Paper lays out new way to think about carbon capture and land use

By Hank Schultz contact

- Last updated on GMT

Paul Grasset / eyeEM / Getty Images
Paul Grasset / eyeEM / Getty Images
A paper publishing today in Nature posits a new paradigm for measuring the carbon capture potential of land uses. Deciding whether a plot is best used for supporting a forest or if agriculture is a more appropriate use requires this baseline calculation, they argue.

The research letter, titled “Assessing the efficiency of changes in land use for mitigating climate change”​ was written by researchers from Princeton, and institutions in Sweden, Germany and France, and will be available this afternoon.  It argues for a new factor in the equation for land use, that being the potential of the land itself for the capture of carbon. The analysis is aimed solely at carbon capture and its role in restricting greenhouse gas emissions.  The values of biodiversity that a given hectare of land might represent need to be analyzed separately, they said. 

With food demand rising, how best to capture carbon?

Using a complicated economic metric, the authors, led by Princeton researcher Tim Searchinger, PhD, measured the carbon capture potential of various uses of land.  It’s important to remember, they noted, that global food demand will rise by as much as 50% in the coming decades.  Adhering to a line that land must in every instance possible be kept in its pristine condition might not be realistic, they said.

“Intuitively, if a hectare of land produces maize well and forest poorly, maize should be the more efficient use of land, and vice versa,”​ the authors wrote.

The authors developed an index that can be applied to various types of land uses, including growing common crops and raising meat animals. 

“We find that these choices can have much greater implications for the climate than previously understood because standard methods for evaluating the effects of land useon greenhouse gas emissions systematically underestimate the opportunity of land to store carbon if it is not used for agriculture,”​ they maintained.

Embedded CO2

The paper includes tables that represent the embedded CO2 in the production of various agricultural commodities.  Maize, rice, wheat soybeans and pulses come out well on this measure, both in terms of kilograms of CO2 per kilocalorie and per kilogram of protein produced.  Beef does not.  According to the authors’ analysis, 23 kilos of CO2 are emitted to produce each kilo of wheat protein.  The figure for beef is 1,250 kg of CO2.

Beef is particularly inefficient in several ways.  It’s a big, relatively slow growing animal that needs a lot of feed. And cows typically have only one calf at a time.  Pork, on the other hand, requires much less in the way of land area and sows can have large litters on a fairly frequent basis.  And poultry is more efficient still.

So diet choices are a key element in the climate change debate, the authors argue.  They estimate a vegan diet costs about 2 tons of CO2 emitted per year per capita.  The figure for the baseline Westernized diet featuring plentiful amounts of beef and dairy products is about 9 tons.

Contribution of dietary supplement production

The production of dietary supplement ingredients amounts to not even a rounding error in that debate.  But Searchinger said that in the future, the impact of land use for every hectare will need to be examined if natural carbon capture is to be optimized.

“In a world where there is going to be demand for beef, or corn, or turmeric, as long as that land use meets that demand, we argue you should be producing it as efficiently as possible,” ​he said.

But for the question of carbon capture, that might not always be a bad thing. For example, the paper includes a surprising analysis of grazing areas cleared from former forest land in the Atlantic forest zone of Brazil.  The authors’ analysis led them to conclude that using the best intensive grazing practices, which produce more kilos of beef protein per hectare, could actually be a better use for carbon capture.

“We looked at what would be the benefit of replanting forest in those areas as opposed to using them to produce meat more efficiently.  We found that if you could graze those areas well, you would be better off,” ​he said.

Promise of algae

Algae is one raw material stream that is an up and coming player in the supply of dietary supplement and food ingredients.  It’s a production mode whose proponents often tout its sustainability bona fides.  Searchinger said that while the sector is still tiny compared to other agricultural sectors, he believes it holds promise.

“We are enthusiastic about algae as a source of animal feed, particularly for the aquaculture industry, or as a source of high quality oil or protein,” ​he said.

Growing demand for commodities

Searchinger said a key part of the debate is to keep in mind that the demand for certain commodities, such as meat protein, staple crops or vegetable oil, is not going to go away but is only likely to increase. It’s highly unlikely that hectares of land now devoted to these uses will be returned to their natural states.  While he and his co authors believe their method will give a more accurate baseline to make policy decisions, it should not be used a panacea to greenwash in effect all land use decisions.

“Where some conversion of natural vegetation to agriculture is inevitable, such as for oil palm in Southeast Asiaor for staple foods in Africa, our index could help to determine the most efficient lands and crops to choose. For policy reasons, however, we advise great caution in using the index to justify conversion of native vegetation based on claims of high food yields,” ​they wrote.

Source: Nature
“Assessing the efficiency of changes in land use for mitigating climate change” 

Authors: Searchinger TD, et al. 

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