Damon Matthews from Concordia University, Canada, and his colleagues have calculated national contributions to climate change using a new methodology that weights each emission according to its atmospheric lifetime and the temperature change it causes. The calculation includes historical emissions as far back as 1750, and represents the sum total of each country’s carbon emissions from fossil-fuel burning and land-use change, plus methane, nitrous oxide and sulphate aerosol emissions. The results are the most accurate national emissions data to date.

When looking at a straight ranking of the figures the US is an unambiguous leader, responsible for 0.15 °C of temperature rise (nearly 20% of observed warming). China and Russia account for around 8% each, Brazil and India 7%, and Germany and the UK roughly 5% each (Environmental Research Letters (ERL)). Between them these countries account for 63% of the global warming up to 2005.

Delving deeper into the data reveals the different reasons for each nation’s place on the guilty list. The UK is the seventh largest emitter because of its historic use of coal, whereas China’s second-place position is connected to recent coal burning. Brazil and Indonesia rank highly because of emissions from deforestation and agriculture. Developing countries such as Mexico and Venezuela have a high position because of the oil they produce, much of which is consumed in developed countries.

But scale the emissions to the geographic size of the country (see figure) and suddenly the climate contributions of Brazil and China don’t seem so out of line – they are perfectly in proportion to the area of the country. In this case the baddies are Western Europe, the US, Japan and India, which are all punching above their weight.

Meanwhile, dividing each country’s climate contribution by its population presents a different picture again. The top seven positions are now occupied by developed countries, and China and India drop down to the bottom of the list.

So how do we move forward from here? In their paper Matthews and colleagues calculate different ways of sharing the burden, assuming that we are all aiming for a global temperature rise of no more than 2 °C.

“Straight division by the number of countries in the world gives you something like 0.01 °C per country,” says Matthews. “The top 12 emitters have already exceeded this allowance, in the case of the US by a factor of 15. Alternatively if you allocate warming by population you get about 0.14 °C per billion people. By this measure the US has exceeded its capita allowance by about a factor of three.”

But should the biggest historical emitters automatically be held most responsible? Not everyone thinks so. “We also need to factor in things like technological progress; developing countries with high emissions today are benefiting from efficient technologies that weren’t available when developed countries went through their industrial revolution,” says Niklas Höhne, Director of Energy and Climate Policy at energy analysts Ecofys in Utrecht, the Netherlands.

Nonetheless, he still believes that national emissions rankings can have a useful role to play. “These calculations are still relevant as a benchmark, to check that different countries’ proposed emissions targets all meet similar standards,” he says.

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