Uncovering the role of water vapor in climate change

October 05, 1999

With global temperatures rising, scientists from around the world are studying both human-caused influences and the Earth's natural fluctuations to explain changes in our climate. Although carbon dioxide gets most of the attention in greenhouse gas discussions, water vapor plays an even bigger role in heating up the Earth's atmosphere. This is because of water's unique molecular structure and potential heat stored within water that has an influence on storm formation and atmospheric circulation. The latest research regarding water vapor's link to global warming and climate change will be presented October 12-15 in Potomac, Md at the American Geophysical Union Chapman Conference on Water in the Climate System.

Georgia Institute of Technology atmospheric scientist Rong Fu will discuss how warmer sea surface temperatures in tropical oceans lead to an increase in atmospheric water vapor. Because sea surface temperatures heat up during an El Niño, it is important to understand how El Niño 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."

Colorado State University atmospheric scientist David Randel uses satellite data to understand the Earth's water cycle. 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 said that 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, says Randel.

Steven Businger, an atmospheric scientist at the University of Hawai'i, has pioneered the use of Global Positioning System (GPS) technology to isolate water molecules in the Earth's atmosphere. "Water plays a crucial role in weather and climate," says Businger, "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, Businger says. Businger will report results of his study at the conference.

Several other researchers at the conference will discuss new ways to achieve a better understanding of the relationship between water vapor and climate.

David Weymiller

John Toon

NASA/Goddard Space Flight Center

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