Another questionable NYT claim: "Humans are cultivating almost 40 percent of the land surface of the earth"

Damaging the Earth to Feed Its People - NYTimes.com

Humans are cultivating almost 40 percent of the land surface of the earth, and nearly a third of all the greenhouse gas emissions that are warming the planet comes from agriculture and forestry.
...
The director general, Thomas A. Lumpkin, told me that the real task at hand was not just to increase food output, but to make agriculture so productive that humanity could begin to restore some of what it has destroyed.

“We need to be really bold here,” he said in an interview. “It’s not just that agriculture needs to keep food prices reasonable. We need to find a way to make a dramatic contribution to the greenhouse-gas problem. We need to make farming so productive that we can get off half the agricultural land out there, so that we can return it to nature.”

If less than 10% of the Earth's land surface is arable, how are we currently cultivating nearly 40% of the land surface?

Arable land - Wikipedia, the free encyclopedia

In geography, arable land (from Latin arare, to plough) is an agricultural term, meaning land that can be used for growing crops...In 2008, the world's total arable land amounted to 13,805,153 km²

Area of Earth's Land Surface

Surface: Land surface 150,000,000 sq km