If we are to keep future temperatures from getting far outside that range, humanity will be forced to reduce fossil fuel emissions to zero by 2050. Halving our emissions is not good enough: we need to get down to zero to stay under the 2 C target that scientists and policy makers have identified as the limit beyond which global warming becomes dangerous.
Many scenarios have been proposed to get us there. Some of these involve rapid deployment of solar and wind power in conjunction with significant reductions in the amount of energy we consume.
However, many of the economists and experts who have developed scenarios for the Intergovernmental Panel on Climate Change (IPCC) believe that the only way to achieve the two-degree goal in a growing world economy is to invest in large-scale carbon capture and storage (CCS) projects. These technologies capture carbon dioxide from the exhausts of power stations and industrial plants and then permanently store it, usually by injecting it into underground rock layers.
Even with massive deployment of CCS over coming decades, most scenarios modeled by the IPCC overshoot the carbon budget and require that in the latter part of the century, we actually take more carbon out of the atmosphere than we put into it. Climate expert Kevin Anderson of the Tyndall Centre for Climate Change Research at the University of Manchester recently reported in Nature Geoscience that, of the 400 IPCC emissions scenarios used in the 2014 Working Group report to keep warming below two degrees, some 344 require the deployment of negative emissions technologies after 2050. The other 56 models assumed that we would start rapidly reducing emissions in 2010 (which, of course, did not happen). In other words, negative emissions are required in all of the IPCC scenarios that are still current.
One favoured negative emissions technology is bioenergy with carbon capture and storage (BECCS). This involves burning biomass – such as wood pellets – in power stations, then capturing the carbon dioxide and burying it deep in the earth. The technology has not yet been demonstrated at an industrial scale. Using the large amounts of bioenergy envisioned in such scenarios will place huge demands on land use and will conflict with agriculture and biodiversity needs.
Even the relatively small use of biofuels in Europe that relies on North American wood pellets is already causing land-use impacts in the southeastern United States (John Upton of Climate Central has recently published an excellent report on this titled Pulp Fiction). The European demand for wood pellets is driven by an EU policy that deems biomass use to be carbon-neutral. However, evidence is mounting that this is not the case. It takes energy to collect, process and transport the pellets. It also matters whether the wood used is waste that would otherwise be left to rot or burn, or whether it is taken from mature trees. And, of course, it can take many decades for a forest to regrow to its previous size.
Six thousand feet under
The scale required of CCS and BECCS in most two-degree emissions scenarios is staggering. Humans consume vast amounts of fossil fuels at present, and the basic chemistry of combustion, which takes up oxygen, means that the mass of carbon dioxide produced is 2.8-3.7 times the mass of the fossil fuel itself. To get to zero emissions using CCS requires that three times or more matter be put back into the ground than was originally taken out.
Read original article at The Quest for CCS
No comments:
Post a Comment