The Intergovernmental Panel on Climate Change (IPCC) met virtually to consider the contribution of Working Group 1 (WG1) to the IPCC Sixth Assessment Report (AR6), for two weeks from 26th July to 6th August, 2021. An online press conference took place on 9th August at which IPCC Chair Hoesung Lee and the co-chairs of WG1 – Valérie Masson-Delmotte (France) and Panmao Zhai (China) introduced the report, as it is published.
The report titled 'Climate Change 2021: the Physical Science Basis' was finalised and approved by 234 authors and 195 governments. This is the biggest update of the state of knowledge on climate science since the release of the IPCC’s AR5 in 2014, and its landmark 1.5 Special Report (SR1.5).
The WGI report examines the physical underpinning of past, present, and future climate change. It looks at fundamentals such as how human-caused emissions are leading to fundamental planetary changes to the climate system. It also gives us an idea of how these changes have caused us to lock in climate impacts already at our current level of warming, as well as mapping how these impacts could worsen if temperatures and emissions continue to rise unchecked.
The WGI release follows a two-week long plenary session in which the report was scrutinized line-by-line for approval by government representatives in dialogue with report authors. Over 14,000 scientific papers are referenced in the report.
Scientists have no doubt that human activities have warmed the planet at a rate that is unprecedented in at least the last 2000 years. In 2019, atmospheric CO2 concentrations were higher than at any time in at least 2 million years and concentrations of methane and nitrous oxide, both significant GHGs, were higher than at any time in at least 800,000 years. The rate of warming is speeding up: global surface temperatures have increased faster since 1970 than in any other 50-year period over at least the last 2000 years. Rapid and widespread changes have occurred in the planet’s climate and some impacts are now locked in.
In response to the report, COP26 President Mr Alok Sharma said: “The science is clear, the impacts of the climate crisis can be seen around the world and if we don’t act now, we will continue to see the worst effects impact lives, livelihoods and natural habitats. Our message to every country, government, business and part of society is simple. The next decade is decisive, follow the science and embrace your responsibility to keep the goal of 1.5oC alive.”
Improved attribution science finds evidence of humankind’s impact throughout the climate system, human-caused emissions are now responsible for an altered, less stable planet. “We can do this together, by coming forward with ambitious 2030 emission reduction targets and long-term strategies with a pathway to net zero by the middle of the century, and taking action now to end coal power, accelerate the roll-out of electric vehicles, tackle deforestation and reduce methane emissions,” adds Sharma.
What does this say about Paris Agreement temperature targets?
The Paris Agreement sets the goal temperature rise by the end of the century to be no more than 2°C, and preferably no more than 1.5°C. The planet will warm by 1.5°C in all scenarios. In the most ambitious emissions pathway, we reach 1.5°C in the 2030s, overshoot to 1.6°C, with temperatures dropping back down to 1.4°C at the end of the century. The WGI report is clearer than ever: both the 1.5°C and 2°C warming limits will be exceeded during the 21st century unless we deeply reduce CO2, along with other greenhouse gas emissions, to net zero around or after 2050. This is unprecedented territory, as the last time earth’s surface temperature was above 2.5°C higher (compared to preindustrial levels) was over 3 million years ago.
Key findings, and how this relates to India
With 7,517 km of coastline, India will face significant threats from rising seas. Across six Indian port cities - Chennai, Kochi, Kolkata, Mumbai, Surat and Visakhapatnam - 28.6 million people will be exposed to coastal flooding if sea levels rise 50 cm, according to one study. The assets exposed to flooding will be worth about US$4 trillion.
Also, in India, glaciers in the Hindu Kush Himalaya Region are a crucial water supply for the 240 million people who live in the region, including 86 million Indians - roughly the equivalent of the country’s five biggest cities combined. Glaciers such as in the Lahaul-Spiti region of western Himalaya have been losing mass since the start of the 21st century, and if emissions do not fall, glaciers in the Hindu Kush Himalaya would decline by two-thirds.
Overall, the WG1 report focuses on the global impacts and signals of climate change. India is currently the world’s fourth largest greenhouse gas emitter (if the EU is counted as one block), but per capita emissions are much lower. The US emitted nearly 9 times more greenhouse gases per capita than India in 2018.
The latest climate science projects increased precipitation and more frequent hot extremes in India. Warming over India is projected to track the global average and the nation is expected to see an increase in frequency and severity of hot extremes. Globally, 1-in-10 year hot extreme events will occur 5 times more frequently at 2°C. At 4°C these 1- in-10 events will likely happen 9.4 times in a ten-year period, nearly once a year on average.
An increase in annual mean precipitation is projected. The increase in rainfall will be more severe over southern parts of India. On the southwest coast, rainfall could increase by around 20%, relative to 1850-1900. If we warm by 4°C, India could see about a 40% increase in precipitation annually.
Monsoon precipitation is projected to increase in the mid- to long term over South Asia. Globally, severe, heavy precipitation events that now occur on average once every ten years, are projected to nearly double in frequency at 2°C (1.7 times in a ten-year period). At 4°C, the likelihood of these events will jump to 2.7 times in a ten-year period.
Key findings for policymakers
- Scientists are clear on the need to tackle greenhouse gases other than CO2 in the near term, emissions of methane - a powerful greenhouse gas - are of particular concern.
- The natural world will be damaged by further warming, and so the land and ocean ecosystems have a limited capacity to help us solve the climate challenge.
- Decision-makers need to implement net zero plans if we are to stop warming. Carbon dioxide removal is a crucial net zero tool, but one that will only be useful when accompanied by swift and deep emissions reductions.
- Estimates of the remaining carbon budget—a simplified way of assessing how much more CO2 can be released—have been improved since previous reports, but the carbon budget remains broadly unchanged.