The host is Stuart Scott of the United Planet Faith & Science Initiative.

Stuart Scott: My name is Stuart Scott, coming to you live from COP21. Those of you who are here know an icon of climate change, Dr James Hansen, who I believe sounded the alarm, he's the Paul Revere of the climate change movement. He's here with us today, it's the first time he's attended the COP.

The topic today is "Speaking Truth to Power". The 2009 book Dr Hansen wrote, "Storms of My Grandchildren", and you can read the subtitle ["The truth about the coming climate catastrope and our last change to save humanity"], it's quite shocking, and this was 2009. We've come quite a bit further in climate change - we haven't come a whole lot further in the negotiations, one might argue - but I would like to start off a discussion, I'm going to let Dr Hansen take it after my initial question.

I asked Dr Hansen before if he'd disambiguate for us between 2 deg C which is what appears in the press, day in, day out, when they talk about climate change, and 1.5 deg C, which is just beginning to appear now in the text, and not yet made it to the media.

James Hansen: Thanks very much Stuart. Actually, I prefer not to speak in terms of temperature targets, but rather atmospheric composition targets. In 2008 I wrote a paper with several of the top relevant experts in the world, in the carbon cycle, paleoclimate, modelling, the relevant disciplines, and we concluded that we should be aiming for no more than about 350 parts per million of CO2 in the atmosphere. And since that time, we've achieved remarkably accurate measurements of the earth's energy imbalance. And what we found is that the planet is out of balance, as you would expect when you add CO2 to the atmosphere it reduces heat radiation to space; therefore we have more energy coming in than heat being radiated to space. It turns out that that imbalance, which is about 0.6 watts per m^2, averaged over the entire planet, land and ocean, implies that you would need to reduce CO2 from the present 400ppm to about 350ppm to restore energy balance. And that's what you need to stabilise climate.

Stuart Scott: Dr Hansen, that 0.6 W/m^2, you've compared that to 400,000 Hiroshima-sized bombs per day?

James Hansen: The amount of energy - 0.6 W/m^2 doesn't sound like much, but if you convert it to to the number of Hiroshima atomic bombs it comes to 400,000 per day, every day of the year. So a lot of energy is going into the ocean and that warming ocean is the source of the biggest threat that we face, and that is the melting of the ice shelves around Antarctica and Greenland, which then speeds up the loss of mass from the ice sheets and the sea level rise.

I would like to talk about "Climate Justice and Governmental Honesty". How can we achieve that? And it's not easy. Our parents did not know that they were causing a problem for future generations by burning fossil fuels. But we can only pretend that we don't know. It's a difficult thing for the public to recognize because the climate changes only slowly because of the inertia of the system. The danger is because the planet is out of energy balance there's more warming that's in the pipeline without any additional gasses and that's going to take us up to, and in to, dangerous territory. We're on the edge of handing our children a climate system in which the consequences will be out of their control. For example, disintegration of ice sheets, sea level rise of many metres, which would mean we would lose all coastal cities - and more than half of the largest cities in the world are on coastlines. That's the one injustice, from one generation to another.

The second is north to south. Because almost all the greenhouse gasses have been added by countries in the north, but the biggest consequences are actually at low latitudes, where the warming is already making it uncomfortable in the summer, and making it difficult to work outdoors. So there's a north-to-south injustice. And there's one species, humans, that are taking over the planet, and threatening the existence of as much as a quarter to a half of the other species on the planet. That's the estimate of the IPCC for the number of species that would be committed to extinction by the end of this century if we stay on 'business as usual'. So these are the injustices.

Today, China is the biggest emitter, the United States 2nd and India 3rd. But it's not today's emissions that caused the climate change. It's the integrated emissions over time. The cumulative emissions. And for that, the United States is responsible for more than one quarter. Europe is responsible for more than one quarter, China for 10%, India for 3%, and so on. But even that exaggerates the responsibility of the developing countries. If you look at the per capita contribution to cumulative emissions, the United Kingdom, the United States, and Germany are by far the most responsible. China is an order of magnitude smaller. And India's contribution is so small it almost disappears on this chart.

