Greenhouse gas emission cuts must be at least 20 per cent deeper than pledged under the Paris climate accord or the world will have to begin the costly direct removal of atmospheric carbon to avoid dangerous climate change, a new study argues.

The Germany-based researchers examined the action needed if nations failed to deliver greater carbon curbs by 2030 but still kept global warming to under 2 degrees, compared with pre-industrial levels.

"Each tonne of CO2 we don't emit, we don't have to remove from the atmosphere afterwards in an expensive and strenuous way," said Jessica Strefler from the Potsdam Institute for Climate Impact Research and the lead author of the paper published on Thursday in Environmental Research Letters.

Computer simulations indicate an industry "comparable" to the size of the global petroleum sector, and able to capture and store at least 5 billion tonnes of C02 annually, will be required - and possibly much larger.

Such carbon removal - whether by reafforestation ($31 per tonne) or direct air capture ($652 per tonne) - would be costly.  "One way of paying for these technologies is imposing a price on carbon emissions and using these revenues to pay for carbon dioxide removal," Dr Strefler told Fairfax Media.