La combustion des carburants fossiles réchauffe la planète depuis des siècles à une vitesse jamais vue depuis des millénaires. De la même manière, le prix des émissions de carbone doit inexorablement augmenter de toute urgence, déclare James Hansen, un climatologue renommé, un scientifique et un défenseur de l’environnement.
James Hansen était le directeur de l'Institut Goddard d'études spatiales de la NASA jusqu’en avril 2013. Il est professeur adjoint dans le département des sciences de la Terre et de l’environnement de l’université de Columbia. Sa déclaration devant le Congrès en 1988 a popularisé pour la première fois la question du changement climatique aux États-Unis. Il s’est confié à Arthur Nelsen d’EURACTIV.
There have been two recent studies on tar sands – one by Stanford University and one by the Jacobs consultancy – which have differently estimated the fuel’s greenhouse gas emissions. Which do you feel is most accurate, and why?
I don’t know the details, but the science make clear that we should not be going after these unconventional fossil fuels. We cannot afford to put that carbon into the atmosphere, as they are more carbon intensive than conventional fossil fuels.
If tar sands fuel could be made less energy intensive by, would you stop campaigning against it?
My position is that we need to put a rising fee on carbon that does not discriminate against any particular fuel, based on dollars-per-tonne of carbon. Unconventional fossil fuels have a larger carbon footprint and as long as that continues to be the case they’ll pay more. But we have to phase out fossil fuel emissions over the next several decades and that requires making them pay their true cost to society.
Many fossil fuel industries may hope that EU climate policies fail so that they have a future…
They may have a future. They can become energy companies. They’re allowed to invest their money in other energies and do so – in small amounts because they know that they can bribe governments more easily than they can make the investments in clean energy.
Do you see a link between the Fuel Quality Directive and the Keystone XL decisions which have both been postponed?
Well, either could help achieve a result of leaving the tar sands in the ground. If Europe puts an added price on tar sands oil and/or if the us declines to build this Keystone pipeline, it will make it less easy to expand the oil sands production and more likely that that stuff will be left in the ground. That’s why [Canada’s Natural resources Minister] Joe Oliver is getting so worried and running around, because they’re afraid. They want to get this infrastructure set up so they can continue to extract that oil source and expand production. In the larger scheme of things it doesn’t make any sense but they can make money out of it so they’re very eager to get started.
President Barack Obama has made statements about the threat climate change poses to future generations and his own willingness to act now if Congress won’t. But we are increasingly hearing that the Keystone XL decision will be balanced off against another decision on regulating emissions from power plants sector. Giving with one hand and taking from the other may make sense in party political terms …
But it makes no sense for the us or the world and frankly, I think [US Secretary of State] John Kerry and Obama will realize that their legacy is going to be gravely tarnished if they approve that pipeline, so I’m cautiously optimistic that they’re going to come to their senses on this and not approve the pipeline, while at the same time reducing power plants emissions.
Have you been disappointed so far by Obama’s climate change policies?
I have been, yes, but it’s still to be determined because he says the right words. It’s just not clear [if] he understands that we have to phase out carbon emissions relatively rapidly, or we will leave our children and grandchildren a situation that is very unjust, with climate consequences that are potentially out of their control.
Would the billions of dollars planned for a NASA Mars mission in 2030 be better spent on reducing carbon emissions now?
No, we don’t… I think that’s a false choice. To reduce emissions we need to put a rising price on carbon and that will be economically stimulative if we do it sensibly, so I don’t see any competition between these issues at all. I would recommend collecting a fee from fossil fuels companies at source – at the domestic mines or points of entry – and if that money is given to the public, it will stimulate the development of energy efficiency, and clean energies, and be economically beneficial.
You’ve said before that if tar sands go ahead, it will be game over for the planet, what does that mean?
It means there is an enormous amount of carbon in unconventional fossil fuels – tar sands, tar shale and even fracking for gas. If we open these up, you can easily see that we are going to shoot way past any targets for limiting global climate change. It’s the first big step into unconventional oil which any rational assessment of the problem says we can’t do.
How many degrees of global warming do you believe we are currently on track for?
It depends on when we decide to put an honest price on carbon. You could stabilise climate by the end of the century if you reduced emissions by 6% a year. That’s very difficult, but it’s easily possible to stay under 2 degrees warming. It just requires that governments begin to do their job, which is to protect the rights of their citizens. Unfortunately, it seems that governments worldwide are more under the influence of the fossil fuels industry than they are looking out for the rights of citizens, including young people. They’re not effectively looking at long-term issues, as opposed to the next two or three years.
There’s been a push by the business lobby in Europe for a re-industrialisation strategy, because of cheaper energy prices in the US. Climate policy is often talked of as a luxury that Europe can’t afford and it seems to be having an effect in Brussels. What would your message be to the Commission on that?
Right now, we do not make fossil fuels companies pay for their effects on human health or on the climate and we even subsidise them, so it is a very short-term argument to say that you should re-industrialise in a way that uses more fossil fuels. It doesn’t even make economic sense from a long-term perspective. By any rational assessment those fossil fuels need to be left in the ground.
