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This process also generates byproducts that the cow’s body does not take up, such as carbon dioxide and hydrogen. Methane-producing microbes, called methanogens, use these compounds to form methane, which the cow’s body expels.

In that work, we showed that supplementing dairy cows’ feed with about 10 ounces of seaweed a day reduced methane emissions by up to 67%. However, the cattle that ate this relatively large quantity of seaweed consumed less feed. This reduced their milk production – a clear drawback for dairy farmers.

We wanted to know whether the seaweed was stable when stored for up to three years; whether microbes that produce methane in cows’ stomachs could adapt to the seaweed, making it ineffective; and whether the type of diet that the cows ate changed the seaweed’s effectiveness in reducing methane emissions. And we used less seaweed than in our 2019 study.

As we expected, the steers released a lot more hydrogen – up to 750% more, mostly from their mouths – as their systems produced less methane. Hydrogen has minimal impact on the environment.

We also found that seaweed that had been stored in a freezer for three years maintained its effectiveness, and that microbes in the cows’ digestive systems did not adapt to the seaweed in ways that neutralized its effects.

For example, we calculate that a producer finishing 1,000 head of beef cattle – that is, feeding them a high-energy diet to grow and add muscle – could reduce feed costs by US$40,320 to $87,320 depending on how much seaweed the cattle consumed.

We don’t know for certain why feeding cattle seaweed supplements helped them convert more of their diet to weight gain. However, previous research has suggested that some rumen microorganisms can use hydrogen that is no longer going into methane production to generate energy-dense nutrients that the cow can then use for added growth.

Commercializing seaweed as a cattle feed additive would involve many steps. First, scientists would need to develop aquaculture techniques for producing seaweed on a large scale, either in the ocean or in tanks on land.

This is not the first time Legates has been involved in a climate controversy. In 2015, Legates was included in a congressman's request for details on grants and support provided to those who have testified in Congress on the issue of human-caused global warming.

Before that, Legates was directed by then-Gov. Ruth Ann Minner in 2007 to stop using his state climatologist title in statements challenging climate change science after he co-wrote a legal brief opposing federal regulation of greenhouse gases after Delaware joined in a multistate lawsuit pressing for federal action.

“Your views, as I understand them, are not aligned with those of my administration,” Minner said.

He stepped down as state climatologist in 2011.