So, what are the companies? Some of them, Citi admits, are not very environmentally friendly at all. For instance, they write of RWE: "Despite emitting about 90 million tons of carbon dioxide, or about
10% of Germany’s total, this “dirty” utility has been enjoying windfall profits in the EU Emissions Trading Scheme"; they also say that TXU Corp, which is building lots of coal-fired power plants, is seeking to take advantage of the fact that the US doesn't have carbon emissions restrictions.

And most of the rest are based in one way or another on energy. Acciona and Iberdrola have many clean technologies; there's also Gamesa and Vestas in wind; Conergy, Evergreen Solar, Q-Cells, Sharp, SolarWorld, Sunpower Corp, Suntech Power, in solar; and Ormat Technologies in geothermal; and Allegheny Technologies, Constellation Energy, Electricité de France, Entergy, Exelonin, Fortum Oyj, FPL Group, Shaw Group, and Siemens in nuclear. Gas stocks are seen as doing well too, so BG group, Centrica, Gaz de France, and Gazprom make the list.

Related are the ethanol and biodiesel plays: ADM, Bajaj Hindusthan and Balrampur Chini Mills in India (ethanol from sugar), Brasil Ecodiesel, Bunge, Cosan, CropEnergies, Deere, DSM, DuPont, Ebro Puleva, IJM Plantations, IOI Corp, KL Kepong, Monsanto, Neste Oil, Noble Group, and Syngenta. Also listed are Potash Corp of Saskatchewan and Terra Industries, which sell the nutrients which allow all these companies to grow those crops.

There's the carbon-trading plays: AIG, The Chicago Mercantile Exchange GFI Group, and Swiss Re.

And there's carbon-reduction companies, like BorgWarner and Magna International in auto parts; Compagnie de St Gobain in insulation; Emerson, Itron, Johnson Controls, Schneider Electric, and SIG PLC in energy; Philips in lighting; and Honda, Peugot, Toyota in smaller, more energy-efficient cars,

Finally, Citi reckons that water in drought-hit countries will become more valuable, so Aguas de Barcelona makes the list.