ChemCafé

A recent issue of Nature featured a series of articles on global warming. Not that it is particularly new, but the interest here was that it was a mix of papers dealing with the current situation and its probable evolution over the next century – with all the likely consequences knocking at our (not well closed) door – and much more optimistic views of researchers trying to find solutions to the multiple issues we’ll be facing sooner or later.

A first of three features, written by Richard Monastersky, explains how keeping carbon dioxide beneath dangerous levels is tougher than one previously thought. The basic question is: how much can the CO₂ concentration in the atmosphere increase before reaching a point of non-return? The pre-industrial level was roughly 250 parts per million (ppm), we are now reaching 400 ppm. It was long thought that a concentration of 450 ppm was a target to avoid, but new studies seems to indicate that a threshold of 350 ppm would have been more reasonable. This raises many questions on how to deal with the ever increasing carbon dioxide level. Studies performed at the University of Bern show that even if all CO₂ emissions stopped when its concentration is 450 ppm, it would take more than 1000 years to reach pre-industrial levels, and 3000 years would be necessary to see global temperatures slightly decrease. Other studies give even more frightening results: if CO₂ concentration reached 550 ppm (not unlikely at all) before all emission stopped, the temperatures would keep increasing for at least a century. Even if the studies are based on unperfect models, they point out the fact that climate will need a long time to recover, essentially due to the thermal inertia of the oceans (they slow up the climate warming now, they’ll delay its cooling in the future) and to the rate at which carbon sinks can absorb CO₂ from the atmosphere.

This rather pessimistic (I sould say, apocalyptic) view is counterbalanced by the two next articles, written by Nicola Jones and Oliver Morton, respectively, who discuss potential solutions to increased CO₂ concentration and global warming. At first sight the proposed ideas look weird: absorbing CO₂ into a solution of NaOH to produce sodium carbonate, that can be converted in calcium carbonate (by addition of calcium hydroxyde), and finally into pure CO₂ (that sould be stored, frozen, sent to space, etc.). Although this works on lab-scale, one may remember that, if the current emission rate is maintained, 650 gigatons of CO₂ will have to be removed from the air by 2100 in order not to reach 450 ppm… a serious scale-up will be required there! Another approach, involving geoengineering, aims at brightening clouds to increase reflexion of sunlight. Some researchers think about ships vaporizing water droplets to form clouds over the oceans, which should in turn cool earth’s atmosphere ! We’re not so far from reaching a good sci-fi novel scenario where a giant shield would be built between earth and sun, protecting us from sunlight until the global temperature has reasonably decreased…

But, if the last news are not good at all, and if we are facing a tremendous challenge, scientists are coming with ideas, trying new concepts and models, that can one day help us and the earth to survive our reckless carbon consumption. Whatever path we chose, it is certain that a compromise will have to be found between the sacrifices we’re ready to make to reduce our carbon emissions, and the consequences (at a climatic, economic, or social level) we agree to suffer. The earlier this compromise is established, the better!