Met Office: Global Warming Pause ‘May Persist’ …

  • Date: 14/09/15
  • Lewis Page, The Register

… But it might not. Hey, we don’t have any idea

One of the most hotly debated issues on climate matters is the fact that there hasn’t actually been any global warming for more than fifteen years. This may be about to change – but a new report from the British climate bureau says, actually, maybe not.

The Met Office climatologists say that a long-expected El Nino is finally starting in the Pacific Ocean, which will probably cause significant warming. The Pacific Decadal Oscillation (PDO), another ocean circulation active in the Pacific, also looks set to heat things up.

But, innopportunely for people who may be desperate for a return to a warming world (perhaps at the Met Office’s Hadley Centre for Climate Science and Services, dependent on global warming for its raison d’être) there’s a third powerful mechanism in play: the Atlantic Multidecadal Oscillation, or AMO.

The AMO has actually been heating the world up since the mid-1990s, but now it looks set to swing into a negative phase and cool the planet off, probably for a long time, as AMO phases typically last several decades. The Met Office’s new report (pdf), just out today, has this to say about the AMO:

The current warm phase is now 20 years long and historical precedent suggests a return to relatively cool conditions could occur within a few years … Observational and model estimates further suggest AMO shifts have an effect on global mean near-surface temperatures of about 0.1°C. A rapid AMO decline could therefore maintain the current slowdown in global warming …

The Met Office doesn’t care for phrases such as “hiatus” or even “pause” to describe the absence of global warming for the last fifteen years or so: it describes the flat temperatures as a “slowdown”.

But it’s all the same thing. One should note that the Met Office report is strongly hedged – its title even ends in a question mark, in the style of headlines-to-which-the-answer-is-no.

But it isn’t just the Met Office that believes the AMO may be headed into a cold spell. Scientists studying Atlantic hurricanes have noted that these massive storms have been mostly less common and less powerful in recent years, and the suggestion is that this trend may be set to continue, with the underlying mechanism being a switch in the AMO to a negative phase.

Meanwhile, it appears quite possible that 2015 will be a record warm year globally – though not in Europe or America. However, as NASA climate chief Gavin Schmidt pointed out in 2013, “one more year of numbers isn’t in itself significant”.

Just as it took quite a few years before the hiatus could be said to be ongoing, it will require several years of climbing temperatures before it can be said to be over.

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