claim: The consensus among scientists and policy-makers is that we’ll pass this point of no return if the global mean temperature rises by more than two degrees Celsius.
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).