Carbon offsets are by no means a long-term solution to the many problems caused by our dependence on fossil fuels, but they can be a good way to help underwrite the construction of a cleaner, greener infrastructure. If you're traveling from outside the region to Providence for the conference, consider investing a little more in your travel and offsetting its carbon footprint!
Not all carbon offset programs are created equal. For an assessment of some good ones, have a look at the Tufts Climate Initiative's run-down. I use Native Energy, and generally pay about $14 for travel within the same half of the country.