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2°C Or Not 2°C: Why We Must Not Ditch Scientific Reality In Climate Policy

Joseph Romm's picture
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2 degrees

Global-mean surface temperature 1880-2013. Grey line shows annual values, and the smoothed blue line highlights the long-term evolution. (Via RealClimate using NASA data)

A new Comment piece in Nature argues we should “Ditch the 2 °C warming goal” as a basis for climate change policy. Here’s why the authors, political scientist David Victor and retired astrophysicist Charles Kennel, are wrong — and why “their prescription is a dangerous one,” as a top climatologist told me.

Their core argument, as Nature sums it up, is “Average global temperature is not a good indicator of planetary health. Track a range of vital signs instead.”

I’ll discuss below why our global temperature is a perfectly reasonable indicator of planetary health — or rather, of planetary sickness, since we have a fever. First, let’s dispense with the notion that tracking a “range of vital signs” would somehow make it easier for humanity to avoid catastrophe.

Consider that way back in 2009, “a group of 28 internationally renowned scientists identified and quantified a set of nine planetary boundaries within which humanity can continue to develop and thrive for generations to come. Crossing these boundaries could generate abrupt or irreversible environmental changes.” Unfortunately, we’ve already crossed some key ones, including climate change and rate of biodiversity loss:

Planetary Boundaries

The inner green shading represents the proposed safe operating space for nine planetary systems. The red wedges represent an estimate of the current position for each variable.

Oops. The thing is, five years ago, Nature actually published a major article (and responses) on these “planetary boundaries.” The key takeaways. First, the planet has already overshot multiple boundaries, including climate change (and is close to doing so in a couple more including CO2-driven ocean acidification).

Second, adding more vital signs just gives people more things to argue about, so it is hardly a recipe for faster or more streamlined international action. Indeed, the whole Victor and Kennel approach would be an excuse for more dawdling. They don’t just want to ditch the 2°C limit but they want to replace the entire effort aimed at developing a global plan to avoid that limit culminating in the December 2015 Paris climate conference. Instead, they write, “New indicators will not be ready for the Paris meeting, but a path for designing them should be agreed there.”

Yes, instead of trying to get the world’s leading governments to agree on the commitments needed to avoid crossing the 2°C target, let’s just ask them to agree on a “path for designing” some new targets. So long Miami, New Orleans, and other coastal cities — it’s been good to know you!

As Michael Mann, director of the Earth System Science Center at Pennsylvania State, wrote me:

Giving up on the 2C warming limit, after so much work has been done to motivate this objective and meaningful target for defining dangerous climate change amounts to kicking the can down the road. It simply provides a crutch for those looking for yet another excuse for not doing the tough but necessary work to stabilize greenhouse gas concentrations below dangerous levels. Sure, it’s possible that we will fail to stabilize temperatures below 2C warming even given concerted efforts to lower our carbon emissions, but simply discarding this goal would make failure almost certain.

I’m sure the authors mean well, but their prescription is a dangerous one in my view.

TWIMC: The scientific reality is that we are already in overshoot!


Homo sapiens already use the equivalent of 1.5 Earths to support our consumption. (Global Footprint Network via WWF)

So what exactly is wrong with the 2°C target that it should be ditched? Sadly, Victor and Kennel offer a bunch of beyond-dubious arguments:

The scientific basis for the 2°C goal is tenuous. The planet’s average temperature has barely risen in the past 16 years

These statements are not merely dubious, they are “disingenuous,” to use the word of Stefan Rahmstorf, Co-Chair of Earth System Analysis at the Potsdam Institute for Climate Impact Research, in his debunking post on RealClimate.

It is truly unfortunate that Victor and Kennel perpetuate the myth that there has been some sort of a pause in warming. Nearly a year ago, a journal article explained that a key reason there appears to be a pause is that one of the major temperature data sets ignores all warming in the Arctic (see here). Also, as Rahmstorf notes, it is very widely known that “picking 1998 as start year in this argument is rather disingenuous –- it is the one year that sticks out most above the long-term trend of all years since 1880, due to the strongest El Niño event ever recorded.”

What’s even more bewildering is even to the extent there has been a slowdown in surface air temperature warming during this cherry-picked period that has no bearing on the argument Victor and Kennel are making, as Rahmstorf shows:

They fail to explain why short-term global temperature variability would have any bearing on the 2 °C limit — and indeed this is not logical. The short-term variations in global temperature, despite causing large variations in short-term rates of warming, are very small — their standard deviation is less than 0.1 °C for the annual values and much less for decadal averages (see graph — this can just as well be seen in the graph of Victor & Kennel). If this means that due to internal variability we’re not sure whether we’ve reached 2 °C warming or just 1.9 °C or 2.1 °C — so what? This is a very minor uncertainty.

