When and how global oil production will peak has been debated, making it difficult to anticipate emissions from the burning of fuel and to precisely estimate its impact on the climate. To better understand how emissions might change in the future, Pushker Kharecha and James Hansen of NASA’s Goddard Institute for Space Studies in New York considered a wide range of fossil fuel consumption scenarios.

The research shows that the rise in carbon dioxide from burning fossil fuels can be kept below harmful levels as long as coal emissions are phased out globally within the next few decades. Previous research has shown that a dangerous level of global warming will occur if carbon dioxide in the atmosphere exceeds a concentration of about 450 parts per million.

To better understand the possible trajectory of future carbon dioxide, Kharecha and Hansen devised five carbon dioxide emissions scenarios that span the years from 1850 to 2100.

Satellites show sources and sinks of atmospheric carbon dioxide across Earth, measured here in 2003. High concentrations are shown in red and lower concentrations are shown in blue.

The first scenario estimates carbon dioxide levels if emissions from fossil fuels are unconstrained and grow by two percent annually until half of each reservoir has been recovered, after which emissions begin to decline by two percent annually.

The second scenario considers a situation in which coal emissions are reduced first by developed countries starting in 2013, and then by developing countries a decade later, leading to a global phaseout by 2050 of coal emissions that reach the atmosphere.

The remaining three scenarios include the above-mentioned phaseout of coal, but consider different scenarios for oil use and supply. One case considers a delay in the oil peak by about 21 years to 2037. Another considers the implications of fewer-than-expected additions to proven reserves due to overestimated reserves, or the addition of a price on emissions that makes the fuel too expensive to extract. The final scenario looks at emissions from oil fields that peak at different times, extending the peak into a plateau that lasts from 2020-2040.

The researchers suggest that the results illustrated by each scenario have clear implications for reducing carbon dioxide emissions from coal, as well as “unconventional” fuels such as methane hydrates and tar sands, all of which contain much more fossil carbon than conventional oil and gas.

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