Can Ground Water Use Exacerbate Global Warming?

Todd Jarvis sent me the link to this article.

Should we use more ground water? Well, that could exacerbate global warming by releasing more CO2 into the atmosphere. This article is from the Kansas City infoZine.

I actually encountered something like this before, albeit not with the degassing of ground water. A few years ago some posited that the pumping of "non-renewable" ground water was contributing "new" (i.e., removed from the hydrologic cycle for millennia) water vapor to the atmosphere. Since water vapor is quite an effective greenhouse gas, this was contributing to global warming.  But this may not be true, because of water vapor's relatively short residence time in the atmosphere, something like one week (see Hornberger et al., Elements of Physical Hydrology, Table 1.1, p. 9).  Contrast that with the average residence time of atmospheric CO2, which can be up to 100 years, depending upon its source (see this article).

William Connolley's Stoat blog has a great post and discussion about this issue. He calls water vapor a "weak" GHG because of its short residence time. He says that increased water vapor will simply mean a new equilibrium is established. My contention is that you're continuously adding "new" H2O to the atmosphere, so even though you may get a new equilibrium, it's quite dynamic, with the net effect being there is more H2O in the atmosphere and more GHG effect.

But I digress - now we have to consider the CO2 contribution, which appears to be more troublesome.

The Law of Unintended Consequences strikes again...

Read on, folks.

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The next time you open a soda can or bottle of champagne, you'll release a tiny amount of carbon dioxide into the air. The bubbles that give such beverages their fizz are transferring CO2 from the liquid into the atmosphere.

Today, a researcher at the University of Kansas is studying this phenomenon on an exponentially larger scale.

Gwen (G.L.) Macpherson, associate professor of geology, said substantial amounts of carbon dioxide are set free as more communities and industries around the world tap underground aquifers. She has found that this growing dependence on groundwater adds significantly to the concentration of gasses responsible for climate change.

"Virtually all groundwater contains carbon dioxide," Macpherson said. "CO2 in groundwater is 10 to 100 times higher than it is in the Earth's atmosphere. Most of the CO2 in groundwater comes from the soil zone. As water passes through the soil on its way to recharging an aquifer, it picks up CO2."

Worldwide, groundwater accounts for approximately one-fifth of total freshwater used for domestic, industrial and agricultural purposes. That number is on the rise because there is roughly 30 times more fresh water underground than on the Earth's surface.

"As we contaminate more surface water sources and withdraw more water from rivers and lakes, less of it is available," said Macpherson. "As population grows, we need more water. There's a lot more groundwater available, which makes it a good resource."

But like the opening of a carbonated drink, the tapping of aquifers results in degassing, or discharge of carbon dioxide into the air. According to the KU researcher, dissolved carbon dioxide in unconfined groundwater is "typically one to two orders of magnitude higher" than in surface waters. As a groundwater chemist, Macpherson now is focused on gauging the extent of CO2 released by all the world's aquifers tapped by humans.

"We're talking about one more piece of the carbon dioxide puzzle," Macpherson said. "My initial calculations show that it could be a fairly significant amount of carbon dioxide that goes into the atmosphere. It's nothing like fossil-fuel-generated CO2 - maybe up to 1 percent of that. Nevertheless, every little bit that we put in there adds carbon dioxide to the atmosphere."

By way of comparison, Macpherson calculates that degassing of aquifers through groundwater extraction represents as much as seven to eight times more than the average yearly CO2 output from the Earth's volcanoes.

Macpherson's research may be unique among hydrogeologists, who collectively have not yet considered the total impact of groundwater usage on the planet's climate. "It might contribute to the greenhouse effect," she said. "This is a new area of inquiry. I don't know of anybody who has tried to see how big of an effect it is."

With 35 wells and 100 soil lysimeters, Macpherson studies CO2 levels within a pristine watershed located at the Konza Prairie Biological Station near Manhattan. She has discovered that underground aquifers act as beneficial "carbon sinks" for mounting levels of carbon dioxide generated by human activity.

"There is an increasing amount of carbon dioxide being stored in groundwater," Macpherson said. "This is a very good thing. It may mean that just like the oceans are soaking up CO2 from the atmosphere, groundwater is doing is the same thing. The mechanism is a little harder to understand - we don't really know what it is. Somehow the soil is shunting this CO2 down into the groundwater system, and it's storing it there for us."

Macpherson recently presented her findings in Denver at the annual meeting of the Geological Society of America (GSA) . Here is a copy of her abstract.

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"Everything is connected to everything else." -- Fundamental Law of Ecology

Comments

[Ana]

Could it be possible that underground water and oil have been working as the earth's internal cooling system?
By pumping out both for human consumption, we have left those underground areas without protection and this has exacerbating the global warming issue.
By pumping water back into those areas – with treated water, even sea water – we would be refilling that cooling system and with time, that water will become available to human consumption.

[Michael]

Hi, Ana.

Interesting comment - thanks. It has been a long time since I took solid-earth geophysics.

Certainly, fluids in the earth have a role in heat transfer, via convection (advection) and conduction through the solid-fluid complex.

My sense is that the effects of removing the earth's fluids have been minimal, simply because the volume of fluid removed has been miniscule relative to the volume of the earth, or even just the volume of the near-surface portion of the earth.