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Carbon versus carbon dioxide

Be careful: some people talk about carbon while others talk about carbon dioxide. When you burn a ton of carbon you get about 3.67 tons of carbon dioxide. Neglecting this can cause big mistakes:

• Joe Romm, The biggest source of mistakes: carbon versus carbon dioxide. A factor of 3.67 makes a big difference when discussing climate.

Just remember: C has atomic mass 12, O has atomic mass 16, so CO₂ has atomic mass 12+16+16=44, so a molecule of carbon dioxide is

times as heavy as the atom of carbon that was burned to form it.

Units

Scientists use GtC as an abbreviation for ‘gigatonne of carbon’. A gigatonne is a billion metric tons, or $10^{15}$ grams, also known as a petagram.

2010 Data from the German Federal Government

The following table compares the carbon dioxide emissions of several contries in 1990 and 2004, the data was compiled and provided by the German government:

2007 UN data

This chart lists the carbon dioxide emissions of countries worldwide:

• List of countries by carbon dioxide emissions, Wikipedia.

This chart includes only CO₂ emitted by fossil fuel burning and cement manufacture, not deforestation, change in land use, etc. Methane and other greenhouse gases are not included. Currently the list is based on data from 2007, taken from this report:

• United Nations Statistics Division, Millennium Development Goals indicators: Carbon dioxide emissions (CO2), thousand metric tonnes of CO2 (collected by CDIAC).

The entire world is listed as having emitted 29.3 gigatons of carbon dioxide in 2007. This corresponds to 8 gigatons of carbon. The top five countries are:

country	gigatons of CO2 in 2007	percentage
China	6.54	22.3%
United States	5.84	19.9%
India	1.61	5.50%
Russia	1.54	5.24%
Japan	1.2	4.28%

2008 IEA data

On 6 October 2010, the International Energy Agency released its own data set (calculated using slightly different methods than CDIAC) for 2008 emissions that listed about 140 countries:

• CO₂ Emissions from Fuel Combustion - Highlights, International Energy Agency website, retrieved 2010-10-06.

Germany

The following chart shows the emission of $CO_2$ by Germany according to the German federal government (Bundesamt für Statistik):

Historical carbon emissions

From this database:

• RCP emissions database

one obtains a total of 355 GtC of fossil fuel emissions from preindustrial times to the year 2005, and about 160 GtC of other emissions (for example, land use changes), for a grand total of 510 GtC.

Future carbon emissions

One can’t predict the future, but one can make projections based on assumptions. Nathan Urban’s paper with Klaus Keller, discussed in “week304” and “week305”, uses this source:

• William D. Nordhaus, 2007. The challenge of global warming: Economic models and environmental policy, Technical report, http://nordhaus.econ.yale.edu/DICE2007.htm.

• William D. Nordhaus, A Question of Balance: Weighing the Options on Global Warming Policies, Yale University Press, New Haven, 2008.

Based on Nordhaus’ work, Urban estimates that in a “business as usual” scenario, by the year 2300 we will have burnt 4800 gigatonnes worth of of carbon, compared to the roughly 510 gigatonnes we’ve burned far.

This projection assumes we get desperate for cheap energy and extract not only coal, oil and gas but also all the hard-to-get fossil resources in oil shales and tar sands, all the remaining coal, etc. It does not include the methane clathrates at the bottom of the sea.

Here’s a graph from Urban and Keller’s paper:

In this scenario carbon emissions peak around 2150 at about 23 gigatonnes carbon per year (84 gigatonnes CO₂). By 2300 they’ve tapered off to about 4 GtC (15 GtCO₂).

The figure of 4800 gigatons in the year 2300 is not the end of the story, because in his book Nordhaus estimates that 6000$\pm$1200 gigatonnes of carbon are available to be burnt (again, not counting methane clathrates).

It’s currently estimated that there are somewhere between 500 and 2500 gigatonnes of carbon in methane clathrates:

• A.V. Milkov, Global estimates of hydrate-bound gas in marine sediments: how much is really out there?, Earth-Sci. Rev. 66 (2004). 183–197.

These recent figures are much less than earlier estimates.