The scientists looked at the 'biogenic fluxes' of the three main greenhouse gases over the last three decades, and subtracted out emissions that existed in pre-industrial times.
These biogenic sources include gas emitted by plants, animals, and microbes, such as methane produced by wetlands, and nitrous oxide released by soil.
But the amounts of these gases have been changed by human activity, plus new sources created by sewage, fertilisers, and cattle.
The scientists added up all the biogenic emissions of carbon dioxide, methane, and nitrous oxide, then subtracted those that occurred naturally.
The study did not include gas emissions from fossil fuel burning or natural gas production.
The surprise finding in the report is that human impact on biogenic methane and nitrous oxide emissions far outweighs the impact on the uptake of carbon dioxide.
In other words, they say this so-called terrestrial biosphere is now contributing to climate change rather than mitigating climate change - and it's all because of human action.