A new study published today in the Proceedings of the National Academy of Sciences shows that about 20-25% of greenhouse gas emissions (CO2 and ozone) are coming from railway, shipping, and car or truck transportation. But the most interesting part of the study are its future projections. "In 2050, as much as 30-50% of total CO2 emissions are projected to come from the transport sector," write the authors. In addition, they say that many of the emissions causing climate change from transportation are not covered in the Kyoto Protocol. Climate forcing from the transport sectors [PNAS]