When you say put an honest price on carbon, the way that has been done here is through the ETS…
It is ineffectual. I have a very strong opinion that you need to put a price on carbon, not a cap, because the business community and consumers need to understand that this price is going to rise continuously and with a cap system, prices fluctuate according to various factors. The cap system also brings big banks into the problem for no good reason. You don’t want a fluctuating market. You want the business community and consumers to understand that fossil fuels are going to continue to get more expensive so that they’ll make appropriate long-term decisions about what vehicles they buy, where they live, what investments are made by businesses. You want to provide incentives for entrepreneurs to develop low energy products.
If you work really hard you can make the cap system have some effect. But if you want a global system, it is basically the Kyoto protocol which means you have to ask each country individually to agree to a system. With a simple carbon price, it is easier to get global action which is essential in the long run. It is not going to work to just have some places limit their emissions as it reduces the demand for fuel [in one place] but other places will burn it.
Last weekend, the Manu Loa observatory found that carbon dioxide concentrations were now about 400 parts per million, the highest since the Pliocene age. You’ve studied Venusian models of global warming before. Do you believe they hold any lessons for global warming here on Earth?
Well we are a long way from Venus, but our civilisation developed during the Holocene [era] which had a relatively stable climate and a stable sea level. If we warm the planet even to the levels of the last interglacial period, it will mean an eventual sea level rise of several metres. If we burn all the fossil fuels, that will take us back to being an ice-free planet. It will take a while for all the ice to melt but sea levels will end up 70 metres higher. You can’t get to the Venus situation quickly because we have an ocean and where you have an ocean, you have a weathering process. It continuously takes CO2 out of the atmosphere. Venus has baked the CO2 out of its crust. It would take a long time to get to a Venus situation but it doesn’t take a long time to have enormous consequences on humans and the other species on the planet.
What would 4 degrees of global warming look like?
Four degrees of warming would be enough to melt all the ice. It would take a while for it to happen, but you would have a tremendously chaotic situation as you moved away from our current climate towards another one. That’s a different planet. You wouldn’t recognise it. The shorelines would not be recognisable. And it’s a degree of change which has only occurred in the earth’s history over very long timescales. But humans are now adding ‘forcings’ more than a magnitude faster than anything we are aware of. There were extreme changes in earth’s history – the Eocene thermal maximum was global warming of 6 degrees, but we are doing on a centuries timescale what previously occurred on a millennial timescale, the most extreme case that we know about. We are on the verge of creating climate chaos if we don’t begin to reduce emissions rapidly. That is not science fiction. It is scientifically crystal clear. The relevant scientific community knows this very well. It is surprising we don’t have stronger statement from scientists. Someone should be going in and pounding on the president’s desk saying, ‘We have got to have policy changes’.
Well government scientists in America recently said that last year’s Midwest drought – which was rated as severe-to-exceptional – wasn’t related to climate change.
That is a particular scientist in NOAA [the National Oceanic and Atmospheric Administration] who always makes that statement with every extreme event. What we showed in a peer-reviewed paper in the National Academy of Sciences last year is that the frequency of these extreme events has increased markedly to a degree that you can say with a high degree of confidence: We would not have got such an extreme situation if it were not for the changing atmospheric carbon concentrations, caused by global warming. The area covered by summer temperature anomalies which 50 years ago occurred only a few tenths of one percent of the time, now happens about 10% of the time. It is a significant change. Extreme summer warmth is accompanied by more intense droughts and more extreme forest fires.
Our stories often receive comments from climatesceptics, who say that such statements are just based on unreliable computer models and climate science is not robust enough to compensate for the economic cost of decarbonisation…
In fact, we base our understanding more on observations of how the Earth has responded in the past to changes in the boundary conditions, including the atmospheric composition. I’m using models less and less – although they are very helpful in confirming our understanding – but it is not correct to say that these assessments are based on models.
Who is most responsible for climate change – all of us equally or are some people more responsible than others?
For fossil fuels use we have very good statistics. The US is responsible for 26% of the excess CO2 in the atmosphere, and china for 10%. The parts of the world that industrialised first are most responsible. The UK is number one, the US is number two and Germany is third.
So should the UN negotiations try to work out how to distribute the emissions which are left…
You will never solve the problem that way because if you let these other countries come up to the level of the developed world then the planet is done for. It’s also in developing countries’ interests to move to a clean energy future. They’ll be better off if they avoid a pollution phase of economic development. There will need to be – for fairness – economic assistance to developing countries and that’s well agreed.
You mentioned shale gas earlier, how far that can contribute to re-industrialisation on the one hand and a low carbon future on the other?
We need a rising price on carbon and in the short run, gas would probably expand and that would not [necessarily] be a bad thing. If it is replacing coal, you’ve made some [emissions] reductions. But you can’t just allow all these different carbon sources to increase. In the long run, gas is also going to be phased out, unless you capture the CO2.
Do you think that is likely in the next few years?
You can’t make that an excuse for continuing to burn, as it will be costly to capture CO2. Let that compete with alternative clean energies. It probably won’t be the wining technology but it should be allowed to compete.