The decomposition of organic material (in particular, our trash) generates Methane gas which, though shorter lived in the atmosphere, is 25 times more potent a greenhouse gas than CO2:

https://www.epa.gov/gmi/importance-methane

Landfills generate a steady and significant amount of Methane each day - 15% of all Methane emissions, according to the EPA:

https://www.epa.gov/lmop/basic-information-about-landfill-gas#methane

We need to make more effective use of our landfill Methane. Presently, at most landfills, there are pipes sunk deep into the landfill which route the Methane vertically to the top. The Methane naturally rises as it is less dense than air. At the top of the pipe is usually a flame for burning the Methane, turning it into CO2 and H2O. Rather than flare off the Methane, we should be concentrating it and either purifying it for use as LNG, or pipe it into a generator to be burned to generate electricity:

https://www.epa.gov/lmop/basic-information-about-landfill-gas

In addition, to generate more electricity and to dramatically reduce the rate at which we fill our landfills, we should be incinerating our trash with the newest, cleanest incinerators. Incinerating trash to generate electricity provides many benefits:

• the fuel is effectively free, so the electricity is cheaper
• less trash is thrown into landfills
• metals can be collected at the bottom of the incinerator for re-use
• toxic materials (arsenic, etc.) are concentrated and more easily controlled
• less methane is generated from the landfill as less material is being thrown away