Days of future passed

The idea that a rise in global temperature of no more than two degrees above pre-industrial levels is a safe target for the world to aim for is widely accepted in political forums where the measures needed to stay within that range are considered. Not universally accepted though. The small island states and many others of the least developed countries already impacted by climate change are adamant that 1.5 degrees is the highest rise that should be considered safe.

Indeed one wonders what the reasoning of the more powerful nations has been in settling on the two degree target. When Mark Lynas trawled through predictions in scientific journals for his book Six Degrees (review here) he found plenty to disturb at two degrees, including  possible desertification and abandonment of agriculture over millions of square kilometres in the US, an extremely hot and drought-ridden Mediterranean Europe, an ice-free Arctic ocean with implications difficult to measure, the bleaching and likely death of many coral reefs, major loss of food production in India, serious population displacement in Bangladesh.

Now Chris Turney (pictured) and his University of Exeter colleague Richard Jones have reported their attempt to reconstruct the temperature during the Last Interglacial between 130,000 and 116,000 years ago. Their paper is published in the Journal of Quaternary Science.  Turney explains its significance in his blog, where he writes:

“Temperatures appear to have been more than 5˚C warmer in polar regions while the tropics only warmed marginally; strikingly similar to recent trends. Not only this, but taken together, the world appears to have been some 1.5˚C warmer when compared to the 1961 to 1990 average. If we take into account the rise in temperature that has happened since industrialization, we find the Last Interglacial was around 1.9˚C warmer. Furthermore, this period also shows the warming in the Indian and Southern oceans took place before that of the northern hemisphere, suggesting these regions may cause further global warming beyond that directly forced by increasing greenhouse gas levels.”

It’s important to recognise what impacts that level of temperature rise brought. Turney points out that we know there was a dramatic decrease in polar sea ice coverage while large parts of the Antarctic and Greenland ice sheets melted. Critically, he says, the warmer temperatures appear to have helped global sea levels become some 6.6 to 9.4 metres higher than today, with a rate of rise of between 60 to 90 millimetres per decade, more than double that recently observed.

Let’s return to today’s “safe target” notion of no more than two degrees above pre-industrial levels.  Here’s one of the key messages from the EU reference document explaining the scientific background for that target:

“Global mean temperature increases of up to 2°C (relative to pre-industrial levels) are likely to allow adaptation to climate change for many human systems at globally acceptable economic, social and environmental costs. However, the ability of many natural ecosystems to adapt to rapid climate change is limited and may be exceeded before a 2°C temperature increase is reached.”

If Turney and Jones’ estimation of the temperature in the Last Interglacial is correct it suggests that  sea levels will rise significantly higher than anticipated. How a sea level rise six to nine metres higher than today could be adapted to “at globally acceptable economic, social and environmental costs” rather beggars the imagination.

So far as Turney is concerned, “The inevitable conclusion is emission targets will have to be lowered further still. Not a popular message.”

It has been apparent for some time that ice sheets are showing signs of less stability than was expected. It is not news that sea level rise this century looks likely to be higher than the IPCC estimates (a possibility recognised in the IPCC report itself). But what Turney and Jones add is evidence that the past may be offering us a specific guide as to what sea level rise we would need to  prepare for if we allowed a two degree temperature rise.

Turney is a geologist whose interest is in researching the past, particularly in relation to climate. His excellent book Ice, Mud and Blood was reviewed on Hot Topic last year. He has continued to figure from time to time on the site because of his connection with the New Zealand firm Carbonscape. We noted his recognition last year by the Sunday Times as one of the modern-day heroes of science and technology.

He finishes his blog with these words:

“Crucially, the scientific and policy implications of the Last Interglacial demonstrate it pays to look back to yesteryear. As the great poet and playwright Thomas Eliot once wrote, ‘Time present and time past, are both perhaps present in time future, and time future contained in time past.’ Fingers crossed these words are heeded.”

