I had a couple of comments on my previous post suggesting some more information on the standard view of land use would be helpful for context.
As noted there, about 12% of the world’s ice-free land surface is currently used for arable crops, and there isn’t that much practical scope for increasing this. However, a second caution for not doing so comes from the Planetary Boundaries group. They set a boundary at 15% for the amount of crop-land, giving the following reason:
Land is converted to human use all over the planet. Forests, wetlands and other vegetation types have primarily been converted to agricultural land. This land-use change is one driving force behind the serious reductions in biodiversity, and it has impacts on water flows and on the biogeochemical cycling of carbon, nitrogen and phosphorus and other important elements.
The effects of converting marginal land are likely to be worse than average on these measures. The need for irrigation, fertiliser, or probably both, will disrupt local cycles even more.
A second observation is that our diet has a large impact on land use. 30% of land is used to graze cattle, and much of our crops also go to feed livestock. A 2010 UNEP report suggests that the only likely way we will be able to feed ourselves by 2050 is by going predominantly vegan. CAT’s Zero Carbon Britain report puts it a different way: in their vision of the future a change in the UK diet means that the land used for agriculture can be reduced from 78% to about a third, freeing up land for other purposes: a doubling of our forest area, and land to grow biofuels.
But I’ve left the most concerning statistic until last. Since about 1950, a third of world arable land has become degraded, some to the point when it is of no longer fit for anything, and has the side-effect of increasing the frequency and severity of floods. George Monbiot this week looks at the position in the UK: a combination of short-term views and inapppropriate practices have meant that soil structure has broken down in large parts of SW England, for instance. And draft EU protection to protect soil quality was lobbied against for years and has now been abandoned.