The calculation that follows is based on this excerpt from the recent (April 2009) BBC Online page on Rainforest El Dorado:
"The fact that tropical forests continue to go up in flames, contributing seven billion tonnes of carbon dioxide into the atmosphere annually (more than all the world's cars, ships and planes)..."
To simplify the calculations we'll assume that:
1. 6.5 billion tonnes of CO2 come from fossil fuels (that's a bit less than 7 billion from the rainforests).
2. All the fossil fuel is octane (gasoline/petrol)
then C8H18 (octane) + 12 O2 = 8 CO2 + 8 H2O + H2
and 2(C8H18) + 25 O2 = 16 CO2 + 18H2O
so, for every molecule of CO2 formed by burning fossil fuel 18/16 molecules of water are formed.
By basic chemistry:
H2O = 2 + 16 = 18
CO2 = 12 + (2 x 16) = 44
so, for every 44 tonnes of CO2 from fossil fuels taken as octane, the amount of water produced is:
18x(18/16) = 20.25 tonnes
and for 6.5 billion tonnes of CO2 that means:
6.5 x 20.25 / 44 = nearly 3 billion tonnes (or cubic meters) of water.
The diameter of Earth is around 12 700km, which gives us a surface area of:
3.142 * (12 700)2 = 506 770 000km2
About 70% of this is water, which gives us a water surface area of 354 740 000km2
Over this surface area, the rise in sea level would be:
3 000 000 000 cubic meters / 354 740 000 000 000 square meters
Canceling a load of zeroes, we get:
3 / 354 740 = 0.000 008 5 meters or 8.5 micrometers
That's about one-twelfth of the thickness of a human hair - and totally insignificant in comparison with annual sea level rise - this from Wikipedia:
"Current sea level rise has occurred at a mean rate of 1.8 mm per year for the past century,[1][2] and more recently at rates estimated near 2.8 ± 0.4[3] to 3.1 ± 0.7[4] mm per year (1993-2003)."
The worrying corollary is this: if burning all the fossil fuel we do is only raising sea level 8.5 micrometers (and by a similar calculation the burning rainforests add another 8 to that), and if we ignore any increase in volume due to ocean temperature rise, the rest of the rise must be down to melting ice.
Simplifying figures again, let's assume the annual sea level rise is 3 mm and burning fuel and trees causes a rise of 20 micrometers.
Then the rise from melting ice is (3 000 000 / 20) or 150 000 times the rise caused by burning fuel and trees.
So the Earth is losing 150 000 times 6 000 000 000 tonnes or 900 Gigatonnes of ice from the glaciers and polar ice caps every year.
Since the density of ice (at 0 degrees C) is about 9/10 that of water, that translates to 1 000 000 000 000 000 cubic meters, or a million cubic kilometers.
Somebody else can cut that rate down by figuring in ocean expansion due to temperature rise; but even if it is reduced a bit, how long can the ice last?
