There are two kinds of energy resource: (1)exhaustible resource (=stock type) and (2)renewable resource(flow type; such as solar-,wind-, hydraulic power and biomass). A flow stock is infinitely large, but it should be limitted within a given period of time. Excessive utilization such as a deforestation cannot sustain a renewable production system. Biomass has both types of resources.

(A) Flow type Biomass. The net primary productivity 170 Gt/yr (about 7 times as much as world energy demand)

(B) stock type Biomass. Mainly in forest; 1800 Gt (about 80 times as much as world energy demand/yr)

Biomass consumption (C) has two variations, putrefaction and utilizing consumption. In natural forest, there are nearly equall amounts of growing and the putrefaction, the equilibrium (A)=(C)would be established.

(A) Flow-biomas —(B) Stock-biomas —(C) Putrefaction or useful consumption 170 Gt/y 1800 Gt (variable)

Although we cannot realize (C)>(A), it is capable to get a bigger share of biomass utilization in the distribution among (C), by our policy and technology.

1.2.2 Carbon neutral

Biomass fuel also emits CO2 by the combustion. But people permit a CO2 indulgence for biomass^ because of the CO2 absorption during the growing process.

That is, [CO2 emission] = [CO2 fixation by the growing process]. However, coal also has a biomass-originated history, the carbon is circulating in long term, several hundred million years. Then under the consideration of term of CO2-repayment, CO2 immunity rate should be estimated.

Just after the biomass combustion, none can pay back its CO2. Therefore, it is estimated that a temperate forest (about 25 years for regeneration time) aquires [CO2 immunity rate=1], as a standard. At subpolar forest, the regeneration time =100 years case, the immunity rate becomes [25/100 = 0.25]. In the case of brown coal (the origin was 25 milion years before), this immunity rate is only 1 ppm. So fossil fuel has no hope to get the effective CO2 indulgence.