Development of arable land is a problem, but our agricultural practices are a major one. I think shanev is speaking about the effects of modern agriculture on top soil. We should prioritise the _creation_ of soil. Instead, top soil is being degraded and then lost though erosion. There are other issues, such as the planting of monocultures, overuse of nitrogen fertilizers and so on.
As climate change brings us longer droughts and larger downpours, we should be farming in ways that build top soil for more resilient farmland.
(edit - adding link to http://www.fao.org/docrep/t0389e/t0389e02.htm)
