SIXTH ASSESSMENT REPORTSIXTHASSESSMENT
Working GroupI – The Physical ScienceREPORTBasis

Working Group I – The Physical Science Basis

9 August 2021

Highlights from the IPCC 2021 report
the physical science basis
Valérie Masson-Delmotte, IPCC WGI Co-Chairwww.ipcc.ch/report/ar6/wg1

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

14 000 scientific publications
multiple lines of evidence

234 authors from 65 countries
600 contributors
1890 reviewers
78,000+ review comments
186 hours online approval

14,000 scientific publications assessed

234 authors from 65 countries
1890 reviewers
78,000+ review comments
186 hours online approval

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

Where are we now?
What are our possible climate futures?
How to limit future climate change?

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science BasisOur greenhouse gas emissions drive global heating
Atmospheric concentrations

CO2CH4

N2O

thousands of years
in the past
thousandsof years in the past

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

Leading to widespread, rapid,
and unprecedented changesSIXTH ASSESSMENT REPORTWorking Group I – The Physical Science Basis

Observed warming of 1.1°C is unusual in more than 2,000 years
Global surface temperature change since 1850-1900+1.1°CSIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

Observed warming is driven by emissions from human activities,
with greenhouse gas warming partly masked by aerosol cooling

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

Every region is affected in multiple ways
Hot extremes

Heavy rainfall

Agriculturaldrought

Human-caused climate change
is making extreme events
more frequent and more severe

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

Where are we now ?
What are our possible climate futures ?

How to scale up action ?

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

Future emissions cause future additional warming,with total warming dominated by past and future CO2 emissions
CO2 emissions
Very highHigh

Intermediate

Net zero CO2Low
Very low

Figure SPM.4

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

Global surface temperature will continue to increase until atleast the mid-century under all emission scenarios considered
CO2 emissions

Very highHighIntermediate
Low

1.5°C

Very low

Near-term

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

Future warming depends on future emissions
CO2 emissions

Very highHigh
Intermediate

2°C

Low
Very low

Mid-term

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

Many changes in the climate system become larger indirect relation to increasing global warming

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

Many changes in the climate system become larger indirect relation to increasing global warming↑ frequency and intensity● marine heatwaves and hot extremes● heavy precipitation● drought in some regions↑ proportion of intense tropical cyclones↓ Arctic sea ice, snow cover, permafrost

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

https://interactive-atlas.ipcc.ch

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

Global mean sea level will continue to rise over thousands of years
at a rate and magnitude depending on global greenhouse gas emissions
Global mean sea level rise relative to 1900 (m)low-likelihood, high impact storyline
including ice sheet instability processes
associated with deep uncertainty

CO2 emissions
Very highHigh
Intermediate
Low
Very low
likely (66%) ranges+16 cm in 1995-2014https://sealevel.nasa.gov/ipcc-ar6-sea-level-projection-toolSIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

Where are we now?
What are our possible climate futures?
How to limit future climate change?

SIXTH ASSESSMENT REPORTWorking Group I – The Physical Science Basis

Every ton of CO2 emissions adds to global warming

Very high CO2 emissions
High CO2 emissions

Intermediate CO2 emissions
Low CO2 emissions
Very low CO2 emissions

Increasing CO2

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

Reaching net zero CO2 emissions is a key condition to limit long-termwarming ; reducing methane emissions is critical to limit near-termwarming and improve air quality

after 100 years

Change in global surface temperature (°C)

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis

Differences in trends in global surface temperature would begin toemerge from natural variability within around the next 20 years
CO2 emissions (billion tonnes of CO2 per year)

CO2 concentration in the atmosphere (ppm)

Global surface temperature(oC)High

CO2 emissions
scenario

HighHigh
Low

Low
Low

differences in the 2020s

differences in the 2040s

SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis“
https://www.ipcc.ch/report/ar6/wg1The climate we experience inthe future depends on ourdecisions now