Climate change targets

There is general international agreement that we must limit temperature increase to 2°C if we are to minimise the impact of climate change. This is known as the 2°C temperature limit. But in some respects, global temperature is a rather arbitrary figure. Why not, for instance, set a target for the maximum ocean acidification or the maximum sea level rise we are prepared to tolerate? After all, rising carbon emissions do not just translate to an increase in surface temperatures but also to a rise in sea level, an increase in ocean acidification and a possible loss of net primary production (net carbon influx into an ecosystem through photosynthesis) on land.

Ocean acidification is a good target to set because the consequences of rising acidity are so tragic.  As the sea water increases in acidity, it becomes corrosive to the shells of marine organisms and is a death sentence for coral reefs. I have been snorkeling on the Great Barrier Reef and it was an extraordinary experience, one of the best I have ever had. Losing the Great Barrier Reef would be a catastrophe by every measure of the word. There will also be enormous economic losses from tourism and fishing if this were to happen. The Caribbean earns over 50% of GDP from activities associated with the reefs. Coral reef ecologist, Peter Sale, suspects that loss of reefs will also impact coastal fish populations negatively. We are talking now about the collapse of an entire ecosystem.

So the question is, how much CO2 would we be allowed to emit if we set targets not just for global surface temperatures, but for other factors as well? A new paper in Nature – Allowable carbon emissions lowered by multiple climate targets – seeks to answer exactly this question.

The authors, from the University of Bern in Switzerland, argue that the climate system refers not just to global mean temperature but also to the hydrosphere, biosphere, geosphere and all of their interactions. If we are to ensure sustainable ecosystems and food production, then we need to consider other factors in addition to global temperature.

They set six targets: global mean surface temperatures, sea level rise, two targets for ocean acidification and two targets addressing the impact on the terrestrial biosphere. What they find is these additional targets can “considerably reduce the allowable CO2 emissions.”  The ocean acidification target, in particular, is much more restrictive and puts a tighter limit on how much carbon we can afford to add to the atmosphere. This target specifically measures the loss of habitat associated with coral reefs. If CO2 rises above 550ppm, it is likely (>33%) that more than 90% of these habitats will be lost. We are likely to reach 500ppm by mid-century. That is very little breathing space for our coral reefs.

Something I have found somewhat irritating about certain media reports and political blogs is an obsession with the apparent temperature “hiatus”. The implication is that surface temperatures have not risen for a decade or so and therefore there is no global warming. There are lots of problems with this view which I’m not going to address here. I just want to say that climate change is more than just a measure of global surface temperatures. This paper is a good example of why we need to look at other factors as well.

25 responses to “Climate change targets”

  1. Very good post. I must read the paper you mention. I’ve just finished a post arguing that we need (the media, scientists, …) to be much more careful about how we discuss the “hiatus” in surface temperatures. We keep saying things like “the warming slowdown” when warming hasn’t slowed. What’s slowed (or is slower than expected) is the rise in surface temperatures and – as you say – is not a particularly good indicator of global warming. However, if we keep associating this slowdown with a slowdown in warming, those who are skeptical will use these statements to argue that global warming has stopped, when it almost certainly has not.

    • I do agree. I’m not quite sure how to respond in those situations because I know the conclusion skeptics want to draw is that there is no global warming, but this is just not the case.

      I’ve discovered through a comment in another thread this article by Yale Economist, William Nordhaus, and he addresses the question of “is the planet in fact warming?” rather well.

    • Wotts ,
      See” Did Murdoch’s The Australian Misrepresent IPCC Chair on Global Warming ?” ,posted on SkepticalScience , by Dana 1981, on 25 February 2013.
      Dana says the warming of global air surface temperatures has slowed over the past decade due to “a preponderance of La Niña events ” ( what about other causes encapsulated in natural variability ?).He maintains of course that the rate of heat accumulation under our feet and in the oceans is continuing ..He stops short of saying ,as some Australian alarmists maintain , that heating is accelerating.( correct me if I’m wrong).
      The answer to Dana’s post is No.Read “Nothing off limits in Climate debate “, Australian, Feb 22, 2013.
      Dana hopefully says there were no quotes attributed to Pachauri ( a red flag ) by Graham Lloyd.Does he seriously think that Pachauri would allow such a significant statement to go uncorrected ? Google to see worldwide press coverage.
      It’ s a bit late to try denying a surface temperature standstill. See Kaufman et al 2011.Pachauri says only 30 to 40 years to go to see if the current hypothesis is invalidated.Can we run the clock from 1 January, 2001, the beginning of the century ? Even better is the Santer et al 2008 deadline of 17 plus years.
      And yes I do understand the issue of ” statistically significant” etc.

