Climate Interactive used their climate policy model, C-Roads, to analyze the Copenhagen Accord and national commitments to reduce greenhouse gas emissions. Their analysis assumes that nations follow their commitments. Their analysis shows:

The Accord adopted in Copenhagen (accessed 19 December 2009) calls for deep cuts in global emissions so as to hold the increase in global temperature below 2 degrees Celsius compared to preindustrial levels. Simulations of the C-ROADS model show that doing so requires global greenhouse gas emissions to peak by 2020 and then fall 50% below 1990 levels by 2050 (a cut of approximately 60% below current emissions).

However, simulations of the C-ROADS model show a large gap between the targets in the final Copenhagen agreement and the commitments offered by individual nations. Using the C=ROADS model, the researchers estimate that current confirmed proposals (that is, submissions to the UNFCCC or official government positions) would raise expected global mean temperature by 3.9 Celsuis by 2100. Including conditional proposals, legislation under debate and unofficial government statements would lower expected warming to an increase of approximately 2.9 C over preindustrial levels.

The graph and table below show simulation results from the C-Roads model for four scenarios: business as usual (calibrated to the IPCC A1FI scenario), current confirmed commitments, potential commitments, and the low emissions path required to achieve an expected warming of 2 degrees C over pre-industrial levels.

Seth Borenstein of Associated Press interviewed John Sterman and Andrew Jones from Climate Interactive as well as Cynthia Rosenzweig and Yvo de Boer:

Going above 450 parts per million “will change everything,” said NASA climate impacts researcher Cynthia Rosenzweig.

“It’s not just one or two things,” Rosenzweig said. “There will be changes in water, food, ecosystems, health, and those changes also interact with each other.”

At that point, among other things, millions of people would be subject to regular coastal flooding, droughts would cause food shortages, coral reefs would dramatically die off affecting the ocean food chain, and about 20 percent of the world’s known species would be significantly endangered, according to Rosenzweig and other climate scientists.

Systems dynamics experts John Sterman of MIT and Andrew Jones of the Sustainability Institute in Vermont compare our carbon problem to a bathtub. Each year we pump carbon dioxide into the atmosphere, much of it remains there. It lasts for about a century, although about half of the carbon dioxide produced is removed each year by forests and oceans.

Sterman and Jones figure the world can afford to churn out another 920 billion metric tons of carbon dioxide between now and 2050. Holding emissions to that level offers a better than even chance at keeping the world under 450 parts per million and avoiding a crucial temperature rise.

But that will be a challenge. Forty years of pumping emissions at the level we have now would exceed the safe level by more than 50 percent. And that doesn’t even account for future levels of greenhouse gases from booming economies like those in China and India.

Ideally, the world should produce 80 percent less in greenhouse gases than we do now, Jones said.

Technically, the delay of at least one year in implementing strict emissions limits — thanks to the nonbinding deal in Copenhagen — may not hurt. But it’s a momentum issue and a compounding interest issue, said Achim Steiner, head of the United Nations Environment Program. It’s like debt on a credit card: Every time a person puts off paying the balance, it grows bigger and harder to resolve.

Every year of delay means the chance of achieving a stable and healthy climate “is getting smaller and smaller,” said Yvo de Boer, head of U.N. Framework Convention on Climate Change, which ran the Copenhagen negotiations. …

Yet de Boer is optimistic.

“I think science will drive it,” de Boer said. “I think business will drive it. I think society will drive it.”