The IPCC report provides the following key points: - Global warming has already reached 1.2 degrees Celsius above pre-industrial levels and further increases are inevitable due to past emissions. - Most regions will see increases in hot temperature extremes, heavy precipitation events, and droughts. - Sea level rise between 50cm to over 1 meter is expected by 2100, threatening coastal and island communities. - Further warming will depend on future emissions but 4 degrees of warming by 2100 is possible without rapid emissions reductions.

1. IPCC
The Intergovernmental Panel on
Climate Change
https://www.ipcc.ch/reports/
August 19, 2021
The Intergovernmental Panel on Climate Change (IPCC) is the United
Nations (UN) body for assessing the science related to climate change.
Review of IPCC Aug’21 report
Author: Marie-Paule Odini

2. <= This Summary for
Policy Makers (SPM)
is a 42 pages report
with a series of 10
graphics explained.
=> The full report (still under final edits).
Includes the Summary (SPM), the technical
summary and the full report
A technical Summary (still under
final edits)
And FAQs
(under final edits)

3. IPCC created in 1988 – 1st report in 1990

5. NEW
The 6th
assessment report
is composed of 3
reports + a
synthesis.
The 1st report was
just issued in
Aug’21
2nd, 3rd report and
synthesis are
planned for 2022

6. The current analysis of average temperature
shows that we have already reached a +1.2
degrees increase and we stand on a +4 degree
line if nothing is done to reduce global
warming

7. The IPCC has also launched a free of charge Interactive IPCC Atlas available online to drill down on
specific regions and huge amount of data collected by IPCC

8. Drill down on Europe shows European warming with temperature in average that does not go anymore
below -3 degrees
-3º

9. Based on temperature average between 1850 and 1900,
the global temperature will probably reach +1.5 degrees
within the next 20 years
Our world today with an average +1.2 degree is not the
same as in 2000 with an average +0.9 degree.
In the near future with +1.5, it will not be the same as
today either
The climate change that we
face has been unseen for
the past 2000 years and the
2010-2019 decade is
probably the warmest in
100 000 years !!
IPCC uses probability:
virtually certain 99–100% probability,
very likely 90–100%,
likely 66–100%,
about as likely as not 33–66%,
unlikely 0–33%,
very unlikely 0–10%,
exceptionally unlikely 0–1%.

10. HIGHLIGHTS
Report Link:
FAQ Link: https://www.ipcc.ch/report/ar6/wg1/downloads/faqs/IPCC_AR6_WGI_FAQs.pdf

11. The IPCC initial report in 1990 was
reporting a number of facts related to
global warming with average temperature
and some ‘projections’ based on initial
models. human influence was just
‘suspected’.
In 2021, the human influence is confirmed!
The average temperature has increased
from +0.6 to +1.2 (double).
The amount of data collected has
increased dramatically from 1887 stations
to 40,000 !
Models are much more granular, regional
and with increased resolution from 500km
to 25-50km !
New elements are introduced in the
models such as atmospheric and ocean
chemistry.

12. Based on reconstructed data from
paleoclimate archives until 1850 and
observed data these past years (1850-
2020), the change that we observe in
average temperature is unprecedented in
more than 2000 years.

13. HOW DOES THIS COMPARE WITH THE PAST ??
In the FAQ, IPCC shows past estimated
CO2 emissions and temperature.
Similar CO2 emission level and
associated warming +1.2/1.5 was
observed about 125 000 years ago.
And slightly higher CO2 emissions
occurred about 3 million years ago with
associated temperature increase of 2.5
to 4 degrees.
Source: IPCC AR6 FAQ

14. Source: futura science , © Ariel Provost, Wikimedia Commons
Note – not in IPCC report 23000 years ago
-5º : last glaciation period
+2º
3 million years ago

15. Climate change is visible at different levels:
- Air
- Land
- Ocean
- Ice
Source: IPCC AR6 FAQ
With different impact in high latitude and low latitude

16. Total observed
Warming is
around +1.2
degrees
Main source
Is Human
activities
Main factor to FIGHT are:
Carbon dioxide & Methane
Observed warming is driven by emissions from human activities, with
greenhouse gas warming partly masked by aerosol cooling
Aerosol*
cooling *Aerosol are tiny particles suspended in the gases that make up our atmosphere
(dust, sand, etc) – not spray…

