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Tuesday, December 9, 2014

An AMOC early warning signal prompts panic at WUWT

Sou | 5:13 AM Go to the first of 8 comments. Add a comment

There's a paper out in Nature Communications, in which PhD student Chris Boulton and colleagues say they've detected signals that can be used as an early warning of a collapse of the Atlantic Meridional  Overturning Circulation (AMOC). They used a coupled climate model that showed that these signals could become significant about 250 years before the start of any collapse, and, going by the charts in the paper, may start to be seen sooner than that.

The AMOC transports heat from the tropics northward in upper levels in the ocean in the northern hemisphere, sending cooler water southward at lower levels in the ocean. You can read more about it here at the Encyclopedia of Earth. Here's a video from YouTube:

The AMOC has been studied a lot and is being closely monitored. If the AMOC were to collapse, it would cause abrupt changes in climates particularly in the northern hemisphere. From the press release at
Experiments suggest that if the AMOC is 'switched off' by extra freshwater entering the North Atlantic, surface air temperature in the North Atlantic region would cool by around 1-3°C, with enhanced cooling of up to 8°C in the worst affected regions.
The collapse would also encourage drought in the Sahel -- the area just south of the Sahara desert -- and dynamic changes in sea level of up to 80cm along the coasts of Europe and North America.

The paper identifies the best spots to detect the early warning signals. It also discusses some caveats, such as if the injection of fresh water were to increase substantially from what is happening at present. Currently, fresh water is flowing into the North Atlantic, which could cause a major change in the AMOC, which is why it's being monitored fairly closely.

There's an article about this at WUWT (archived here), under the headline: "Climate alarmism secures a set of warning signals", which suggests that Anthony Watts doesn't want to know ahead of time. It's just a copy and paste of the press release, which can be also read at His lead-in suggests he doesn't understand the paper (well, he hasn't linked to it so he probably hasn't read it), writing:
"An alarming claim from from the University of Exeter, based entirely on modeling."

He's wrong if he thinks the paper is suggesting an imminent collapse. It's not. What it describes is the results of an experiment to find early detection signals, which could be seen 250 years before any collapse. In the simulation, the collapse happens after 800 years of increasing freshwater injection. He's also wrong in saying it's entirely based on modeling. The experimental design is based on an understanding of AMOC, which is in part derived from paleoclimate observations.

From the WUWT comments

It looks as if JimS wrongly thinks it would mean global cooling. It doesn't. Just in the North Atlantic region.
December 8, 2014 at 8:39 am
“Experiments suggest that if the AMOC is ‘switched off’ by extra freshwater entering the North Atlantic, surface air temperature in the North Atlantic region would cool by around 1-3°C, with enhanced cooling of up to 8°C in the worst affected regions.”
By George, are they finally catching on to the real danger, cooling, instead of warming?

DAV had a similar reaction to Anthony Watts, mistakenly thinking that the paper was about an actual imminent collapse. It's not. It's describing early warning signals and where's the best place to detect them.
December 8, 2014 at 8:41 am
This stuff would be funny if it wasn’t the equivalent of falsely yelling fire in a crowded theater.

Paul asks a good question
December 8, 2014 at 8:47 am
Experiments suggest that if the AMOC is ‘switched off’ by extra freshwater entering the North Atlantic, surface air temperature in the North Atlantic region would cool by around 1-3°C, with enhanced cooling of up to 8°C in the worst affected regions.”
I’m assuming “extra freshwater” is melt water, but wouldn’t the cooling tend to counteract that?
I think the point is that the collapse is fairly sudden - the switching off happens after a certain threshold is reached, after the freshwater is injected. So there's no time for it to slow down as such.

VicV is incoherent, apoplectic, and a paranoid conspiracy theorist:
December 8, 2014 at 8:50 am
Could… could… if… would… could… could… Now give those of us who have reached the status of elite complete control of energy so we can protect our families and you can twist in the hot (or cold) wind of climate change.

