Ocean Oscillations to Slow Global Warming until 2025, Researchers Say

So say a team of researchers led by Noel Keenlyside. (Those interested in seeing the full article, which I bought at the ridiculous price of $32, please let me know during the next week — I’ll send it to you.)

For an excellent report and discussion, see the dean of climate reporters, Andy Revkin at The New York Times (here). To wit:

The team that generated the forecast, whose members come from two
German ocean and climate research centers, acknowledged that it was a
preliminary effort. But in a short paper published in the May 1 issue
of the journal Nature, they said their modeling method was able to
reasonably replicate climate patterns in those regions in recent
decades, providing some confidence in their prediction for the next one.

In other words — hindcasting. Checking a climate model by seeing how well it replicates the climate of the past. By adding calculations for the Atlantic meridional overturning circulation (MOC), the Labrador Sea Convection, and the North Atlantic Oscillation, the researchers’ results improved. Raypierre encapsulates the result well in a comment on Revkin’s blog:

Yes, there’s a decadal vacillation superimposed on an overall
warming trend. Without CO2 increase you’d get warm,cold,warm cold, etc.
with no long term trend. With CO2 increase, instead you get
warming,plateau,warming,plateau, warming,plateau. The value of this
kind of study is that it lets you say more about what is going on when
you observe the warming to be interrupted for a while. Any model with a
good enough ocean will have some kind of PDO [Pacific Decadal Oscillation] in it. The difference with
THIS study is that they try hard to initialize it with an accurate
representation of the current state of the ocean, and therefore try to
get the PHASE of the PDO right, so they can attempt a prediction of
what will happen in the coming years.

This study makes a lot of sense to me. Looking over long term
simulations in some of the AR4 models, I’ve often gotten the impression
of a decadal warming/plateau alternation (and in some the Dust Bowl
warm years even line up with a warm phase). This study makes that much
more precise and convincing.

This is why we need models. Without a study like this to tell us
what is going on, we might see a temporary interruption in the warming
and think “aha, CO2 isn’t doing anything anymore,’ or “clouds are
saving us from warming, finally!’ This study shows the pause is
temporary, and says that the plateau will be compensated by more rapid
warming later. Time will tell whether they have it right, but it’s a
good direction to go in.

And for the graphically-minded, a chart! (To put it as simply as possible: the black line represents a previous consensus projection; the orange line represents a Hadley Centre dataset, and the green line represents the new decadal projection, based on a more skillful understanding of the data.

One does wonder about the substantial gap as of the year 2000 between the observations and the hindcast/forecast, but presumably that will narrow as skill improves.