes how temperatures at the North Atlantic sea-surface tend to fluctuate over periods of 50 up to 70 year. PDO (Pacific Decadal Oscillation), however, is more variable over longer timescales. Researchers only examined the multidecadal portion of PDO – they call it PMO (Pacific Multidecadal Oscillation). The authors conducted several climate simulations and found that AMO and PMO were not strongly correlated. They aren’t, however, part of the global stadium wave oscillation, contrary to some claims. Professor Mann directs the Penn State Earth System Science Center. Pacific Ocean causes slower warming. The Pacific Ocean caused slower warming in the Northern Hemisphere. This was not due to AMO’s relatively flat trend, but because of a sharply downward-trending Pacific Ocean. The cooler Pacific Ocean is preventing global warming. Scientists concluded that global warming’s unusually slowdown over the last ten years and its downtrending PMO are due to the heat trapped beneath the tropical Pacific, and an inclination for La Nina-like conditions. According to the authors, “While paleoclimate data suggests that such a response may be caused by subtle climate features that climate models don’t currently capture,” Prof. Mann stated that “Our findings have significant implications for the attributions of recent climate shifts.” Researchers predict that recent global cooling in the Pacific Ocean will soon reverse and add to the human-induced heat. Citation: “Atlantic & Pacific multidecadal oscillations & Northern Hemisphere temperature,” Byron A. Steinman, Michael E. Mann et Sonya K. Müller. Science. 27 February, 2015. DOI: 10.1126/science. 1257856.
