Reservoirs are contributing 1.5% of global greenhouse gas emissions

Global warming is going to require a massive, species-wide effort to counteract. The problem gets worse every day. When do we decide to stop?

We're already pretty far gone. Now it's a matter of controlling how Earth-shattering the damage is.

> But if that is not producing methane in the reservoir then in will be producing methane elsewhere

Not necessarily. The article explains methane production as so:

[...] bacteria eating this dead organic matter to depend on other molecules containing oxygen. These include nitrate, phosphate, sulfate, and carbon dioxide. The least appealing molecule to breathe for these microbes is carbon dioxide because it requires the greatest energy to break the molecule apart to access the oxygen. When these microbes have no choice than to breathe carbon dioxide, a process called “methanogenesis” occurs.

Methane is produced by anaerobic digestion, which I would think is much more likely to happen when a whole area is flooded at once. The same biomass bring broken down in atmospheric oxygen would have a significantly lower effect. Agree the mix of ongoing and one-off effects is confusing.

To borrow a phrase from Sheldon Brown, "As always, Bill Mollison has the answer." :)

(for those unfamiliar with what I affectionately call the "Perma-cult": https://en.wikipedia.org/wiki/Bill_Mollison)

>So, it seems as though hydropower is not as clean as we once thought. But that’s isn’t a good reason to be ripping out dams. Hydropower generation often replaces much dirtier sources of energy, such as coal and even natural gas. In addition, dams provide us a wide range of public benefits such as flood control, recreation, and water management.

It sounds like the Permaculture strategy of disfavoring singular large dams (huge concrete construction projects) and favoring smaller "farm dams" (cheap earthen construction) is the way to go. The smaller scale means more surface area:volume, increasing the equilibrium oxygen level in the water and reducing methanogenesis.

Also, the typical Permaculture dam construction practice is to scrape off and conserve all the topsoil from the inside of the dam. This should further reduce methane production (which also represents squandered biomass, ie stored carbon). This technique is practical on the scale of a farm dam, but totally impractical for a huge reservoir.

Farm dams have cost advantages in flood control and water management over monolithic dam projects, since they're near to the big consumers of water (farms). So the largest diversion canals and tunnels never need to be built. Simple gravity-fed water run through plastic pipes serves for irrigation purposes, so it improves on-farm water security.

>groundwater storage may be a ‘cleaner’ alternative. Groundwater recharge basins are regularly maintained to have less organic matter at the bottom, since it can clog the percolation of water into groundwater aquifers beneath. In addition, recharge basins are shallower than man-made reservoirs and periodically become empty during dry periods when less water is available to recharge groundwater. This periodic drying out helps keep soils aerated, whereas man-made reservoirs can stay inundated with water for longer periods of time.

I wonder how "groundwater recharge basins" differ from swales (long on-contour ditches)? They also intercept large quantities of runoff and divert it to recharging groundwater. They also require minimal earth movement, since it's a small surface feature compared to farm dams. Swales can also feed into dams, dramatically increasing their total catchment and infiltration capacity (since before the dam overflows, it floods and soaks the length of the swale).

https://www.youtube.com/watch?v=E79C9tdcgEA

http://permaculturenews.org/category/earthworks-earth-resour...

but energy isn't their main benefit. flood control and proving water to cities and even farms is the main benefit. throw in the recreational opportunities, increased tax base because all that lake front is worth something, and it seems they are more than worth it.

to be honest I walked into that article expecting another dam killer tirade with an all new reason to take down more and was pleasantly surprised they defend the use of them in the end

A reason to not include water vapor in a list of "greenhouse gases" is its short lifetime in the atmosphere. If you inject extra water vapor there, it rains down and exits the atmosphere in a matter of days, whereas methane etc stay for years --- humans emitting water vapor vs. CO2/etc to the atmosphere has very different relevance for the physics. Of course, the vapor does have effect on the radiation physics, and the fact that the equilibrium concentration depends on temperature leads to the positive feedbacks.

People leave out water vapor because, as you note, its concentration changes depending on temperature. It's an effect, not a cause. Emit lots of steam and you don't increase the temperature, you add to the rain.

Water vapor does amplify the climate effect of other greenhouse gases.

Methane is about 25-100 times more potent than CO2. Nitrous oxide about 300 times than CO2.

Although, the biggest worry is the stored methane. [1]

The amounts stored are equivalent (in CO2) to about 20-35 years of human activity (2014 CO2 output). If that gets quickly released, who knows what will happen.

[1]: https://en.wikipedia.org/wiki/Arctic_methane_emissions

Good point.

I would add that presumably water vapour, methane and carbon dioxide have been in the atmosphere influencing temperatures since before anthropogenic climate change. I imagine rising concentrations of atmospheric water vapour are partly a consequence of emissions of carbon dioxide and methane emissions. (I believe that methane breaks down into chemicals including water.)

I imagine that humans are more responsible for levels of atmospheric water vapour indirectly (through carbon dioxide and methane emissions) than directly.

I imagine temperature and concentrations of atmospheric water vapour are in equilibrium in the absence of changes in the concentrations of other greenhouse gases.

The most potent greenhouse gas is actually SF6 (Sulfur hexafluoride), a chemical used in some industry processes. Water vapor is however the most common one.

Perhaps these shade balls could work. It does mention that they inhibit microbial growth and slow evaporation.

http://news.nationalgeographic.com/2015/08/150812-shade-ball...

I think ruminants including cows do significantly contribute to methane emissions by burping.

"Cows don't emit 400 quarts of daily flatulence, as the term is usually understood. According to Professor Johnson, they emit 400 quarts' worth of burps,known in polite circles as eructation." http://www.straightdope.com/columns/read/832/do-cow-and-term...