It all depends on the type of green house gas. Different green house gasses have different absorption rates. Like carbon dioxide takes about 200 years while methane takes about 20 years. You can read all about it at http://en.wikipedia.org/wiki/Greenhouse_effect.
Carbon is sequestered by living organisms who consume carbon dioxide (plants and algae) in their life cycle, or by mechanical means (sequestration underground). CO2 makes up 60% of the greenhouse gasses, and it has increased from 250 ppm to 380 ppm since pre-industrial times. The cause is assumed to be man-made emission. 1. How long does it take to reduce CO2 by natural means? The normal cycle assumes steady-state models, and results in a number around 180-220 years. Sequestration by mechanical means could reduce this by 5% at most; assuming adding biological means, this could be reduced by an additional 10-15% within 30 years. The cost for mechanical would add 30% to the cost of electricity and 40-50% to the cost of gasoline. The cost of biological means would add about one-quarter more. 2. Is there a global warming, and is it uniformly bad for people? The data suggest a small warming of .7 degrees on a global scale, over the last 50 or so years. This is not without precedent and in the last warming period (Medieval Warming Period), mankind thrived with a global warming over 1.5 degrees. It was the period of the Renaissance. There is no evidence that it resulted in massive polar melts. 3. Is carbon dioxide the reason for increased temperatures? There is a bit of a consensus that it plays a part, but the extent and cause-effect is still being debated. Some claim carbon dioxide rise is historically connected to warnings, but are a lagging indicator: temperatures rise, and as a result carbon dioxide rises, perhaps due to sea organism blooms. 4. Can we reduce CO2 at an acceptable cost? This is the hardest issue. 60% of the problem is due to coal-fired power plants and other fossil fuel burns. Switching to cleaner fuels can help, but China and India will not comply with this as they have a growing economy and are due to be the biggest emitters within 5-10 years. Cost for our implementing a cocktail of solutions might result in a loss of GDP equaling the last 10 years of growth, doubled. The result would be a power grid more open to insult and less capable to supply the one thing that has made us a first-world nation: clean, cheap, dependable power. It's still true that the only thing that can provide immediate surge ability is an already spinning motor, and these are only powered by hydro, fossil fuels or nuclear. I doubt America will sacrifice their power grid, their lifestyle, or their jobs to a plan that will not produce any reduction in CO2 worldwide. Why sacrifice if it won't create any change?