Question

You will establish whether or not current global fossil fuel combustion CO_2 emissions can offset by planting trees? If all cropland was covered with slow-growing trees, how much fossil fuel CO_2 emissions can you offset? How much with fast-growing trees? What happens when you use fast-growing trees on all arable land? Is this realistic? If this were to be done, what other issues would you need to consider? Some key factoids: The surface of the Earth is 5 times 10^14 m^2? cropland is Tilde 11% of the land surface all arable land is Tilde 45% of the land surface fast-growing trees will produce Tilde 10 metric tons of dry matter/hectare-year (with optimal placement and areal density) slow-growing trees will produce Tilde 1 metric tons of dry matter/hectare-year (with optimal placement and areal density) typical dry matter is Tilde 50% carbon by mass there are 10,000 m^2 per hectare current fossil fuel emissions: Tilde 10 times10^9 metric tons carbon/year

Answer 1

a) Total cropland = 11% of land surface

thus (11/100)*5*10¹⁴=5.5*10¹³m²=5.5*10⁹ hectartoe

Now slow growing trees fix = ~1 metric of dry matter / hectare / year

and 50 % of it is carbon. Thus actual offset = ( 50/100) * 1= 0.5 metric ton of carbon / hectare / year.

Thus amount of offset if all croplands replaced with slow growing trees will be 5.5*10⁹*0.5= ~2.75*10⁹ metric ton of carbon/hectare/year

b) Simillarly b) can be solved. Answer is 2.75*10¹⁰ metric ton of carbon / hectare/ year

c) Simillarly c) will be ~ 1.125*10¹¹ metric ton of carbon / hectare /year.

d) No, I dont think this is realistic. It is not practical to replace all croplands and arable land with fast growing trees. Even if we did replace them, its not going to have very profound impact because the amount of emission is still very very high compared to the offset that will be achieved.

e) If itthis were to be done, serious issues will have to be taken in consideration. for example

1. How to take care of food production for the huge population?

2. What will happen to the different existing plant and animals which together form the ecosystem?

3. How to take up such large scale plantation and replacement?

4. To convince the people about such a thing.