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SIXTH ASSESSMENT REPORTSynthesis

Climate Change 2015 to 2023

Climate policies:
a plea for timely and ambitious action
Hans-O. Pörtner
Co-Chair IPCC Working Group II
in the 6th Assessment Cycle

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SIXTH ASSESSMENT REPORTSynthesis

Existential threats: Climate Change (and Biodiversity)
WGI

WGII

WGIII

Special Reports

AR6 Climate Change 2021:
The Physical Science Basis

Climate Change 2022:
Impacts, Adaptation andVulnerability

Climate Change 2022:
Mitigation of Climate Change

Ocean and Cryosphere in aChanging Climate

AR6 Synthesis Report,
March 2023

IPBES-IPCC Workshop
Report, 2021

Climate Change and Land

Global Warming of 1.5 ºC

Science ReviewPaper, 2023

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SIXTH ASSESSMENT REPORTSynthesis

Climate – Biodiversity – Human society:
Current imbalance between three interacting systems
Basic understanding:
The Earth’s climate andecosystems influence eachother and define the basisof life for humans, who inturn shape nature andclimate through their own
actions which are notsustainable, causing- climate change,- biodiversity loss,- land degradation,- pollution, etc.
[Axel Guibourg CC BY-NC-ND 2.0; Hugh Han / Unsplash; Axel Fassio/CIFOR CC BY-NC-ND 2.0]

3SIXTH ASSESSMENT REPORTSynthesis

Temperature

IPCC AR6 SYRFigure SPM.2a42

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SIXTH ASSESSMENT REPORTSynthesis

Precipitation

IPCC AR6 SYRFigure SPM.2c

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SIXTH ASSESSMENT REPORTSynthesis

Soil moisture

IPCC AR6 SYRFigure SPM.2a63

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3.3SIXTH– 3.6billion people
live in hotspots of high
ASSESSMENTREPORTvulnerability to climate change… large parts ofAfrica, South Asia, Central and South America,
small islands and the Arctic.

Switch to blue
logo for contrast
when necessaryMove/scale
shape basedon amount oftext tomaximize
photo space[Denis Onyodi / KRCS CC BY-NC 2.0]

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SIXTH ASSESSMENT REPORT
Synthesis

Heat-humidity risks to human health*Conclusion: Human habitat is lost from lower latirudes.
IPCC AR6 SYR Figure SPM.3b8* without “technical” adaptation measures4

22.10.23

Our choices now and in the near term
define how hot it gets for humankind...
And it is not just about us…

9SIXTH ASSESSMENT REPORT
Synthesis

Regional species losses – resulting from evolutionary
adaptation limits
IPCC AR6 SYR Figure SPM.3aConclusion: Loss of habitat – Animal life retreats from the tropics.
It is high time to act: emissions reductions need to keep global warming close to 1.5°
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SIXTH ASSESSMENT REPORT
Working Group II – Impacts, Adaptation and Vulnerability

Loss of tropical habitat due tothermal stress
Lacking:
Explained T dependent marine
biodiversity across latitudes …
Mechanism-based understanding
is insufficient how temperature
underpins biodiversity distributionand defines species habitat andecosystem functioning, considering
species composition, adaptation
capacities and limits

Latitude (°)[IP C CW G II

A R 6 ,C h h a yae ta l.

2 0 2 1 ]11SIXTH ASSESSMENT REPORT
Synthesis

Co-Sponsored Workshop Report on Biodiversity and Climate Change

Ambitious emissions reductions can maintain biodiversity and its
contributions to climate mitigation and adaptation
Climate change and biodiversity loss are central risks for ecosystems and human societies:

At all latitudes carbon storage by forests is constrained by warming, droughts and degradation

Productivity loss due towarming= less carbon binding
and storage
Monate über Topt

Aktuelles Klima

Monate über Topt

RCP 8.5, 2040…. cocomitantly
greenhouse gas
release from melting
permafrost anddegrading soils

Breitengrad

Duffy et al., Sci. Adv. 2021

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SIXTH ASSESSMENT REPORT
Working Group II – Impacts, Adaptation and Vulnerability

SROCC
The IPCC concept of risk

Evaluating risks

Climate action entails
risk reduction byadaptation and mitigation…. considering limits toadaptation[IPCC SROCC, WGII AR6]

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SIXTH ASSESSMENT REPORT
Working Group II Report

Humans and nature are exposed to diverse risks.