Fingers crossed indeed. Against the seemingly unstoppable drive to exploit fossil fuels we need some signs of hope that society’s leaders are going to wake up to the dangers we are heading for. There are glimmers, as I pointed to in my post yesterday, perhaps even gleams if William Hague is representative, but a far wider section of our political and economic leadership needs to become fully acquainted with the lessons from the past.

Gareth adds (because he was going to blog this, but Bryan got his post in first)]: The period that Turney and Jones are considering — the last interglacial (LIG), better known (at least to me, though Turney’s blog provides other names) as the Eemian, is interesting because it provides an example of where we may be heading. During the LIG CO2 peaked at under 300 ppm, and sea levels were 6m to 9m higher than present, with rates of sea level rise of at least 6cm to 9cm per decade. The last time CO2 was at 300 ppm was before Dave Keeling started taking accurate measurements in the late 50s (it was about 312 ppm in 1958, and we’re nudging 390 ppm at present). In other words, the equilibrium response (that is, the long-term — century to millennial scale — response, when the oceans and ice sheets have had a chance to catch up) to the greenhouse gas levels more than 50 years ago is sea level at least 6 metres higher than now — and as Turney and Jones find, a global average temperature 1.9ºC above pre-industrial. The 2ºC “target” being bandied around as “achievable” (50% odds only) at 450 ppm is likely to be a mirage — it might hold true in the short term, but 450 ppm commits us to something well beyond the LIG/Eemian, when, as you will not need reminding, there were crocs and hippos in the Thames. When James Hansen was looking at long term targets, he selected 350 ppm as compatible with a planet with ice sheets at both poles. Turney and Jones synthesis of data on the Eemian suggests that if that’s our goal we need to be looking at 300 ppm — and a much bigger task. Over to Bill

Turney, C. S. and Jones, R. T. (2010), Does the Agulhas Current amplify global temperatures during super-interglacials?. Journal of Quaternary Science, 25: 839–843. doi: 10.1002/jqs.1423

[Moody Blues]

20 thoughts on “Days of future passed”

  1. When you look at a graph that plots both CO2 and temperature over the last 800,000 years it is quite obvious that 125,000 years ago the world had 300ppm and the temperature was 5c more than today.
    We are now at 390 PPM and rising. This is not a good scenario.
    I am surprised that the world only had an increase in sea level of 6 meters.
    One meter wipes out Holland, London, Florida, New Orleans (again) and many other industrial areas including our own Christchurch.
    The real danger is that 3c rise will bring about massive crop failure. What we are unsure about is the timing.

  2. It’s worth mentioning again that the sea level associated with present CO2 levels is more like +25 meters.

    I would be very interested in seeing an analysis contrasting the Eemian forcings/feedbacks with the present ones. My impression is that the relatively short Eemian got a pretty hard push from orbital forcings, which then reversed rather quickly, in contrast to our present situation of orbital forcing not playing a major role. Basically, how can the effects of GHG-focused forcing be expected to differ from those of orbital forcing as we move into the future?

    1. Steve: Interesting questions. Orbital forcings are called Milankovitch cycles. Variations in eccentricity, axial tilt, and precession of the Earth’s orbit determine climatic patterns.

      It is most important to understand that in the past, CO2 increased as a feedback from extra warmth due to orbital forcings. This is a common denier talking point, saying “CO2 lags temperature”, which is a logical fallacy.

      Agreeing that increased warmth causes increased CO2 levels DOES NOT mean that CO2 does not cause warmth. If fact this is an example of a Positive Feedback where: +CO2 => +Heat => ++CO2

      This situation is far worse for the deniers because it means that soon simply stopping CO2 emissions will not be sufficient to stop warming: We will have to actively remove CO2 (and maybe Methane) from the Atmosphere to preserve its habitability.

      That’s how much is TRULY at stake as we natter and delay over when to begin the inevitable change-over to a low-carbon economy.

  3. Bob, note that the global T difference was more like 2C. The 5C was at the poles (thus the ice sheet melting). Based on the mid-Pliocene (~3 mya), global average T only a degree or so warmer than the Eemian peak led to polar temps in the +15C range (relative to present).

