Man-made carbon emissions amount to over 40 billion metric tons annually, according to a quick Google search. Worldwide terrestrial plant carbon exchange amounts to less than 2.5% of the CO2 humans release, if plants take in 1 billion tons per year.

From the perspective of averting climate change it is indeed very small.

The article linked by 8bitsrule says:

A team of scientists led by Cornell University, with support from the Department of Energy’s Oak Ridge National Laboratory, used new models and measurements to assess GPP from the land at 157 petagrams of carbon per year, up from an estimate of 120 petagrams established 40 years ago and currently used in most estimates of Earth’s carbon cycle.

Whether 157 billion tons or 120 billion tons, these numbers are large compared to anthropogenic releases. Of course most of this carbon is quickly cycled back out from land plants due to animals/bacteria/fungi consuming the biomass produced by land plants.

You still need to turn incredible amounts of biomass into charcoal or other stable forms of carbon to make a dent in atmospheric co2. It would take decades of hard work on gigantic scales to unburn and bury the fossil fuels we used.

That's the pay-off of our 150-year rush to monetize as much of the Earth's natural resources as possible -- while making stringent efforts to keep quiet knowledge - or suppress any efforts - to utilize the benefits of free solar energy.

Having polluted and despoiled much of the biosphere, of course we'll be donating our supposed wisdom and that hard work to the future generations that will enjoy the fruits of our labors and entreasurement.