For a couple of years I volunteered for a climate change group at the University of Victoria. My area of focus was transportation - how to reduce the university's carbon footprint by encouraging people to take the bus, ride bicycles, car pool, etc. One of the most interesting aspects of working with this group was that it helped me understand how incredibly reliant we are on fossil fuels in our society. They underlie every aspect of our life because almost everything is manufactured using fossil fuels - from our houses, appliances, and cars, to the food we eat, and even the water we drink. In a northern country like Canada each of us has an enormous footprint due mainly to heating costs, transportation over large distances, and importing food from far away.
Sailing on a boat in the tropics goes a long way toward reducing one's short term carbon footprint, even though the energy needed to build our boats in the first place is large. For a start, we have been eating food that is grown locally and organically - some of which we have actually picked ourselves. It has been estimated that each calorie of a typical food in Canada requires about 10 calories of fossil fuels to grow, process, package, and transport. So eating locally grown un-processed foods goes a long way to reducing this consumption.
Heating a modest home in Nova Scotia, Canada, which does not have particularly cold winters used to consume about 32000 liters of heating fuel (diesel) per season. Combined with driving a car (1500 liters) and electricity consumption (via diesel generators - say 500 liters), that would have a couple burning 5200 liters of diesel per year. On Ladybug, we have used about 220 liters of diesel to move the boat over 8 months from Mexico to Tonga and around the islands along the way. Some of this (maybe 20 liters) was used to recharge batteries when we had a problem with our fridge not shutting off. We have also burned about 22 kilograms of propane for cooking. We have not had to use our little propane heater because the places we have visited are warm. Oh - we use about 3 liters of oil per engine oil change - every 100 hours of running.
Because we generate our electricity primarily via solar panels, the carbon footprint from this is the initial cost of manufacturing the panels and controller. I will not try to estimate this, but we can assume that the cost would be amortized over 20-25 years - the life of the panels. Many cruisers have additional fuel costs for generating electricity, mainly to run larger fridges or freezers and to make water.
So our extrapolated yearly consumption of fuel for transport, charging, and heating is about 250 kgs * 1.5 (12/8 months) = 375 kgs/year. This compares to about 5200 kgs/year if we were living in a house in Nova Scotia and driving a car - about 7 percent or 1/14 as much.
One spanner in the works is air travel. Back in British Columia, when I lived on a boat and drove only a bicycle, this made up a very large part of my carbon footprint . Each year I would fly across the country to visit my parents. Similarly Rani would visit her parent in the UK. Here the problem is worse. Rani will fly home to the UK from Aukland in a few weeks. This is a trip about half way around the world. Based on the ticket cost (about 2.5 times that of a ticket from Vancouver to UK) we can safely assume that our footprint from air travel will more than double during this voyage. The way we are minimizing this is for only one of us to make the trip this year.