IPCC Sixth Assessment Report (AR6) — UPSC Notes

The Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6) is the most comprehensive, authoritative stocktake of climate science released to date. Its three Working Group reports (2021-22) and Synthesis Report (March 2023) defined the scientific basis for COP26, COP27, COP28 and the Global Stocktake. For UPSC GS-III, AR6 is a consistent source of factual anchors for climate change answers.

What is IPCC?

• Established in 1988 by the WMO and UNEP.
• Nobel Peace Prize, 2007 (with Al Gore).
• Based in Geneva.
• Does not conduct original research — assesses existing peer-reviewed scientific literature.
• Reports prepared by three Working Groups + a Task Force.

Working Groups

Assessment cycles

• FAR (1990) — led to UNFCCC.
• SAR (1995) — led to Kyoto Protocol.
• TAR (2001).
• AR4 (2007).
• AR5 (2014) — led to Paris Agreement.
• AR6 (2021-23) — current cycle.

AR6 structure

WG-I — The Physical Science Basis (August 2021)

WG-II — Impacts, Adaptation, Vulnerability (February 2022)

WG-III — Mitigation (April 2022)

Synthesis Report (March 2023)

Plus three Special Reports:

• 1.5°C Report (2018) — landmark.
• Climate Change and Land (2019).
• Ocean and Cryosphere (2019).

AR7 cycle began in 2024; its Synthesis Report is scheduled for 2028.

Key findings of AR6

Climate change — unambiguous

• "Unequivocal" — human influence has warmed atmosphere, ocean, land.
• Widespread and rapid changes in atmosphere, ocean, cryosphere, biosphere.
• Recent changes unprecedented over many thousands of years.

Global warming

• Global surface temperature is 1.07°C higher than 1850-1900 pre-industrial baseline (AR6 WG-I).
• Updated 2024 data: already around 1.3-1.4°C above pre-industrial.
• 1.5°C and 2°C will be exceeded in the 21st century unless deep cuts in CO2 and other GHGs occur.

Greenhouse gases

• CO2 dominant cause of warming — will remain so under all emissions scenarios.
• Methane (CH4) — accounts for ~25% of warming; 80x more potent than CO2 over 20 years.
• Aerosol cooling offsets about 30% of GHG warming; reducing air pollution may temporarily accelerate warming.

Carbon budget

• For 50% chance of keeping to 1.5°C: ~500 GtCO2 budget remaining (as of early 2020).
• At current emission rates (~40 GtCO2/year), this budget will be exhausted by ~2030.

Regional findings — South Asia

• South and Southeast Asian monsoon weakened in the second half of the 20th century due to anthropogenic aerosols.
• Annual and summer monsoon precipitation will increase through 21st century, with enhanced interannual variability.
• More intense flooding.
• Heat waves and humid heat stress will intensify.

Mountain regions

• Freezing level height rising; snow and ice conditions altering.
• Warming increases with altitude — Himalayas, Alps, Andes.
• Elevation-dependent warming → faster changes in snowline, glacier equilibrium line.

Oceans

• Marine heatwaves more frequent.
• Deoxygenation persisting for centuries.
• Ocean acidification increased globally.
• Indian Ocean warming faster than global average.
• Global mean sea level rising from continuing deep ocean heat uptake and ice-sheet mass loss.

Polar regions

• Arctic sea ice declining; near-ice-free summer Arctic in some scenarios by mid-century.
• Permafrost thaw releases carbon.
• Greenland + Antarctic ice loss accelerating.

Tipping points

AR6 confirms several Earth-system tipping points that could be triggered between 1.5°C and 3°C of warming:

• Greenland and West Antarctic ice sheet collapse.
• Amazon dieback.
• Permafrost methane release.
• AMOC weakening.
• Coral reef die-off.
• Indian summer monsoon destabilisation.

AR6 — Mitigation pathways (WG-III)

1.5°C-consistent pathways

• Global GHG emissions peak before 2025.
• Reduce 43% by 2030 below 2019 levels.
• Reduce 60% by 2035.
• Reach net zero CO2 around 2050.
• Net zero all GHGs around 2070-80.

Required transformations

• Renewables: 70-85% of electricity by 2050.
• Electrification of transport and buildings.
• Carbon Capture mandatory for residual emissions.
• Dietary shifts and food system changes.
• Halting deforestation and restoring degraded lands.

AR6 — Adaptation findings (WG-II)

• 3.3-3.6 billion people live in contexts highly vulnerable to climate change.
• Adaptation gap: current pace insufficient; finance needs 10-18x more than current flows.
• Maladaptation risk — some adaptation actions can worsen vulnerability.
• Just Resilience required — addressing vulnerable groups (poor, Indigenous, women, elderly).

Policy implications

• Global Stocktake 2023 under Paris Agreement used AR6 heavily.
• Dubai Consensus (COP28) explicitly called for "transitioning away from fossil fuels" — first time under UNFCCC.
• COP29 Baku — NCQG finance architecture informed by AR6 gap estimates.
• India's updated NDC and LiFE campaign both reference AR6 scientific basis.

Criticisms of AR6

• Conservative estimates — real-world emissions sometimes run ahead of AR6 scenarios.
• Policy relevance constrained by Summary for Policymakers negotiated line-by-line with governments.
• Scenario narratives (SSPs) can be misinterpreted.
• Developing country expertise under-represented in lead authorship, though improving.

Latest developments (2024-26)

Updated context: verify specific figures with IPCC AR7 announcements.

• AR7 cycle — began 2024; Synthesis Report due 2028.
• Special Reports AR7 — on cities and climate, and on climate and water.
• UNEP Emissions Gap Report 2024 — reinforces AR6 findings.
• WMO State of Global Climate 2024 — 2024 confirmed as warmest year on record (~1.55°C).
• IPCC expert meetings on methane, DAC, ocean-climate.

UPSC relevance

GS-III mapping

• Climate change.
• Conservation and pollution.

Prelims bullets

• IPCC established — 1988.
• Founding bodies — WMO and UNEP.
• Nobel Peace Prize — 2007.
• Secretariat — Geneva.
• AR6 Synthesis Report — March 2023.
• Pre-industrial baseline — 1850-1900.
• Three WGs — Physical Science, Impacts, Mitigation.
• 1.07°C warming figure in AR6 WG-I.

Mains angles

• "Discuss the key findings of the IPCC Sixth Assessment Report relevant to South Asia."
• "AR6 establishes the 'unequivocal' role of human influence in climate change. Examine its policy implications for India."
• “What are the tipping points identified by the IPCC and how do they affect Indian climate risk?”

Essay hooks

• Climate science and public policy — the IPCC model.
• From evidence to action — the gap AR6 exposes.
• Equity in the climate science narrative.

Quick revision

Bottom line for UPSC: AR6 is the scientific foundation of every current climate policy debate — from Net Zero 2070 to Loss & Damage to carbon markets. Cite it confidently and specifically; it remains the gold-standard evidence base until AR7 is released in 2028.