At the Paris climate conference a surprise result was for the world to aim to hold “the increase in … temperature to well below 2°C … and to pursue efforts to limit the temperature increase to 1.5°C”.
Fred Pearce in the New Scientist now takes a look at what some are saying needs to be done.
It is generally agreed that attaining 1.5°C will involve overshoot and negative emissions, sucking CO2 out of the air. The idea according to Joeri Rogelj and others is that we should limit emissions to 800 GT of CO2 by 2050 when we should reach net zero emissions. Then we should suck 500 Gt of CO2 out of the air from 2050 to 2100.
Pearce says a study looked at several ways to chemically absorb CO2 directly from the air. They are all prohibitively expensive, costing about $270 trillion and consuming a quarter of the world’s energy supply.
The easy way would be to plant lots of trees. But planting enough to soak up 500 Gt of CO2 over 50 years would require 10 million square kilometres, an area as big as the United States. It’s simply not possible.
The article then looks at three technologies that might together achieve the aim.
The first is bioenergy with carbon capture and storage (BECCS), where trees are grown then burnt to produce power. The carbon emitted is captured and buried. We have the capacity to bury 500 GT of CO2 about 20 times over in former gas and oil formations or in saline aquifers, if you think that’s a good idea. Problem is compressing and transporting the stuff. Also 500 Gt would still require somewhere between 3.8 and 7 million square kilometres of land.
Pete Smith of the University of Aberdeen, UK, who headed a global study of negative emissions options published during the Paris conference thinks BECCS is the most promising option.
Pressing on, Pearce identifies biochar as a possibility, where agricultural waste like straw, manure and unused food is been pyrolysed to charcoal, ground up and ploughed into the soil. Smith reckons biochar could provide up to 125 Gt of the negative CO2 required.
The third technology is the cultivation of microalgae, already undertaken in Australia, for example, to produce “biodiesel, new algae-based food, animal feed and nutraceuticals”.
Brian Walsh at the International Institute for Applied Systems Analysis (IIASA), the same place where Rogelj hangs out, reckons microalgae could be good for 25 Gt of CO2 a year. Microalgae can be grown on non-arable land using fresh, brackish or saline water, so it doesn’t compete with agriculture for land.
By mid-century, there could be up to 50 million hectares growing billions of tonnes of biomass and feeding 10 per cent of the world’s livestock.
Whether these technologies will work or not I was disappointed by the climate science assumptions. The strategies are based on the notion that limiting emissions to 430 ppm will limit temperatures to an increase of 2°C. In the post The game is up in June 2014 I pointed out that in terms of CO2 equivalence, counting all greenhouse gases, we were already at 480 ppm.
In that post I quoted David Spratt:
- We have to come to terms with two key facts: practically speaking, there is no longer a “carbon budget” for burning fossil fuels while still achieving a two-degree Celsius (2°C) future; and the 2°C cap is now known to be dangerously too high.(My bold)
Rather than go over it all I’ve listed a number of related posts at the end of The folly of two degrees.
I’ve been saying that for a safe climate we need zero net emissions by 2030 and need to take CO2 out of the atmosphere to get concentrations below 350 CO2e ppm by 2050.
David Spratt has now published a post at Climate Code Red which asks how fast we need to go if we take Paris and 1.5°C seriously. They say:
- Justin Gillis of the New York Times reported Sunday that limiting warming to 1.5°C would require global industrial greenhouse gas emissions to come to an end by 2030. Climate researcher Glenn Peters has projected that meeting the 1.5C target would require a global fossil fuel phase-out between 2025 and 2030, as well as a large-scale effort to remove excess carbon dioxide from the atmosphere. Similarly, a group of scientists writing in The Hindu found that developed countries such as the U.S. would need to reach zero emissions in “the next 5-10 years” for a 50 to 66 percent chance of limiting warming to 1.5°C.