Climate inertia

Imagine you’re on a supertanker that needs to change its direction in order to avoid a collision. What would you do? Would you continue going full steam ahead until you can see the collision object right in front of you? Or would you try to change course early, knowing that changing a supertanker’s course takes a considerable amount of time?

The supertanker’s inertia means that you have to act in time if you wish to avoid a collision.

The climate system also has a tremendous amount of inertia built in. And like with the supertanker, this means that early action is required if we want to change the climate’s course. This inertia is a crucial aspect of the climate system, both scientifically but also societally – but in the latter realm it’s a very underappreciated aspect. Just do a mental check: when did you last hear or read about the climate’s inertia in mainstream media or from politicians?

The inertia of the climate system could be compared to that of a supertanker: if we want to change its course, it’s important to start steering the wheel in the desired direction in time.

Why is it so important? Because intuitively many people might think that as soon as we have substantially decreased our CO2 emissions (which we haven’t), the problem will be solved. It won’t, not by a very long shot. Even if we reduce CO2 emissions to zero over a realistic timeframe, the CO2 concentration in the atmosphere – and thus also the global average temperature- will remain elevated for millennia, as can be seen in the figure below. The total amount of carbon we put in the atmosphere over the course of a few hundred years will affect life on this planet for hundreds of thousands of years. And if we want to reduce the amount of warming that we commit the future to, we need to reduce our carbon emissions sooner rather than later. The longer we postpone emission reductions, the stronger those emissions reductions would need to be in order to have the same mitigating effect on long-term warming.

That’s why climate inertia is so important.

Modeled response of the atmospheric CO2 concentration (panel b) and surface air temperature compared to the year 2000 (panel c) to prescribed CO2 emissions (panel a). The CO2 concentration remains elevated long after CO2 emissions have been reduced, because the long-term sinks for CO2 operate very slowly (see e.g. IPCC FAQ 6.2 for an explanation of these carbon sinks). Since CO2 impedes infrared heat loss, for millennia the globe will remain warmer than it was before CO2 concentrations rose. The temperature lags behind the CO2 concentration because of the time it takes for the oceans to warm up. Figure from Zickfeld et al (2013).

As I wrote before: Postponing meaningful mitigation action until the shit hits the fan comes with considerable risk, because many changes in climate are not reversible on human timescales. Once you notice the trouble, it’s only the beginning, because of the inertia in the various systems (energy system, carbon cycle and climate system). The conundrum is thus that those who caused the problem are in the best position to solve it, but since the full consequences will not materialize until much later, they have the least incentive to do so.

Over at Bits of Science two Dutch science journalists, Rolf Schuttenhelm and Stephan Okhuijsen, published an interesting piece that focuses on the same issue: we only see a portion of the warming that we have committed ourselves to, due to the thermal inertia provided by the oceans. Just as a pot of water doesn’t immediately boil when we turn on the stove, the oceans take time to warm up as well. And since there’s a lot of water in the oceans, it takes a lot of time.

They included the following nifty graph, with the observed surface temperature but also the eventually expected temperature at the corresponding CO2 concentration (which they dub the ’real global temperature’), based on different approaches to account for warming in the pipeline:

Observed and eventually expected (“real”) temperature at concurrent CO2 concentration, via Bits of Science

This is a nice way to visualize the warming that’s still in the pipeline due to ocean thermal inertia. From a scientific point of view the exact execution and framing could be criticized on certain aspects (e.g. ECS is linearly extrapolated instead of logarithmically; the interpretation that recent record warmth are not peaks but rather a ‘correction to the trend line’ depends strongly on the exact way the endpoints of the observed temperature are smoothed; the effect of non-CO2 greenhouse gases is excluded from the analysis and discussion), but the underlying point, that more warming is in store than we’re currently seeing, is both valid and very important.

Timescales, timescales, timescales. Why art thou missing from the public discussion about global warming?

Update: ClimateInteractive has a good simulation of how this inertia works out in practice. By moving the slider at the bottom the figure you can choose between different emission scenarios. In the graphs above you then see the effect this has on the CO2 concentration, the global average temperature, and the sea level, and how this response is damped. The further down the cause-effect chain, the more damped – or better: the more slowed down- the response is. The sea level will continue to rise the longest (even long after the temperature has stabilized or even starts decreasing), but will take a while to get going. This simulation only runs to the year 2100 though.

A Dutch version of this post can be found on my sister blog KlimaatVerandering.

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BBC interview: global warming pause, climate sceptics, long timescales

I was interviewed by Matt McGrath from the BBC last week, as were several other Dutch climate spokespeople (including PBL’s senior scientist Arthur Petersen and skeptical science writer/journalist Marcel Crok). Short parts of these interviews have appeared on the web  and on Radio 4 (“The World Tonight”, 26-09). Below I try to provide a bit of context to my quotes.

Both pieces are centred, as is fashionable these days, on the apparent smaller rate of surface warming in the past 15 years. The web piece is entitled “Climate sceptics claim warming pause backs their view”. Of course they claim it does. What sceptics did achieve –credit where credit is due- is to put this so-called “pause” on the agenda of mainstream media, until it got so fashionable that they all feel forced to use it as an anchor for any reporting on climate. But, as Gavin Schmidt is quoted as saying:

focus on a global warming pause over the past 15 years is a “misplaced” distraction that misses the big picture. He said, “The IPCC and the issue of climate change is not about the weather next year or the next five years; it’s about the long-term climate change that we are engendering.”

See also this useful figure from Stefan Rahmstorf, underscoring the silliness of drawing all too strong conclusions from 15-year trends.

