4 October 1999

The Role of Water Vapor in Climate Change

by Kate Melville

With all the worry about rising temperatures and the greenhouse gases, it's not suprising that scientists from around the world are studying both human-caused influences and the Earth's natural fluctuations to explain changes in our climate. Normally carbon dioxide gets most of the attention in greenhouse gas discussions, but water vapor plays an even bigger role in heating up the Earth's atmosphere!

This hypothesis is examined in four papers recently presented at to the American Geophysical Union Chapman Conference on Water in the Climate System. In the first paper presented by Georgia Institute of Technology atmospheric scientist Rong Fu, presented at the. Fu's contention is that because of water's unique molecular structure and potential heat stored within water that has an influence on storm formation and atmospheric circulation. Warmer sea surface temperatures in tropical oceans lead to an increase in atmospheric water vapor - because sea surface temperatures heat up during an El Nino, it is important to understand how El Nino climate patterns can change the amount of water vapor in the atmosphere, says Fu. "Especially because climate models predict that water vapor contributes more to global warming than carbon dioxide."

In the second presentation, Colorado State University atmospheric scientist David Randel will report results from the first study to combine all the components of the hydrological cycle, including water vapor in the atmosphere, cloudiness, rainfall, and evaporation. Randel uses satellite data to understand the Earth's water cycle. According to Randel, "scientists are concerned with the impact of warmer global temperatures on the water cycle, because warmer temperatures may increase the frequency and magnitude of tropical storms, flooding, and severe weather. Normal changes in the water cycle occur as seasons change over the course of a year, causing increasing temperatures that result in an increase water vapor, clouds, and rainfall, making understanding the system very difficult."

The3 final paper was presented by Steven Businger, an atmospheric scientist at the University of Hawai'i, who pioneered the use of Global Positioning System technology to isolate water molecules in the Earth's atmosphere. Says Businger, "Water plays a crucial role in weather and climate, and identifying the amount of water vapor in the atmosphere will help scientists understand clouds, severe weather, precipitation, hydrology, and global climate change."

Since GPS signals are strongly refracted or bent by water molecules, the amount of time it takes a signal to travel from the satellite to an Earth-based receiver increases causing a delay. Water vapor delays the signal differently than other particles in the atmosphere and this delay can be used to measure the total water vapor in the atmosphere between a GPS satellite and an Earth-based receiver. The ability to better monitor the amount of water vapor in the atmosphere helps scientists investigate a range of questions related to weather and climate.

All three presentations are very interesting science, but as to whether they have any impact on the mind set of Joe Public towards the problems of global warming remains to be seen.