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CO2, not water vapour, causing global warming

Q. Could water vapour be responsible for the global warming? Are the amounts of CO2 being added really making a difference?

A. A leading climate change scientist (Professor Susan Solomon) recently suggested that the rapid increase in temperature in the 1990s and the flattening of the temperature rise in 2000s was due to changes in water vapour 10 miles up in the stratosphere.

The implication is that the changes in temperature in the last two decades are more affected by changes in water vapour levels than by other greenhouse gas emissions, such as the emission of CO2.

While water vapour is an important greenhouse gas, it is only when humans have added CO2 to the atmosphere that the balance of this warming has started to shift. The effects of increasing CO2 concentrations is to warm the atmosphere, which allows more water vapour to be held in the atmosphere. This exacerbates the warming.

As Professor Solomon says, her analysis does not change the view that climate change is being primarily driven by human activity.

The increase in stratospheric water vapour is only one factor in decadal temperature changes. The dominant factor on longer timescales is still greenhouse gases.

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Climate change:
the facts

We face unavoidable climate change effects for the next 30 years due to the CO2 (carbon dioxide) and other greenhouse gases which we have already emitted, and so we need to adapt to the inevitable consequences.