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Doha infographic gets the numbers wrong, underestimates human emissions

  • 07 Dec 2012, 15:30
  • Christian Hunt and Mat Hope

Screen Shot 2012-12-07 At 15.14.55

An extract from the infographic - click to enlarge © Information is Beautiful

There's a startling  infographic on the Guardian's datablog today from designers Information is Beautiful. Timed for UN climate talks in Doha, it presents some top-line numbers about human-caused carbon emissions, followed by a whole page listing potential impacts of climate change according to temperature rise.

But one of the key top-line figures is wrong, and several others are confusingly presented - so we're happy to report that the graphic is being revised.

We've focused on trying to understand where the top line numbers come from and haven't gone over the whole graphic in detail. The infographic asks: "How many gigatons of carbon dioxide have we released to date?". It also suggests figures for how much we can "safely release" based on a global carbon budget, and how much carbon dioxide there is "left to release" if remaining fossil fuel reserves were burned.

Let's take each of them in turn.

How many gigatons of carbon dioxide have we released to date?

The graphic states the world released 530 gigatons of carbon dioxide between 1850 and 2000, and 380 gigatons of carbon dioxide since 2000.

This makes a total of 910 gigatons of carbon dioxide released by human activity.

This seems low -  the World Meteorological Organisation (WMO)'s annual greenhouse gas bulletin, released two weeks ago, gives a higher figure:

"Since the industrial revolution, about 375 billion tonnes of carbon have been emitted by humans into the atmosphere as carbon dioxide (CO2)."

Converting this (roughly ) to a tonnage of carbon dioxide gives 1,374 gigatons - substantially higher than the infographic estimate.

One of the researchers explained to us how the figures had been calculated. They were done in two parts. The figure for emissions since 2000 is based on analysis in a recent report from NGO Carbon Tracker, and appears to be right.

But the 520 gigatons figure for pre-2000 emissions is, we think, wrong, and underestimates human carbon dioxide emissions.

An Information is Beautiful researcher told us how it was calculated. It's based on the increase in atmospheric concentrations of carbon dioxide from before the industrial revolution to now. For every eight gigatons of carbon dioxide emitted into the atmosphere, the atmospheric concentration of carbon dioxide goes up by approximately one part per million.

This means that according to Information is Beautiful's analysis, there is 851 gigatons more carbon dioxide in the atmosphere now than in 1850. The researchers then subtracted a figure for human-caused carbon dioxide emissions since 2000, to get a number for emissions pre-2000.

But unfortunately, this rough calculation ends up producing the wrong number. This is because natural carbon sinks absorb just over half of human carbon emissions. So the amount of carbon dioxide that stays in the atmosphere is only about half of the carbon dioxide humans emit - the planet absorbs the other half.

As the WMO notes, manmade emissions before 2000 were actually significantly higher.

How many more gigatons of carbon dioxide can we safely release?

Carbon Tracker's report cites a global carbon budget, giving the amount of carbon dioxide the world can release while staying below a temperature rise of two degrees above pre-industrial levels. It says:

"Research by the Potsdam Institute calculates that to reduce the chance of exceeding 2°C warming to 20%, the global carbon budget for 2000-2050 is 886 gigatons CO2."

Information is Beautiful calculates that 500 gigatons is the (rough) amount left in this budget, taking emissions between 2000 and now into account.

How many more gigatons of carbon dioxide are there "left to release" in fossil fuel reserves?

The graphic states that based on the reserves of the top 100 coal, gas and oil companies, they are capable of releasing a further 745 gigatons of carbon dioxide. This figure is also from the Carbon Tracker report.

But the graphic is unclear here. Carbon Tracker actually calculates that the 745 figure accounts for the potential emissions from the reserves of the top 100 coal, and top 100 oil and gas companies listed on the stock exchange. So, that's 200 listed companies. It seems likely that this is just some confusing grammar, rather than an error. (As we publish, this has just been corrected.)

Finally, the graphic says that there are 2,050 gigatons of carbon dioxide left to release from all known fossil fuel reserves.

This is calculated from the same Carbon Tracker report but appears to be based on some incorrect arithmetic. Carbon Tracker estimate that there are 2,795 gigatons of potential carbon dioxide emissions remaining in all the earth's proven reserves. Information is Beautiful appears to have subtracted the 745 figure that apparently accounts for coal, oil and gas companies' potential emissions, leaving 2,050 gigatons of carbon dioxide from all fossil fuel reserves. (This has also just been corrected.)

Overall, it's a shame that the numbers at the top of the graphic ended up being unclear or incorrect. Infographics are really powerful ways to get across complex information to a wide audience. But unfortunately if the information is wrong, that rather defeats the purpose.

However, good news! Information is Beautiful has been quick to respond to our questions, which we really appreciate. It's going to update the graphic addressing the issues we've raised, with revised figures based on the World Meteorological Organisation data.

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