Feasible Emission Scenarios Identified That Could Keep CO2 Below Climate Threatening Levels

(In response to news published by ANI on September 11, 2008)

NASA researchers have identified feasible emission scenarios that could enable keeping carbon dioxide (CO2) levels below that considered dangerous for climate by scientists.

When and how global oil production will peak or will decrease has been debated, making it difficult to anticipate emissions from the burning of fuel and to precisely estimate its impact on climate.

To justify 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.

For a better understanding of the possible trajectory of future carbon dioxide emissions, Kharecha and Hansen devised five carbon dioxide emission scenarios that span the years 1850-2100. Each scenario reflects a different estimate for the global production peak of fossil fuels, the timing of which depends on reserve size, recoverability and technology.

The first scenario estimates carbon dioxide levels, if emissions from fossil fuels are unconstrained and follow along “business as usual” growing 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 emissions from coal are reduced first by developed countries starting in 2013 and then by developing countries a decade later, leading to a global phase out by 2050 of the emissions from burning coal that reach the atmosphere.

The reduction of emissions to the atmosphere in this case can come from reducing coal consumption or from capturing and sequestering the carbon dioxide before it reaches the atmosphere.

The remaining three scenarios include the above-mentioned phase out of coal, but consider different scenarios for oil use and supply.

Next, the team proposes to use a simplified mathematical model, called the Bern Carbon Cycle model, to convert carbon dioxide emissions from each scenario into estimates of future carbon dioxide concentrations in the atmosphere.

The unconstrained “business as usual” scenario resulted in a level of atmospheric carbon dioxide that more than doubled the pre-industrial level and from about 2035 onward levels exceed the 450 ppm threshold of this study.

Even when low-end estimates of reserves were assumed, the threshold exceeded from about 2050 onwards.

The other four scenarios, however, resulted in carbon dioxide levels that peaked in various years but all fell below the prescribed cap of 450 ppm by about 2080 at the latest, with levels in two of the scenarios always staying below the threshold.

The researchers suggested 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.

By Arunava Das