Figure showing NASA GISS global average temperatures with trendlines from 1992-2006 (light blue) and 1998-2012 (green) as well as the most recent 30-year trend in red. Naturally, starting in a very cold volcano-influenced or very warm El Nino influenced year will inflate or deflate the trend. (source: Stefan Rahmstorf)

I am quoted in the BBC piece as follows:

Bart Verheggen is an atmospheric scientist and blogger who supports the mainstream view of global warming. He said that sceptics have discouraged an open scientific debate.

“When scientists start to notice that their science is being distorted in public by these people who say they are the champions of the scientific method, that could make mainstream researchers more defensive.

“Scientists probably think twice now about writing things down. They probably think twice about how this could be twisted by contrarians.”

The discussion was about to what extent climate science isn’t open/transparent enough, as contrarians routinely claim. Matt also asked to what extent skeptics actually play a positive role in making science more open/transparent and more self-critical. I said ideally they would. People who are critical usually have a good influence that way. But many climate contrarians don’t just stop at raising partly valid criticism, but go on to distort the science. That has the opposite influence, as scientists noticing this behavior become more careful and more defensive, and(have to) think ahead how their words might get twisted by contrarians. So they may become less open and less frank, and more careful in how they chose their words.

That is the opposite of what contrarians claim they want to achieve, so it’s quite ironic (though entirely logical) that this is the more likely effect of their behavior. It shows quite a lack of self-awareness on their part that they don’t see how their actions and their behavior affect the dynamics of the public debate. For the worse, in most –though not all- cases.

There may also be some lack of self-awareness among the mainstream that they respond in a way that’s not conducive to a long-term open and frank dialogue with society. From an older comment of mine:

If the valid criticisms wouldn’t be packaged in such conspiratorial/accusative/exaggerated (c/a/e) ways, they would be welcomed much more than they currently are. The art that mainstream scientists and their defenders must learn is to take the valid parts of the criticisms and deal with/respond to them, and leave the c/a/e packaging for what it is. That is increasingly difficult because the critics and their supporters will try to keep the c/a/e in (presumably because this packaging is what is most effective at decreasing the scientists’ credibility and sowing doubt). That dynamic needs to be broken. It needs effort from both sides, as difficult and unfair as it sounds.

As I wrote in my earliest (and still rather positive) reflection on the Curry-turn:

There is a tendency of ‘circling the wagons’ within the scientific community, in response to the continuous attacks on the science. Attacks that are mostly based on smear and insinuation rather than solid arguments. (…) I think the ’us-versus-them’ feeling amongst many scientists and their supporters is understandable (as a reaction to the contrarian c/a/e attacks on the science), but counterproductive in the long run.

In the Radio 4 show (at ~33:50 min in; earlier in the downloadable mp3 version), I am saying a few things about the timescale of the problem and of the solution. I brought this up when the discussion was about whether we now have more time to respond to climate change. This is a vastly underappreciated point in the climate discussion:  The climate system will take much longer to cool down than it did to warm up. This is a consequence of how the carbon cycle works. In this context, I said the following:

We’re going somewhere, and if we don’t like where we’re going, we have to turn that wheel in time.  As when you’re on a giant supertanker on the ocean, you can’t say “oh, I’ll wait until I can feel the iceberg with my pinkie and then I’ll turn the wheel”. Then you’re a bit late, so you have to start doing that in time. That’s the other side of the coin. But if you keep banging the drum saying “it’s five to twelve! It’s five to twelve!” doesn’t work either. And that could be counter-effective to engage those who are a bit more skeptical.

Global warming is a problem in slow-motion, hence the “five to twelve” line is not the most useful one to get people on their feet, because if it remains five to twelve for too long, they will tune you out. That’s what happened in the aftermath of COP15 in Copenhagen for example (where the 5-to-12 line was used a lot, and not much has changed in the years since). The supertanker analogy is more appropriate I find, since that makes clear that even though the problematic situation that’s on your path isn’t in close proximity yet, it is necessary to change course, if you wish to avoid it.

What are the pros and cons of reducing CO2 vs other warming agents?

That is the question I’ve been pondering earlier this year and which’ pontifications you can now read on Planet3.

The difference is mainly in the timescale: CO2 lasts a lot longer in the atmosphere than most of the other warming agents (e.g. black carbon, ozone, methane). This means that the temperature will decrease faster when the emission of shortlived compounds is decreased, as compared to that of a longlived compound such as CO2.

The other side of the coin is that for long term warming, the cumulative emissions of CO2 are dominant, even if in the short term changes in its emission are relatively ineffectual. Other important aspects in this discussion are health effects from air pollution (e.g. soot and ozone) and political practicability (gridlock in global climate negotiations).

So the question is: Are you more concerned about the short term or the long term effects of climate change? Which is a similar question that is often implicitly present in climate debates: Weighing the right of this generation to economic wellbeing (through cheap fossil energy) with the right of future generations to a pleasant planet to live on (through us not using too much cheap fossil energy). Strangely enough, that central and deeply ethical question is usually embodied in the discount rate (as used in economics when comparing investments with the expected rate of return).

My conclusion:

It’s clear that for long term climate stabilization, cumulative CO2 reductions are paramount, and that for the short term, reducing other forcings can offer faster results and offer other benefits as well. So the answer to the question “what should we focus on” is “all of the above”. I would applaud more attention to the non-CO2 forcings in the International policy arena. However, let’s not forget that there’s a hefty price and/or climate tag to pay in the end for delaying CO2 emission reductions.

You can read the whole thing over at P3.

 

Planet3 is a community new(s) blog, aptly described by main driving force Michael Tobis (in an interview with Andy Revkin) as

opinionated yet skeptical, informed yet passionate

 

Conflict of interest statement: I live on the planet in question.

(via Elmar Veerman)