The environment would not be polluted should human being be not alive on the earth; therefore, human activity is the origin of pollution. Two things are inevitable in human activities: food and fuels in order to satisfy energy needs. Both food and fuels are composed mainly of elements carbon and hydrogen, and the products of con- suming energy are CO₂ and H₂O. H₂O is not offensive, but the accumulated CO₂ causes abnormal climate change. The author indicated [1] that the global CO₂ is linearly correlated with world population for the past 160 years as shown in Figure 1 with a correlation coefficient of 0.99. It means more people, more pollution and zero CO₂ emission when the world population is less than 1.3 billion. In fact, CO₂ is only part of wastes generated in human activities. Many cities/towns of China are presently surrounded by urban garbage (Figure 2). Urban

garbage is only part of solid wastes of human activities, and large quantity of agricultural refuses is generated in farming and relevant activities. Aquatic weeds flourish in lakes, rivers and oceans due to pollution with nutri- tious wastes (Figure 3). Different kinds of solid wastes generated in human activities are also a form of carbon accumulation, and carbon left after carbonizing the wastes. Accumulation of carbon above the earth broke up the ecological balance and was reflected in environmental pollution.

Because carbon and hydrogen are the most abundant elements in food and fuels and in the products of consum- ing food and fuels as well, forced carbon circulation (FCC) is proposed to bring the carbon element back to eco- logical cycle from refuses through carbonization and carbon reduction. Most organic and/or biomass refuses can be carbonized at relatively low temperature (300˚C - 500˚C), and poisonous gases such as dioxins do not occur at such temperature. In addition, quite many heat sources of low heat value are available in industry. Inorganic carbon and flammable gas are major products of carbonization as shown in Table 1 for an experiment with coal [2] . The inorganic carbon is used as reductant of acid/acidic oxides resulted in consuming fossil fuels. The FCC strategy is effective in treating urban garbage, agricultural refuses, aquatic weeds, and the flue gas of fuel com- bustion. It can also be applied to the FeO/Fe₃O₄/CO cycle for the production of hydrogen [2] .

Urban garbage is finely classified and reutilized in developed countries; however, garbage classification seems difficult in practice for developing countries as is the situation of China, and only minor part of refuses is reuti- lized. Garbage incineration relies on large quantity of additional fuel, and poisonous gases such as dioxins occur

at the incineration temperature. Therefore, garbage incineration often encounters protest of nearby residents and most cities depend on landfills of garbage. It occupied quite large field and deteriorates the near-by environment. According to FCC strategy, garbage is classified just into two groups: that can be carbonized (CBC) and that cannot be carbonized (CNBC). The management of garbage becomes simple: carbonize CBC at about 300˚C - 500˚C and use CNBC to build up dams on sea coast or spread it over deserts. Additional fuel may not be re- quired for carbonization since flammable gas is generated in the process of carbonization. The resulted inorganic carbon is directly applied in the reaction of carbon reduction as described in subsequent section.

How to deal with aquatic weeds is a headache for Dianchi Lake, Kunming, Yunnan Province and quite many other lakes, rivers, and coastal water of China. According to FCC, the aquatic weeds provide large quantity of energy in a simple way: get the aquatic weeds out of water, and dry them up, then carbonize them at relatively low temperature and normal pressure. About 10 wt% flammable gas is expected to obtain in addition to inor- ganic carbon. The same applies to agricultural refuses. Instead of in-situ burning, farmers may sell stalks to a professional contingent. As much as 8.4 × 10⁷ tons of flammable gas will be obtained in China if 1/10 of the to- tal stalks transforms to. The obtained inorganic carbon can be used as chemical reductant or just back to culti- vated land as potassium fertilizer. The carbonized agricultural stalks usually have developed porous structure with specific surface area raged in an order of magnitude 10 to 10² m²/g. They deserve well of cheap adsorbent for waste water treatment and once again carbonization is resorted to when saturated.

