A report by the UN Intergovernmental Panel on Climate Change (IPCC) released on 8 October warns that unprecedented change is needed to limit global warming. The special report, “Global Warming of 1.5 degrees”, was commissioned by governments at the Paris climate talks in 2015. It will inform the COP24 summit in Katowice, Poland in December.

The IPCC said in a statment accompanying the repor that limiting global warming to 1.5°C compared to 2°C "would require rapid, far-reaching and unprecedented changes in all aspects of society".

The target of limiting global warming to 1.5°C lies at the most ambitious end of the Paris Agreement pledge. which was adpoted by 195 nations in December 2015. Even half a degree beyond that target could significantly worsen the risks of drought, floods and extreme heat. IPCC says the target is affordable and feasible but will require replacing coal for electricity generation to reduce carbon emissions drastically, the report said.

The report highlights some impact of climate change that could be avoided by limiting global warming to 1.5°C compared to 2°C, or more. For instance, by 2100, the global sea level rise would be 10cm lower with global warming of 1.5°C degrees compared with 2°C. The likelihood of the Arctic Ocean being of sea ice in summer would be once per century with global warming of 1.5°C, rather than at least once per decade with 2°C. Coral reefs would decline by 70-90% with global warming of 1.5°C, whereas more than 99% would be lost with 2°C.

The IPCC issued the latest report from Incheon, South Korea, after hundreds of scientists and government representatives examined 6000 scientific reports to assess what could happen with global warming of 1.5°C. The report was prepared under the leadership of all three IPCC working groups. Working Group I assesses the physical science basis of climate change, Working Group II covers impacts, adaptation and vulnerability; and Working Group III deals with the mitigation of climate change.

The report looks at a number of “pathways” noting that several energy supply characteristics are evident, including growth in the share of energy derived from low carbon-emitting sources, including nuclear. In most 1.5°C pathways, by the middle of the century, the majority of primary energy comes from non-fossil-fuels – essentially renewables and nuclear.  The IPCC maps out four paths to achieve 1.5°C, with different combinations of land use and technological change. Reforestation is essential to all pathways as are shifts to electric transport systems and greater adoption of carbon capture technology.

“One of the key messages that comes out very strongly from this report is that we are already seeing the consequences of 1°C of global warming through more extreme weather, rising sea levels and diminishing Arctic sea ice, among other changes,” said Panmao Zhai, co-chair of  Working Group I. UN secretary-general António Guterres, commenting on the report, said it is not impossible to limit global warming to 1.5°C, but it will require unprecedented and collective climate action in all areas. “There is no time to waste,” he said on social media.

Many scenarios considered in the IPCC report foresee an increase in the use of nuclear power through existing mature nuclear technologies or new options. These include Generation III and IV reactors, fast breeder reactors, new uranium and thorium fuel cycles, small reactors or nuclear cogeneration, the report said. However, the report notes that the deployment of nuclear energy is constrained by social acceptability in many countries notably because of concerns over risks of accidents and radioactive waste management.

Health risks are low per unit of nuclear electricity production, and land requirements are less than for other power sources, but societal concerns are a problem. There were different responses to the 2011 Fukushima-Daiichi accident with five countries confirming or accelerating a policy to phase out nuclear energy, while 30 others have continued using nuclear power, with 13 building new capacity, including China, India and the UK.

Costs of nuclear power have increased in some developed nations, mainly due to market conditions. In liberalised markets de-risking instruments have been employed through long-term contracts with guaranteed sale prices. In the UK, for example, public guarantees cover part of the upfront investment costs of newly planned nuclear capacity. However, in countries such as China and South Korea, monopolistic conditions in the electricity system allow for reducing investment risks and deploying series effects.

The report noted that, while the political, economic, social and technical feasibility of solar energy, wind energy and electricity storage technologies has improved dramatically over the past few years, that of nuclear power has not shown similar improvements.

"Nuclear power increases its share in most 1.5-degree pathways by 2050, but in some pathways, both the absolute capacity and share of power from nuclear generators declines," the Summary for Policymakers of the report says.

There are big differences in nuclear power between models and across pathways. This is due, in part to the fact that the future deployment of nuclear can be constrained by societal preferences. Some 1.5-degree pathways no longer see a role for nuclear fission by the end of the century, while others project over 200 EJ yr of nuclear power in 2100, according to the report.

"Even though historically scalability and speed of scaling of nuclear plants have been high in many nations, such rates are currently not achieved anymore," the report notes, referring in particular to the French programme.  It cites the current time-lage between the decision to proceed with a nuclear plant and the commissioning of plants as 10-19 years.