We Absolutely Must Suck CO2 from the Air, but We Must Be Very Careful
by Michael Marshall
Sept. 12, 2018 – A major report published today hammers home a point that most people thinking about climate change have long suspected.  Cutting our greenhouse gas (GHG) emissions isn't going to be enough to stop dangerous climate change.  We are also going to have to actively remove GHGs from the air, on an industrial scale.
The challenge will be to do this without accidentally causing an ecological catastrophe as a side effect.
The report, Greenhouse Gas Removal, was jointly produced by the Royal Society and the Royal Academy of Engineering.  It 1st explains that, in order to limit global warming to 1.5 or 2°C - the targets set out in the 2015 Paris Agreement - human society must rapidly cut its GHG emissions over the next few decades, so that we are emitting zero new GHGs by the 2nd half of this century.  That is going to be very hard.  That’s partly because some sectors of the economy, such as farming, are difficult to entirely decarbonize; and partly because we have left it till so late to start making cuts, instead of beginning in the 1980s and 1990s, once it was clear that climate change posed a major threat.
So instead, we must game the system, by sucking CO2 out of the air and trapping it somewhere.  In this way, we can make up for our own tardiness.
The bulk of the report is a discussion of the many CO2 removal technologies.  Much of the coverage has focused on one recommendation: that the UK plant a lot more trees, which will incorporate CO2 into their bodies and lock it up for many decades.  This is a good idea for many reasons: more forests will also help reduce the risk of flooding and provide habitat for other species.  But it will not be enough by itself.  And planting forests is not a good idea for everyone.  In particular, planting forests in snowy regions would probably be counter-productive, because the dark trees would absorb more of the Sun's heat than the white snow - leading to more warming.
The fact is that we will need many of these technologies, not just one, if we are to remove enough CO2.  That is where the real problem arises, because these technologies bring their own threats.
Take BECCS, which stands for "bioenergy with carbon capture and storage".  The idea is to grow a biofuel crop, then burn it to make electricity.  The CO2 emission from this power plant then need to be captured and stored somewhere - perhaps deep underground.
Our only "plan" (if you can call it that) for avoiding dangerous climate change relies heavily on BECCS.  Climate modelers routinely use a set of 4 scenarios to simulate what might happen this century.  One of them, called RCP2.5, was designed to limit global warming to 1°C by 2100.  But it only achieves this by assuming that BECCS is used on an enormous scale.
The problem there is that growing all those biofuel crops will take up a lot of land.  To some extent, we could chip into the land currently used for growing food, by finding better ways to farm.  But there are presumably limits, so we will end up farming on even more land than we already are.  That means destroying more wilderness where threatened species live.
In other words, we could solve the climate change problem, but at the cost of exacerbating the biodiversity crisis.  This is a nasty trade-off to have to consider.  Rapid climate change is definitely dangerous to human civilization, but so is degrading even more of the ecosystems upon which we rely.  Nobody really knows how much biodiversity can be lost before ecosystems start collapsing, but we seem to have caused significant damage to 60% of the land-based ecosystem.  Maybe the biosphere could tolerate all that BECCS if we dialed back on all the other things we're doing to nature, but it doesn't seem like a safe experiment to try.
The lesson is that we're going to have to find ways to tackle climate change and the biodiversity crisis together.  Otherwise, we may leap gaily from a frying pan and land smack bang in the middle of a fire.
www.forbes.com/sites/michaelmarshalleurope/2018/09/12/we-absolutely-need-to-suck-carbon-dioxide-out-of-the-air-but-were-going-to-have-to-be-very-careful/#2e98500b468d