The Intergovernmental Panel on Climate Change has published a report – Global Warming of 1.5^oC – which has described the stark differences to humans and the planet between an average global temperature rise of 1.5^oC and one of 2.0^oC above pre-industrial levels. The starkest are in respect to the Arctic – the likelihood of an Arctic Ocean free of sea ice in summer would be once per century with global warming of 1.5°C, compared with at least once per decade with 2°C – and warm water corals, with 10% of coral surviving with global warming of 1.5°C, compared less than 1 percent with 2°C. However, there are also significant additional impacts to coastal and river flooding, small scale low-latitude fisheries, terrestrial ecosystems, heat-related morbidity and mortality, and crop yields. According to Debra Roberts, Co-Chair of IPCC Working Group II, the next few years “are probably the most important in our history” because the policy decisions and action made in the coming years will have a huge impact on how climate change is tackled. It is understood that it is the next 12 years that are identified as the most important. These are extremely strong words, and other periods in history quickly come to mind, but the claim is made with some justification. Global temperatures have risen by between 0.75 and 0.99^oC already since pre-industrial times (the reference is the average temperature between 1850-1900), meaning that there is only 0.51-0.75^oC remaining, with the global average temperature currently increasing by 0.1-0.3^oC per decade.

The report lays out four indicative possible pathways that could be followed to achieve the 1.5^oC, some with temporary “overshoots” of more than 1.5^oC before carbon is sucked out of the atmosphere at a greater rate than emissions to the atmosphere. In respect to power generation, the scenarios feature high rates of renewables in electricity production, from a 25-60% share in 2030 to a 63-81% share by 2050. One scenario (P1) has no use of carbon capture and storage, but does include afforestation as a form of “carbon dioxide removal” (a term which otherwise includes “afforestation and reforestation, land restoration and soil carbon sequestration, bio-energy with CCS, direct air carbon capture and storage (DACCS), enhanced weathering and ocean alkalinisation”). The other three scenarios include large amounts of the use of CCS, typically with a large part being BECCS. Primary energy from coal is to decline to 0-2% of present levels by 2050 under all four scenarios, although it is unclear why the possibility of zero-emissions coal firing is not considered as a potential option. (The report does state that for “electricity generation, shares of nuclear and fossil fuels with carbon dioxide capture and storage (CCS) are modelled to increase in most 1.5°C pathways with no or limited overshoot.”) Gas use rises to 2050 in one scenario, while oil use drops in all scenarios by 2050. Carbon capture and storage (and perhaps utilisation) will be required for industry. Each of the scenarios sees nuclear power as increasing hugely to meet the 1.5^oC target, by 59-106% by 2030 and 98-501% by 2050. Considering the very long build times for nuclear plants, it seems highly improbable that any of the 2030 goals for nuclear could be met in reality. There are even bigger rises foreseen for non-biomass renewables, with rises of 110-470% by 2030 and 832-1327% by 2050. While these are enormous increases, they may be more possible than those for nuclear considering the rather low present share of renewables in the world and their recent rapid uptake and falling prices. (However, the environmental and social impact of wind power may have been severely underestimated, according to a new study by Harvard University not taken into consideration by the IPCC report.)

Overall, the report acts as intended, a “clarion bell” to demonstrate the urgent importance of limiting temperature increases to below 1.5^oC. That the practicability of the pathways to do so are questionable – as the report puts it, “these systems transitions are unprecedented in terms of scale” – makes the challenge an even greater one. While Jim Skea, a co-chair of the working group on mitigation said that “we show it can be done within laws of physics and chemistry. Then the final tick box is political will,” this tick box masks a great deal of complexity. To create political will, better understandings of psychology, communications, education, economics, sociology, the structure of political systems, business and law, as well as ethics are likely to be required. In the field of combustion, the report clearly indicates the need for carbon capture and storage, energy generation efficiency, biomass development, and possibly the embrace of hydrogen as a clean fuel.