17. North America: NWN (North-Western North America,
NEN (North-Eastern North America), WNA
(Western North America), CNA (Central North
America), ENA (Eastern North America),
Central America: NCA (Northern Central America),
SCA (Southern Central America), CAR (Caribbean),
South America: NWS (North-Western South America),
NSA (Northern South America), NES
(North-Eastern South America), SAM (South American
Monsoon), SWS (South-Western South America), SES
(South-Eastern South America),
SSA (Southern South America),
Europe: GIC (Greenland/Iceland), NEU (Northern
Europe), WCE (Western and Central Europe), EEU
(Eastern
Europe), MED (Mediterranean),
Africa: MED (Mediterranean), SAH (Sahara), WAF
(Western Africa), CAF (Central Africa), NEAF (North
Eastern
Africa), SEAF (South Eastern Africa), WSAF (West
Southern Africa), ESAF (East Southern Africa), MDG
(Madagascar),
Asia: RAR (Russian
Arctic), WSB (West Siberia), ESB (East Siberia), RFE
(Russian Far East), WCA (West Central Asia), ECA
(East Central Asia), TIB (Tibetan Plateau),
EAS (East Asia), ARP (Arabian Peninsula), SAS
(South Asia), SEA (South East Asia),
Australasia: NAU (Northern Australia), CAU (Central
Australia), EAU (Eastern Australia), SAU (Southern
Australia), NZ (New Zealand),
Small Islands: CAR (Caribbean), PAC (Pacific Small
Islands)
 Most regions in the world if not all now observe a High increase in hot extremes
 Less impact in New Zealand and Madagascar
(note: the world map is not in IPCC original graphic)

18. Heavy Precipitations
 Major increase in
northern hemisphere
 No decrease
Droughts
 Major increase in
northern hemisphere
 Major increase in Africa,
Southern Australia &
South East America
 Decrease in Northern
Australia

19. IPCC report considers 5 scenarios:
- SSP1-1.9
- SSP1-2.6
- SSP2-4.5 -> same until 2050
- SSP3-7.0
- SSP5-8.5
SSPx-y, where ‘SSPx’ refers to the Shared
Socio-economic
Pathway or ‘SSP’ describing the socio-
economic trends underlying the
scenario, and ‘y’ refers to the
approximate level of radiative
forcing (in W m–2) resulting from the
scenario in the year 2100.
Looking into:
- CO2
- Methane
- Nitrous Oxide
- Sulfur Dioxide
Net negative CO2
High & very high
emissions
Based on CMIP6: Coupled Model Intercomparison Project Phase 6 of the World Climate Research Programme. These models include new and better
representation of physical, chemical and biological processes, as well as higher resolution, compared to climate models considered in previous IPCC
assessment reports.

20. Observations until 2019.
In blue reverse radiating =
Cooling
In orange = warming
The lifetime in atmosphere
shows the huge impact of
Methane

21. 5 scenarios
Baseline: 1850-1900 = 0
Today: dark shade
Considering:
- CO2
- Non CO2 GHG
- And compensation from
aerosol (tiny particules
in the atmosphere that
obstruct sun lights and
reduce temperature)
TODAY
Projection 2081-2100
 Major impact is again CO2
 Which explains why we have a focus on carbon neutral/carbon free

22. Based on previous graphic and the 5 scenarios
Decrease CO2
NOW
Decrease CO2
After 2050
CO2 keeps increasing
We will reach
+1.5 degrees 
before 2040 !!
We will reach
+2 degrees 
before 2060 !!
Since we keep
Increasing CO2
Emissions …
We may
remain
below 3
degrees if
we reach
net zero
around
2050 …
Last time the planet hit +2 degrees
Was 3 million years ago …

23. THE EVOLUTION of TEMPERATURE,
PRECIPITATIONS and DROUGHTS will vary
- Per region
- Over land versus ocean
- Have more frequent extremes
- Will impact soils, environment and our life !!

