Methane is a(n) gas. excess of methane in the atmosphere will lead to .

Increased greenhouse effect

Explanation:

The methane is one of the so called ''greenhouse gases''. This gas has the ability to trap the heat. Because of this, when the reflected heat from the surface of the Earth moves back toward the space, the methane manages to trap big portion of it, leading to increase in the greenhouse effect. Even thought he CO2 is the most talked about greenhouse gas because it is much more common, the methane is actually a gas that manages to trap more heat than the CO2, though it is more effective in this only for a short period of time.

chordata is the answer