I was sure, that we have lots of buildings, but in reality, we have less than 0,7% of the land area covered with them. However, combining buildings and cropland, we changed almost 22% of the land area. Is that a lot? Subjective question!

The real percentage might be higher because I did not count grasslands used as pastures (which might have been forests before becoming grasslands), changing inland waters (shrinking Sea of Azov for example), growing deserts or barren land due to human activities. Let’s say, that those 22 percent is an obvious change even an alien would immediately identify with humans.

What: Land Cover according to European Spatial Agency Climate Change Initiative annual land cover maps, which were produced by the Université catholique de Louvain.
When: 2015
Where: Land area of the whole planet including inland water.
Source: FAO