Analysis

The IPCC's sixth assessment report sets out the physical science basis for climate change. It follows the fifth assessment, published in 2013-14, which paved the way for the 2015 Paris Agreement. Summarising existing research, the report states unequivocally that human influence has warmed the atmosphere, oceans and land, causing rapid, widespread changes in natural systems.

Anthropogenic emissions have increased carbon dioxide (CO2) levels in the atmosphere to annual averages of 410 parts per million. Alongside increased atmospheric levels of methane and nitrous oxide, these emissions are responsible for an increase in observed global surface temperatures of 1.1 degrees Celsius between 2011 and 2022, compared to the 1850-1900 period.

This change in the Earth system is having profound effects worldwide. Between 1901 and 2018, global mean sea levels rose by 0.2 metres, a rate faster than any preceding century in at least the last 3,000 years. This rate is accelerating, with sea levels rising 3.5 millimetres per year between 2006 and 2018. Human-induced climate change is already responsible for affecting weather and climate extremes worldwide, causing heatwaves, heavy precipitation and droughts.

Future scenarios

These changes will continue regardless of policy. The IPCC report considers five 'Shared Socio-Economic Pathways' (SSPs) -- scenarios that encapsulate broad narratives of future socio-economic development. Under all of the SSPs, global surface temperatures would continue to increase until at least the middle of this century. Unless there are drastic reductions in CO2 and other greenhouse gas (GHG) emissions, global warming will exceed 1.5 degrees this century, in contravention of the targets in the Kyoto Protocol and Paris Agreement.

Under the best-case scenario outlined, warming will peak at 1.6 degrees in 2060 and cool to 1.4 degrees by 2100. Under the very high emissions scenario, the best estimate is an increase in temperatures of 4.4 degrees by 2100.

As identified in a 2019 IPCC Report, limiting warming to 1.5 degrees would have substantial environmental, social and economic benefits, helping to stem risks to natural and human systems. Threats of increased vector-borne diseases and food and water insecurity are less concerning at 1.5 degrees. The economic implications are also profound, with one 2017 study, published in Science, concluding that each degree of warming could lose the United States 2.3% of its GDP.

Globally, temperature increases of more than 4 degrees would be transformative, making extreme temperature events more likely. Agricultural and ecological droughts in dry regions that occur once every ten years or so in a climate without human influence would be 4.1 times more likely to occur and one standard deviation drier. Sea-level rise would inundate vulnerable cities and threaten Small Island Developing States (see INT: Cities are at the fore of global warming threats - October 8, 2019).

In order to limit human-induced global warming to a specific level, it will be necessary to reach net-zero CO2 emissions and drastically reduce other GHG emissions.

Notably, the report is sceptical of carbon removal technologies, or geoengineering, arguing that implementation is not yet possible at the scale required, and could produce undesired side effects. Proponents nevertheless argue they could be necessary. Earlier this year the National Academies of Science recommended funding geoengineering research by USD100mn-USD200mn over the next five years, to gain a better understanding of the feasibility of interventions (see INT: Reversal technology will not undo climate change - October 16, 2018).

COP26

COP26 will be a key moment within broader climate politics, with many governments and policymakers focusing on "building back better" after the COVID-19 pandemic. Although CO2 emissions fell by 7% last year due to the pandemic, they are forecast to jump this year by nearly 5%, the second-largest annual rise in history, due to stimulus cash driving fossil fuel investment. World leaders, policymakers and scientists will gather at the COP26 facing high expectations of meaningful action (see INTERNATIONAL: COVID-19 climate impact may be brief - March 27, 2020).

The G7 pledged in May to limit warming to 1.5 degrees Celsius and start phasing out international financing for coal. Since 2010, 59% of G7 coal power capacity has either been retired or marked for retirement by 2030. However, with the G20 responsible for 80% of global GHG emissions, the limitation of warming to 1.5 degrees will require a significant uptake of emission reduction targets beyond the G7.

As of August 16, 112 countries had submitted new or updated Nationally Determined Contributions to the Secretariat of the UN Framework Convention on Climate Change. Notably absent from the list were China and India, the world's largest and third-largest emitters respectively. China has set the target of reaching peak emissions in 2030, and net-zero by 2060.

In light of this report, there will be increased pressure for all states to phase out the burning of coal. However, it is unlikely that an international agreement on ths will be reached in November, due to opposition from fossil fuel-dependent states. At talks between G20 climate and energy ministers in July, China, Russia and India all resisted agreeing on a pathway to eliminating coal-fired power generation (see INDIA: Delhi will defy pressure over climate policy - August 25, 2021).

There will also be discussion of climate financing for less developed nations. In Copenhagen in 2009, industrialised countries promised to mobilise USD100bn a year in climate finance by 2020; with this still unmet, there will be increasing pressure for countries to honour it.

Future activism

Attribution science is a growing field of research that assesses whether, and to what degree, human-caused climate change has affected the frequency and/or intensity of extreme events. The report notes that the attribution of observed changes in extremes to human influence has strengthened since the fifth assessment report.

An increasing number of environmental campaigners are likely to take governments and companies to court over climate science. An example of this is the Urgenda Climate Case in the Netherlands, which, in 2019, saw the Dutch Supreme Court rule that the government must reduce GHG emissions immediately, in line with its human rights obligations. Since 2015, the cumulative number of climate-change-related cases has more than doubled, suggesting more will be successful in the future.

COP26 will increase attention on these issues. Working Groups 2 and 3 of the IPCC will publish their reports on Impact, Adaptation and Vulnerability, and the Mitigation of Climate Change respectively next year, further supporting calls for action.