It is time to stop quivering in our boots in pointless fear of the future and just roll up our sleeves and build it.
- Ray Pierrehumbert

Monday, August 23, 2010

Is Anthropogenic Forcing Quasi-Linear?

In following up on the World Climate Report (Pat Michaels' sute) article comparing 1936 to 2010


July 1936 T anomaly



July 2010 T anomaly


a couple of folks have hastened to provide anomaly maps of 1936 and 2010 on the same scale. Sure enough, they are not exactly identical. (Click for better images) Surely the author of the article ought to have done as much. In fact, it isn;t difficult to produce comparable anomaly maps here as contributor NewYork points out.

I'm not sure how compelling this all is either way.

What I find even less compelling is the argument on the WCR site from telconnection indices. That just restates the problem; it doesn't resolve it. And then there is this:

The WCR article concludes:

There are several things of note:

1) The July 2010 combined value is the highest since 1950—nearly 50% greater than the second highest value which occurred in 1952.

2) The combined index has been mostly positive since 1981, and mostly negative from 1955 through 1980. This behavior imparts an overall positive trend since 1950.

3) The 2010 value is about 3 times greater than the value expected based on the trend alone.

Is anthropogenic global warming behind any of this behavior?

It is hard to know for sure, but one thing that is certain is that if global warming does have a hand in the game (perhaps through the trend term), what it’s holding is pretty weak.

(emphasis added).

The argument seems to be that since this year is so far off the trend line, that the anomaly cannot possibly be caused by the same "thing" that caused the trend. One would expect a sounder argument from a professional, but I am seeing versions of this all over the place. The system is nonlinear. There are thresholds, and regime shifts. "Tipping points" if you will. The current year is so anomalous in so many ways that it demands explanation. The fact that it is off the trend line is no secret. The idea that its strangeness cannot possibly be because of anthropogenic forcing since the trend itself has been modest simply doesn't hold water.

Examples in mundane life? How about blowing up a balloon? The more pressure you put into the balloon, the larger it gets. Up to a point. Then the balance of forces shifts, and it finds a new equilibrium, in shreds all over the room.

This reminds me of the argument that n-g made about the fraction of the Nashville flood (the earlier one, remember?) attributable to anthropogenic change. I simply don't think these linear arguments stand. There are reasons to anticipate new configurations of the atmosphere during the rapid shifts we have now initiated. It's not reasonable to assume that it's just business as usual plus a gentle additive trend in all variables. It may turn out that way (one can hope) but you can't assume it. And on the evidence of this year, that mild scenario is not the one that is going to play out.

To be fair, the WCR article didn't really commit to this argument, but it seemed to me to wave in that general direction. A lot of the people who think we are not in very deep trouble seem to have a small-perturbation view of anthropogenic climate change. But it's only a small perturbation until it ain't, and nobody really knows when nonlinear adjustments cut in. The simulation models seem unexcitable on this front, but how much do we trust the simulations outside the realm of observational experience?

19 comments:

Oale said...

As the imbalance of incoming and outgoing energy gets greater the engine will run faster (basic description of a heat engine) and this produces friction in the engine parts that will eventually manifest itself as an engine failure (insert a nondescribed extreme aberration in the (not-so-stable) climate system.)

Steve Bloom said...

Oale, I'm not sure this is a good analogy. It's more like the engine is being lubricated and running somewhat faster but also more powerfully, albeit backfiring all the way, and if things go too far is transformed into a different engine (accompanied by some really big backfires).

Oale said...

thanks Steve Bloom, I'm not an engineer of engines, as you may have guessed. Might the cranking noise while switching external gears in a bike work as an analogy for climate disruption?

Chip said...

Michael,

We showed a combined teleconnection index that was trending towards a more frequent hotter western Russia configuration--perhaps a sign of the influence of global warming. Perhaps not. But, as we pointed out, the trend doesn't get us anywhere near this summer's conditions. But maybe it contributed something. The NOAA PSD analysis found no trend towards this summer's conditions at all. And in fact, concluded that the level of heat could fully be explained by the atmospheric configuration alone--didn't even require any extra heating from background global warming, aerosols, urbanization, et al.

I guess there are two hypotheses that could fit this data:

1) rare, but natural variability
2) tipping point has been reached

I am not sure how to adjudicate between these two, at least for the time being. I guess if the balloon has burst, and the tipping point has been reached, we'll now start to see intense heat waves in western Russia nearly every summer? If not next summer or the summer after that, then how long do we have to wait? Do we now expect a trend after the tipping point has been reached? If all was quiet until 2050 and another heatwave of similar magnitude struck western Russia which hypothesis would that argue for?

