Science

Vanished global warming may not return – UK Met Office

But it might. Hey, we don't know, we're the Met Office

There hasn't actually been any global warming for the last fifteen years or so - this much is well known. But is this just a temporary hiccup set to end soon? A new report from the UK's weather bureau says it just might not be.

The Met Office boffins believe that, yes, a long-expected El Nino is at last starting up in the Pacific. This will probably mean warming. The Pacific Decadal Oscillation (PDO), another hefty Pacific mechanism, also looks set to bring some heat.

But, no doubt upsettingly for some, there's a third and very powerful factor to consider: the mighty Atlantic Multidecadal Oscillation (AMO).

The AMO has actually been heating the world up since the mid-1990s - though not strongly enough to raise temperatures - 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.

Those climbing temperatures may be imminent - but quite possibly not. ®

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