Greenhouse Gasses: Water Vapor

Now I have to worry about water?

Yes, water vapor is a greenhouse gas; it is the most abundant of the greenhouse gasses and also has the highest warming potential.

map of earth's clouds

Where does water vapor come from?

One of several Earth Systems is the hydrosphere, the entire sum of water on the planet. This includes not just bodies of water such as oceans, lakes, and rivers; the hydrosphere also includes water in the air- mist, fog, clouds- as well as the moisture in soil and vegetation.

Water vapor is a natural component of this Water (or Hydrologic) Cycle; water vapor concentrations vary with atmospheric temperatures.

We all know that atmospheric concentrations of carbon dioxide, methane, and nitrous oxides are increasing due to human activities. These gasses then have a “forcing” effect in the climatic system. As a result, more of the Earth’s reflected heat is trapped in the atmosphere, causing it to warm. Since warmer air holds more water, as temperatures rise more water vapor forms in the atmosphere. (This is why it rarely snows in Antarctica: it is too cold for much water vapor to form.) This water vapor then acts like the other greenhouse gasses, trapping more heat, causing additional warming. Water vapor is responsible for an estimated 66-85% of the greenhouse effect!

water vapor greenhouse gas
By John Evans and Howard Periman, USGS –

Since the Earth is a closed system, as water vapor increases in the atmosphere, it must come from somewhere. The oceans and other bodies of water supplies much of this water. Some also comes from from soil and plant matter.

Columbia University found we can expect increased drought and aridity feedback due in part to this water vapor feedback. “Concurrent soil drought and atmospheric aridity have dramatic impacts on natural vegetation, agriculture, industry, and public health,” says Pierre Gentine, associate professor of earth and environmental engineering and affiliated with the Earth Institute.

As the plant mass of the Earth becomes drier, we can expect more and more devastating wildfire seasons like the current 2019/2020 season in Australia. This will not be limited to that continent.

Australia wildfires water vapor

The recent, and ongoing, tragedy due to fires in Australia go well beyond lives lost and property damage. Horrific images of kangaroos and koala bears burned alive, or worse, burned and still alive, don’t even begin to account for the massive loss of life: other mammals, birds, frogs, bats, insects, various other creatures, along with the unique plant life. The best estimate is 1 Billion animals dead (Mother Jones did some great work in digging into that number). The absolutely appalling devastation to the these ecosystems, some of which may never recover, is almost too much to fathom.

Australia’s recent fires have almost doubled the country’s entire human made carbon emissions for the year! Forest fires not only release additional carbon into the atmosphere, they also destroy the mechanisms that store carbon in the plants and ground. Additional carbon in the atmosphere causes warming, allowing more water vapor to form, drying out the land more, making it more vulnerable to additional fires, and less able to effectively store carbon, creating a dangerous feedback loop.

there is Hope

We don’t have to manage this problem directly! If we focus our efforts on the other GHGs and work to reduce those, atmospheric temperatures will begin to normalize, allowing water to eventually fall as rain.

Water vapor may be the biggest contributor to global warming, but it only lasts in the atmosphere for around 10 days. Compare this with carbon dioxide (100 years), methane (25 years), and nitrous oxide (300 years).

There is evidence that water vapor may also act as a cooling agent. From NOAA: As water vapor increases in the atmosphere, more of it will eventually also condense into clouds, which are more able to reflect incoming solar radiation (thus allowing less energy to reach the Earth’s surface and heat it up).

As we can’t impact water vapor directly, we can focus our efforts around mitigating the effects of drying lands. All over the world, there are indigenous and traditional methods for managing the land. Northern Australia, where traditional land management practices have been in use for decades, is relatively untouched by this season’s fires. The NY Times article is better written, but Al Jazeera also covered this if you can’t get behind the paywall.

take Action

We have less than 10 years to make massive changes if we want to avoid even more disastrous climate scenarios.

The next 10 years are critical! 
What you do counts! 
Make sure your elected officials share your sense of urgency. Vote for environmentally conscious politicians. 
Help local activists to get your city to declare a Climate Emergency. Support initiatives like the Green New Deal. 
Get involved in activist groups like Sunrise Movement and Extinction Rebellion.