A ton too far (more bad news)

At the Climate Futures Forum in Wellington a couple of weeks ago, David Karoly discussed the idea of considering carbon emissions as a “stock” problem, not a “flow” problem. If we want to give ourselves a 75 percent chance of coming in below a 2ºC rise in the global average temperature, then we (as in all humanity) can emit around one trillion tonnes of CO2 (for more see Meinshausen et al here, discussed in the context of emissions targets at HT in this post). It doesn’t much matter when we do the emitting, because CO2 hangs around in the atmosphere for a long time, but stick to that limit we must if we’re serious about avoiding damaging warming. I like that way of thinking about the issue, as I noted in my report on the Forum, but it seems that I may have been rather optimistic about the height of the ceiling we’re living under, and our chances of hitting a 2ºC target. A new study by a team of Canadian climate modellers, Arora et al, Carbon emission limits required to satisfy future representative concentration pathways of greenhouse gases in Geophysical Research Letters, 38 (5) DOI: 10.1029/2010GL046270 (pdf here), suggests that:

…we have already surpassed the cumulative emission limit and so emissions must ramp down to zero immediately. The unprecedented reduction in fossil‐fuel emissions implied by either of these scenarios suggests that it is unlikely that warming can be limited to the 2°C target agreed to in the 2009 Copenhagen Accord.


The paper (based on modelling runs for the next IPCC report, using new emissions scenarios) notes that previous estimates of the carbon budget have assumed that the cooling effects of future aerosol emissions will cancel out the warming effects of non-CO2 greenhouse gases. This, the authors suggest, is unlikely, and future carbon emissions will effectively warm the planet more:

[…] our results suggest there is little room (∼160 ± 80 Pg C) to limit the warming in 2100 to the 2.3°C associated with the RCP 2.6 concentration scenario. It would require an immediate and rapid ramp down of emissions, followed by negative emissions (sequestration) in the later half of this century.

Hitting a 2ºC target means using up all that headroom. We therefore have to move to zero emissions more or less immediately. If that sounds eminently unfeasible, then that’s probably because it is. The world is therefore heading for something a lot worse than a mere two degrees of warming. Through their failure to confront this stark reality our politicians are conspiring to condemn future generations to a living hell. If you’re reading this, Nick Smith, I would welcome your considered reply…

Hat tip: James Hrynyshyn at Class: M

[Worth noting that the AGU press release covering Arora et al makes for grim reading, with papers on ice melt and Aussie floods and droughts. See also trillionthtonne.org and their interesting FAQ.]

8 thoughts on “A ton too far (more bad news)”

  1. Welcome back. Some interesting glitchiness still around – ∼160 ± 80 Pg C, and lots of 2ºC f’rinstance. ( And ‘Gnarly dude, you 404’d it!’ ? Like, for real? 😉 )

    As for the post itself [*sighs*]…

    1. Something went wrong in the database file, and it took an age to sort out — still not sure what worked in the end. Something seems to have corrupted or changed character set, which is why we’re seeing those strange characters standing in for ” and º. I’m updating recent posts to clean them up, but it will take forever to go through four years worth and clean the lot. Unless you know someone who knows what they’re doing in SQL…

      1. Wahaay – all perfectly legible now! SQLs of delight! Isn’t it amazing how often you never do get to really understand what fixed the problem in this internet age?

        1. Thanks Thomas. I’ll check out those links, but I’m going to be very careful about what I do – I’d hate to further damage four year’s worth of posts and comments!

  2. I’m probably the last one to realize this, but it has just occured to me that Joe Fone’s “surname” does not rhyme with tone but with pony. (But I see that the post I was going to refer to has gone, so never mind that for now)

    “Zero emissions now” is not going to happen without the aid of an unprecedented disaster, because too many people see this as a future problem. We have been experiencing the equivalent of a slow poisoning. Until the results are suddenly severe (and I believe they have been for a while, but Joe Public doesn’t) no one with clout is going to take any action.

  3. Those depressed by this news – proving you have a functioning brain – might, provided they like their humour a little black, get some much-needed enjoyment out of graph number three, as displayed on this Skeptical Science post.

    This is so firmly rooted in a world beyond parody that, although I have every faith in the source, I just had to check the original, because surely not even Monckton…? Sure enough, it’s really there!

    1. bill. This just reinforces the validity of my frequent visits to DenialDepot. It’s always good for a chuckle.

      No matter how ridiculous the posts, it now seems that if such nonsense hasn’t already appeared elsewhere, It will appear some time. I never, ever expected to see that axis tilting technique used by anyone with an apparently straight face, but nevertheless it’s there for all to see.

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