The argument by Victor and Kennel that there’s no “scientific basis” for the 2°C limit or that it was “uncritically adopted” by governments is thoroughly debunked at length by Rahmstorf (see also Mann’s “Defining Dangerous Anthropogenic Interference).”

Rahmstorf points out that the work of the Intergovernmental Panel on Climate Change (IPCC) underscores the need for the 2°C limit with their reviews of the climate science literature in 2007 (AR4) and over the last year (AR5):

One needs to keep in mind that 2 °C was already devised based on the risks of certain impacts, as epitomized in the famous “reasons of concern” and “burning embers” (see the IPCC WG2 SPM page 13) diagrams of the last IPCC reports, which lay out major risks as a function of global temperature….

One of the rationales behind 2 °C was the AR4 assessment that above 1.9 °C global warming we start running the risk of triggering the irreversible loss of the Greenland Ice Sheet, eventually leading to a global sea-level rise of 7 meters. In the AR5, this risk is reassessed to start already at 1 °C global warming. And sea-level projections of the AR5 are much higher than those of the AR4.

The argument by Victor and Kennel is especially disingenuous because all the most recent scientific observations and analysis point to the fact that a truly rational species would keep as far away as possible from 2°C warming.

Even since the AR5, new science is pointing to higher risks. We have since learned that parts of Western Antarctica probably have already crossed the threshold of a marine ice sheet instability (it is well worth reading the commentaries by Antarctica experts Eric Rignot or Anders Levermann on this development).

If anything, there are good arguments to revise the 2°C limit downward. Such a possible revision is actually foreseen in the Cancun Agreements, because the small island nations and least developed countries have long pushed for 1.5 °C, for good reasons.

The required response in the face of scientific reality is not “The Paris agreement should call for an international technical conference on how to turn today’s research measurements into tomorrow’s planetary vital signs.” It is, as Rignot notes, “Holy Shit” because “the time to act is now; Antarctica is not waiting for us.”

Finally, Victor and Kennel argue that a “nasty political problem” has emerged about the 2°C limit: “the goal is effectively unachievable.” The fatal flaw in that argument is the scientific and economic literature as summarized by the IPCC and agreed to by every major government in the world! I discussed this in my April post on the AR4 “mitigation” report. Indeed, the “cost” of the 2°C path is to reduce the median annual growth of consumption over this century by a mere 0.06%.

Now Victor and Kennel are certainly entitled their political opinion that the world isn’t going to adopt the 2°C path. But no matter how credible that opinion is, it should “not be confused with a geophysical, technological or economic infeasibility of limiting warming to below 2°C,” as Rahmstorf puts it. I’ll end where he ends:

If one wanted to sabotage the chances for a meaningful agreement in Paris next year, towards which the negotiations have been ongoing for several years, there’d hardly be a better way than restarting a debate about the finally-agreed foundation once again, namely the global long-term goal of limiting warming to at most 2°C. This would be a sure recipe to delay the process by years.

That is time which we do not have if we want to prevent dangerous climate change.

The post 2°C Or Not 2°C: Why We Must Not Ditch Scientific Reality In Climate Policy appeared first on ThinkProgress.

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David Lewis's picture
David Lewis on Oct 3, 2014

Schellnhuber, who had as much to do with getting the EU to accept 2 degrees C as a target as anyone, was saying prior to Copenhagen that unless civilization got serious at that point, it would be impossible to limit global warming to 2 degrees.  He at least is not pretending he didn’t know what he was talking about then. 

He is saying now (eg at the recent Berlin Climate Engineering conference, starting at minute 2:45 into this video) that the best that can be done is 2.6  degrees. 

Why pretend otherwise? 

Few at that Berlin conference were as optimistic as him.  Most were there because they are interested in what emergency measures can be developed in time to present as options to civilization when it finally wakes up to the fact it faces an existential threat. 

As for the Nature article, why does it matter what gibberish a political scientist and a retired distinguished astrophysicist have to say, when it comes to assessing how serious climate change is?  It is easy in the US to find arrogant people ignorant enough to believe they know more than the scientists who have distinguished themselves as they spent their entire working lives studying climate. 

What is disturbing is that the editors of Nature thought the article worth publishing. 



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