A new study aims to offer unique insights into countries’ historical responsibility for global warming, by translating their emissions into a proportion of observed temperature rise.
How responsible different countries’ are for climate change to date has long been a contentious issue. Contributing differently to the build-up of greenhouse gases in the atmosphere, some countries are considered more to blame for warming than others.
As well as carbon dioxide from fossil fuel burning and land use change, they examined methane, nitrous oxide and sulphate aerosol emissions.
The researchers then looked at the relationship between these emissions and temperature rise – weighing each type of emission according to the lifetime of the temperature change it causes.
By working out how much each country has emitted, they were able to work out how much temperature rise it had caused.
Unsurprisingly the research showed how a small number of countries account for a large share of greenhouse gas emissions. Together, the US, China, Russia, Brazil, India, Germany and the UK have been responsible for 63% of emissions.
Using the new method, the US – which takes top place in terms of historical emissions and contributing more than double the emissions of 2nd place holder China – is responsible for 0.15°C of warming. That’s close to 20% of the total temperature rise witnessed so far.
China and Russia come next in the rankings – responsible for around 8% of emissions each – contributing around 0.06°C to global temperature rise, followed by Brazil and India, responsible for around 7% of global emissions and 0.05°C temperature rise each.
Germany and the UK come in sixth and seventh – responsible for around 5% of emissions and 0.03°C of temperature rise.
The researchers experimented with various methods of illustrating the difference between countries’ emissions.
They examined contribution to temperature rise relative to population size (per capita emissions).
Here China and India fall to the bottom of the rankings. The UK jumps to first place ahead of the US when population size is considered – with the top seven countries all coming from the developed world.
They examined also emissions relative to geographical area.
Here countries, such as the UK and Japan jump up the rankings, having caused disproportionately more warming than the size of their country would suggest, while Canada and Australia fall down the table.
Understanding countries’ total historical emissions is a hugely complex task – and the researchers warn the latest results should be considered as a “reasonable best guess”.