Tag Archives: ipcc scenarios

Gang of four: can developed and developing countries act in concert to avoid a world of 2ºC plus?

A recent article in Nature: climate change highlights the growing consensus that if action isn’t urgently taken to reduce greenhouse gas emissions (GHGs) humanity we will fail to keep global average temperatures below 2ºC:

On going climate negotiations have recognized a “significant gap” between the current trajectory of global greenhouse-gas emissions and the “likely chance of holding the increase in global average temperature below 2 °C or 1.5 °C above pre-industrial levels”.

The article by Glen Peters, Robbie Andrews et.al titled The challenge to keep global warming below 2ºC examined looks at historical GHG emission levels and compares those to the emissions scenarios used in all previous four IPCC reports:

Long-term emissions scenarios are designed to represent a range of plausible emission trajectories as input for climate change research. The IPCC process has resulted in four generations of emissions scenarios: Scientific Assessment 1990 (SA90), IPCC Scenarios 1992 (IS92), Special Report on Emissions Scenarios (SRES), and the evolving Representative Concentration Pathways (RCPs) to be used in the upcoming IPCC Fifth Assessment Report.

One merely needs to look at the following graph to see how we are tracking:


Note the black line – historical emissions – and contrast that to the mass of other lines, the alternative emission pathways. For the uninitiated or confused it shows GHG emissions inline with the various “business as usual” (BAU) scenarios developed in the previous four IPCC reports. Each year we are pumping increased levels of CO2 and other GHGs into the atmosphere.

Just in case it isn’t clear this alternative graph from the same paper shows the annual percentage increase in CO2 emissions and how they track against the various scenarios:


Emissions have been growing at least 2% per annum without pause – exactly what you’d expect to see under BAU scenarios. In the IPCCs Fourth Assessment report these were referred to as the A1 scenarios:

The A1 storyline and scenario family describes a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies.

Within the A1 group of scenarios there are several scary emission pathways you want to avoid if you don’t want to push average global temperatures 2ºC and beyond. In the upcoming fifth assessment report the high emissions path will be referred to as RCP8.5 (there are four RCPs or Representative Concentration Pathways).

Short version?

We’re well on track for a world of 2ºC if we don’t act within the next few years. The authors note we can avoid such a situation but only if we act with a sense of urgency by 2020:

Current emissions are tracking slightly above RCP8.5, and given the growing gap between the other RCPs (Fig. 1), significant emission reductions are needed by 2020 to keep 2 °C as a feasible goal. To follow an emission trend that can keep the temperature increase below 2 °C (RCP3-PD) requires sustained global CO2 mitigation rates of around 3% per year, if global emissions peak before 2020…

To translate “sustained global CO2 mitigation rates” means rapidly decarbonising our economies over a period of many years – decades even. Emission rates need to fall dramatically and sooner rather than later.

It’s worth thinking about this in context of the most recent round of negotiations at Doha (COP18), which like nearly all of its predecessors has delivered underwhelming results.

The Gang of Four and beggar they neighbour: who needs to lead?

The authors note the close cooperation and coordination of four countries (or three countries and one region) will be key to mitigating GHG emissions:

To move below the RCP8.5 scenario — avoiding the worst climate impacts — requires early action and sustained mitigation from the largest emitters such as China, the United States, the European Union and India.

These four regions together account for over half of global CO2 emissions, and have strong and centralized governing bodies capable of co-ordinating such actions. If similar energy transitions are repeated over many decades in a broader range of developed and emerging economies, the current emission trend could be pulled down to make RCP3-PD, RCP4.5 and RCP6 all feasible futures.

They make a key point: the “Gang of Four” account for over 50% of all global GHG emissions and all of them have the capacity to lead the world in implementing solutions to bring down emissions to safe levels.

The developing nations – lead by China and India – have been exhorting the developed nations to make deep cuts to emissions, assist in technology transfer and provide funding for mitigation and adaptation initiatives. Nor should we forget the fact that both China and India have seen profound economic growth over the past several decades: they’re not keen to sacrifice this unless the United States and other developed nations act in concert with them.

The developed nations – the United States chief among them – have been unwilling to undertake the deep cuts or pledges for technology transfer and funding out of self interest. Nor do they wish to surrender their present economic and political advantages to developing nations such as China.

Each of the Gang of Four fears it will be a case of beggar thy neighbour: in making sacrifices they will be taken advantage of.

But really it is a case of the tragedy of the commons: acting unilaterally and out of self interest each party not only beggars the other, but also their own future.  

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