Global warming of 1.5°C:
IPCC’s approach to producing Reports
during the Sixth Assessment Cycle (AR6)
WGII: Impacts, Adaptation and Vulnerability
Hans‐O. Pörtner,
CLA Ocean Systems AR5 WGII Ch. 6
AR5 Synthesis Report
Co‐Chair IPCC WGII AR6

Avoided Impacts and Risks:
Guiding AMBITION in
mitigation and adaptation

Impacts of global warming 1.5°C:
Where should we go?
At 1.5°C compared to 2°C:

Jason Florio / Aurora Photos•Less extreme weather where people live,
including extreme heat and rainfall•By 2100, global mean sea level rise will bearound 10 cm lower …. but may continue
to rise for centuries•

10 million fewer people exposed to risk ofrising seas (…less coastal ecosystemsexposed)

Where do we want to go?
At 1.5°C compared to 2°C:

Andre Seale / Aurora Photos•

Lower impact on biodiversity and species•

Smaller reductions in yields of maize, rice,wheat crop yields•

Global population exposed to water
shortages is up to 50% less (also less water
shortages for ecosystems)

Terrestrialbiodiversity
P. Smith et al. 2018At 1.5°C compared to 2°C:
• Lower impacts on biodiversity and species

no impact
on biodiversity
at 1.5 vs. 2°C
beneficial
for biodiversity
at 1.5 vs. 2°C
Terrestrial Meta‐analysis as in SR1.5

ILLUSTRATIVE EXAMPLEDrivers of change: Warming and velocity....

+2°C AR5: Marine biodiversity
RCP 4.5
Garcia‐Molinos
et al. 2015,2017 NCC

RCP4.5 versus 8.5
Ultimate Species Heat Limits surpassed in Tropics+4°C

RCP 8.5
Large changes in community composition expected
driven by local invasions and losses

ILLUSTRATIVE EXAMPLE

Where do we want to go?
At 1.5°C compared to 2°C:

Natalie Behring / Aurora Photos•Lower risk to fisheries & the livelihoods that
depend on them•

Up to several hundred million fewer people
exposed to climate-related risk andsusceptible to poverty by 2050

• Sea level slide Andres
2°C

1.5°C

SR 1.5

Where do we want to go?
At 1.5°C and 2°C:
•Disproportionately high risk for Arctic,
dryland regions, small island developing
states and least developed countries

At 1.5°C compared to 2°C:

Jason Florio / Aurora Photos•Lower risks for health, livelihoods, foodsecurity, water supply, human security andeconomic growth•

A wide range of adaptation options can reduceclimate risks; less adaptation needs at 1.5°C

|
2.0°C
1.5°C

Arctic Sea Ice
Coral Reefs

Global biodiversity

Confidence level : M, medium; H, high; VH; very high

IPCC SR1.5, 2018

|….half a degree matters… every bit of warming matters….
… for ecosystems, biodiversity and humankind

2.0°C
1.5°C

...less loss and damage at 1.5°C
Confidence level : M, medium; H, high; VH; very high
IPCC SR1.5, 2018OBSERVATIONS

0.8 to 1.0°C

Vulnerable ecosystem identified in AR5 and SR1.5
Warm water coral reefs under various pressures
Assessing risk of global warming

Even in a 1.5°C warmer
world.... high risk oflosing 70 to 90% of coral
reefs and their services
to humankind; … evenhigher losses at 2°C

2.0°C
1.5°C
20062015

low mod. high very highRisk level
Verons 20092016

Vulnerable ecosystems identified in AR5 and SR1.5:
Arctic summer sea ice systems

1.5°C≥2°CRCP 2.6

RCP 8.5

ambitious mitigation

business as usual

1 in 100 years
ice‐freeat 1.5°C> 1 in 10years ice‐
free at2°C©H.O. Pörtner

AR5 WGI SPM.7b, 8cSea level rise beyond 2100 may challenge
biological and human systems:~ 1.5°C~ 2°C

Long‐term sea‐level rise (m)High ambition mitigation needed

1.5°C....affecting habitat, freshwater
resources, human society throughflood events

Coming close to Paleo‐findings....
5‐9 m : ...during the last interglacial(Eemian, 125.000 ya, at 0.7‐2°C
above pre‐industrial)>7m : ...last time when theatmosphere had 400 ppm
CO2 (in Pliocene, 3‐5 Mya)
Knutti et al., Ngeo 2015

Global mean temperaturechange (°C)

TO BE
ASSESSEDIN AR6

AR5 SYR

1.5°C

Increasing risk
associated withhigh sea level
beyond 2100
underRCPs > 2.6~1.5°C (2300)
However.....
Contribution ofAntarctic ice sheet
likely underestimatedSYR 2.5

Avoided impacts: guiding ambition in adaptation and mitigation

How do we get there?
•To limit warming to 1.5°C, CO2 emissions
fall by about 45% by 2030 (from 2010levels)Compared to 20% for 2°C•To limit warming to 1.5°C, CO2 emissions
would need to reach ‘net zero’ around 2050
Compared to around 2075 for 2°C•Gerhard Zwerger‐Schoner / Aurora Photos

Reducing non-CO2 emissions would havedirect and immediate health benefitsBillion tonnes CO2 per year (GtCO2/yr)

Different pathways and mitigation strategies could limit global
warming to 1.5°C, variable needs for negative emission
technologies….bringing their own risks

BECCS: Bioenergy andCarbon Capture andStorage

Risks forecosystems,biodiversity, foodsecurityYearAmbitious emissions reduction
minimizes the need for carbon
dioxide removal, e.g. BECCS• Co‐benefits for• Human health• Ecosystem restoration and carbon
storage (soils and biomass)• Biodiversity conservation• Reduced competition for land
• Food security for humankind
Peter Essick / Aurora Photos

