Can we pay back the time by substitute fossile fuel using biofuel?
Kirschbaum(2003a) and Kirschbaum(2003b) were indicate that it is not same climate effect when carbon was captured by photosynthesis and carbon emit by burning those biomass.
I think the important thing is that it does not pay back the time and temperature damage when we effect to the global warming.
But Carbon Negative biofuel would be provide a new carbon sink effect more than before our practice.

MUF Kirschbaum, Biomass and Bioenergy,24,(2003a),pp.297-310.
MUF Kirschbaum, Climate Change,58,(2003b),pp.47-71.

HK - i agree. do you have any info or links on successful carbon negative biofuel production? im assuming you are referring to algae...

i am making biodiesel out of waste vege oil only and fueling several buses and cars in Monteverde, Costa Rica. im hoping to scale up to larger production and spread our processor designs to other people as fast as possible.

i think one of the big issues we need to address here is our reliance on centralized industrial processes. it just can't last - we need to shift to more local production of our energy and food resources - cut out the big corporations and industries that value the rainforest as nothing more than a neat place to chop up and throw some oil palm down on.

thanks,
ryan
ryking@myway.com

Thank you for your kind attention.
Carbon Negative biofuel can be refered from Mathews(2008) or following website.

http://biopact.com/2007/10/towards-carbon-negative-bioenergy-us.html

http://news.mongabay.com/2007/1106-carbon-negative_becs.html

J.A. Mathews, Energy Policy, 36(3), (2008), pp.940-945.

Ryan, HK pointed you to a great source: biopact.com -- perhaps the best place for information on the emerging carbon negative biofuels concept.