How many square kms of land are currently being used for agricultural production?

Question

Is this a rising or falling trend and how does it reflect the upper limits of potential production?

Answer 1

One source of info is wikipedia. You can see what is there under agriculture but you may have to look up individual regions and get their statistics and add them all up. Below is a link for world statistics going back more than 50 years, and covering a huge number of topics.

Answer 2

Based on figures form the World Food and Agriculture Organization, there is a total of 1,230,000,000 Hectares or about 4,747,000 square miles of arable land in the world, about 8% of the total land area.