Can we limit climate change by switching to renewables or are other carbon reduction measures also needed? The first and most obvious point is that, despite the rapid expansion of renewables, we are not doing very well globally on carbon emissions.

After remaining flat for three years, total global CO 2 emissions in 2017 rose by 1.4%, dashing hopes that they had peaked. Indeed, energy sector carbon emissions will rise in 2018, according to Fatih Birol, the head of the International Energy Agency (IEA), who warned that the aim of keeping global warming at “well below“ 2 °C and at 1.5 °C if possible was unlikely to be achieved: “the chances of meeting such ambitious targets, in my view, are becoming weaker and weaker every year, every month“.

That may be too pessimistic, given that there are scenarios suggesting that renewables can be ramped up much faster so that emissions will fall. Indeed, the International Renewable Energy Agency is looking to renewables to supply maybe 85% of global electricity and two thirds of all energy by 2050. However, that still means that fossil energy continues to play a major role – in fact, an expanding one, since energy demand is rising in most places, often led by demand in the transport sector. So emissions may continue to rise. Carbon capture and storage (CCS), which the IEA has in the past seen as a key way to slow emissions, has so far only developed very slowly, and of course CCS could not help (directly) with emissions from fossil-fuelled vehicles.

Demanding efficiency

It is conceivable that renewables could expand much faster, to supply near 100% of global electricity by 2050, or perhaps even all global energy so avoiding emissions in all sectors. That would require a massive effort, but it would be made easier if it was possible to cut energy demand significantly. Most of the high renewable scenarios assume that demand is cut, but some say much more can and should be done, including the IEA, which says that “the right efficiency policies could…enable the world to achieve more than 40% of the emissions cuts needed to reach its climate goals without requiring new technology“. Certainly, there are improvement in energy use efficiency and fossil fuel substitution that can lead to significant cash and carbon saving – enough, some say, to halt overall energy demand growth or even reduce global energy demand to 40% lower than today.

That is all good news and may help us to keep below 2 °C, but it’s far from certain to happen. So far, only 16 of the 197 countries that signed the Paris Climate Agreement have defined national climate action plans ambitious enough to meet their carbon reduction pledges. What’s more, even if it was all done and done instantly, it would not reduce the cumulative level of CO 2 in the air, which will stay high for some while, whatever we do about current and future energy use. That includes nuclear power, which in any case is more or less stalled globally and unlikely to grow for a while, if at all. So there is a risk of carbon over-shoot and major climate impacts. That is why there are calls for the rapid adoption of negative-emission technologies (NETs), to extract CO 2 from the air.

Negative positives?

It seems like a desperate measure and some fear that it is just a way to compensate for continued fossil fuel use. After all, you could equally say that efforts to get renewables going faster should be made. But if you don’t think renewables and energy saving can expand fast enough and don’t like the prospects of massive nuclear expansion, then NETs may be seen as the only way to avoid carbon over-shoot. That certainly is what the Intergovernmental Panel on Climate Change has suggested may be needed to hold the temperature increase to 1.5 °C: “Global net human-caused emissions of carbon dioxide (CO 2 ) would need to fall by about 45% from 2010 levels by 2030, reaching ‘net zero’ around 2050. This means that any remaining emissions would need to be balanced by removing CO 2 from the air.” It is also what the UK Energy Research Centre (UKERC) says may be needed; to meet climate targets, global net carbon-dioxide emissions must become negative between 2060 and 2070 in all the scenarios it looked at. So NETs are vital – and urgent.

If we are really serious about moving towards 1.5 °C then any further delay is not a realistic option UKERC

However, there is a range of NETs. Which ones should be used? The most talked about carbon negative option is biomass energy with carbon capture and storage (BECCS), with the CO 2 produced when biomass is burnt being captured, but there are others, including direct air capture (DAC) — absorbing CO 2 chemically. In both cases, the captured CO 2 is stored geologically, but in the case of DAC, energy is needed to power the extraction process, whereas with BECCS you get energy production. The disadvantage of BECCS is that you need large areas of biomass plantation, whereas DAC plants can be sited anywhere there is room and a power supply. However, both options assume that CCS is viable on a large scale, which is far from clear — many fossil CCS projects have been halted.

Nevertheless, assuming that the NETs route is tried, how much of each option might be needed? The UKERC’s modelling found that “when we compare the amount of NETs required in both the ‘well-below 2 °C’ and ‘towards 1.5 °C’ scenarios, then two things become clear. First, that a 2 °C target can be met with BECCS only, and second, that this is not the case for 1.5 °C, which requires about double the amount of negative emissions. In this instance, even with significant availability of biomass worldwide, substantial amounts of other NETs beyond BECCS will be required. These include direct air capture, afforestation and advanced weathering, and will need to be about enough to capture between 250–700 Gt CO 2 .”

The IPCC also put some numbers to what might be expected from what it calls carbon-dioxide removal (CDR) technologies: “In pathways limiting global warming to 1.5 °C with limited or no overshoot, BECCS deployment is projected to range from 0–1, 0–8, and 0–16 Gt CO 2 /yr in 2030, 2050 and 2100, respectively, while agriculture, forestry and land-use (AFOLU)-related CDR measures are projected to remove 0–5, 1–11, and 1–5 Gt CO 2 /yr in these years.” However, it added that “some pathways avoid BECCS deployment completely through demand-side measures and greater reliance on AFOLU-related CDR measures”.

That caveat reflects the view that there are other, arguably better, NETs/CDRs available, which don’t need CCS, including changed land use/farming practices and forestry — growing more trees. For most environmentalists these bio-options have more attractions than complex technology, and in the case of BECCS, vast biomass plantations, and, as I have noted in an earlier post, there have been studies making that case.

Whichever options are used, the UKERC insists that rapid action is needed on all fronts, including NETs and renewables, as well as demand reduction. It says it will all get harder if we delay: “delaying action always means that faster rates of emissions reductions are required, which may prove to be technically difficult to achieve and may result in a higher reliance on negative emissions later in the century. If we are really serious about moving towards 1.5 °C then any further delay is not a realistic option”.

In my next post, next year, after the seasonal break, I will look at how the UK Energy Technologies Institute sees the options for the future: there certainly are some choices to be made.