At this point it is hard for me to tell the difference between a tipping point from AGW and a bolt-out-of-the-blue. At what point do you suggest that history becomes a useful arbiter?

-Chip

Michael Tobis said...

Chip, a fair question.

The fact that there is no obvious answer is not reassuring to me. But indeed that is the right question.

I think we have to study the whole set of events and determine whether it requires conditions that would have been unlikely without anthropogenic forcing.

I don't know as we are guaranteed a timely answer. What the rational policy response is to such a single severely anomalous year is also unclear.

If the world does decide to give us a clear answer, that won't be good news. That much is clear. It's important, I think, to acknowledge that there is no way to treat these events as reassuring.

n-g said...

Michael - Your argument would be more credible if the doubled CO2 equilibrium model runs showed dramatically different weather regimes than their baseline runs. I don't know offhand if they do or not, but it's your argument, so look it up...

Aaron said...

Chip,

Let us consider the concept of black swans. As the first naturalists sailed from Europe to Australia, they did not see a progression of light gray, dark gray, and then black swans. No, up to the moment that they saw their very first black swan, they thought all swans were white.

We know small changes in the temperature of the surface of the Pacific Ocean (El Nino) rapidly affect the weather around the world. However, with anthropogenic global warming, we have large areas of ocean with significant, long term temperature anomalies. There is no reason why these ocean temperature anomalies cannot push gradual weather changes as dramatic as the abrupt weather changes associated with El Nino.

That we have not seen such weather changes is likely symbolic of a failed approach to weather attribution. The weather changed as a result of anthropogenic forcing, but weathermen called it “natural variability”. A warming North Atlantic is one case, another case is the American Plains. In the early 1930’s, we plowed the plains, breaking the sod, changing the albedo, and drying the soil; thereby causing the “Dust Bowl”. (Certainly not what today we call AGW, but it was anthropogenic desertification.) Weathermen point to the warmth of 1936 as “natural variability.” Recent warm summers in the US do not look out of the range of natural variability because the heat of the dust bowl is assumed to be natural, rather than anthropogenic. Likewise, Russia had its failed attempts to open new farmland that resulted in broad anthropogenic desertification that should be accounted for in a climate history of Russia. This is not done in the NOAA PSD.

The nature of interactions between air over the Arctic and the jet stream has changed, See http://virga.sfsu.edu/pub/jetstream/jetstream_norhem/1007/10073106_jetstream_norhem.gif ). The analysis talks of “blocks”, but are the conditions that generated the 2010 block the same that caused the previous blocks? In previous periods of Russian “blocking” the Arctic was colder and dryer. This summer the Arctic is moist. The jet stream moved north and flowed south (across open Arctic Ocean) toward Russia. The NOAA PSD does not acknowledge just how different the behavior of the jet stream and Arctic atmosphere was this summer from previous blocking episodes. I think that ultimately the (AGW driven) melt and warming of the Arctic Ocean will be tied to the jet stream blocking that produced the abruptly different weather of the summer of 2010.

We are to moving from the “white swan weather events” that we knew to “black swan weather events” of a warmer world without seeing many gray swans in between. That is, the Earth’s weather system is moving from one equilibrium state to different (higher energy) equilibrium state(s) that produce weather we have not seen before.

Steve Bloom said...

Sure, Oale, with progressively less lubrication.

Aaron said...

Chip,

Let us consider the concept of black swans. As the first naturalists sailed from Europe to Australia, they did not see a progression of light gray, dark gray, and then black swans. No, up to the moment that they saw their very first black swan, they thought all swans were white.

The nature of interactions between air over the Arctic and the jet stream has changed, See http://virga.sfsu.edu/pub/jetstream/jetstream_norhem/1007/10073106_jetstream_norhem.gif ). The analysis talks of “blocks”, but are the conditions that generated the 2010 block the same that caused the previous blocks? In previous periods of Russian “blocking” the Arctic was colder and dryer. This summer the Arctic is moist. The jet stream moved north and flowed south (across open Arctic Ocean) toward Russia. The NOAA PSD does not acknowledge just how different the behavior of the jet stream and Arctic atmosphere was this summer from previous blocking episodes. I think that ultimately the (AGW driven) melt and warming of the Arctic Ocean will be tied to the jet stream blocking that produced the abruptly different weather of the summer of 2010.

We are to moving from the “white swan weather events” that we knew to “black swan weather events” of a warmer world without seeing many gray swans in between. That is, the Earth’s weather system is moving from one equilibrium state to different (higher energy) equilibrium state(s) that produce weather we have not seen before.

Steve L said...

I like this post, but I wonder if extreme weather is all part of coming to a new equilibrium. Not that I think we're reaching an equilibrium ... perhaps it would be more appropriate to use a 'market correction' as an analogy. What I mean is that 2010 has seen a lot of extreme weather, and maybe we shouldn't expect that to increase in the near term. Maybe things will go back to 'near normal' for a while until another 'correction' happens.

With Fraser R sockeye, last year's return was the worst in over a hundred years. This year's return is the best since 1913. I can't imagine subsequent years generating more extreme variance very often.

Chip said...

Aaron,

Don’t get me wrong, I agree that we (humans) have impacted the weather (through among other things, greenhouse gas emissions). I just wonder whether we can tell.

I tend to think it will reveal itself through gradual changes rather than produce sudden, unhitherto seen weather. But certainly, I can’t rule that possibility out.

The question I was posing, is aimed at what the hypothesis is and how to set up a test of it.

We know black swans exist, the question we’d like the answer to is how they got that way.

-Chip

Michael Tobis said...

John, a fair challenge, but some caveats apply:

I'm not sure an equilibrium 2xCO2 run tells us very much about the detailed dynamics because of the crude ocean models used.

I think a CGCM with a ramp stands a better chance, but even then, these things seem somewhat overdamped to coax them into line with present conditions.

It's becoming clear that the ocean and the sea ice and possibly the land ice are players, and I think aerosols are too. It's hard to know what to include and what not to...

Also there's the question of how to categorize 2D flows as normal or weird. I've thought about it some today and nothing jumps out at me as a practicable clustering technique. I've seen some attempts at this that seemed hopelessly wrong, but I don't know of anything satisfactory.

Chip said...

Looks like some folks are thinking pretty hard about how to detect tipping points.

-Chip

Chip said...

NOAA's Martin Hoerling pretty much clears up the rational behind the conclusions from their analysis in this interview by the CEJournal.

Not really all that different from the sentiments expressed in our two articles over at World Climate Report (despite the protestations of some).

-Chip

Steve Bloom said...

Sure it's not all that different, Chip, minus the factoids aimed at your climate-illiterate readership.

Aaron, thanks for the link to that site, but I couldn't locate any sort of discussion. Pointer?

Re the Arctic dipole anomaly, it's relevant to note that the models failed to predict it (also answering John's comment somewhat). That they would also fail to predict down-latitude consequences isn't surprising. As you say, the PSD folks really needed to at least mention a possible role for the dipole anomaly, plus take into account the Pakistan situation.

Steve Bloom said...

Steve L, we can talk about new climate conditions, but not about any sort of equilibrium so long as we continue to rapidly force things.

Steve Bloom said...

Michael was in on the discussion, but I had managed to miss this comment from Stu Ostro. The first graph shows a distinct 15-year trend toward high pressure centered over eastern Russia. The PSD team looked for a trend in blocking events in that location and didn't find it, but has there been enough time for that?

It's interesting to see the bland responses to the unarguable fact that the whole atmospheric circulation is changing before our eyes such that the past has ceased to be a very good guide to what to expect in the future.

Aaron said...

Steve,
No discussion, just that, in the past, cold dry Arctic air tended to move south at lower altitudes, i.e., the classic Arctic cold front. What bothers me is that everyone talks about the melting Arctic sea ice and nobody talks about increased water vapor in the air over the Arctic Ocean. Moist air rises, dry air sinks – we have to assume that moist air over the Arctic Ocean rose and then moved south. That is different. That means that the Arctic air mass does not cool the ground. That means that the Arctic Air mass does not lift up other air masses up causing them to drop their moisture as those other air masses rise and cool.

I say moist air rising from the Arctic Ocean is resulting in completely new patterns of jet stream flows. One result is huge amounts of water vapor are flowing over, condensing, and precipitating onto Greenland.

People have not incorporated the idea of a moist Arctic into their thinking about the weather.

Aaron said...

On more general point on weather statistics and attribution.

In the US, 1936 was a warm year in part due to poor farming practices in the preceding years. It was not AGW as we know it, but it was anthropogenic desertification that resulted in temperatures that would not have occurred without human activities. The “dust bowl” was largely manmade. Russia had similar bouts of aggressive sod breaking (5-Year Plans), resulting in anthropogenic desertification, warm temperatures, and blocking. Modern weathermen look at these warm temperatures and call them “natural variance”. And, they assume that the blocking by those thermal highs was natural. That is like calling London “Pea Soup Fogs” and LA smog, “natural”.