A NASA Space Sleuth Hunts the Trail of Earth’s Water


JPL NASA – January 3, 2007

This is good but sad news.  I am extremely happy that we are continuing to invest scientific effort and money in the gathering of data and the understanding of our climate.  That is the good news.  The sad news is that there are some in this world that believe that we don’t need to do this scientific process because they already know the answers: the world is going to end due to human fault and we need to spend billions (trillions?) reversing the process.

I am aghast that anyone can come to a significant and earth shaking conclusion when we are still trying to understand how the Earth’s water travels around the planet and we find out that our assumptions may not have been valid.  As the article points out – water is the most abundant greenhouse gas and quite likely the most influential.

For the first time, NASA scientists have used a shrewd spaceborne detective to track the origin and movement of water vapor throughout Earth’s atmosphere. This perspective is vital to improve the understanding of Earth’s water cycle and its role in weather and climate.

A team of scientists … used the instrument’s observations of heavy and light water vapor to retrace the “history” of water over oceans and continents, from ice and liquid to vapor and back again. Heavy water vapor molecules have more neutrons than lighter ones do.

By analyzing the distribution of the heavy and light molecules, the team was able to deduce the sources and processes that cycle water vapor, the most abundant greenhouse gas in Earth’s atmosphere.

The team found that tropical rainfall evaporation and water “exhaled” by forests are key sources of moisture in the tropical atmosphere. They noted that more water than they had expected is transported over land rather than ocean into the lower troposphere (Earth’s lowermost atmosphere), especially over the Amazon River basin and tropical Africa.

Co-author Dr. David Noone: “One might expect most of the water to come directly from the wet ocean. Instead, it appears that thunderstorm activity over the tropical continents plays a key role in keeping the troposphere hydrated.”

The team found that in the tropics and regions of tropical rain clouds, rainfall evaporation significantly adds moisture to the lower troposphere, with typically 20 percent and up to 50 percent of rain there evaporating before it reaches the ground. The atmosphere retains this water, which can be used to make clouds. The strength and location of this evaporation give scientists new insight into how water in Earth’s atmosphere helps move energy from Earth’s surface upwards.

The team also found evidence that water transported upwards by thunderstorm activity over land originates from both plant “exhalation” in large forests and evaporation over nearby oceans.

Noone:  “This link between vegetation, hydrology and climate has implications for how societies choose to manage their ecological resources. Our measurements provide a baseline against which future changes in vegetation-climate interactions can be measured.”

Noone: “Better knowledge of these processes ultimately leads to a clearer understanding of the factors that drive the global water cycle and its importance in climate and global climate change.”

Noone and his co-authors said there has been a general lack of information on the way water moves around in Earth’s atmosphere where it comes from and where it ends up.

Read the article here.  The study is printed in February 1 issue of Nature.

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