1.5°C facilitates reaching SDGs

|

Indicative linkages between mitigation and sustainable
development using SDGs (the linkages do not show costs and benefit)

1.5°C linked toreaching SDGs

Limiting warming to 1.5°C
Would require rapid, far-reaching andunprecedented changes in all systems
A range of technologies and behavioural changes
Scale up in annual investment in low carbon energy
and energy efficiency by factor of five by 2050
Renewables supply 70‐85% of electricity in 2050
Coal declines steeply, ~zero in electricity by 2050
Oil and especially gas persist longer – gas use rises
by 2050 in some pathways
Deep emissions cuts in transport and buildings
Changes in land use and urban planning
Mint Images / Aurora Photos

The Paris agreement provides a sense of urgency:
Overcoming societal and political inertia, acceleratingtransformation....
Feasibility at various levels:• Keeping warming to 1.5 according to thelaws of chemistry and physics ‐‐‐‐ yes• Technologies to support mitigation andadaptation measures ‐‐‐‐ yes• Redirection of financial flows ‐‐‐‐ yes(stopping fossil fuel subsidies)
A common response evenamong those who (should)
know...including us!?

• Informed policy leading and directing
societal transformation ‐‐‐‐ may be .....?
BOTTLE NECKHalf a degree… every bitof warming matters
Each year matters
Each choice matters

Ashley Cooper/ Aurora Photos

Sixth Assessment Cycle (AR6)Special Reports
1.
2.
3.

October 2018 - Special Report on Global Warming of 1.5 °C (SR15)
August 2019 - Climate Change and Land (SRCCL)
September 2019 - Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC)

Methodology Report update
May 2019: 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas
Inventories

AR6 Main Report
2021: Working Group I, II, and III contribution to the Sixth Assessment Report
April 2022: Synthesis Report of the Sixth Assessment Report* Dates are subject to change

IPCC WRITING AND REVIEW PROCESS= Lead Author Meetings (LAMs)

Special Report on the Ocean andCryosphere in a Changing Climate (SROCC)
1. Framing and Context of the Report
2. High Mountain Areas
3. Polar Regions
4. Sea level rise and implications for low lying islands, coasts
and communities
5. Changing ocean, marine ecosystems, and dependentcommunities
6. Extremes, abrupt changes and managing risks+ Cross-chapter box: Low lying islands and coasts

Outline of Special Report on
Climate Change and Land (SRCCL)
Summary for Policy Makers
Technical Summary
Chapter 1:
Chapter 2:Chapter 3:
Chapter 4:
Chapter 5:
Chapter 6:
Chapter 7:

Framing and Context
Land-Climate Interactions
Desertification
Land Degradation
Food Security
Interlinkages between desertification, landdegradation, food security and GHG fluxes: Synergies,
trade-offs and Integrated Response Options
Risk management and decision making in relation tosustainable development

Boxes, Case Studies and FAQs

Working Group II Outline
Chapter 1: Point of departure and key concepts
SECTION 1: RISKS, ADAPTATION AND SUSTAINABILITY FOR SYSTEMSIMPACTED BY CLIMATE CHANGE
Chapter 2: Terrestrial and freshwater ecosystems and their services
Chapter 3: Ocean and coastal ecosystems and their services
Chapter 4: Water
Chapter 5: Food, fibre, and other ecosystem products
Chapter 6: Cities, settlements and key infrastructure
Chapter 7: Health, wellbeing and the changing structure of communities
Chapter 8: Poverty, livelihoods and sustainable development

Working Group II Outline (cont’d)
SECTION 2: REGIONS
Chapter 9: Africa
Chapter 10: Asia
Chapter 11: Australasia
Chapter 12: Central and South America
Chapter 13: Europe
Chapter 14: North America
Chapter 15: Small Islands

Each chapter to cover regional oceans
and specific land ocean interactions

SECTION 3: SUSTAINABLE DEVELOPMENT PATHWAYS: INTEGRATING ADAPTATION AND
MITIGATION
Chapter 16: Key risks across sectors and regions
Chapter 17: Decision‐making options for managing risk
Chapter 18: Climate resilient development pathways

CROSS‐CHAPTER PAPERS (built by chapter authors)(with material for TS/SPM as appropriate)
integrating sectors, regions and updating from special reports

Biodiversity hotspots (land, coasts and oceans)chs. 2,3,9‐15, SROCC, SRCCL
Cities and settlements by the sea
chs. 3,6,9‐15,16‐18, SROCC
Deserts, semi‐arid areas, and desertificationchs. 2,4,5,9‐14, SRCCL
Mediterranean region, chs. 3,6,9‐15,16‐18, SROCC, SRCCL
Mountains, chs. 2,9‐14, SROCC
Polar regions, chs. 2‐8,10‐15, SROCC, SRCCL
Tropical forests, chs. 2,9,11,12, SRCCLAR6 schedule
WGI, II, III

May 2019
Emission
inventories

Oct. 2018

Oct. 2019

Globalwarming of
1.5 oC

Oceansand cryosphere

Facilitative
dialogue
UNFCCC

April 2021

October 2021

April 2022

WGI: The PhysicalScience Basis

WGII: Climate
Change Impacts,Adaptation andVulnerability

The Synthesis
Report (SYR)

WGIII: MitigationofClimate Change

LandAug. 2019

Special Reports

Global stocktake
2023
UNFCCC

July 2021

Main Reports

All Authors, Review Editors selected based on government and bureau nominations
Become involved: e.g. as Expert Reviewer, Contributing Author, see ipcc.ch

Do not forget….

Half a degree… every bitof warming matters
Each year matters
Each choice matters

Ashley Cooper/ Aurora Photos

Thank you for your attention