A grim warning about the 2°C target – but then what?

Last week PWC released the 2012 version of its “Low carbon economy index”, the fourth edition of a publication that started just prior to the Copenhagen COP. The main message delivered by the publication is a grim one, although hardly surprising, that the much discussed 2°C target is now effectively out of reach.

 We estimate that the world economy now needs to reduce its carbon intensity by 5.1% every year to 2050 to have a fair chance of limiting warming to 2°C above pre-industrial levels. Even to have a reasonable prospect of getting to a 4°C scenario would imply nearly quadrupling the current rate of decarbonisation. The decarbonisation rate required for a 2°C world has not been achieved in a single year since World War 2. The closest the world came to that rate of decarbonisation was during the severe recessions of the late 1970s/early 1980s (4.9% in 1981) and the late 1990s (4.2% in 1999). The expected reduction in emissions resulting from the current economic slowdown has not materialised, partly because of sustained growth in emerging markets.

Even more bad news follows, with an analysis of the various national pledges made following the Copenhagen COP. Not only does the publication make it clear that the cumulative impact of the stated contributions is insufficient for a 2°C pathway, but that many nations appear to be falling short of actually meeting them.

Even more worryingly, with eight years to go, it is questionable whether several of these pledges can be met.

The resurgence of gas in the global energy mix features in the report as an important driver of change, albeit with the concern about long term lock-in. Nevertheless, growth in natural gas production is leading to a real reduction in emissions in some parts of the world, but particularly the United States.

No matter which country or region you look at, progress made is pretty dispiriting. In a table of some 20 key countries, the worst performer in 2011 was Australia, although over the last decade it hasn’t done too badly in terms of its change in carbon intensity. I suspect that is more due to the fact that it didn’t plunge into recession like almost everybody else, so carbon intensity continued to fall as growth remained high. Therein lies a problem with using carbon intensity as the metric – appearances can sometimes be deceiving.

With 2°C pretty much condemned to the history books, the report goes on to look at the increasing risk of a much higher temperature rise over this century. Even the possibility of an excursion to 6°C is mooted. This outlook isn’t too far off the Shell Scramble (2008) scenario which resulted in CO2e levels approaching 1000 ppm by the end of the century and a consequent temperature rise of over 4°C and rising. By contrast, Blueprints saw temperatures beginning to plateau at between 2°C and 3°C.

None of this is good news, particularly given the amount of change that can take place in the global ecosystem as a result of small changes in temperature. Take sea level, for example. Although it could take well over a millennium to reach a new equilibrium level, the end result is incredibly temperature sensitive. We shouldn’t be surprised by this given that sea level was over 100 metres lower than today during the previous ice age, when temperatures were lower by about the amount we are worried they may rise in the future. As indicated below, a shift from 2°C to 2.5°C adds about 10 metres of eventual sea level rise (although not anytime soon).


All this raises the question as to what we should or could do, given that 2°C is not feasible. The “numbers guys” at PWC don’t go there and arguing for a higher target is a political non-starter, but at some point the discussion is going to have to happen.

 Based on the work of Allen, Meinshausen et al, which equates a given stock of atmospheric CO2 with long term temperature rise, it is possible to derive a chart which shows, for a given annual reduction until emissions are zero, the impact in terms of expected (midpoint) temperature rise.

For example, starting today, 2°C requires about a 2.5% year on year reduction in emissions – and this is now deemed infeasible by PWC. But if we delay until 2025, the required reduction is over 4% p.a.

Knowing that the world isn’t going to do much until 2020 when a new global agreement is scheduled to kick in, a 2.5°C goal requires about a 1.6% p.a. reduction, assuming action starts immediately. This would mean no new emissions from 2020, plus some 100 very big CCS projects (1 GW power station) starting up each year through the 2020s on existing facilities – and so on. This isn’t very different to the rate at which new coal fired power plants are appearing today, so it is probably feasible from an implementation perspective. Of course keeping all other emissions in check will be a further challenge, but that task could potentially be achieved by aggressive fuel switching and renewable energy deployment, supported by efficiency improvements.

The PWC report is a timely reminder of the situation that we are now in and the ambition that the proposed new global agreement is going to have to aspire to.

  •  Allen, M. R. et al (2009) Warming caused by cumulative carbon emissions towards the trillionth tonne, Nature, 458:1163-1166, which argues that a one trillion tonne release of carbon gives a most likely warming of 2°C, with a likely (one-sigma) uncertainty range of 1.6-2.6°C.
  • Meinshausen, M. et al (2009) Greenhouse gas emission targets for limiting global warming to 2°C, Nature, 458:1158-1162, which argues that a total release of 0.9 (0.71) trillion tonnes of carbon gives a 50% (25%) risk of temperatures exceeding 2°C.
  • Allen, M. R. et al (2009) The Exit Strategy, Nature Reports Climate Change, 3:56-58, which provides a commentary on the implications of the above papers for non-specialists.