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By J.P.

IN JUST a few years, the aim of a carbon-free energy system has gone from the realms of green fantasy to become official policy in the world’s richest countries. Meeting on June 7th and 8th in Bavaria, the Group of Seven (G7) industrial nations ended their summit by talking of the “decarbonisation of the global economy over the course of this century”. The members of the club—America, Japan, Germany, France, Britain, Canada and Italy—also promised to cut greenhouse-gas emissions by the “upper end” of a range between 40-70% of 2010 levels by 2050.

True, no fossil-fuel-burning power station will be closed down in the immediate future as a result of this declaration. The goal will not make any difference to the countries’ environmental policies, since they are mostly consistent with this long-range goal anyway. Where they are not (some countries are increasing coal use, for example) they will not be reined in because of the new promises.

Still, the announcement matters for three reasons. To begin with, it puts the logic of full decarbonisation into the official sphere for the first time. That logic goes something like this. When global temperatures were more or less stable before industrialisation, the atmosphere contained roughly 280 parts per million (ppm) of carbon dioxide. Most scientists think that, if the policy goal of restricting global warming to 2°C is to be achieved, carbon concentrations will have to be kept below about 400 ppm. That level has already been exceeded: the latest reading from the Mauna Loa observatory (source of the most reliable measurements) was 404 ppm in May.

Moreover, concentrations are rising. Many climate models reckon that by the second half of this century, the level may well have reached 600ppm—a concentration that would be consistent with 4°C or 5°C of warming. Since carbon takes thousands of years to drop out of the atmosphere, the only way of bringing concentrations down again within a reasonable time is for greenhouse-gas emissions to drop drastically—perhaps to zero, perhaps to less than that (ie, carbon will have to be taken out of the atmosphere and sequestered). So if the goal of keeping global warming to 2°C is still being taken seriously (a big if), then decarbonisation may be the only way to keep overall carbon concentrations within bounds.

Next, though a 50-year time horizon is meaningless politically, it is relevant in the world of energy planning, where power stations can have life cycles of more than 50 years and where traditional (unfracked) oilfields can keep producing longer than that (see this story). A move towards decarbonisation short of stopping fossil-fuel use might also shift investment patterns between different fuels, away from the most carbon-intensive (coal) towards the least (gas).

Third, the G7’s declaration could make a difference to negotiations for a new global climate treaty, which is supposed to be signed in Paris at the end of the year. Over the past few months, the negotiations for that treaty have been troubled. The UN’s top climate official, Christiana Figueres, recently admitted that the national promises made so far which are supposed to form the basis of the treaty “will not get us to the 2°C pathway.” Two of the many areas of disagreement have been whether to include long-range goals in the treaty and how much money will be available to poor countries to combat climate change. Cheerleaders for a treaty point out that the G7 has made a first proposal for a long-term goal. The group was also a bit more precise than it has been about stumping up its share of $100 billion for climate mitigation (Germany, for example, recently said it would double its contribution).

All that said, the G7’s climate effort raises as many questions as it answers. The group seems to have rejected proposals for more demanding targets, such as decarbonisation by 2050. A lot of other problems remain to be ironed out if a climate treaty is to be signed. Most of all, the industrial countries are talking about getting all their energy from renewable sources—at a time when it is still unclear whether renewables can provide more than a third of power without serious instability in the electric grid. No treaty or bold promise will solve that problem.