The quasi-biennial oscillation (QBO) is a major oscillation with a characteristic period of 28 months that influences substantially the stratospheric circulation and chemistry. This exploratory study investigates its possible change by direct simulation of the QBO in a doubled CO2 climate for a range of gravity wave sources. It is found that a QBO spin-up is likely. In the most extreme case the period is nearly halved. Important accelerating factors are the decreased tropical upwelling and increased gravity wave drag, while increased filtering of eastward gravity waves in the upper tropical troposphere acts as a decelerating factor.