The Intergovernmental Panel on Climate Change has released its Synthesis Report of the Sixth Assessment Report, itself constituted by working group reports The Physical Science Basis, Impacts, Adaptation and Vulnerability, and Mitigation of Climate Change, which have been released over the last 18 months and covered in the Combustion Industry News. Also forming the basis of the Synthesis Report are the special reports Global Warming of 1.5°C, Climate Change and Land, and The Ocean and Cryosphere in a Changing Climate.

As a synthesis report, little of the content is new, but is worth being reminded of the content. It should be noted that the Summary Report for Policymakers states it should not be cited, quoted or distributed, but given that the IPCC itself is distributing the document via its website, and would presumably like as much attention focussed on the report as possible, quotes do follow.

• “Human activities, principally through emissions of greenhouse gases, have unequivocally caused global warming, with global surface temperature reaching 1.1°C above 1850–1900 in 2011–2020. Global greenhouse gas emissions have continued to increase, with unequal historical and ongoing contributions arising from unsustainable energy use, land use and land-use change, lifestyles and patterns of consumption and production across regions, between and within countries, and among individuals.” The likely range of net global surface temperature change from 1850–1900 to 2010–2019 is 0.8°C–1.3°C, with a best estimate of 1.07°C, and of this, the GHG contribution has been 1.0°C–2.0°C, while the cooling effect of aerosols has been 0.0°C–0.8°C, the natural (solar and volcanic) drivers have shifted the temperature by –0.1°C to +0.1°C, and  internal variability changed it by –0.2°C to +0.2°C.
• The estimate of GHGs emitted between 1750 and 2019 is 2400±240 GtCO₂ equivalent, 58% occurring between 1850 and 1989, and 42% in the thirty years 1990-2019. (Relatively nothing was released between 1750 and 1850.) Atmospheric concentrations of CO₂ are now the highest in at least 2 million years, and for methane and nitrous oxide the highest in at least 800,000 years. GHG emissions in 2019, at 59±6.6 GtCO₂-eq, were about 12% higher than in 2010. (This data indicates that annual emissions in 2019 were 2.5% of all emissions since 1750, a confronting portion.) Emissions per capita varies hugely between countries.
• “Human-caused climate change is already affecting many weather and climate extremes in every region across the globe. This has led to widespread adverse impacts and related losses and damages to nature and people. Vulnerable communities who have historically contributed the least to current climate change are disproportionately affected.”
• The global mean sea level rose by 3.7 mm (a likely range of 3.2 to 4.2 mm) per year between 2006 and 2018, with sea level rise between 1901 and 2018 being 0.2 metres (a range of 0.15-0.25 m).
• “Climate change has caused substantial damages, and increasingly irreversible losses, in terrestrial, freshwater, cryospheric, and coastal and open ocean ecosystems”, with hundreds of losses of species having been driven by extreme heat waves, with “with mass mortality events recorded on land and in the ocean”. Heatwaves have also, of course, contributed to human mortality.
• “Although overall agricultural productivity has increased, climate change has slowed this growth over the past 50 years globally (medium confidence), with related negative impacts mainly in mid- and low latitude regions but positive impacts in some high latitude regions.”
• “Ocean warming and ocean acidification have adversely affected food production from fisheries and shellfish aquaculture in some oceanic regions (high confidence). Roughly half of the world’s population currently experience severe water scarcity for at least part of the year due to a combination of climatic and non-climatic drivers.”
• Impacts will continue to intensify, but most crucially, the extent of those impacts will be determined by the GHG mitigation efforts of the coming years, and the impact on humans and the natural world will depend to some extent on adaptation measures enacted.
• “Policies and laws addressing mitigation have consistently expanded since AR5. Global GHG emissions in 2030 implied by nationally determined contributions (NDCs) announced by October 2021 make it likely that warming will exceed 1.5°C during the 21st century and make it harder to limit warming below 2°C. There are gaps between projected emissions from implemented policies and those from NDCs and finance flows fall short of the levels needed to meet climate goals across all sectors and regions.”
• While policies have contributed to some avoidance of emissions, there is still a significant “emissions gap” (between what is needed and what is being done/has been pledged) and decarbonisation needs to accelerate. On the positive side, there are a lot of technically viable and increasingly cost-effective measures to decarbonise available that have public support, including “solar energy, wind energy, electrification of urban systems, urban green infrastructure, energy efficiency, demand-side management, improved forest- and crop/grassland management, and reduced food waste and loss.”

It is sobering to reflect that even though the adverse impacts of climate change are already highly appreciable at 1.1°C of warming, the world is on track to exceed 1.5°C; indeed, Climate Action Tracker projects warming of 1.6°C-2.6°C based on current pledges and targets, and 2.1°C-3.7°C based on current policies and action. The difference in those scenarios is hugely impactful.

In its presentation associated with the press release, the IPCC understandably chose to focus on what can be done from here to avoid the worst impacts of climate change. Options are available, and ‘equitable’ climate action will reduce losses and damages for nature and people, while creating co-benefits, such as improved health and livelihoods, reduced poverty and hunger, and more clean water and air. Emissions need to be cut quickly and sharply – halved by 2030 – and practices and infrastructure needs to be scaled up to enhance resilience.

“Fairness is one of the solutions” – meant particularly in relation to historical emissions and current emissions per capita compared to impacts experienced, suggesting that the burden of action, or at least financing, falls more on the richer countries. Around 3-6 times the current climate investment is required, with external funding needed by developing countries, but the IPCC believes there should be sufficient capacity to meet increased funding levels, should the will be present. Political commitment, inclusive governance, international cooperation, effective ecosystem stewardship, and knowledge sharing are the ingredients to successfully address the climate problem, along with the human factors of trust, collaboration, sharing of benefits and burdens, and recognition “that some can contribute more than others”.

Speaking at the launch of the report, UN Secretary General António Guterres said that the “climate time-bomb is ticking”, and although the “1.5C limit is achievable” it “will take a quantum leap in climate action”. He urged rich countries to strive for net-zero goals by 2040 rather than 2050.