Climate change – metrics and targets

It’s not only the climate that changing. The debate over how to resolve the issue is also shifting rapidly.  Ten years ago it was an argument between believers and deniers. Today the deniers are a small minority and the real issue is whether you see global warming as a challenge or a catastrophe.

Until very recently, it tended to be seen as a challenge – a serious and unprecedented one – but one could still be resolved affordably over a decade or so. However, an increasing number of influential voices are now saying that it is a major emergency, comparable to a war in terms of the short-term effort required to  mobilise people and assets, change behaviour and ration resources.

Much will depend on which of these views prevails in the remaining months before world leaders meet in Copenhagen in December 2009. There, under the auspices of the UN Framework Convention on Climate Change (UNFCCC), they are due to sign a successor to the Kyoto Treaty, which runs out in 2012, and the nature of that agreement will dictate the way that civilisation responds to climate change. 

To appreciate the way the ground is shifting we need to look at what people are saying about four key metrics. The first is the temperature rise. How hot can the planet be allowed to get? The debate tends to revolve around whether we should aim to limit the rise to 1, 2, 2.5 or 3°C above pre-industrial levels.

The second key metric is the concentration of greenhouse gases (GHGs) in the atmosphere. You can think of this as the thickness of the blanket surrounding the earth, which is widely held to be responsible for the warming. For 650,000 years up to 1750 – which includes all 200,000 years or so of human history - the carbon dioxide level had stayed under 300 parts per million (ppm). But then humans started burning coal, oil and gas which emit GHGs in huge volumes and cutting down vast swathes of forests that absorb CO2 - and today the CO2 concentration has risen to 380ppm.  We are now thickening the layer of GHGs by about 2ppm annually (and last year saw a rise of 2.4ppm – tied as the record highest increase with 2005[1]).   The aim is to stop this figure rising and stabilise it – along with concentrations of other GHGs such as methane and nitrous oxide.  But at what level? 400ppm, 450ppm, 500ppm?

The third variable is the annual rate of emissions of carbon dioxide and other GHGs. The blanket gets thicker because we keep pumping more gases into the air. Today’s CO2 emissions from all sources are around 38 billion tonnes a year, compared with 21 billion in 1970. Add in methane and nitrous oxide, the other two main GHGs, and the total is around 50 billion tonnes in carbon dioxide equivalent terms, up from 29 in 1970 and growing at around one billion tonnes a year. [2] So we need to stop increasing these emissions and start reducing them – and the targets are usually framed in terms how much lower emissions need to be in percentage terms by 2050.

And finally, given that emissions are currently rising but need to fall, they will have to peak at some point. So on what date should that happen?  This is becoming a critical focus for the debate.

Keeping these four metrics in mind, if we look at some of the key reports from past four years, we can see how the targets and timescales are shifting. Let’s concentrate on two – the thickness of the blanket of CO2 and the date of the peak in emissions.

In 2005, for example, a commonly discussed scenario was stabilizing carbon dioxide levels at 550ppm, with a peak in 2030. The World Business Council for Sustainable Development (WBCSD), taking a lead in examining what was then the prevailing wisdom, published a report based on what was needed to achieve this goal, having said that a stabilisation level of less than 500ppm would be “very difficult to achieve”.

But in 2006 when Sir Nicholas Stern produced his major report for the UK Government, he had decided that, difficult or not, the world had to aim below 500ppm. He recommended[3] that CO2 should be stabilised between 400 and 490ppm[4]. He said that 400ppm – the lower limit - was “likely to be unachievable”. However, he calculated that stabilising GHG levels at the upper end of the range, around 490ppm of CO2, would require emissions to peak within 10 to 20 years. 

But then in November 2007, the stakes were raised again. When the Intergovernmental Panel on Climate Change (IPCC) – the body established by the UN in 1988 to be the official source of scientific authority on the issue - published its latest report, its Chairman Rajendra Pachauri, speaking to the UN, cited the section of the report which said that to keep the temperature rise to 2°C-2.4°C GHGs needed to be stabilised at or below 400ppm of CO2, the very target Stern had called “likely to be unachievable”.  This means, not the 25 year timeframe examined by the WBCSD in 2005, nor the 10-20 year horizon foreseen by Stern in 2006, but a peaking of emissions in 2015 – just five or six years on from the prospective Copenhagen deal. 

We should add that the IPCC doesn’t recommend targets. It leaves that to politicians. It simply puts forward scenarios to indicate what temperature rises can be expected from different stabilisation and emissions levels.

However it’s worth noting which scenario the IPCC chairman chooses to highlight. Whereas Pachauri in 2007 highlighted the 2015 peak scenario, his predecessor, Robert Watson, making the equivalent speech in 2001, chose to highlight a much less ambitious scenario in which emissions would peak in 2025 and CO2 would be stabilised at 550ppm. He talked of having to deviate from business as usual scenarios “within a few decades” – a timescale that many of today’s key players would regard as disastrously complacent.[5]

The idea of a 2015 peak is now gaining wide currency. For example, Tony Blair, who has taken on the task of trying to broker an agreement between governments, has also advocated exactly the same target.  

The targets are being tightened for three reasons: first, greater understanding of the potential impacts of different temperature rises; second, fears over wild card ‘feedback’ impacts – factors that could dramatically accelerate the warming process; and third, increasingly clarity over the scale of emissions reductions needed to prevent a catastrophic rise.

This table shows the range of options set out by the Intergovernmental Panel on Climate Change (IPCC).