The new study is published in the journal Nature Climate Change by a team of 32 authors from 24 institutions in eight countries.
Carbon dioxide emissions from industrial society have driven a huge growth in trees and other plants.
A new study says that if the extra green leaves prompted by rising CO2 levels were laid in a carpet, it would cover twice the continental USA.
Climate sceptics argue the findings show that the extra CO2 is actually benefiting the planet.
But the researchers say the fertilisation effect diminishes over time.
They warn the positives of CO2 are likely to be outweighed by the negatives.
The authors note that the beneficial aspect of CO2 fertilisation have previously been cited by contrarians to argue that carbon emissions need not be reduced.
Co-author Dr Philippe Ciais, from the Laboratory of Climate and Environmental Sciences in Gif-sur‑Yvette, France (also an IPCC author), said: “The fallacy of the contrarian argument is two-fold. First, the many negative aspects of climate change are not acknowledged.
“Second, studies have shown that plants acclimatise to rising CO2 concentration and the fertilisation effect diminishes over time.” Future growth is also limited by other factors, such as lack of water or nutrients.
The scientists say several factors play a part in the plant boom, including climate change (8%), more nitrogen in the environment (9%), and shifts in land management (4%).
But the main factor, they say, is plants using extra CO2 from human society to fertilise their growth (70%).
Harnessing energy from the sun, green leaves grow by using CO2, water, and nutrients from soil.