By enriching the carbon-dioxide content of the atmosphere from its impoverished pre-industrial levels, human beings have increased the productivity of the entire biosphere - so much so that roughly one out of every seven living things on the planet owes its existence to the marvelous improvement in nature that humans have effected.
Putting aside for the moment the question of whether human industrial CO2 emissions are having an effect on climate, it is quite clear that they are raising atmospheric CO2 levels. As a result, they are having a strong and markedly positive effect on plant growth worldwide. There is no doubt about this.