He was one of the first – in 1988 – to alert the world to climate change. Almost forty years later, the former NASA climatologist, James Hansen, continues to play the Cassandre, even getting part of the scientific community on the back. According to the recent work of this teacher in Columbia, the objective of the Paris Agreement – limit planetary warming to 2 ° C during the present century – is definitively buried. Unless a radical change in our policies, the rise in temperatures is likely to deregulate ocean currents, resulting in deleterious effects. The options? Establish a carbon tax on all fossil fuels, develop nuclear and study geo-engineering closely. In case.
L’Express: You say in your last studies that the objective of limiting warming to 2 ° C will not be achieved. What to do?
James Hansen: Precision is essential: we say that the objective of limiting planetary warming to 2 ° C compared to the beginnings of the industrial era will not be reached, unless a miracle. This nuance is important. We do not believe that such a miracle will occur. Our work also shows that this famous threshold will probably be reached by 2045. However, it could theoretically not be crossed if we used geoengineering, by sprinkling, for example, particles in the atmosphere in order to cool it. For the time being, we do not have the necessary knowledge in order to launch this kind of initiative. In addition, the public would undoubtedly not support such an action. At present, the closest thing to a miracle, which is conceivable, would be the large -scale adoption of a increasing carbon tax that the fossil fuels would pay. In addition to being effective, this policy would cost nothing. But we don’t take the way.
The United States has rather chosen to subsidize green technologies with inflation Reduction Act. What do you think of this policy?
The result is catastrophic! The Biden government has abundantly funded already mature technologies – solar and wind -, which has stimulated inflation without reducing greenhouse gas emissions. Worse, this policy has created an epidermal reaction from the Republicans, and the adoption of an energy policy favorable to fossil fuels! So far, governments have not taken the question of climate change seriously. Over the next decades, they will eventually understand that it is a priority. The situation at the end of the century will then depend on collective decisions, if global governance is still possible.
These last twelve months, many heat records have been broken, causing amazement. Should scientists review their models?
The jump of 0.4 degree of global temperatures in 2023-2024 is easily explained. This warming was caused equally by El Niño [NDLR : un réchauffement cyclique des eaux superficielles du Pacifique équatorial] And by a decrease in aerosols, that is to say tiny particles which are notably issued by ships. Since 2020, the international maritime organization has required a strict limit on hydrogen sulfide and carbon dioxide emissions. However, these aerosols serve as nuclei for the formation of clouds and the latter have the particularity of thinking about sunlight towards space. If they are less present in the atmosphere, global warming increases. We are therefore faced with a dilemma: either we accept air pollution, which kills millions of people each year. Either we reduce it, which increases the global temperature.
Has this ambivalent role of aerosols been underestimated by scientists so far?
Absolutely. This is one of the major conclusions of our last work. And a source of divergence with IPCC analyzes. The first models used by climatologists included simple cloud treatments. In order for these models to correspond to global warming observed during past decades, the disturbances related to aerosols had to remain practically unchanged. However, we have evidence today that this “forcing” [NDLR : l’effet des particules sur le réchauffement] in fact increased during this period. It is difficult for an organization as important as the IPCC to modify its position on this subject. But in the end, I’m sure, physics will prevail.
In your opinion, the sensitivity of the climate to CO2 emissions has also increased compared to the previous costing. What does this mean for our future?
This is not good news. The acceleration of global warming will lead to an increase in the melting of ice in the Arctic. Consequently, a stop of the Amoc – a complex circulation of marine currents in the Atlantic – could take place in the next twenty to thirty years, unless high impact measures on our CO2 emissions are taken very quickly. If we let this phenomenon occur, humanity will face, in cascade, to major problems, starting with an elevation of several meters from sea level. For us, it would be a point of no return.
How has your work been welcomed?
The scientists of yesteryear, such as the meteorologist Jule Charney or the mathematician Francis Bretheton, would probably have said that our study is serious. They would reflect on the observations necessary to confirm and clarify the questions raised by our work. Today, it is unfortunately different. Our research arouses many surprising and non -scientific answers. Some climatologists refuse, for example, to talk about our work to the press. One of our studies on the melting of ice, published in 2016, does not appear in the sixth synthetic report of the IPCC which compiles the scientific knowledge acquired between 2015 and 2021: not a single mention in this document which makes several thousand pages. However, science progresses when new data becomes available. Their taking into account ends up causing corrections within the dominant opinion – some minors, other adults.
Is the role of nuclear energy also a factor of discord?
Effectively. Nuclear must play an important role in the decarbonation of global energy systems. But the simple fact of asserting it limits our ability to obtain public and philanthropic support for our research organization, the climate science, Awareness and Solutions. By penalizing nuclear energy, which has the potential to be the least costly energy source, twenty-four hours a day, while having the weakest environmental footprint, we attach an arm in the back.
And it is to link the other arm to prohibit, in principle, any research on the geoengineering of the climate. Today there is a need to clarify current policies. Can they really lead to climate stabilization by the middle of the century? It is clear that the COP system does not work, which places the young generations in a dead end. It’s time to open your eyes.
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