On February 28, a panel of experts gathered at Jones Bay Wharf in Pyrmont, Sydney, Australia, for the fourth and last Principal Voices roundtable of 2006-7. The guests discussed measures to address global warming through reducing greenhouse gas emissions, notably the increasing practice of carbon trading, in front of an invited audience.

An essay about the discussion can be read here, and there is also a full transcript of the event here.

Following is a short series of key quotes from the participants:

James Cameron, vice chairman of Climate Change Capital, a London-based investment bank which specializes in low carbon emission businesses

"We face, with the climate change threat, a level of risk that we have never experienced before in human society. The science of climate change is as solid, possible more solid, than any other area of scientific endeavor."

"These are people who have strategic interests in the marketplace, and are also trying to invest to reduce risk over time. But, they're not doing this for charity, for good will, for environmental purposes. They're doing this for commercial returns. They're absorbing risk and they expect returns that are commensurate for that risk."

"We've been involved in transactions in China, and have caused to be reduced, at very low cost, the equivalent of Sweden's total annual output of greenhouse gases from across its economy."

"I like to have a picture of the evening news in 10 years' time, where the rather boring bits and pieces of economic data are analyzed to say, well today, the interest rates are here, the employment rates are here and carbon prices are here. I want to know how quickly we can get to that vision, and I want to see leadership in politics and business to get us there fast."

Paula DiPerna, executive vice president of the Chicago Climate Exchange, the first pilot US program for greenhouse gas emissions trading.

"A cap is a kind of umbrella, and right now there are two umbrellas in the world. One is over the European Union, which is the European Union Emissions Trading Scheme, which was a child of the Kyoto Protocol, and the Chicago Climate Exchange, which is a functioning cap and trade within the United States right now... Without the cap, offsets may be moving things around. If you have the cap, you are required to be achieving reductions. I suppose you can say that for the moment, in the absence of a global umbrella, there's certainly a bit of leakage around the two umbrellas."

"From the political point of view, what we're looking for is a very visionary approach to this. I think you'll see a movement towards enforcement in the United States, I hope within my lifetime, but I would bet even within the next couple of years."

"What's traded is not the right to pollute but the value of the scarcity. And until to experiment with what the market will bear, you can't know what the price will be."

"I think the moral case is very, very present, but in the environmental movement, as long as I've been involved in it, the challenge has been to demonstrate that environmental stewardship can be profitable, that there are going to be costs but it can be profitable."

Martijn Wilder, head partner of Global Climate Change, Clean Energy and Emissions Trading Practice for global law firm Baker & McKenzie

"With a lot of environmental issues, it's often the scientists who find the issues, such as the ozone layer, and law and policy makes come in and start regulating with rules to control the problem, as we saw with the hole over the ozone layer."

"We have a range of clients and people who are interested who must comply, because they have a legal obligation such as under the European trading scheme and have a legal target to meet. But there are a lot of companies who have decided that this is a market in which there are real opportunities they can develop."

"We don't know for certain what the effects are going to be. We know that there is a very dangerous experiment going on, where emissions have gone through the roof. You need to ask yourselves, are we prepared to take a very significant risk of not taking action now, giving the sort of risk that these sorts of increasing emissions is likely to present. I would be saying that we have to try everything now, if some things don't work then sure, they don't work, but we should be trying all different solutions."

"Even if you take the IPCC, the IPCC at the moment has different scenarios [for the future effects of emissions], if you take their most extreme scenario, you could say there is a one in 10 chance of that happening. How many people in this room will take a one in 10 chance? If you were getting on a jumbo in New York today to fly back to Sydney and you were told that 50 of the 500 passengers were likely to be shot, would you take that risk?"

Warwick McKibbin, professor of international economics at the Australian National University in Canberra, also an adviser to the Australian government on power.

"That's the key feature of the climate change problem, that every aspect of it has cascading degrees of uncertainty: How the climate will respond to changes in carbon emissions; what will carbon emissions be in 50 years; what will concentrations be; where will be the weather events; what will be the distribution across time and across countries."

We need 2050, 2070 targets. They're not priced into any of these markets at the moment. They should be. That's the flaw in the Kyoto Protocol, the black hole after 2012.

"The other issue which is important in the role of government is in research and development funding. That's the critical role government plays. But without a carbon price signal it's very hard to know how you allocate the R & D funding."

"Underlying everything has to be the hip pocket. If people have to pay more for something carbon intensive, they will have the incentive to change their behavior. It all comes back to why you want a carbon price in the world economy."