The problem is that fossil fuels appear to the consumer to be the cheapest energy. They're not really cheapest, because they don't include their full cost to society. They're partially subsidized, but mainly they don't include the effects of air pollution and water pollution on human health. If your child gets asthma, you have to pay the bill, the fossil fuel company doesn't. And the climate effects, which are beginning to be significant and will be much larger in the future, are also not included in the price of the fossil fuels. So the solution would be fairly straightforward. Let's add in to the price of fossil fuels, the total cost - which you can't do suddenly, but you can do it gradually over time, so people have time to adjust.

So I argue that this should be done - it has to be across the board, across all fossil fuels, coal, oil, and gas, at the source, the mine or the port of entry. And I also argue that that money should be given to the public. Give an equal amount to all legal residents of the country. That way the person who does better than average in limiting their carbon footprint will actually make money. 2/3 of the people would come out ahead. It would also address the growing income inequality in the world, which is occurring in almost all countries, because low income people would tend to have a lower carbon footprint. People who fly around the world and have big houses would pay more, but they can afford to do that.

That's a transparent, market-based solution, a conservative solution, which stimulates the economy. The economic studies in the United States show that after 10 years at $10/ton[/year] of CO2 carbon fee, distributed the money to the public, after 10 years it would reduce emissions 30%, and after 20 years more than 50%. And it would spur the economy, creating more than 3 million new jobs.

Furthermore, this is the only viable international approach. You cannot ask each of 190 countries to individually limit their emissions. What we have to do is have the price of fossil fuels honest. That requires only a few of the major players to agree, "Let's have a rising, common, carbon fee", and those countries that don't want to have that fee, we'll put a border duty on products from those countries, and furthermore we will rebate to our manufacturers the carbon fee when they export a product to a non-participating nation. This, economists agree, is a fair way to do it, and could rapidly move us off of fossil fuels.

Stuart Scott: You pointed out that if 3 major economies did this, all other nations would be forced to go along.

James Hansen: Almost all would go along, because they would rather collect the money themselves than have us collect it at our borders. So its a very simple way to give you a control of the system.

But what we are hearing is, Christiana Figueres said, "Many have said we need a carbon price and (investment) would be so much easier with a carbon price, but life is much more complex than that." So what we're talking about instead is the same old thing. The same old thing that was tried in Kyoto. Asking each country to promise, "Oh, I'll reduce my emissions, I will cap my emissions, I'll reduce them 20% or whatever they decide they can do." You know, in science, when you do a well-controlled experiment, and get a well-documented result, you expect that if you do the experiment again you're going to get the same result. So why are we talking about doing the same thing again?

I don't like to use crude language, but I learned this from my mother so I'll use it anyway. This is half-assed and it's half-baked. It's half-assed because there's no way to make it global. You have to beg each nation. I went to Germany to speak with - I hoped to speak to Merkel, but I got cut off at Sigmar Gabriel, the minister, and he said "Oh, we're going to do cap and trade with offsets". I said, "That won't work, we've tried that. What's the cap on India?" And he said, "We'll tighten our carbon cap." Germany is now 2% of world emissions! Him tightening the German carbon cap is not going to solve the problem! You've got to have something that will work globally.

It's half-baked because there's no enforcement mechanism. What I hear is, all the ministers are coming here, or their heads of state, and they're planning to clap each other on the back, and say, "Oh, we're really doing great. This is a very successful conference. We're going to address the climate problem." If that's what happens, then we're screwing the next generation, and the following ones, because we're being stupid in doing the same thing again that we did, what, 18 years ago.

Stuart Scott: You pointed out last night that if one nation, even a large nation, does a cap, and forces down their emissions, that also forces down demand, forces down prices.

James Hansen: Yes. You try very hard and say, "We're going to reduce our nation's emissions." Or an individual reduces their emissions. One effect of that is to reduce the demand for the product and keep the price low. As long as fossil fuels are dirt cheap they will keep being used. Burning coal is like burning dirt. You just get a bulldozer and you can bulldoze it out of the ground. It's cheap, but it does not include it's cost to society. It's a dirty fuel with some negative effects which we now understand very well. We can't pretend that we don't know what's going to happen if we stay on this path.

This is the path we're on. To pretend that what we're doing is having any effect... it might slow down the rate of growth, but that's not what's needed. Science tells us we have to actually reduce emissions rapidly. And furthermore, the economics studies show that if you put an honest price on carbon emissions, you would reduce emissions rapidly. But if you don't have that price on there, you're not going to reduce the emissions. You'll reduce emissions someplace, but that keeps the price low, so somebody else will burn it.