    That raises a further wrinkle to my prior comment: The Eemian being so short and sharp, do we know that climate had a chance to get to any sort of equilibrium? If not, we may be looking at a lagging indicator.

    1. On the “short sharp” Eemian, the paper discussed under the link A Coral Room (at the end of the post) suggests there may have been a 2 – 3 m surge in as little as 50 years at the end of the warm period – which would indicate a lack of equilibrium — at least for ice sheets in a 300 ppm climate.

  4. I take a bit of issue with your description about the “drive to exploit fossil fuels”. I realise that this wasn’t the point you were making, but we’re not “exploiting” them, we’re squandering them.

    In two ways. Firstly, oil. Oil is much, much more valuable as a source of carbon fibre and other long-lived applications rather than as a substitute for “any old stuff we could burn”.

    Secondly, we’re burning our grandchildren’s inheritance. Even if we believed that burning things is better than other techniques, we have no excuse for being so wasteful in the design of engines and power plants that use far more carbon materials than is needed for the task required.

    1. adelady: I like the cut of your Jib! We should be husbanding our complex hydro-carbons so that in the future, the first generation of earth ships will have the resources needed to set off for the Stars.

      Anyone fancy a family trip to Gliese 581-G? It should be only about a 200 yr cruise… Talk about quality family time!

  5. In the short term its difficult to see how we can manage without oil for transport as our whole civilisation is built around road transport.
    My big issue is with coal which we use to generate electricity because is is cheap. Each ton of coal produces two tons of CO2 and a handy sized power station burns 10,000 tons a day.
    We can replace coal with hydro, thermal or wind if we had the will. The government has plans to increase natural energy but they are too modest.
    If we want a green image we need a bold plan to shut Huntley.

            1. Artful Dodger
              Supplies of Thorium are estimated to last several hundred thousand years, so for all intents and purposes there is an infinite supply.

              How long does the average wind farm last before replacement? Answer is around 20 years.

              What are wind turbines made of?
              Answer: plastics and metal that comes from the ground.

              What are hydro stations made of?
              Answer: concrete and metal that comes from the ground (and these silt up too, so do not have an infinite lifetime)

              What are solar PV cells made of? Answer: metals that comes from the ground. What is their lifetime? Not sure, but currently it takes more (fossil) energy to create a PV cell than you get back in its lifetime, as far as I know.

              Yes, you can recycle some of these materials. How effective is this at pulling bits out of rusted hulks of offshore wind farms though?

              As far as I know, the only truly renewable energy source that doesn’t require digging something out of the ground is wood, and bare sun. of course.

  6. # John D

    “…or Nuclear, you forgot that option Bob”

    Did he or is Bob a tad sharp?

    How will you be cooling these plants down with high temperatures and a general lack of water?

    GW It’s only just starting to kick in and…

    Looks like nuclear power is the fools gold of clean energy.

  7. I don’t have preconceptions about nuclear and believe we will have to use it for sea transport. However NZ really does have an abundance of natural energy and could lift its game even further.

    1. Can you imagine the security connotations of a world were fissionable material is deregulated to the point it can be used for ocean transport? Not to mention the high likelihood that reactor safety would suffer in favor of affordability.

      I would much rather live in a world where we don’t rely on the economic and political repression of the so called “developing” countries to provide us with cheap nikes and flatscreen tvs, and localize the means of production.

  8. Agreed Bob, we all need to raise our game further not just NZ, and in a number of cases a great deal further after all…

    “What’s the use of having developed a science well enough to make predictions if, in the end, all we’re willing to do is stand around and wait for them to come true?”

    — Nobel Laureate Sherwood Rowland (referring then to ozone depletion)

  9. This debate started out about the danger to the world through burning fossil fuels and this a very real danger and when the climate changes millions of people will die and our lives will change dramatically.
    One of our problems is the amount of energy we all use to keep civilisation going and keep ourselves alive.
    We are going to have to stop burning coal first as it is the dirtiest. The next to go will be oil as it will get expensive.
    For some energy requirements we need real grunt and nuclear can provide it. We could get cargo and people to Europe in ten days in a nuclear powered ship.

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