Conclusion: Limit warming close to 1.5°C

IPCC AR6 SYR Figure SPM.4b147

22.10.23

SIXTH ASSESSMENT REPORTWorking Group II Report

Risks are occurring sooner than assessed earlier.

Conclusion: Limit warming close to 1.5°C

IPCC AR6 SYR Figure SPM.4a15

SIXTH ASSESSMENT REPORT
Synthesis

Risks caused by sea level rise

1.5°C

Risks for coastal regions increase with sea level and depend on the responses taken.

Conclusion: Limit warming close to 1.5°C!

IPCC AR6 SYR Figure SPM.4c16822.10.23

SIXTH ASSESSMENT REPORT
Synthesis

Climate - Humans - Biodiversity: Positive Interactions determine solution
space
Our choices:
Stopping the global
megatrends throughsystem transitions:- Human systems- Ecosystems- Climatestabilization[Axel Guibourg CC BY-NC-ND 2.0; Hugh Han / Unsplash; Axel Fassio/CIFOR CC BY-NC-ND 2.0]

17SIXTH ASSESSMENT REPORT
Synthesis

Our adaptation measures and socioeconomic development define climate risks.
Successful risk reduction reflects feasibility and effectivenessConclusion: Limit warming close to 1.5°C in order tomaintain adaptation capacity!

IPCC AR6 SYR Figure SPM.4d189

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SIXTH ASSESSMENT REPORTSynthesis

There are multiple
opportunities for
scaling up
climate action.

IPCC AR6 SYR Figure SPM.7

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SIXTH ASSESSMENT REPORTSynthesis

Adaptation

Mitigation

Feasibility ofdiverse solution
options:
Adaptation often
has synergies withmitigation.

IPCC AR6 SYR Figure
SPM.2c2010

22.10.23“…the WGII view of the world!“From current imbalance …

… towards a sustainable future?

21SIXTH ASSESSMENT REPORT
Working Group II Report

Guiding principles

Sustainability through mosaic land-, sea- and freshwater scapessustaining gradients between well protected and used spaces• Quantify effective andecosystem-specific needs• Include species migration
corridors• Effective and socially justprotection measures to restore
biodiversity on 30-50% of Land-,Freshwater and Ocean systems
can help Planetary Health,including resilient ecosystemservices (Nature‘s contributions topeople)
IPBES-IPCC: Co-Sponsored Workshop on Biodiversity and Climate Change2211

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SIXTH ASSESSMENT REPORT
Working Group II Report

Guiding principles for ecosystem stewardship• Mosaic spatial planning andimplementation• Conservation and stabilization of C-richhabitats with enhancement of C storage
in organisms and soils.
• Consideration of adaptation limits• "Net gain": implement compensatory
measures with net gain for biodiversity• Land gain through reduced meat andmilk consumption, agroforestry,woodland pasture• Integration of human interests, e.g.
adaptation, livelihoods, health

Source:
IPCC WGII AR6SPM Figure 1

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SIXTH ASSESSMENT REPORTSynthesis

There is a rapidly
narrowing time
window of opportunity
to enable higher
climate resilient
development.

IPCC AR6 SYR Figure SPM.625

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SIXTH ASSESSMENT REPORT
Synthesis

Our future is decided
now!
All aspects of life wouldchange when avoiding
greenhouse gas
emissions andminimizing climate risks.
Each decision counts!

Conclusion:
Limit warming close to 1.5°C in order to maintain adaptation capacity!
IPCC AR6 SYR Figure SPM.2c

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SIXTH ASSESSMENT REPORT
Synthesis

thinking and responses

Conclusion:
Societal and political will are required
to accelerate climate action!
IPCC AR6 SYR Figure SPM.6

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SIXTH ASSESSMENT REPORT
Synthesis Report

The science is clear.
Any further delay in concerted
global action will miss a brief
and rapidly closing window tosecure a liveable future for all.
IPCC AR6 reports offer solutions.
However, it is getting late.
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Working Group II – Impacts, Adaptation and Vulnerability

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