Iris hypothesis
The iris hypothesis is a partially-discredited theory that suggested increased water vapor in the atmosphere would result in reduced cirrus clouds and thus more visible-length radiation leakage from Earth's atmosphere. The fallacy was that more infrared radiation would be trapped, cancelling out the cooling from the visible-wavelength radiation leakage.
In the event, actual satellite measurements showed that more heat was trapped, not less. New satellites (launched in 2004 and 2006) are/will be able to measure clouds' properties vertically (see Aqua and others of the "A-Train").
The increased water vapor results from increased carbon dioxide and other greenhouse gases in the atmosphere absorbing radiation that otherwise would have escaped into space, thus heating the atmosphere. As the atmosphere heats, it can hold more water vapor, which then traps even more radiation (water vapor is 8 times more efficient at trapping radiation than carbon dioxide). A doubling of carbon dioxide concentration in the air is estimated to increase water vapor radiation absorption by 13%.
See also
External links
- NASA summary of Global Warming and Iris Hypothesis
- Evidence against the Iris Hypothesis
- New satellites to resolve Hypothesis
- Cloudsat and CALIPSO satellite summary
Categories
Climatology | Climate change feedbacks and causes