Question

Methane and carbon dioxide gas are two harmful greenhouse gases. Identify two sources of these gases and discuss what society can do to reduce their impact on the environment.

Answer 1

industry, cars and so forth...
they can be reduced by using green energy, windmills (windfarms), nuclear energy, water energy (damns)...

Answer 2

Burning fossil fuels such as coal and oil are major examples and, as mentioned above, can be reduced by using "green" energy - geothermal energy, solar energy, hydroelectricity, etc.

Answer 3

Both methane and CO2 are actually mostly produced from natural sources, e.g. plant and animal respiration and the decay or organic material. Humans add only a small sliver to that stream.

This is important because it is important to understand that methane and CO2 are not strange alien substances that only human activity produces. Rather, they are both part of mighty recirculating streams of material that naturally move between various parts of the biosphere, hydrosphere, and geosphere in vast multi-thousand-year cycles.

For example, here an illustration from Wikipedia of the Earth's "carbon cycle," during which carbon is recirculated as part of carbonate rocks, dissolved carbonates in the ocean, living material, and CO2 in the atmosphere:

http://en.wikipedia.org/wiki/File:Carbon_cycle.jpg

Notice that, for example, human emissions of 9 Gt per year are dwarfed by the amount that goes back and forth through plant and microbe respiration (120 Gt/year), or photosynthesis in the ocean (90 Gt/year).

But what's important about human activity is that it's not balanced: we do not take OUT of the atmosphere as much greenhouse gases as we put IN. All the other parts of the cycle are balanced (as they would have to be, for the situation to be stable).

So what is the best solution? Trying not to burn things is silly, in my opinion. Combustion is the most obvious and efficient and least pollution power source when you live at the bottom of a giant pool of free oxygen -- and, indeed, every other living thing on the planet uses combustion and the carbon reduction/oxidation cycle to power itself. We should certainly listen respectfully when Mother Nature tells us this is how she prefers to power her own creatures.

All we need to do, therefore, is close the human cycle: take as much carbon out of the atmosphere as we put in, that is. This can be accomplished many ways. The most obvious is just to grow more plants, and this is the idea behind "carbon neutral" and "carbon offset credits" schemes. But a better ultimate solution is to find ways to "grow" the fuels we burn, the same way living plants do. This is only a challenge because we tend to use much more reduced forms of carbon as fuel (and raw material) than are typically produced by plants and microbes. However, with the ability to genetically engineer microbes in particular, we are now gaining the ability to "reprogram" things like algae and microbes to synthesize hydrocarbon fuel and raw materials for our industry, directly from CO2, water and sunlight. When that is achieved, we will have closed the human cycle, and we can burn as much fuel as we like -- confident that the waste products will all be recycled back into fuel again, by the ultimate "solar cell" -- a living photosynthesizing cell.