The planet’s forests have dwindled by 3% − equivalent almost to the land area of South Africa − in the last 25 years, according to a newassessment by the UN Food and Agriculture Organisation.

While the planet continues to lose its forests – albeit at a slower rate – through felling, burning or being turned into farmland, another UN study predicts that the economic cost of degraded agricultural land in the form of lost ecosystem services now amounts to up to US$10 trillion a year.

Within 10 years, 50 million people could have been forced to abandon their homes and livelihoods to become migrants. If all those people were assembled in one place, they would constitute the planet’s 28th biggest nation in terms of population.

Increasing levels

Forest loss and farmland degradation are both part of climate change accountancy. The rise in greenhouse gases is in part linked to the loss of forest cover to soak up the carbon dioxide released by the burning of fossil fuels.

But increasing levels of heat and drought are likely to accompany climate change, increasing the area of desert or land too arid to support life and industry.

So in losing forest, and in watching farmland become saline because of over-irrigation, or exhausted by intensive cultivation or overgrazing, or simply increasingly too arid to support vegetation, humans are witnessing the loss of all sorts of valuable services not normally recorded by accountants.

Ideas such as “natural capital” and ecosystem services are attempts to place a practical value on things that nature normally delivers for free.