Filed under: Climate science
By Seth Masia
For years, a debate has raged between climatologists who forecast global climate change based on greenhouse gas forcing, and global-warming deniers who say it’s just part of a natural cycle and we can expect things to cool off again someday.
Deniers often point to a phenomenon called the Atlantic Multidecadal Oscillation as a natural cycle causing climate heating and cooling. The AMO is a 70-year cycle in ocean-surface temperature first identified in 1994 by Michael Schlesinger and his team at the University of Illinois. Schlesinger doesn’t like the name, because the same cycle can be found in Pacific and Indian Ocean waters, too. The temperature oscillation can be traced back to the last ice age, and beyond. The cycle last “bottomed” 35 years ago, and it has just peaked.
Last August, a group of researchers at the British Met Office reported that the AMO’s upcoming cooling mode is likely to “flatten” global warming for the next few years. Now a team of climate modellers at the Leibniz Institute of Marine Sciences at Kiel University confirm that prediction. They say the AMO cooling trend will flatten out most global warming trends for about 10 years. After that, their model predicts, temperature will soar upward again, assuming we don’t reduce greenhouse gas emissions sharply in the interim. According to both the British and German models, as long as greenhouse gases continue to rise, average global temperature will snake upward in a 70-year stepping pattern: upward for several decades, then flat for awhile, then upward again — but never downward.
The danger, of course, is that climate change deniers will jump on any “flattening” we may experience as evidence that global warming is a myth.
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