Hydrogen, vector of the energy transition

It was in 1972 that the Stockholm Conference, convened under the aegis of the United Nations, first placed environmental degradation, due to excessive emissions of greenhouse gases such as CO ₂ , as an international concern. In 1997, most industrialized countries (except the USA) signed the Kyoto Protocol, committing themselves to a 5% reduction in greenhouse gases compared with 1990 levels. However, the level of CO ₂ in the atmosphere in 1990 was close to 360 ppm ...it now exceeds 410 ppm! This failure is the most commonly accepted cause of the climate change observed in recent decades, which disruption is already having serious consequences for the environment.

This negative assessment led to a new agreement: the Paris Agreement, ratified in October 2016 by 174 countries and the European Union. This agreement took as its main objective to contain the rise in average temperature, compared with pre-industrial levels, well below 2°C, and limit it as far as possible to 1.5°C, a very ambitious goal that requires intensive reductions in CO ₂ emissions. Now, these emissions derive essentially from the use of fossil fuels, hitherto unavoidable energy sources, which satisfy 80% of the world's energy needs. The equation therefore becomes simple to pose, if not to solve: we need to drastically reduce the consumption of fossil fuels, emitters of CO ₂ , of which we have already consumed, in less than two centuries, half of the initial reserves while the Earth has more than 4 billion years of life left! So, having to gradually abandon carbon-based fossil energies is becoming a necessity, and this means having to replace them in large part with renewable energies that are inexhaustible on the scale of life on Earth, namely essentially those supplied by the solar machine. The question is whether this vision is realistic, and how it can be implemented and transformed into energy sources that are as reliable and easy to use as fossil fuels.