According to Nobel Prize-winning atmospheric chemist F. Sherwood Rowland, who discovered the threat to the ozone layer by CFCs, the answer is, yes they could.

From a May 29 posting at the NYT's Dot Earth blog, by Andrew C. Revkin:

Carbon dioxide emissions result from almost every activity in lives both prosperous and poor — from burning forests to microwaving popcorn or flying to Tokyo.

That linkage between emissions and lifestyles is one reason the concentration of the gas has been rising relentlessly, to around 385 parts per million now after never topping 280 parts per million for at least 650,000 years. (United States emissions from energy use dropped slightly in 2006 but yesterday the Energy Department reported they rose 1.6 percent in 2007.)

Avoiding a lot of warming and climate change while heading toward 9 billion people seeking a decent life will require an utter transformation of the multi-trillion-dollar energy system, Dr. Chu said. An audience member wondered whether spiking gas prices would propel the change. Dr. Chu said higher energy prices would not be enough on their own, adding that the necessary energy transformation will also require decades of sustained research, development, and deployment of new technologies.

During a break, I asked Dr. Rowland two quick questions. The first: Given the nature of the climate and energy challenges, what is his best guess for the peak concentration of carbon dioxide?

(Keep in mind that various experts and groups have said risks of centuries of ecological and economic disruption rise with every step toward and beyond 450 parts per million, with some scientists, most notably James Hansen of NASA, saying the long-term goal should be returning the atmospheric concentration to 350 parts per million, a level passed in 1988.)

His answer? “1,000 parts per million,” he said.

My second question was, what will that look like?

“I have no idea,” Dr. Rowland said. He was not smiling.

According to the IPCC, a peak of 1,000 parts per million of carbon dioxide in the atmosphere would likely lead to a temperature rise of 3.7 degrees above 1980-1999 levels by 2090-2099, with an increase of two to 5.4 degrees as the likely range.

Here are some of the predictions made by British author Mark Lynas in 2007. At the higher end, the consequences become progressively more dire.