The other potent greenhouse gas
Contact: Paula M. Davis
Aug. 25, 2016
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KALAMAZOO, Mich.—Carbon dioxide is often discussed as the driving force behind global climate change.
Research has shown that excessive carbon in the atmosphere as a result of humanity’s unrestrained penchant for burning fossil fuels is contributing to throwing the Earth’s climate systems out of whack. And human activity has increased the warming effect of atmospheric carbon, according to climate scientists.
“We’re dialing up Earth’s thermostat in a way that will lock more heat into the ocean and atmosphere for thousands of years,” says Jim Butler, director of the National Oceanic and Atmospheric Administration’s Global Monitoring Division.
The increased concentration of atmospheric carbon just happens to be the start of the whole climate change process, explains Dr. Todd Ellis, assistant professor of geography and an expert in atmospheric science, with specialties in weather research and climate education.
“Water vapor—the gas form of water—is a way more potent greenhouse gas than anything that comes out of the fuel we use,” he says.
This doesn’t take humanity off the hook for creating a global climate conundrum; human activity just started an unfortunate chain reaction.
As Butler remarked, extra carbon dioxide in the atmosphere also puts extra energy into the Earth’s surface, warming the planet’s crust and its huge store of surface water. The Earth earned its colloquial moniker the Blue Planet because of this huge store of water; some 70 percent of the surface is covered by it.
“When the surface is a little warmer and the air near the surface is a little warmer, more water vapor can exist there,” Ellis says. “We call it the water vapor feedback. A little change in the things we control create much bigger changes in the amount of water vapor.
“So, we care about the greenhouse gases we make. But it’s the effect of those greenhouse gases on the big one—water—that tends to drive energy. It also changes where it precipitates and how often, pretty substantially in fact.”
Rising waters
By way of example, for the past several years, parts of Texas, namely the Houston area, have dealt with devastating floods. During the spring of 2015, rain came down in torrents, resulting in property damage in wide swaths and even fatalities.
Again in the spring of 2016, torrential rain came for the region, with much the same result. In Harris County (Houston is the county seat), 240 billion gallons of rain dropped onto the community during one 24-hour period in mid-April that year, according to the Harris County Flood Control District. Harris and surrounding counties were deemed a federal disaster after storms waylaid the area for several days.
While one can’t point to a single weather event like this one and conclude it is the result of climate change, patterns matter, Ellis says.
“Houston has had a bunch of these (rain events) over the last decade and a half. ... That is something we can point directly to climate change and its impacts on water vapor. You put more water into the atmosphere, and then the right system comes along, and it’s got all of that extra water to tap into and turn into rain.”
Harris County is in southeast Texas, just 50 miles from the Gulf of Mexico. As a result of its proximity to the gulf, there is a ready supply of surface water to be converted to water vapor, and so the air is often near its maximum limit of moisture, Ellis explains.
“The primary thing that defines that upper limit (of water vapor) is the temperature. As the atmosphere warms, that limit is just going to keep going up, increasing the amount of water vapor that can hang around in the atmosphere waiting for some system to come along and tap into it.”
Think back to elementary school Earth science lessons on the hydrologic cycle. In this process, water evaporates from the surface, moves through the atmosphere, condenses as clouds and returns to Earth as precipitation. But as the climate warms, studies have shown that the water cycle slows down.
“If you could put a tracking tag on a single water vapor molecule and watch it go through that whole cycle, you’d see that for a doubling of carbon dioxide, (the molecule’s) journey is slowed by a few days,” Ellis explains.
So, a process that would normally take seven days, for instance, could take nine or 10. While that delay doesn’t seem very substantial, Ellis says “the impact is essentially how easy is it for us to see rain form and when it does form, how much rain falls.
“When storms occur, more rain falls, but that, in turn, deprives other areas from accessing that water. So it has two impacts put into one simple phrase: The wet areas get wetter and the dry areas get drier.”
While Houston’s water-related woes offer an example of what can happen with an overabundance of precipitation, other areas of the western United States have suffered from ongoing dry conditions.
During 2016, Lake Mead, the largest man-made reservoir in the United States when at capacity, hit its lowest level since it was created some 80 years ago. Thanks to about 16 years of drought coupled with demand for water, the lake was at 37 percent of its capacity in May 2016, according to the U.S. Bureau of Reclamation’s Lower Colorado Region. Formed by the Hoover Dam, the reservoir serves Arizona, California and Nevada. When this resource shrinks, the impact is felt by people, animals and business, including agricultural industry.
Follow-on effects
There are myriad ways both scarcity and excessive water lead to suffering and economic stress.
“Those stresses hit all of us, but it’s going to hit the people who are already at a socio-economic disadvantage first because there’s no safety net. That works both within our own society and when looking at countries as a whole,” Ellis says, pointing to the crisis that led refugees from Syria to flee for safe havens in Europe.
"While the refugee crisis around Syria has more to do with war than it does water, that is a part of the world that has had civilizations collapse because of lack of rainfall in the past. ...
“Pakistan has had the opposite situation, really significant flooding, and they don’t have the infrastructure to deal with it either. So it really starts to bleed into some significant geopolitical questions in places where you don’t want to have those kind of extra stresses,” he says.
Ellis opines that in a changing climate, understanding how water moves is one of the most important questions there is.
“There are a lot of important questions to be asked about climate change, but water is a resource for all of us. And none of us as humans has figured out how to live without it yet.”
Read more about WMU researchers and their ongoing work in the WMU Magazine, which is published quarterly by WMU's Office of Marketing and Strategic Communications.