Companies announce CO2 air conditioning systems

With European Union legislation banning the use of R134, it's time once again to look for another refrigerant. This time around, C02 looks to be the fluid of choice, with Behr and Visteon preparing to introduce systems by 2009. Both of the aforementioned are greenhouse gases, but R134 is supposedly much worse (the link below - registration required - states that R134a depletes the ozone, but that is not correct). Given that only a small portion of refrigerant leaks into the atmosphere, and the decreased efficiency of CO2 refrigerants, is it possible that a switch to CO2 systems could cause an increase in the greenhouse effect? Oh, the irony.