Sunday, November 9, 2008

Who is the biggest emitter of greenhouse-gas (GHG) emissions – the US or China?

Many news stories in recent times suggest that China has overtaken the US as the world's biggest emitter of greenhouse-gas (GHG) emissions. Others insist that the US is still "ahead". Hot Spot readers should understand that these are highly political numbers. Reality is more complex than a two-horse race.

The issue is that people choose the numbers that tell the story they want to hear. Those who want to say that China is overtaking the US (and, hence, that developing countries are as responsible for climate change, if not more so, than industrialised countries) will cite annual emissions. And they will refer to absolute emissions, that is, tons of GHG emissions.

It is true that, in some year not too far from now, China will overtake the US in annual absolute emissions. There are many data sources, but for the purposes of this column, let us use a single source that has compiled and checked data from many places, the Climate Analysis Indicator Tool, which gives us as consistent a data set as is available (see http://cait.wri.org).

The table shows that the gap is narrowing; in 2000, the US emitted over 2 000-million tons (Mt) of carbon dioxide (CO2) – both from energy and land use change and forestry – more than China. By 2004, the gap was down to 684 Mt. So, by this measure, some year soon, China will overtake the US.

But when one considers per capita emissions – in other words, if one allows each person an equal right to use the atmosphere to take up GHG – then China is nowhere near overtaking the US. Similarly, when one considers historical responsibility – measured by cumulative emissions – the data paints a different picture. On both of these measures, China will not overtake the US for a long time – for decades.
The key point is that what one counts matters. A somewhat careful walk through what the data tells us will show the difference. When counting all six gases covered by the Kyoto Protocol, the gap was 1 630 Mt CO2 equivalent in 2000, the latest year for which data is available for all gases.

Both historical responsibility and emissions per capita are important for equity. Historical responsibility can be approximated by the emissions emitted over time, called cumulative emissions. Indeed, this is what the atmosphere really cares about, since it is the closest approximation to concentrations of GHGs in the atmosphere and, hence, changes global surface temperature. (There are more complex ways of establishing this relationship, beyond the scope of this column.)

Historical cumulative emissions are critical for responsibility, since it is the emissions already up there in the atmosphere that are causing the problem. By this measure, China ranks only third, and its emissions are 59% of those emitted by the US over the second half of the twentieth century. It will take decades before China overtakes the US and that ranking order changes.

Per capita emissions is another measure of equity. In principle, each person should have the same right to use the (limited) capacity of the atmosphere to absorb GHG without harm to the planet. But then we must also recognise that countries' natural resource endowments differ, which impacts on per capita emissions. On a per capita basis, China's emissions in 2004 ranked only seventy-third in the world. The US also drops from first to seventh, surpassed by a few small countries with high energy dependence but small absolute emission shares.

What is clear is that the average American emits five times the average Chinese. And emissions support very different lifestyles and patterns of production, including the dynamic that about one-third of Chinese emissions (1 700 Mt of CO2) are due to production of goods for export. Fairness in emissions accounting may still become an important debate.

South Africans emitted 9,2 t of CO2 per capita in 2004, roughly half the emissions of Americans but double those of the Chinese. If one combines the cumulative emissions and per capita measures, Americans' cumulative emissions per capita are 7,5 times the figure for China.

As the table shows, many other factors matter, including the gases counted – CO2 only, or also methane, nitrous oxide and three trace gasses. Other factors are whether emissions from energy are counted (higher shared in developed countries) or also land use change and forestry (typically higher in developing countries) and whether emissions from bunker fuels count – that is, from international shipping and aviation.

What matters, in the end, is that all these emissions need to be reduced, by all of these countries – some in absolute terms and some initially in relative terms – in a fair way. But we should be careful what we count, and should not reduce the complexities of reducing GHG emissions to the dubious honour of who is first past the post.

Harald Winkler is Associate Professor at the Energy Research Centre, University of Cape Town, and can be contacted at Harald.Winkler@uct.ac.za.