As usual Greenpeace is being sniffy about NETs. https://unearthed.greenpeace.org/2018/10/08/ipcc-climate-change-carbon-capture/
Of course in a sense they are right. NETs are unproven at scale and very uncertain as to cost. It would be better to cut emissions hard now than to continue emitting CO2 that will be removed from the air later. Prevention is better than cure and so on.
In a sense. But it's almost certain that we won't cut emissions hard enough so we will have to capture CO2 from the air. You have only to look at the pathways in the recent IPCC report on staying below 1.5 degrees to see that they represent, and are explicitly stated to require, an almost unprecedented economic transformation.
We have been making this argument for 20 years. We have stressed the costs of inaction, the human benefits of mitigation, the moral case to reverse the harm we have done. And emissions have risen. Actions have been inadequate at best. Need I mention Putin, bin Salman and Trump? Perhaps not.
We are imposing large economic costs, the destruction of much of the natural world and perhaps a high death rate on future generations - now probably in our grandchildren's lives - to avoid cost and inconvenience to ourselves. This is a serious moral failure on the part of almost all governments, and indirectly of us. But that is now the baseline.
We cannot now avoid presenting future generations with the bill for NETs. The best we can do NOW is to invest in the technologies needed, starting with CCS and a selection of NETs.
So where are we with NETs? Greenpeace cites an authoritative report on NETs which says that NETs "offer only limited realistic potential to remove carbon from the atmosphere and not at the scale envisaged in some climate scenarios".
The reasons for this conclusion are not clear. The report also notes "A recent study (Marcucci et al., 2017) concluded that ....substantial deployment of (direct air capture] (several gigatonnes of carbon removals per year by 2100) would allow these targets to be met." The big issue is simply cost. DAC will cost a lot more per ton than CCS used on a power station or cement works but the costs are highly uncertain, being quoted as $30-$1,000 per ton CO2!
There are still many technical options. The sooner we put serious money into R&D and pilot plants the better!