To better understand the possible trajectory of future CO2, Kharecha and Hansen devised five emissions scenarios spanning the years 1850 to 2100. Each reflects a different estimate for the global production peak of fossil fuels, the timing of which depends on reserve size, recoverability and available technology. "Even if we assume high-end estimates and unconstrained emissions from conventional oil and gas, we find that these fuels alone are not abundant enough to take carbon dioxide above 450 parts per million," Kharecha said.
The first scenario estimates CO2 levels if emissions from fossil fuels follow "business as usual," growing 2 percent annually until half of each reservoir has been recovered. After this, emissions begin to decline by 2 percent annually. In the second scenario, emissions from coal are reduced, first by developed countries starting in 2013, and then by developing countries a decade later, leading to a global phaseout of emissions by 2050. The phaseout could come either from reducing coal consumption or by capturing and trapping CO2 from coal burning before it reaches the air.
The remaining three scenarios include the 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 fewer-than-expected additions to currently proven reserves, or taxes on emissions that makes fuels 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 team used a mathemat
|Contact: Kevin Krajick|
The Earth Institute at Columbia University