Stuart Scott: That economic study you're referring to also found that if you put on $10/ton and increased it $10/ton over 10 years, - what was the effect in jobs?

James Hansen: In the case of the United States' economy, where the study was done in detail, it was 3 million new jobs in 10 years, and significant increase in GDP. We need energy. People thinking, "Oh, we have to use less" - well, yes, we have to have energy efficiency, but that would be encouraged by a rising price - we do need energy, we need energy to raise the poor people out of poverty. That's the best way to keep population under control. Those countries that have become wealthy now have fertility rates that are below the replenishment level. And the reason these countries became wealthy is because they had energy, and that energy was fossil fuels. Unfortunately, we can't continue to use that mechanism to get out of poverty. We need to have clean energy, and the way to make that happen is to have this [carbon fee]. You know, I've met with captains of industry, leaders of not only utilities but even oil companies. These people have children and grandchildren. They would like to be part of the solution. If the government would give them the right incentive by putting an across-the-board rising carbon fee, they say they would change their investments and they could do it rapidly.

So it's not that the problem can't be solved, but it's not been solved. Nothing that I've heard so far indicates that we're intending to... it's not too complex! It's the simplest approach you could have! An honest, simple, rising carbon fee.

Stuart Scott: So how do we solve it now? I wanted to do a little bit on one of the solutions that Dr Hansen was talking about last night. There's a movement that's begun in the United States and yesterday was an international launch. In the US it's called the Citizens' Climate Lobby; internationally it's called the Citizens' Climate Engagement Network. It's been rather successful in the US, it's grown leaps and bounds over the years. Every year a group that grows exponentially comes together and lobbies congress. Every single member of congress or their staff has a meeting with people from their state, their constituents. It's been very effective. People all year round write letters to the editor, op-eds, and it's being expanded internationally. We've got to go from the ground up if we're going to put our leaders' feet a little closer to the fire, because there appears to be some other birdie whispering in their ear advice that is not in the best interests [or] best welfare of current and future humanity.

Now I've been asked also, Dr Hansen is one of four scientists who will hold a press conference tomorrow, it's open to the public, it's outside the COP, but inside Bourget, at the Air and Space Museum, I encourage you to attend that. If you've seen the webcast, please encourage everyone to come to Dr Hansen's presentation tomorrow which will also be eye-opening.

We do have a bit of time left so we can entertain some questions from the audience.

Q: What kind of agreement do you expect at the end of this summit, what would you like it to be? You've said that this carbon price is not happening, so what happens after Paris, what are the next steps you see?

James Hansen: We have to have that agreement. I think that story will be clearer fairly soon, if it's not at this conference. And frankly it does not require 190 nations to get together. The US, China, the EU are the main players. If they would agree, and even if two of the three would agree, you could make it happen. It doesn't look like it's going to happen here. But it has to happen soon. The other thing that has to happen is technology development. It has not... The thing that I'm doing the week after this is over is going to China, because it needs to be led in China. They have the need for more energy, they have the ability to fund it. But still, you need to have this spur. And they want to clean up their atmosphere. They've got to find something alternative to fossil fuels. The danger is, if we go several more years, if we go to the next UN meeting, we may have pushed the system beyond the tipping point for the West Antarctic Ice Sheet. That's already questionable. We don't understand that well enough to know that... we're warming the ocean and that's going to have some effect. Really, we've got to get things to happen soon.

Q. Dr Hansen, David Holmes from The Conversation in Australia. Your preference is to look at parts per million as targets. But given that the conference's terms of reference are in terms of temperature, where would you draw the line from a science standpoint on what is dangerous climate change, because, 2 degrees being put up as a guardrail, - is that already dangerous in your view?

James Hansen: Yes, absolutely. 2 degrees would make it warmer than the Eemian in which sea level was 6 to 9 metres higher than now. We don't know long it would take to get there, but 2 degrees is definitely dangerous. So we're at a point now, this year temperature is going to hit the 1 degree mark, and there's more in the pipeline. The El Nino is kicking that up, it'll drop back below 1 degree, but it's on a path to go above 1 degree, even if we reduced emissions 5% or 6% per year we would hit about 1.1 or 1.2 degrees. If we would get emissions to go down a few percent per year - 5 or 6 may not be practical, but a few percent would be practical - temperature would peak at something like 1.5 degrees, and start to go down. That is perhaps the best that we could hope for. That does require a price on carbon.