The IPCC finds that our planet's climate is getting hotter due to human activities emitting Carbon Dioxide and other greenhouse gases (GHGs), with a range of consequences causing increasingly severe harm to humans and other living beings. We need to adapt to unavoidable changes whilst acting to minimise avoidable ones, most importantly by reducing the amount of CO2 and other GHGs we emit to net zero (i.e. if we emit some somewhere, we must actively remove them elsewhere). Tools we have for doing this include switching to low carbon-emitting energy sources such as renewables and nuclear, and using Carbon Capture and Storage (CCS) with carbon-emitting fuels such as fossil fuels and biomass.

What is the IPCC?

The Intergovernmental Panel on Climate Change is a body of the United Nations that is dedicated to providing the world with objective, scientific information relevant to understanding the scientific basis of the risk of human-induced climate change, its natural, political, and economic impacts and risks, and possible response options. Thousands of scientists and other experts contribute on a voluntary basis to writing and reviewing reports, which are then reviewed by governments. IPCC reports contain a "Summary for Policymakers", which is subject to line-by-line approval by delegates from all participating governments. Typically, this involves the governments of more than 120 countries. The IPCC provides an internationally accepted authority on climate change, producing reports that have the agreement of leading climate scientists and consensus from participating governments. The mandate of the IPCC is to produce assessments which are “policy relevant” but not “policy prescriptive”

Amongst the various groups that make up the IPCC are its working groups which assess the scientific evidence:

  • Working Group I: Assesses scientific aspects of the climate system and climate change.
  • Working Group II: Assesses vulnerability of socio-economic and natural systems to climate change, consequences, and adaptation options.
  • Working Group III: Assesses options for limiting greenhouse gas emissions and otherwise mitigating climate change.

Assessment Reports

The IPCC works in cycles assessing evidence and producing reports. The first was produced in 1990 and the most recent is its fifth: Assesment Report 5 (AR5), published in 2014. It is currently working on AR6, due in 2022. The reports are produced in volumes (nowadays electronically rather than on paper) corresponding to the work of Working Groups I, II and III.

Wikipedia's article on the IPCC (from which the above introduction was adapted) has a more comprehensive description of the IPCC and its work.

Evidence for climate change

In AR5 Working Group I finds that:

  • Our climate is warming:
  • Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia Atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years
  • Human activities are causing it:
  • Human influence on the climate system is clear screenshot of IPCC WG1 AR5 SPM p17

Effects of climate change

Working Group II finds that climate change will cause:

  • Sea level rises:
  • screenshot of IPCC WG2 AR5 SPM p17
  • Extreme weather events and heat waves:
  • Extreme weather events: Climate-change-related risks from extreme events, such as heat waves, extreme precipitation, and coastal flooding, are already moderate (high confidence) and high with 1°C additional warming (medium confidence). Risks associated with some types of extreme events (e.g., extreme heat) increase further at higher temperatures (high confidence).
  • Reduced crop yields:
  • Based on many studies covering a wide range of regions and crops, negative impacts of climate change on crop yields have been more common than positive impacts (high confidence).
  • Impacts on freshwater supplies:
  • Freshwater-related risks of climate change increase significantly with increasing greenhouse gas concentrations (robust evidence, high agreement). The fraction of global population experiencing water scarcity and the fraction affected by major river floods increase with the level of warming in the 21st century.
  • Fires, heat related deaths, and the spread of diseases:
  • Until mid-century, projected climate change will impact human health mainly by exacerbating health problems that already exist (very high confidence). Throughout the 21st century, climate change is expected to lead to increases in ill-health in many regions and especially in developing countries with low income, as compared to a baseline without climate change (high confidence). Examples include greater likelihood of injury, disease, and death due to more intense heat waves and fires (very high confidence); increased likelihood of under-nutrition resulting from diminished food production in poor regions (high confidence); risks from lost work capacity and reduced labor productivity in vulnerable populations; and increased risks from food- and water-borne diseases (very high confidence) and vector-borne diseases (medium confidence). Positive effects are expected to include modest reductions in cold-related mortality and morbidity in some areas due to fewer cold extremes (low confidence), geographical shifts in food production (medium confidence), and reduced capacity of vectors to transmit some diseases. But globally over the 21st century, the magnitude and severity of negative impacts are projected to increasingly outweigh positive impacts (high confidence). The most effective vulnerability reduction measures for health in the near term are programs that implement and improve basic public health measures such as provision of clean water and sanitation, secure essential health care including vaccination and child health services, increase capacity for disaster preparedness and response, and alleviate poverty (very high confidence). By 2100 for the high-emission scenario RCP8.5, the combination of high temperature and humidity in some areas for parts of the year is projected to compromise normal human activities, including growing food or working outdoors (high confidence).

Climate change mitigation

Working Group III finds that "The energy supply sector is the largest contributor to global GHG emissions" and that

"The energy supply sector offers a multitude of options to reduce GHG emissions (robust evidence, high agreement). These options include: energy efficiency improvements and fugitive emission reductions in fuel extraction as well as in energy conversion, transmission, and distribution systems; fossil fuel switching; and low-GHG energy supply technologies such as renewable energy (RE), nuclear power, and CCS"

Nuclear energy is a mature low-GHG emission source of base-load power, but its share of global electricity generation has been declining (since 1993). Nuclear energy could make an increasing contribution to low-carbon energy supply, but a variety of barriers and risks exist (robust evidence, high agreement). Its specific emissions are below 100 gCO2eq per kWh on a lifecycle basis and with more than 400 operational nuclear reactors worldwide, nuclear electricity represented 11 % of the world’s electricity generation in 2012, down from a high of 17 % in 1993. Pricing the externalities of GHG emissions (carbon pricing) could improve the competitiveness of nuclear power plants. [7.2, 7.5.4, 7.8.1, 7.12]

Barriers to and risks associated with an increasing use of nuclear energy include operational risks and the associated safety concerns, uranium mining risks, financial and regulatory risks, unresolved waste management issues, nuclear weapon proliferation concerns, and adverse public opinion (robust evidence, high agreement). New fuel cycles and reactor technologies addressing some of these issues are under development and progress has been made concerning safety and waste disposal (medium evidence, medium agreement). [7.5.4, 7.8.2, 7.9, 7.11]

Whilst the IPCC identifies "barriers to and risks associated with an increasing use of nuclear energy" it does not support those who reject either the continued or increased use of nuclear energy, and in Chapter 7 of their report Working Group III discusses nuclear energy in more detail — Resources and their availability, costs, environmental and health effects, technical risks, public perception etc — as they do also for Renewable Energy and Carbon Capture and Storage technologies.


The IPCC's 2018 Special Report on Global Warming of 1.5 ºC (SR15), the first report in the sixth assessment (AR6), addresses the most ambitious and challenging target: of staying within 1.5C of pre-industrial temperatures.

All the scenarios the report shows illustrating ways of staying under 1.5C require certain amounts of nuclear energy. The scenario using least nuclear (and no CCS or BECCS) is the most optimistic in terms of "social, business and technological innovations". The most realistic in terms of societal and technological development following historical patterns – the "middle-of-the-road scenario" – requires the most.

Pathways for limiting global warming to 1.5C accordingtomodels assessed by the IPCC in its SR15 report