The chances of keeping temperatures below a 2-degree-Celsius rise over preindustrial levels drop precipitously the longer policymakers dither, according to a new study that finds political will is the biggest uncertainty in fighting climate change.

Enacting immediate and swift climate change policies would, in the most optimistic scenario, give the world a 90 percent chance of meeting the 2-degree target for averting catastrophic global warming. But a 20-year delay, scientists found, would mean the probability of hitting that goal drops to 50 percent -- no matter how much money countries spend in the effort.

"The biggest choice is when we would start with globally comprehensive action, for which an agreement is needed," said Keywan Riahi, energy program leader at the Austria-based International Institute for Applied Systems Analysis (IIASA) and a co-author of the paper published yesterday in the journal Nature.

The study underscores the concerns that small island nations and others raised at last year's U.N. climate conference in Doha, Qatar. Though nations have agreed to work out a new emissions plan, it will not go into effect until 2020 -- far too late, scientists say, to save vulnerable countries from rising sea levels, increased storm surges and other impacts.

In examining the chances of keeping average global temperatures in check, IIASA researchers quantified and ranked several "uncertainties" associated with reducing greenhouse gas emissions, like the actual impacts of rising temperatures, future energy demand and technological developments, to see which factors have the biggest impact on the chances of averting warming.

Riahi said the goal was to put those unknowns -- often used to postpone action on climate change -- into context. The result of their findings: The biggest uncertainty of all is the timing of global political action.

"If there is a delay in action, despite all the other uncertainties there are certain targets that will be out of reach," he said.

Delay may be 5 times more expensive
In large part, the chance of reaching the 2-degree goal skips out of reach because of the emissions that continue to rise with every passing year. So crashing on emissions cuts two decades from now and even achieving negative emissions output would mean countries could not compensate for the additional rise.

Meanwhile, Riahi said, if carbon emissions were taxed at what he described as a "modest" price of $20 per metric ton, the world would have a 60 percent chance of meeting the 2-degree goal. If policymakers delayed putting a price on carbon until 2020, achieving that same probability would necessitate a tax of $100 per metric ton.

"So you're talking about a fivefold increase in the price signal in order to achieve the same likelihood for staying below 2 degrees," he said. Waiting another decade after that, he said, could be disastrous. By 2030, the 60 percent probability rate becomes out of reach, no matter how high the price on carbon becomes.

Some of the probability rates do change if nations can achieve lower energy demands. Researchers found that if energy growth is limited, there could be a 50-50 chance, with high carbon prices, of reaching the 2-degree goal from a 2030 starting point.

"My hope is at least that more research is done in this direction that it can support negotiations to find an agreement that would help to reduce emissions globally to stay below the 2-degree target, because that's definitely the biggest factor," Riahi said. "There's numerous studies that have shown it is in principle possible, but of course it requires dedicated policies and action that won't happen without the political will to reduce emissions."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500