24. a) Comparing :
- observed data from Berkeley
data set with linear regression
to remove isolated variations.
White indicates not enough
data to make calculation
- And Simulation
=> Very similar, so model is good !
Land is much more impacted
than ocean (x2) and north pole
even more (x3 or more)
b) Projections for +1.5, +2 and
+4 degrees
 The average is land +
ocean, but land is much
more than the average !!
 Ex +2, lands are +3.5 or 4
 +4 , lands are 6.5 or more

25. => The increase in precipitation is more likely than increased dryness, except north part of south America or Australia.
Precipitations will become important in high latitudes incl poles, and middle east/Africa subtropical region

26.  Despite an increase in precipitation, the temperature and evapotranspiration leads to soil dryness major
increase in many parts of the world !!
 (not in GIEC report, but major impact is expected on forest & agriculture, as well as water supplies)

27.  Land Heat extreme are getting more frequent … IPCC shows that events (hot temperature extremes) that used to
occur once every 10 years now occur 2.8 times every 10 years and would occur 9.4 times per 10 years with a +4
degree average warming.
 Similarly events that occur once every 50 years, now occur 4.8 times per 50 years and would occur 39.2 times per 50
years with a +4 degree average warming.

28.  Heavy precipitations with storms and flooding are also more frequent. What used to be once every 10 years is
now 1.3 times every 10 years (in average ! with regional occurrence much more frequent as we see in northern
latitude for instance) and would increase to 2.7 times with +4 degree warming
 Similarly intense drought will become more frequent

29. => The more we
produce CO2, the less
Ocean & Land can
absord in %

30. Ocean is
particular have
accumulated a
huge excess of
CO2 already

31. Surface Temperature
2050: +2 degrees most likely
(versus 1.2 today)
2100: will vary a lot depending
on scenario
Between 2.5 and >4 degrees !!

32. Droughts around
Mediterranean sea for
instance will impact
forests, agriculture
and drinkable water

33. Arctic : North , banquise
Antarctic : South , continent
(Note: not in IPCC report – Antarctic water is equivalent to an increase of 57m of global mean sea level - GMSL)
“The Arctic is projected to be practically ice-free near mid-century under midand high GHG emissions scenarios.”
Note: melting of the Arctic does not increase sea level – it is like ice cube, same water level
Ice free
Becoming
Ice free

34. IPCC : “Very likely ranges are shown for SSP1-2.6 and SSP3-7.0.”
pH is a logarithm function
So pH7 is 10 times more acid
than pH8
The pH scale runs from 0 to 14,
with 7 being a neutral pH.
Anything higher than 7 is basic
(or alkaline) and anything lower
than 7 is acidic.
OCEAN pH decrease impacts Acidity
From 8.05 today to 8- 7.95 in 2050 and would vary a lot depending on the scenario

35. Global Mean Sea Level (GMSL) evolution
IPCC “It is virtually certain that global mean sea level will continue to rise over the 21st century”
“under a very high GHG emissions scenario (SSP5-8.5) (low confidence) – cannot be ruled out
due to deep uncertainty in ice sheet processes”
=> IPCC has low confidence in IPCC models for high GHG emission scenario simulation for sea
level projections due to uncertainty on mechanism around ice sheet melting
Likely scenarios by 2100:
SSP1-2.6 => 0.46-0.99 m
SSP2-4.5 => 0.66-1.33 m
Rise between 50cm and 1.3m
By 2100

36. 2050: 30cm
2100: between 50cm and 1.3m
Global Mean Sea Level (GMSL) evolution

37. MELTING OF ICE SHEET
Time to melt
Time to freeze
Ice Sheet can melt very fast due to :
Ocean temperature or
Air temperature
But it takes thousand of years to rebuild

38. Climatic impact-drivers (CID) A total of 35 climatic impact-drivers (CIDs)
grouped into seven types are shown: heat
and cold, wet and dry, wind, snow and ice,
coastal, open ocean and other
Almost all (96%) regions are projected to
experience changes in at least 10 CIDs and
50% in at least 15 CIDs.
Changes refer to a 20–30 year period
centered around 2050 and/or consistent
with 2°C global warming compared to a
similar period within 1960-2014 or 1850-
1900.
8 CID are particularly impactful:
• Surface temperature
• Extreme heat
• CO2 at surface (pollution)
• Relative sea level
• Coastal flood
• Coastal erosion
• Marine heatwave
• Ocean acidity

40. Every tCO₂ emissions adds to global warming
Baseline 1850 – 0
2019: 2390 (± 240; likely range) GtCO2
=> The more we add CO2 the more temperature
increases but also other impacts increase
IPCC: “If global net negative CO2 emissions
were to be achieved and be sustained, the
global CO2-induced surface temperature
increase would be gradually reversed but other
climate changes would continue in their
current direction for decades to millennia
(high confidence). For instance, it would take
several centuries to millennia for global mean
sea level to reverse course even under large net
negative CO2 emissions (high confidence).”

