Reducing methane emissions with seaweed

Last year I read about a study suggesting that feeding cow’s seaweed could dramatically reduce their emission of methane. Coincidentally it also makes for healthier animals.

This however left me with two questions:

  • What would the impact be of reducing methane emissions from ruminants?
  • What does the economics of making it happen look like?

The impact of reducing methane emissions

CO2 is not the only greenhouse gas, but the most significant and therefore justifiably get’s the most attention. As a result CO2 emission growth has by some estimates stalled in the last 3 years. This is by no means a guarantee that we’ve reached the peak, but it’s encouraging.

The second most significant greenhouse gas is methane. CO2 constitutes 82% of the greenhouse gas emissions where as Methane is only 9%.

However, methane traps up to 100 times more heat than CO2 within a 5 year period and 72 times more within its 12-year atmospheric lifetime. For this reason, methane actually accounts for 20% of the total radiative forcing.

This sounds encouraging, but CO2 has a 200-year lifecycle in the atmosphere, so we need a better metric to compare the two. Global Warming Potential (GWP) is the recognised metric for this.

The GWP of a greenhouse gas is defined as “the [cumulative] radiative forcing from the instantaneous release of 1 kg of a trace substance relative to that of 1 kg of a reference gas”. The reference gas is almost always carbon dioxide…

Global Warming Potential for different greenhouse gases.


Right knowing this it should be fairly clear that all other things being equal if you could spend the same amount of money to displace 1 tonne of emissions of either CO2 or Methane you should go for the methane.

But how much of methane emissions come from ruminants? in other words, would a reduction here be a good idea? To which the answer is ≈14% and yes respectively.

To put that into perspective. The concentration of methane in the atmosphere is only increasing by 22 Mt per year. Anthropogenic Ruminants (that is cattle, sheep, etc. raised for Human consumption) account for roughly 50-100 Mt per year. Feeding cows ruminants could lead to a stagnation of methane concentration in the atmosphere.

Economics of feeding cattle seaweed

How much would we need?

Seaweed production globally is booming, with more than 25 million tonnes (measured when wet) farmed each year, which is about double the global commercial production of lemons.

Producing enough Asparagopsis to feed 10% of the almost 1 million feedlots and 1.5 million dairy cattle in Australia would require about 300,000 tonnes a year, and millions of tonnes if it were to be scaled up globally.

With selection and breeding of seaweed varieties for higher bioactivity, this figure could come down, but perhaps only by half, and it would still require large areas of land and water. With typical seaweed production rates at 30-50 tonnes of dry matter per hectare, this suggests that to supply 10% of the Australian livestock industry will require at least 6,000 hectares of seaweed farms.


To put that into perspective. The global cattle population is closer to 1 billion. If the goal was to feed 2% seaweed to 10% of cattle globally we would need 12 million tonnes a year. Which translates into 240.000 hectares of seaweed farms. That’s 240.000 Rugby fields apparently or just shy of Funen the third largest island in Denmark. If we wanted to produce enough for all cattle the area would be more like the size of Sicily.

Where can we produce it?

I couldn’t find any information on the environment suitable for asparagopsis taxiformis nor examples of commercial farming. The closest I could get was commercial farming of Asparagopsis armata in Ireland. Suggesting it would be less limited than I would have anticipated.

But seaweed is typically not grown at depths deeper than 7 meters, which does complicate locating farming area.

Production is currently very labour intensive as no commercially viable machines have been built for automating or semi-automating the production at scale. Again eliminating countries with high labour costs from the pool of viable area’s for farming unless advances were made in automation.

What would be the cost in time and money to set that up?

I’m gonna assume that production of seaweed will be no-more expensive for the environment than producing the current fodder for the animals. The remaining interesting figure is the unit price.

I found a great article about the cost of farming seaweed in the North Sea versus more traditional area’s of farming.

Yearly costs per hectare for Nordic facilities:

$18,594 Fixed cost
$418 Labour cost
$1,380 Harvesting cost
$570 Transport cost
$13,800 Material cost
$690 Maintenance cost
$135 Insurance cost
$35,587 total cost

This is 3x the cost of facilities in South East Asia. Each hectare is estimated to produce 20 metric tonnes of dry seaweed (it should be noted that this number is significantly lower than the 30-50 tonne per hectare cited earlier).

So in South East Asia each tone should be roughly ≈$600.

We needed 12 million tonnes a year to feed 10% of the global cow populous or $720.000.000.

Can we get farmers to buy it?

Around 15% of feed expenses are lost in methane emissions. As feed is the primary expense for livestock farmers, this is no small problem.


That should recoup the cost of the seaweed right there.

Secondly, seaweed has been linked to health improvements in cattle in the past as well. Reducing the need for antibiotics (granted they are cheap), but it’s an important marketable improvement.

Thirdly it should be possible to lobby for getting carbon credits for reducing methane emissions which could then be sold.

Fourthly there are bound to be environmentally conscious consumers willing to pay a premium for meat sourced in a way the hurts the environment less.


A few interesting tidbits I learned while researching this.

Methane concentration in the atmosphere has actually had a relatively bigger increase than CO2.

Table of CO_2 vs CH_4 vs N_2O concentration and impact on the climate


Deforestation accounts for 10-25% percent of global warming depending on the year and who you ask. But nowadays closer to 10%.

Roughly 30% of methane emissions come from bacteria in wetlands. The bacteria produce the most methane at 37-45ºC so the current trend of increasing temperatures could increase methane emissions.

Although currently neither a source nor a sink, methane hydrates are by far the largest store of methane on the planet and account for 53% of all fossil fuels on earth. An increase in temperature could cause large parts of these deposits to be released into the atmosphere as the arctic permafrost melts.

Further reading: