Help! How can I offset travel?

I totally support "Staycations" and living in the Redwoods in Northern California seems to feel like one everyday. But I promised myself that I would visit every continent by the time I was 30. Unfortunately I had put this project on hold for too long--- marriage and moving and changing jobs can do that to you. Now that I'm turning 30 and have the cash, I am planning a big trip to South America, Central America, Europe, and North Africa.

My plans once I arrive are as eco-friendly as can be, but I can't help thinking about the impact of the long flights. I used a carbon calculator and it put all my round trip flights at 12 tons of carbon! My carbon footprint for the rest of my lifestyle is pretty light and so I would like to do something about this obvious blemish.

I looked into purchasing carbon offsets at http://www.nativeenergy.com. Are there any other carbon offsets for travel that I should look into?

Also I almost feel like I'm not doing enough by just funding negative carbon projects. Most of my previous travel was for work in my field of Oceanography and so I felt like I was doing the good while I was flying or on a boat. For example, my travel to Antarctica was part of a research project looking at the affects of climate change. Most of the travel I will be doing this year will be personally indulgent-- touring the pyramids, scuba diving, hiking--- but one of my trips will be to do a solar installation in a rural village. Are there local projects I could get involved in to offset my carbon? How many trees would I have to plant to make up for a flight to Africa??

Please share you ideas with me. I'd be interested to see what's out there...