"Temperature tipping points are approaching quickly, which will trigger abrupt and irreversible climate impacts, including loss of summer sea ice in Arctic, loss of snow and ice in Himalayan-Tibetan Plateau, disintegration of Greenland ice sheet [and] die-off of Amazon," Durwood Zaelke of the Institute for Governance and Sustainable Development, US, told environmentalresearchweb. "The fast-action strategies [that] we outline can [be] started quickly with existing governance mechanisms, such as the Montreal Protocol. They do not need to wait for the current climate negotiations to conclude, nor to wait for ratification and implementation of whatever agreement is produced through that process."

Zaelke and colleagues from the University of California, San Diego; the Montreal Protocol Technology and Economics Assessment Panel in India and the US; Scripps Institution of Oceanography; and the National Environment Tribunal of Kenya looked at four approaches: reducing hydrofluorocarbon emissions; reducing black-carbon aerosol concentrations; cutting emissions of ozone precursors; and boosting biosequestration. All of these could be substantially implemented within 5–10 years and produce a climate response within decades, they say.

The Montreal Protocol has already cut down greenhouse gases by reducing emissions of chlorofluorocarbons and other ozone-depleting substances. Indeed, there are claims that by 2010 the benefit of the Montreal Protocol to the climate will be five or six times larger than that of the Kyoto Protocol.

In 2007 the parties to the protocol agreed to accelerate phase-out of HCFCs, the transitional replacement for CFCs. But this could lead to a rapid increase in HFCs, which although less damaging to the ozone layer than HCFCs, are also greenhouse gases and are included in the Kyoto Protocol.

There are, however, substitutes for HFCs with low global-warming potential, for example HFO-1234yf. With this in mind a group of small island nations led by the Federated States of Micronesia and Mauritius has proposed an amendment to the Montreal Protocol to phase down the use of HFCs with high global-warming potential.

The protocol could also provide additional climate mitigation by preventing emissions of ozone-destroying substances from discarded refrigeration and air-conditioning equipment. Pilot projects are underway.

Black carbon is emitted by the incomplete combustion of fossil fuels and biomass. In aerosol form it causes warming in the atmosphere by absorbing solar radiation and, once deposited onto snow and ice, it can darken their surface and accelerate melting. Black-carbon aerosols can also affect cloud formation. This either causes low-level clouds to be burnt off, letting more solar radiation through or, if other water-soluble aerosols are present, increases the persistence of low-level clouds and cools the surface.

There are estimates that black carbon could be halved by 2030 by applying existing technologies, primarily to cut diesel emissions and to improve cooking stoves. Around half of the world uses fossil fuels for cooking and the associated black carbon can also cause respiratory illness. Zaelke's co-author Ram Ramanathan has set up Project Surya to try to cut such black-carbon emissions.

Tropospheric ozone has increased by around 30% since pre-industrial times and it contributes around one-fifth as much as carbon dioxide does to global warming. Ozone precursor gases, such as carbon monoxide, nitrogen oxides, methane and other volatile organic compounds, all contribute to the formation of the pollutant. The UK's Royal Society reckons that the rigorous implementation of air-pollution regulations across the globe could reduce nitrogen oxide and carbon monoxide emissions by more than 50%. This would cut anthropogenic forcing from tropospheric ozone from 20% to 10%.

Biosequestration measures, such as preventing deforestation, boosting afforestation and reforestation, and biochar production could all mitigate carbon emissions to varying degrees.

"We can delay climate forcing by several decades and reduce the risk of passing the temperature tipping points for abrupt climate change," said Zaelke. "The race is close, with tipping points and the threat of accelerating feedbacks that will lead to run-away warming. But if we move immediately, we may still be able to get ahead of the warming, and actually reverse it using carbon negative strategies, such as biochar."

Zaelke stresses that there is a real need to focus on speed, that non-carbon dioxide factors provide half of man-made forcing, and it's the fast half. "We need to remember that we can't win the climate battle without also winning on the carbon dioxide side, which is the other 50%," he said.

Now the researchers, who reported their work in PNAS, plan to work on a better metric to measure the time to produce cooling.