      • Douglas, I’m not entirely sure that I’m following your argument here. I know that there has been a standstill (or slowdown or whatever term you wish to use) in global surface temperatures. The basic point I was making was that by saying “there’s been no warming” allows people to interpret the slowdown in global surface temperatures as a slowdown in global warming, which it isn’t. I was simply making the case that scientists should be careful about how they describe this standstill or slowdown. I wasn’t suggesting that it hasn’t happened (although there is the issue of statistical significance, but we can bypass that for now). I, also, wasn’t suggesting that they shouldn’t be honest either. If anything, I’m suggesting they should be more precise in how they describe this. It’s not a standstill in the warming, it’s a standstill (slowdown) in the global surface temperatures.

      • Wotts ,
        Our disagreement then concerns only the issue of whether there has been a slowdown (standstill) in global warming overall.There has been for global surface temperatures,as you acknowledge.but you maintain that OHC and Earth Heat Content continue to rise.There we disagree,in that I do not accept that Nucitelli et al 2012 shows that global warming continues.See SkepticalScience post under that title on 12 Octoberb,2013. I do not accept that figure 1 on that post is scientifically “robust”.See Douglass and Knox in contradiction of Nucitelli’s position.I am not in a position to adjudicate on who is correct.

      • Indeed, that does appear to be our main disagreement. I’ve already commented elsewhere in a response to you, though, why I think the Douglass & Know paper makes some questionable assumptions. It’s also not only Nuccitelli, there’s Loeb, there’s Levitus. You can also look up satellite measurements of the energy imbalance and there are recent satellite observations of the change in the outgoing spectrum, showing that GHGs are indeed absorbing more energy in certain bands than they were 10 years ago. The evidence is very strong, if not compelling. You, of course, are not obliged to agree.

  2. Below 350 ppm is probably ‘safer.’ 400 is destructive. 450 is very harmful. 500 is deadly. And 550 is a mass extinction event, especially if it happens over the next 50 years or so. Anything above 550 is beyond catastrophic.

      • That will be difficult, subject to trouble (leaks, release) and very expensive (moreso than rapid transition to renewables, likely). But you are probably right. If you’re talking about atmospheric capture, the cost is at least 5 times mitigation by preventing the emission in the first place (current tech). But better than dealing with the consequences, IMO.

    • Robertscribbler,
      Your targets may be impossible.For Australia ,see ” An evaluation of the targets and timetables of proposed Australian emissions reduction policies” by Roger A.Pielke Jr., Environmental Science and Policy.( 2011) 20-27.
      The paper argues that proposed Australian carbon policy proposals present emissions reduction targets that will be almost impossible to meet creative approaches to accounting.Rates of decarbonisation of various worldwide economies are profiled.

      • Let’s consider a few things, for a moment.

        1. The amount of warming and climate response we are seeing now is already resulting in extreme, difficult to deal with events.

        2. The damage that is ongoing is the result of emissions that happened 20-30 years ago.

        3. So even if we stopped emitting now, if all the carbon sinks were good and kept drawing down carbon, and if the Arctic didn’t continue to increase carbon emission feedbacks, we’d probably be in for a worsening climate for the next 2 to 3 decades (at least).

        4. It’s probably an impossible target to stop emitting now.

        5. So we are in for at least 4-8 decades of worsening climates and, probably, centuries of sea level rise even if the targets Pielke describes as ‘potentially impossible’ are reached. (And would put us at a horrendously risky 460-510 ppm).

        6. Risky because this level will almost certainly result in strong amplifying feedbacks coming into play over the decades and centuries timescales. What this means is that there is a high potential, 50% or greater, of a practically indefinite period of worsening weather, climate and environmental conditions even if these targets are reached.

        7. So we’d better hit those targets and more.

        8. What Pielke shows is that current policy is not aggressive enough (requiring creative accounting to validate).

        9. As for whether or not the infrastructure and needed efficiency gains can be built and enacted… such costs pale in comparison to the cost of adapting to a climate in which the initial human emission pushes us to 500 ppm or more. At that point, for Austrialia alone, the yearly damage will be many, many times the current cost of mitigation.

        10. So it’s not a question of what’s possible under current policy. It’s a question of what must be possible.

  3. Doug,

    The whole point of an emission trading regime is that if Australia cannot get its emissions down sufficiently then it will have to pay: buying emission credits from nations that are disciplined and creative enough to do so. As other nations get their house in order, it will become increasingly expensive for Australia.

    Global mean surface temperature is not necessarily a good proxy for measuring climate change, as Rachel pointed out, as a large part of the Earth’s surplus heat balance is absorbed by the oceans. In fact 2012 was for the United States the hottest year by far since reliable climate records were established. Usually, temperature records are broken by a small fraction of a degree, but 2012 was hotter than ever before by a full degree F,

    The US Department of Energy has just issued a wake up call over the vulnerability of that nation’s infrastructure to climate change:

    ‘The effects are already being felt, the report says. Power plants are shutting down or reducing output because of a shortage of cooling water. Barges carrying coal and oil are being delayed by low water levels in major waterways. Floods and storm surges are inundating ports, refineries, pipelines and rail yards. Powerful windstorms and raging wildfires are felling transformers and transmission lines.