Fossil fuels will soon be exhausted and natural renewable energy cannot, as pointed out by David MacKay [3] , satisfy human requirement when fossil fuels depleted. Hydrogen energy entails the hope of human future be- cause it is theoretically renewable. The renewable hydrogen does come from water; however, cannot through direct decomposition. Thermo-chemical cycles allow partial decomposition of water in such a way that the oxy- gen valence does not change while hydrogen escapes from water molecule so that the TEG (theoretical energy gain) [4] is larger than unity. The author proposed a FeO/Fe₃O₄/CO cycle where

The yielded CO₂ disappears in the reaction of carbon reduction at 900˚C:

All reactions proceed at ambient pressure without the aid of catalysts. The carbon generated in FCC can be here used as reductant. The net product of the cycle is H₂ and CO. They are normally obtained through SMR (steam methane reforming) process at 700˚C - 1100˚C from natural gas with the aid of catalysts and used for the synthesis of chemical products such as methanol, fertilizer, artificial fiber, plastics, etc.

Coal is a major energy source and a major pollution source either. It provides the largest share of total energy used for electricity generation, for example, 78% in China, 69% in India and 50% in the United States. Removal of acid gases (SO₂ and NO_x) from the flue gas of coal combustion doubled the cost of power generation, and the capture of CO₂ costs at least equivalent to double the market price of power coal [5] . The extremely high cost means abandon of capture. Zero emission is possible if FCC applies to the coal-combustion flue gas. In addition to minor content of SO₂ and NO_x, the major products of coal combustion are CO₂ and H₂O. All of them can be reduced by carbon to useful or inoffensive substances:

Reactions (4) and (5) are endothermic, and their conversion can be calculated based on fundamental thermo- dynamic data as that listed in Table 2 [6] . The calculated theoretical conversion of the two reactions is shown in Figure 4 as a function of temperature. Complete conversion is expected at 900˚C. Reactions (6)-(8) with minus thermal effects are exothermic and complete conversion is theoretically assumed at ambient temperature when- ever reactions initiated. The carbon monoxide here generated can be sent to the FeO/Fe₃O₄ oxidation/reduction cycle for the production of hydrogen as above mentioned, and the carbon here used can be provided by carboni- zation of solid garbage/aquatic weeds or agricultural refuses.

Technical strategy and/or methods known to us are essentially useless for the elimination of carbon emission and the abnormal climate change it caused. The CCS strategy is not practical because the capture cost is too high to be applied in practice and it can only capture the centralized emission. However, the centralized emission ac- counts for only 1/4 to 1/3 of the total. Electricity driven vehicles are something like that said by a proverb: plug one’s ears while stealing a bell because the electricity is most likely produced in burning coal so that the global carbon emission unchanged while some places are locally cleaned. Natural energy cannot satisfy the energy needs presently and even for the future. Compared to them, the FCC strategy is practical and efficient to alle- viate environmental pressure.

However, as the linear relationship between global CO₂ emission and world population revealed that the es- sence of environment problem is the problem of population. People must realize the crisis, the living crisis, is stepping closer and closer if considering environmental problem in connection with the depletion schedule of natural resources. Think about the situation 65 years later. The world population will be doubled (more or less

around 14 billion) if the present growth rate (1.14%) is keeping on, and the global emission of CO₂ is almost doubled either. Oil and natural gas have been run out, and the other natural resources are also either empty or closing depletion. Fresh water may be in very short since glaciers may have been disappeared and rivers lost headstreams and draught. Food may also be in very short because most farm land might have been severely pol- luted. Competition and fighting for the last living resources to survive would be severer year by year. The earth likes just a ferryboat. It would sink when the ferryboat passengers are overloaded. People can imagine what would happen on the boat when it is sinking. The most important for us to do is not the development of econo- my following conventional model, but to survive human civilization gently, i.e., switching the growth rate of world population to negative immediately. The curve of world population growth rate (Figure 5) [7] shows a downward peak at the end of 50’s and early 60’s last century, which is largely due to the ridiculous “Three Red Banners” policy that led to a great famine in China and quite many people died in hungry [8] . A re-

markable yet gentle decrease is shown for 1970’s due largely to the “One Child Policy” of China issued in 1975. Of course nobody wants Mao’s policy returned, but the world’s attention must switch from “carbon emission” to “breeding control”. The personal right and freedom to breed must subordinate the world No. 1 target of surviv- ing human civilization. Lao Tzu told people “following nature (Dao Fa Zi Ran)”. It means human activities must be compatible with natural limitation. Any theory or policies are not valid or harmful if it does not consider the compatibility of its consequence with nature.