What will you do with your 50 TONNES?
MORE RECENT NEWS - Latest research strongly suggests figures below are wrong. The sustainable continuous emissions threshold should now be regarded as zero. Rapid reduction of atmospheric CO2 concentration to below 350ppm is now required.
If each of us emits 50 tonnes of carbon (equal to about 175 tonnes of CO2) global temperatures are as likely as not to reach 2 degrees C above pre-industrial levels. This is considered the maximum tolerable global temperature.
50 tonnes is not a yearly figure, nor an emissions limit for each of us for our entire lifetime. It is a "one off" which each of us must share with our children and their descendents, effectively for ever.
How has this been calculated?
There are several papers providing different figures for the "lump sum" of fossil carbon that can be tolerated by the atmosphere. One of the later ones, Meinchausen (in Nature, April 2009) has been used here to calculate a personal figure. Meinchausen's calculations are based on emissions between 2000 and 2050, but several modellers have observed that emissions spread over any period up to hundreds of years have the same effect. For a 50% chance of 2 degrees C above pre-industrial temperatures, Meinchausen indicates cumulative CO2 emissions of 1,440 Gt CO2. This is 392.7 Gt of carbon (GtC). Known 2000 to 2006 emissions are said to be 234 Gt CO2 (63.8 GtC). This is 10.6 GtC / year, so a crude extrapolation gives emissions of 106.4 GtC from 2000 to 2010. 392.7 GtC were said to remain available to emit in about 2010. 392.7 GtC - 106.4 GtC equals 286.3 GtC left to emit from 2010. At 10.6 GtC / year, that's 27 more years, so up to 2037.
The 286.3 GtC left available to emit globally is about 47.7 tC each. (If 27 years remain, that's 1.19 tC / year.)
For someone like me, with no descendents and little interest in the future welfare of humanity, that doesn't sound too bad. I can continue my fairly frugal lifestyle and, based on my gender, lifestyle and so on, I expect to be dying at about the time the rest of the world hits the buffers.
Other people might think it should be possible to do better, though. They might want to leave some carbon for their children to use, or much less for each of their descendents over the next 500 or 1,000 years, or whatever. This probably still isn't the wisest use, though. Instead, carbon spent on infrastructure now should make life more possible after no capacity remains in the atmosphere. Such infrastructure might be trains (that could run on wood) or non-fossil power stations, or greenhouses, or water meadows, or whatever might be preferred. In view of the predicted food shortages and end of fertiliser production, we might just want to convert some forest to agricultural land.
So, what will you do with your 50 tonnes?