 Adding hydrogen at a petroleum refinery improves the product mix, and making hydrogen is a necessary first step in making ammonia (NH 3 ) and nitrogen fertilizer. Currently these two uses, between them, elicit an annual production of 40 MtH 2. Almost all this hydrogen is made from fossil fuels, because it is cheaper than hydrogen produced from nuclear energy or renewable energy; production from fossil fuels does not require the costly intermediate step of electrolysis of water.  The second output when hydrogen is produced from fossil fuels is CO 2. Currently, at least 100 MtC is vented annually as CO 2, often at high purity, at H 2 production sites

 For each 100 GtC of carbon emissions from oil, 860 billion barrels of oil are extracted from the ground. By 2000, the world had extracted almost exactly this amount. Estimates of ultimately recoverable conventional oil currently still in the ground are in the range of 2000 ± 1000 billion barrels.  Currently, Sasol produces 165,000 barrels per day of synfuels and chemicals from coal in Secunda, South Africa, east of Johannesburg (S49). This is the world's largest synfuels facility, and it is similar in scale to a typical large refinery. Assuming the average specific gravity and carbon content of these synfuels is the same as reference crude oil, there is a carbon flow of 7 MtC/y in the synfuels leaving the Sasol plant. The Sasol plant is the largest point source of atmospheric CO 2 emissions in the world.  Comparing 165,000 barrels per day synfuels production from Sasol's plants with our estimate that 1 GtC/y will be available for capture in 2054 from 30 mbd of coal-tosynfuels production, a wedge is an activity that, over 50 years, achieves the ability to capture the CO 2 emissions from 180 Sasol-scale coal-to-synfuels plants.

 Treating the energy stored in hydrogen and stored in gasoline as equivalent leaves out many critical issues. Hydrogen scores less well than gasoline from the perspective of safety and storage. Hydrogen scores better than gasoline, if the full promise of fuel cells can be realized. The NRC Report postulates that fuel cells deliver a 67% premium in energy efficiency for hydrogen, relative to hybrid vehicles running on hydrocarbons.  Then, each kilogram of hydrogen fuel backs out five kilograms of carbon in conventional fuel, and each 100- mpgequivalent hydrogen car requires 100 kgH2 per year and prevents 500 kgC/y of tailpipe emissions. Where two billion 60-mpg-equivalent cars required 330 million tons of hydrogen per year, two billion cars with a fuel economy of 100-mpgequivalent require 200 million tons of hydrogen per year.

 A hectare of land used to produce biofuels has the potential to have a larger effect on the atmospheric carbon balance than a hectare of land used as a carbon sink. There are two reasons:  Most of the new carbon fixed by vegetation each year is allocated to construct short-lived and fast–decomposing tissue, such as leaves and fine roots. Because of its short residence time in ecosystems, such tissue cannot contribute substantially to a carbon sink, but it can be collected and used to produce biofuels.  A hectare of land dedicated to biofuels can produce these fuels indefinitely, displacing a stream of fossil carbon indefinitely, whereas a hectare of land used as a carbon sink has a certain capacity to store carbon and then its contribution to carbon accounts "saturates.”  Ethanol is currently the principal modern biofuel, because in the natural world there are bacteria that can produce ethanol by fermentation with high selectivity. A world with extensive biofuels production can be expected to produce a wide range of biofuels, including methanol, dimethyl ether (DME), and "biodiesel" fuels.  Assuming an average value of 250 GJ biomass yield per hectare, one- eighth of a hectare of dedicated land will be required for each car.