A team of researchers have determined that the ongoing rise in atmospheric carbon dioxide (CO2) from burning of fossil fuels might be kept below harmful levels if emissions from coal are phased out within the next few decades.
The research has been carried out by climatologist Pushker Kharecha and James Hansen, director of NASA Goddard Institute for Space Studies.
According to them, less plentiful oil and gas should be used sparingly as well, but that far greater supplies of coal mean that it must be the main target of reductions.
The burning of fossil fuels accounts for about 80 percent of the rise of atmospheric CO2 since the pre-industrial era, to its current level of 385 parts per million.
However, while there are huge amounts of coal left, predictions about when and how oil and gas production might start running out have proved controversial, and this has made it difficult to anticipate future emissions.
To better understand how the emissions might change in the future, Kharecha and Hansen considered a wide range of scenarios.
"This is the first paper that explicitly melds the two vital issues of global peak oil production and human-induced climate change," Kharecha said.
"We found that because coal is much more plentiful than oil or gas, reducing coal emissions is absolutely essential to avoid dangerous climate change," he added.
CO2, which accounts for about half of the human-caused greenhouse gases in the atmosphere, concerns scientists because it can remain for centuries.
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.
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.
"We're illustrating the types of action needed to get to target carbon dioxide levels," Kharecha said.
"The most important mitigation strategy we recommend-a phase-out of carbon dioxide emissions from coal within the next few decades-is feasible using current or near-term technologies," he added.