    ‘“We don’t have a robust energy system, and the costs are significant,” said Jonathan Pershing, the deputy assistant secretary of energy for climate change policy and technology, who oversaw production of the report. “The cost today is measured in the billions. Over the coming decades, it will be in the trillions. You can’t just put your head in the sand anymore.”

    ‘The study notes that 2012 was the hottest year on record in the contiguous United States, and last July was the hottest month in the United States since record keeping began in 1895.

    ‘The high temperatures were accompanied by record-setting drought, which parched much of the Southwest and greatly reduced water available for cooling fossil fuel plants and producing hydroelectric power. A study found that roughly 60 percent of operating coal plants are in areas with potential water shortages driven by climate change…’

    Climate change has stopped?

    • Australia should not be deliberately placing itself at an economic disadvantage with most of its competitors for something that many believe is unproven. That is the basis of all the arguments. The science is definitely not settled.
      And why pay up to four times the going price anyway?
      What Australia does makes no difference to the world.
      California is broke, Rachel. Go there, brave the San Andreas fault and see what it’s like. Or, alternately peach from your base in New Zealand, secure in the knowledge that your government hasn’t inflicted the same economic harm on its citizens. Perhaps, you could consider making an individual monetary contribution to the cause though so you don’t miss out?

      • Eve said, “Perhaps, you could consider making an individual monetary contribution to the cause though so you don’t miss out?”

        I’ve often had arguments thrown at me like this or what are you doing personally to show your commitment or do you own a car etc. I’ll steal the words of someone else as a rebuttal here:

        “This problem is a tragedy of the commons. Suggesting that people arguing to limit the abuse of the commons should have to show THEIR commitment by abandoning it to more “greedy guts” abusers is simply asinine. The commons can ONLY be saved by the collective action of the society, to regulate its use of the commons. It can NEVER be saved by individual action. Your solution to lifeboat ethics is to toss the folks who point out the water shortage out of the lifeboat? Really smart.”

        (Source is one of the comments of this article –

    • Mike, you are correct in what you and the NY Times say about the US surface temperatures.
      However I am looking at the UAH Global Temperature Report 2012.In the US ,2012 set a new record , at 0.555C above seasonal norms for the coterminous 48 States.
      Globally, 2012 was the ninth warmest year of the last 34 years,with an annual average global temperature that was 0.161C warmer than the 30 year baseline average, according to Dr.John Christy at UAH.Eleven of the 12 warmest years in the satellite record have been since 2001. Only 2008 was cooler than the long term norm for the globe.
      On the other hand ,the coolest area of the globe last year was Eastern Mongolia where Temperatures were as much as 4.55C cooler than seasonal norms.This fact gets little coverage in the New York Times however.
      The point of all this is ,so what? Despite the string of warmer than usual years since 2001,and the fear-mongering by Jonathan Pershing there has been no measurable warming trend on UAH since about 1998.The long term warming trend reported in the satellite data is calculated using data beginning on November 16 , 1978.The latest anomaly shows the trend at + 0.30 C over that period.And as Rachel and you say ,it’s dangerous to put too much reliance on surface temperatures.
      And as President Obama will tell you ,Chicago experiences annual temperature variations of -5 degrees F to + 95 degrees F.Yes, I know , it’s weather not climate.
      And may I remind Mr. Pershing, that in the IPCC SREX Report , 220 scientists from 62 countries tell us that we do not know if the climate is becoming more extreme from so called “weather events” , things that we used to call storms ,drought , cyclones etc.

  4. A new paper looking at risks to coral reefs from ocean carbonate chemistry finds that aggressive reductions in CO2 are needed if we are to maintain waters safe for reefs to the end of the century.

    Our results indicate that if civilization continues along
    its current carbon dioxide emissions trajectory (which is
    currently steeper than even RCP8.5), by the end of the
    century all existing coral reefs will be surrounded by ocean
    chemistry conditions well outside of preindustrial (or even
    present day) conditions. This result is consistent across all of
    the Earth System Models simulating ocean biogeochemistry
    in the CMIP5 ensemble. On the timescales and within the
    range of scenarios considered here, carbonate chemistry of
    waters surrounding reefs is closely related to atmospheric
    CO2 concentrations and is not sensitive to the pathway by
    which those concentrations are reached. With deep emission
    cuts, the fraction of reefs that remains sustainable from a
    chemical point of view depends sensitively upon the critical
    value of a. Only with large emissions abatement efforts will
    a significant fraction of reefs remain in ocean waters with
    aragonite saturation states of three or more, and only under
    the most aggressive policies, possibly including direct capture
    of CO2 from the atmosphere, will reef-amenable carbonate
    chemistry conditions be preserved around a majority of reefs.

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