IPCC AR6 WGI – Key Findings

ipcc ar6 release – key findings & what to expect

*Post originally written on August 9, 2021. Most of this is summarized notes and quotes from the IPCC Sixth Assessment Report – Working Group I contribution. AR6 Climate Change 2021: The Physical Science Basis.

what happened?

• The IPCC’s released its latest comprehensive assessment of climate science on Monday morning: Sixth Assessment Report, Climate Change 2021: The Physical Science Basis
  • The IPCC consists of 195 governments and has emerged as one of the most credible sources of climate science
  • This effort brought together 234 authors across 66 countries together to analyze more than 14,000 studies to provide the most up-to-date physical understanding of the climate system and climate change, bringing together the latest advances in climate science
  • The Summary for Poliycmakers” (~42 pages) is a more concise version of key takeaways compared to the full report (~4,000 pages)
• Carbon Brief published a helpful In-depth Q&A: The IPCC’s sixth assessment report on climate science

what can we expect?

• Governments from 197 countries will meet this November in Glasgow for COP26 to discuss vital UN climate talks and negotiate climate targets globally.
  • At COP21 in December 2015, 195 nations adopted the Paris Agreement: ‘holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels’.
    • All Parties to the Paris Agreement are requested to submit updated pledges (Nationally Determined Contributions, NDCs) before, setting tougher targets for reducing emissions by 2030.
• Given the latest information presented by the IPCC confirms that we are on course to exceed 1.5°C within the next decade and faster than expected just years ago, we can expect participating countries to take a more serious tone to these negotiations and perhaps set more ambitious climate targets. The 1.5°C threshold is important because beyond this, so-called “tipping points”―positive feedback loops where global warming causes a permanent shift in earth systems, locking in further warming―become more likely. Reaction and commentary from figureheads suggests the tone has gotten more serious:
  • António Guterres, the UN secretary general, called for an end to new coal plants and to new fossil fuel exploration and development, and for governments, investors and businesses to pour all their efforts into a low-carbon future.
  • Boris Johnson, prime minister of the UK, hosts of COP26, said: “Today’s report makes for sobering reading, and it is clear that the next decade is going to be pivotal to securing the future of our planet… I hope today’s report will be a wake-up call for the world to take action now, before we meet in Glasgow in November for the critical COP26 summit.”
  • President Biden tweeted, “We can’t wait to tackle the climate crisis. The signs are unmistakable. The science is undeniable. And the cost of inaction keeps mounting.”
    • John Kerry, special envoy to US president Joe Biden, said: “The IPCC report underscores the overwhelming urgency of this moment. The world must come together before the ability to limit global warming to 1.5°C is out of reach… Glasgow must be a turning point in this crisis.”
• As a result of the IPCC’s findings and with COP26 upcoming, companies may be under pressure to commit to more aggressive emissions reduction targets and provide increased disclosure around the potential climate risks to their business models.
  • If they have not set an emissions reduction target, there will be pressure to announce a plan. For companies that have set weak targets, there will be pressure to sign onto more ambition, science-validated targets.
    • Companies that have business models that rely on burning fossil fuels, deforestation, or cause releases of methane may come under serious near-term pressure to enact more aggressive emissions reduction plans.
  • Securities and Exchange Commission Chair Gary Gensler said he wants mandatory disclosure on climate risks and he wants the agency to develop a rule by the end of the year.
  • Currently, there are 1,000+ companies worldwide setting emissions reduction targets through the Science Based Targets Initiative. They vary in scope and ambition.

key takeaways from the report:

• Global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered. Global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in CO2 and other greenhouse gas emissions occur in the coming decades.
  • This Report reaffirms with high confidence the AR5 finding that there is a near-linear relationship between cumulative anthropogenic CO2 emissions and the global warming they cause. Each 1000 GtCO2 of cumulative CO2 emissions is assessed to likely cause a 0.27°C to 0.63°C increase in global surface temperature with a best estimate of 0.45°C.

• In the scenarios studied by the IPCC, there is a more than 50% chance that the 1.5°C target is reached or crossed between 2021 and 2040 (with a central estimate of the early 2030s).
  • The 2021-2040 period is a decade earlier than the range the IPCC estimated in the Special Report on Global Warming of 1.5°C released in 2018 (due to larger estimates of historical warming and future near-term warming).
  • All five of the new report’s temperature scenarios show the 1.5°C marker passed by 2040, before cooling down below that mark in only one of five scenarios. Achieving that cooling will depend on large-scale removal of carbon dioxide from the air.

• Humanity will have about a 50% chance of staying below the 1.5°C threshold called for by the Paris Agreement if CO₂ emissions from 2020 onwards remain below 500 billion tons.
  • This amounts to about ~10 years before we exhaust the budget, based on trends in recent years.
  • If we collectively fail to curb emissions in the 2020s and reach net-zero CO2 emissions by around 2050, limiting warming to 1.5°C slips out of reach.
    • Even if the world manages to limit warming to 1.5°C, some long-term impacts of warming already are likely to be inevitable and irreversible. These include sea level rises, the melting of Arctic ice, and the warming and acidification of the oceans. Drastic reductions in emissions can stave off worse climate change, according to IPCC scientists, but will not return the world to the more moderate weather patterns of the past.

• The IPCC found that the combined effects of human activity have already increased the global average temperature by about 1.1°C above the late 19th-century average. The contribution to global warming of natural factors, such as the sun and volcanoes, is estimated to be close to zero.
  • Of the 1.1 degrees C of warming we’ve seen since the pre-industrial era, the IPCC finds that less than 0.1 degrees C is due to natural forcings, such as volcanos or variations in the sun.

• Many changes in the climate system become larger in direct relation to increasing global warming. They include increases in the frequency and intensity of hot extremes, marine heatwaves, and heavy precipitation, agricultural and ecological droughts in some regions.
  • Twenty years ago, researchers couldn’t link a specific weather event directly to human-made climate change, meaning that the scientific likelihood of a specific storm or heat wave being tied to warmer temperatures wasn’t knowable. Today, many of these weather attribution studies can be produced within days or weeks of an event. Projected changes in extremes are larger in frequency and intensity with every additional increment of global warming.