As you say in your article about so-called green bonds, “reducing the risks of climate change is not a technological problem,” but the problem is that available technologies are expensive (“A Dull Shade of Green,” October 29, 2011). Green bonds look like any other fixed-income instruments, you explain, except that the proceeds are invested in environmentally friendly projects. So, alternative ways to generate electricity, drive cars, or grow crops without emitting much carbon dioxide can reach capital markets. Neat, this. The only rub is that it is pretty difficult to tell which technologies actually reduce the risks of climate change. Electric cars, for instance, certainly do not. They are powered mostly by oil, gas, and coal. Making sure that bonds are really green is nigh impossible with our poor understanding of all the inputs that go into a so-called green technology. Chances therefore are that green bonds will only assuage the conscience of trusty investors without achieving much by way of reducing the risks of climate change. And that all sorts of scams will soon dominate the market in these new fixed-income instruments.