claim: Water vapor helps trap heat, and is a far the strongest of the major greenhouse gases, contributing 36–72 percent of the greenhouse effect.
evidence: By their percentage contribution to the greenhouse effect on Earth the four major gases are : water vapor, 36–70% carbon dioxide, 9–26% methane, 4–9% ozone, 3–7% It is not possible to assign a specific percentage to each gas because the absorption and emission bands of the gases overlap ( hence the ranges given above ).