With carbon dioxide (CO2) in the air approaching alarming levels, even halting emissions altogether may not be enough to avert catastrophic climate change.

A new study by Carnegie Institution scientists suggests that while removing excess CO2 would cool the planet, carbon cycle complexities would limit the effectiveness of a one-time effort.

To keep CO2 at low levels would require a long-term commitment spanning decades or even centuries.

Previous studies have shown that reducing CO2 emissions to zero would not lead to appreciable cooling, because CO2 already within the atmosphere would continue to trap heat. For cooling to occur, greenhouse gas concentrations would need to be reduced.

“We wanted to see what the response would be if carbon dioxide were actively removed from the atmosphere,” says study co-author Ken Caldeira of Carnegie’s Department of Global Ecology.

Caldeira and study co-author Long Cao, also at Carnegie, did not focus on any specific method of capturing and storing CO2 from the air.

The possibilities include approaches as diverse as industrial-scale chemical technologies and changing land use so more CO2 is naturally absorbed by vegetation.

According to the simulations conducted by the researchers, for every 100 billion tonnes of carbon removed from the atmosphere, average global temperatures would drop 0.16 degrees Celsius, said a Carnegie Institution release.

Further simulations showed that in order to keep CO2 at low levels, the process of CO2 extraction from the air would have to continue for many decades, and perhaps centuries, after emissions were halted.