In April 2006, the price of carbon indulgences in the European Union Emission Trading Scheme (EU ETS), the largest emission market in the world, was 30 euro per ton of CO2 emissions: see this graph. However, in May 2006, the price decreased a little bit, more precisely by a factor of pi - below 10 euro per ton of CO2.
In November 2006, when the price was still around 9 euro per ton, we predicted its fall to 2 euro per ton. This seemingly bold prediction was realized at the beginning of February 2007. However, the price continued to approach the actual market value, namely zero.
Yesterday, the EUA (European Union Allowances) price closed at €0.93 for 2007 Futures: click the chart on the left. The price correction by a factor of more than 30 in the right direction and in less than one year is a sign that the free market kind of works. It would be nice if the number of global warming journalists, climate change pseudoscientists, catastrophic charlatans, and their funding decreased by a factor of 30, too.
Update: Today, one ton closed at €0.85, a ten-percent decrease per day.