The dream of tackling climate change with biofuels has been tarnished by the rush to produce them on land. Not only are there serious environmental costs, including deforestation, water use, production of greenhouse gases, and energy-efficiency limitations, but there are rising concerns about the effects on the world’s poor. Already the price of food is being driven up as land is taken away from food production, increasing the cost of food and nutrition for those who can least afford it. It is curious then that, bar a brief mention in a recent paper on sustainable biofuels by the UK-based Royal Society, the potential for biomass production at sea is largely ignored.
A vast resource
The oceans are the largest active carbon sink on the planet, covering more than 70 per cent of its surface area, and are predicted to grow as sea levels rise. Our seas also receive a larger proportion of the world’s sunshine than land does, particularly in the tropical and subtropical belt where land is more scarce. To agriculturalists, the oceans are vast and grossly underused fields well-provided with sunlight and water.
The full potential for sea cultivation (mariculture) has only recently been recognised. The ‘blue revolution’ of freshwater aquaculture and mariculture is growing exponentially.
Statistics from the UN Food and Agriculture Organization show mariculture is strongest in Asia and the Pacific. While aquaculture production has risen sixty-fold since the early 1950s (to 59.4 million tonnes in 2004) and is worth around US$70 billion, 91.5 per cent of this was produced in Asia and the Pacific.
Similarly, 99.8 per cent of the eight million or so tonnes of seaweed produced each year, with a market of nearly US$6 billion, come from Asia and the Pacific, primarily China, Japan and Korea.
Seaweeds as fuel
Until now, seaweed has been valued mainly as food, but also as fertiliser, animal feed, and recently for a growing phycocolloid industry producing algin, agar and carrageenan. But it could also be a major fuel.
Macro-algae (seaweeds) are cultivated at sea, mainly by simply tying them to anchored floating lines. Seaweeds do not require soil, and are already provided with all the water they need, a major advantage over land production of biofuels since water is the most limiting factor for most agricultural expansion, especially with climate change.
One concern is that harvesting massive amounts of naturally occurring seaweed for bioenergy could have comparable effects on atmospheric carbon dioxide and habitat loss or fragmentation as large-scale deforestation. But cultivation is a different matter.
In Costa Rica and Japan, seaweed farming has been re-established to produce energy. It can quickly yield large amounts of carbon-neutral biomass, which can be burnt to generate electricity. High-value compounds — including some for other biofuels — can be extracted beforehand.
We have calculated that less than three per cent of the world’s oceans — that’s about 20 per cent of the land area currently used in agriculture — would be needed to fully substitute for fossil fuels. A small fraction of that sea area would be enough to fully substitute for biofuel production on land.
As with land-produced biofuels, the contribution to carbon dioxide reduction would come from cutting net carbon dioxide additions via equivalent decreases in fossil fuel combustion. This happens because biofuels — fuels derived from recent photosynthesis — are basically carbon neutral because all carbon released by burning has recently been taken from the atmosphere.
In contrast, fossil fuels come from ancient photosynthesis, thus the carbon released by burning had been stored for ages and thus represents a net addition into the atmosphere.
The main input needed for the large-scale farming this would require is nutrients — because large quantities of them will be removed at harvest. Common agricultural fertilisation — costly and energy consuming — could add large amounts of nutrients to the oceans, with unknown results.
But there is a great and grossly misused nutritional source on hand: domestic wastewaters or the product after their treatment. Growing large seaweed fields for energy using nutrients from wastewater could be an economically-sound use for the millions of tonnes of untreated wastewater dumped daily into our seas worldwide — and the seaweed helps clean it up in the process.
This idea has been tested successfully using human wastewater in experiments at US institutions, including the Woods Hole Oceanographic Institution and the Harbor Branch Oceanographic Institution.
As with agriculture, considering that seaweed production is economical for food and other products, it follows that at least some of the options should also be economical for biofuels and bioenergy. However, the analogy with agriculture does not stop there, and a careless farming of the seas could be as damaging as careless agriculture.
But the greatest spin-off from switching biofuels production to the oceans would be the return of land to food production, making food and nutrition more easily available to the world’s poor.