O Olson makes one of the silliest remarks, but not the silliest:
December 8, 2014 at 9:07 am
So now it’s gone from “we only have a few years left to act” to “early warning signals are present up to 250 years before it collapses”? So when absolutely nothing happens (like for maybe 18 years or so) they are trying to tell us to give them another 250 years to carry on with the same old fear mongering?

Scottish Sceptic wants to boast about his ignorance and how much he despises knowledge:
December 8, 2014 at 9:19 am
More natural variation wrongly interpreted as “signs of impending doom”.
Why don’t they just read the signs from entrails like the soothsayers of old. It would have as much credibility, it would cost a lot less and at least there’d be a lamb supper afterwards. 

Does Alan the Brit think that modeling is real life observations rather than an experiment? Perhaps he thinks that time travel is possible too.
December 8, 2014 at 9:30 am
“Experiments suggest”????? Since when is modelling, experiments?
“The study is the most realistic simulation of the climate system in which this type of early warning signal has been tested.” So they’d like us all to believe!

Chris A. Boulton, Lesley C. Allison & Timothy M. Lenton. "Early warning signals of Atlantic Meridional Overturning Circulation collapse in a fully coupled climate model." Nat. Commun. 5:5752 doi: 10.1038/ncomms6752 (2014). (open access)


  1. This comment has been removed by the author.

    1. Oh drat, I wanted to add something to my earlier post and deleted it. Anyway I was going to add that this reminds me of another AMOC shutdown study but instead deals with paleoclimate modeling that injected a large amount of freshwater from Lake Agassiz using the MIT GCM. 5 Sverdrups at once versus the maximum of .4 Sv per year in this study. It really puts studies like this Boulton paper into proper context.

      My original comment was unrelated to the article and had to do with some astroturfing I've been seeing from the WUWT crowd. I've been going back and forth with Rick Cina over at livescience for the past week now and it's obvious he's either being paid per post by Anthony Watts or actively encouraged. He also goes by the name kennethrichards@WUWT. Anyway pop over there and read some of his comments if you want a good laugh.

    2. Ah, that must be 'rcina', who posts only on climate-related threads over at Bad Astronomy. I used to frequent there, but gave up on BA months ago as it is an unmoderated food fight. Some of the denialists have been running 2 or 3 socks over there for a long time, every post being the functional equivalent of "Nyah, nyah warmists! You suck." Waste of time.

  2. All of science is based on modeling -- that's the whole point: coming up with increasingly accurate models of how things work.

    Pseudo-science also works with models, but frees itself of the stifling limitation that models should be consistent with reality and with each other.

  3. When the AMOC shuts down it would compensate a part of the global warming for Europe and Russia, while the blocking libertarian in the US are burning in the hell they wanted. A just shift in the world power balance.

    1. *Northern* Europe. The change will enhance heating farther south, note.

  4. I haven't checked on the data lately and don't have time to do so just now, but IIRC the AMOC had been determined to be significantly slowing recently. There was a bit of a kerfuffle when the initial data pointing to this (based on a new sensor array) came out about 5 years back, including an RC post that concluded it was too early to panic and that we should wait and see if subsequent data supported a trend. Well, when the data did just that there was barely a ripple of reaction in the news media or even the blogosphere. I found that very strange. Of course even assuming that the most recent data continues the trend, it's still early days.

    "...if the injection of fresh water were to increase substantially from what is happening at present."

    There's no "if" about it. Just look at the GRACE mass loss data trend for the Greenland ice sheet and note especially that the NE Greenland glaciers, until very recently thought not to be very sensitive to current warming, have undergone a sharp acceleration of ice loss in the last few years. This latter actor is crucial since those glaciers are far less kinematically constrained than many of the other big ones elsewhere in Greenland (IOW they reach the sea via much larger "gates" that make for poor brakes on ice loss acceleration).

  5. wasn't it the melting of the laurentian ice sheet that had an effect during the end of the last ice age?
    It seems we have a lot less ice now and it would take a long time to happen. That seems the reason there is not much interest.
    also if we are talking 200 years, the global temp might be 4-6° higher than now so the decrease in Europe would not be that great compared to now. thinking there will be other things of greater concern then.


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