One Degree Makes All The Difference


By: Kate Good

Among the laundry list of harmful “greenhouse gases” that are thought to be responsible for global warming, water vapor just does not seem to fit in. It is known that water vapor in the lower stratosphere dominates temperature as it is able to absorb and radiate heat, much like water vapor can on Earth’s surface. This ability to hold heat qualifies water vapor as a viable greenhouse gas. However, new research shows that water vapor has not only played a key role in global warming but now may be responsible for the recent plateau in global temperatures.

A team of researchers from the National Oceanic and Atmospheric Administration in Boulder, Colorado, reported a 10% drop in the amount of water vapor in the stratosphere (the atmospheric layer 10-50 km above Earth’s surface) since 2000. This decrease in stratospheric water vapor offset the previous predictions for greenhouse gas warming by approximately 25%.

Interestingly, water vapor projections from researchers at the University of Reading, UK, in 1999, found that an increase of stratospheric water vapor could have boosted present day warming by up to 40% compared to carbon dioxide on its own. Meaning, the current decrease of water vapor levels is a very good sign.

While the exact cause for this sudden decrease of stratospheric water vapor is unknown, scientists believe that the simultaneous drop of 1° Celsius in the temperature of the stratosphere is to blame. The colder temperature freezes out water vapor that would have otherwise entered the stratosphere and added to warming. However, like the fall in the amount of water vapor, the fall in temperature is too not yet completely understood.


2 thoughts on “One Degree Makes All The Difference”

  1. Interesting! You don’t hear a lot about water vapor as a greenhouse gas. I wonder if we’ll find out more about factors affecting the amount of water vapor in the atmosphere soon. It seems like something we wouldn’t have much control over. Did the study mention if humans contrubute to amount of water vapor in the atmosphere? It seems important that there would be some water vapor in the atmosphere; maybe there’s an optimum amount? It seems a bit unclear if the decrease in water vapor led to a decrease in temperature or vice versa- any thoughts?

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