41. COVID IMPACT
IPCC: “Emissions reductions in 2020 associated with measures to reduce the spread of COVID-19 led to
temporary but detectible effects on air pollution (high confidence), and an associated small, temporary
increase in total radiative forcing, primarily due to reductions in cooling caused by aerosols arising from
human activities (medium confidence). Global and regional climate responses to this temporary forcing are,
however, undetectable above natural variability (high confidence). Atmospheric CO2 concentrations
continued to rise in 2020, with no detectable decrease in the observed CO2 growth rate (medium
confidence)”
 Visible on air pollution decrease
 But not visible on atmospheric CO2 concentration

42. The Gulf Stream is the biggest
current in the North Atlantic
Ocean.
It transports about 30B kg/s of
water northward past points
on the east coast of North
America.
It is a warm current, with
temperatures 5°C to 15°C
warmer than surrounding
waters, so it carries warmer
water (thermal energy) from
its southern origins and
releases warmth to the
atmosphere and surrounding
water.
Gulf Stream may slow down
Which would lower Europe
temperature
IPCC: “Based on models and theory …the Gulf Stream will not change much and would not shut down totally”

43. To limit global warming to 1.5 degree, remaining carbon budget is 500Gt !! And 1150Gt for 2 degree !

44. OTHER SOURCES
(not in IPCC 2021 report)

45. Amount of water on earth 1 400 millions de km3:
• Ocean: 1300 million de km3
• Rest: about 30M km3
• Antartica 90% - 29M km3
• Groenland – 2.5M km3
• Glacier – 0.2M km3
Drinkable water
=> If this water melts and goes into the
ocean, we loose drinkable water –
and ocean could raise 84m
=> Salted water
3 million years ago, the world temperature was about +2 degrees.
Antarctica melted partially and global sea level raised 20 m
Source: Victoria University, Australia
If Antarctica melts, global sea level increases 57m
If Groenland melts, global sea level increases 6m
Understanding Global Sea Level rise (1)

46. Understanding Global Sea Level rise (2)
NOAA: National (US government entity)
<= 2 main sources :
- Thermal expansion: when temperature
increases, water takes more space, oceans
‘grows’
- Melting of continental glaciers: Antarctica,
Groenland, mountain glaciers
 NOAA projection is for water level to rise
between 1m & 2m by 2100 with
intermediate/high scenarios
 But the concern is increase in Big High Tide
Occurrence
Source: NOAA, US Climate org

47. IPCC : “Very likely ranges are shown for SSP1-2.6 and SSP3-7.0.”
pH is a logarithm function
So pH7 is 10 times more acid
than pH8
The pH scale runs from 0 to 14,
with 7 being a neutral pH.
Anything higher than 7 is basic
(or alkaline) and anything lower
than 7 is acidic.
 The more CO2 (carbon dioxide) the ocean absorbs , the more CO2 + H2O => H2CO3 generates carbonic acid , which
then dissociate into bicarbonate (HCO3 -) : H2CO3 => H+ + HCO3 - H+ increases ocean acidity
 Then HCO3 dissociate again: HCO3 => H+ + CO32- , into additional H+ and carbonate ions (CO32-) useful for shells &
corals by combining calcium and carbonate from seawater
 But more and more H+, more acidity and equation reverses: CO32- combines with H+ to produce HCO3
 resulting in fewer carbonate ions available for calcifying organisms … and making it more difficult for organisms like
oysters and corals to make hard shells and skeletons by combining calcium with carbonate ions (CO32-)
UNDERSTANDING OCEAN pH (1)

48. UNDERSTANDING OCEAN pH (2)
As ocean acidification increases, more H+ is available and
carbonate ions (CO32-) bond with excess hydrogen, resulting
in fewer carbonate ions available for calcifying organisms to
build and maintain their shells, skeletons, and other calcium
carbonate structures. If the pH gets too low, shells and
skeletons can even begin to dissolve.
Key reversible equations !
Source: Nature