Oh, crud. :-(

Obligatory disclaimer...

You know, as much as I recognize the potential problems of biofuels, I still believed that at least some of them held promise. It seems I'm wrong. Biofuels have problems in completely different areas.

Rapeseed biofuel 'produces more greenhouse gas than oil or petrol.

...
Rapeseed and maize biodiesels were calculated to produce up to 70 per cent and 50 per cent more greenhouse gases respectively than fossil fuels. The concerns were raised over the levels of emissions of nitrous oxide, which is 296 times more powerful as a greenhouse gas than carbon dioxide. Scientists found that the use of biofuels released twice as much as nitrous oxide as previously realized.
...


One of the issues that bugs me about AGW and climate change disaster proponents is their fixation on CO2. CO2 has a limited role within the greenhouse effect; a role that decreases as the amount of CO2 increases. Personally, I've come to believe that increased amounts of CO2 is a good thing. N2O, however, may be another story. It's actually a rather safe gas. Also known as laughing gas, it's used medicinally, as well as in food production. It's not any more dangerous than CO2 is, but it apparently behaves differently in the atmosphere.

...While its radiative warming effect is substantially less than CO₂, nitrous oxide's persistence in the atmosphere, when considered over a 100 year period, per unit of weight, has 296 times more impact on global warming than that per mass unit of carbon dioxide ...

Nitrous oxide also attacks ozone in the stratosphere, aggravating the excess amount of UV light striking the earth's surface in recent decades, in a manner similar to various freons and related halogenated organics. Nitrous oxide is the main naturally-occurring regulator of stratospheric ozone.

Now, I take anything on Wikipedia with a huge grain of salt. Also, I don't know is if increasing amounts of N2O continues to have an exponentially increasing effect, or if, like CO2, its effect decreases. I also have questions about just how much we know about what does or doesn't damage the ozone layer, as I've found considerable debate on the subject.

In the end, though, it's just one more strike against the use of biofuels.