Sparing half the Earth for nature while still feeding humanity

By Mark Lynas

August 29, 2018

Setting aside half the planet’s most biodiverse land area for nature conservation will not be possible unless major efforts are made to intensify agriculture, a new scientific study suggests.

The study makes clear that unless crop yields grow very rapidly in order to offset food supply losses resulting from allowing farmland to revert back to nature, it will likely not be possible to meet the “Half-Earth” target advocated by many leading conservationists while still feeding the current human population of more than 7 billion people.

The paper, published in the peer-reviewed journal Nature Sustainability, is titled “The challenge of feeding the world while conserving half the planet.” The study assesses different scenarios for meeting the half Earth target. At the global scale, setting aside half the planet’s land surface for nature appears relatively easy, as agriculture and human settlements currently cover 37 percent of ice-free land. Much of the remainder is relatively barren, however, being tundra, mountains or deserts.

Protecting the most valuable ecoregions, on the other hand, which most conservationists advocate in order to slow the loss of global biodiversity, requires some heavy trade-offs because it means giving up useful or productive land in more densely-populated areas.

If the nature-sparing approach aims to create contiguous reserves — important for the survival of many megafauna, and for biological connectivity — across 50 percent of each ecoregion, this implies the global loss of ~31 percent of cropland, ~45 percent of pasture, ~25 percent of non-food calories and ~29 percent of food calories, the researchers calculate.

In other words, all other things remaining equal, sparing half the planet for nature would mean wiping out a third of humanity’s food supply.

The amount of food calories lost depends to a large extent on assumptions made in the model. If a “nature sharing” approach is adopted, with efforts to adopt more wildlife-friendly farming practices instead of excluding agriculture altogether from nature reserves, more food can be produced.

The lead author is post-doctoral researcher Zia Mehrabi at the University of British Columbia (UBC) in Canada, while co-authors are geographer Erle Ellis at the University of Maryland and Mehrabi’s UBC colleague, Navin Ramankutty.

They write: “Simply put, the trade-offs between agriculture and Half-Earth will be much lower if landscapes are allowed to remain as mosaics of shared land uses, and will be much higher if large contiguous areas are given back, as may be required for the conservation of some species, such as megafauna.”

So how can this conundrum be solved, and nature spared without condemning a third of the planet’s human population to starvation?

The authors point out that “potentially massive calorie losses would need to be offset by massive increases in the intensity of food production” — in the order of 45-70 percent above today’s productivity levels — in order for the Half-Earth strategy to work without disastrous impacts on food security, which would disproportionately affect the world’s poor.

The paper also supports the efforts of vegans and those adopting animal-free diets by pointing out that 36 percent of crop calories are currently fed to animals. If diverted to direct human consumption, far more land could be spared for nature without adversely harming food security.

A 2013 study by Cassidy et al in the journal Environmental Research Letters found that “growing food exclusively for direct human consumption could, in principle, increase available food calories by as much as 70 percent.” In other words, an entirely vegan planet should also be able to spare half its most biodiverse ecoregions for nature and reverse biodiversity losses.

The current challenge is even greater, Mehrabi et al point out, because future increases in human population and consumption are not factored into the analysis, which looks only at today’s population level. Therefore “our findings should be seen as conservative with respect to Half-Earth’s potential negative impacts on agriculture,” they write.