Thomas StockerClimate and Environmental Physics, University of Bern

IPCC AR5: The Physical Science Basis (2)Lecture 4:

14th International Seminar on Climate System and Climate Change, Zhuhai

Lecture 4:IPCC AR5: The Physical Science Basis (Part 2)

1. Effective communication: A duty for scientists

2. Projecting anthropogenic climate change

3. Achieving climate stabilization, climate targets

14th International Seminar on Climate System and Climate Change, Zhuhai

Warming of the climate system is unequivocal, [...]

Human influence on the climate system is clear.

Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.

What are the characteristics of Headline Statements?

• firmly rooted in the scientific assessment

• avoid jargon and excessive use of numbers

• part of an overarching narrative

• hierarchical: from simple to complex

D. Understanding the Climate System and its Recent Changes

Human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations, [...]

D.1 Evaluation of Climate ModelsClimate models have improved since the AR4. Models reproduce [...]

• 10 bullet points with numbers, likelihoods and confidence.

Observational and model studies [..] provide confidence in the magnitude of global warming in response to past and future forcing.

• 7 bullet points with numbers, likelihoods and confidence.

D.2 Quantification of Climate System Responses

[..] It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.

• 12 bullet points with numbers, likelihoods and confidence.

D.3 Detection and Attribution of Climate Change

D. Understanding the Climate System and its Recent Changes

Human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations, [...]

D.1 Evaluation of Climate ModelsClimate models have improved since the AR4. Models reproduce [...]

• 10 bullet points with numbers, likelihoods and confidence.

Observational and model studies [..] provide confidence in the magnitude of global warming in response to past and future forcing.

• 7 bullet points with numbers, likelihoods and confidence.

D.2 Quantification of Climate System Responses

[..] It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.

• 12 bullet points with numbers, likelihoods and confidence.

D.3 Detection and Attribution of Climate Change

WGI 12th Plenary:Finally, a sentence is approved ....

Lecture 4:IPCC AR5: The Physical Science Basis (Part 2)

1. Effective communication: A duty for scientists

2. Projecting anthropogenic climate change

3. Achieving climate stabilization, climate targets

14th International Seminar on Climate System and Climate Change, Zhuhai

IPCC 2013, TS Box 1.1, Figure 1

Carbon Emissions inferred from using a simple climate model:

IPCC 2013, TS Box 1.1, Figure 3

IPC

C 2

013,

Fig

. SPM

.7a

Global mean surface temperature change from 1986-2005

Continued emissions will cause further warming and changes in all components of the climate system.

IPC

C 2

013,

Fig

. SPM

.8

4.5°C world2°C world

The contrast in precipitation between wet and dry regions and between wet and dry seasons will increase, [...]

Change in average precipitation (1986-2005 to 2081-2100)

RCP8.5

IPC

C 2

013,

Fig

. SPM

.8b

RCP 2.6 (annual) RCP 8.5 (annual)

IPCC 2013: Atlas of Global and Regional Climate Projections

Regional Changes in Eastern Asia (2081-2100)

10 more frequent

Emissions Scenarios A1B, A2:

A 1-in-20 year hottest day is likely to become a 1-in-2 year event by the end of the 21st century

IPCC Special Report on Managing Extreme Events and Disasters to Advance Climate Change Adaptation

IPCC 2011, SREX SPM.4A

up to 4 more frequent

Emissions Scenarios B1, A1B, A2:

A 1-in-20 year annual maximum daily precipitation amount is likely to become a 1-in-5 to a 1-in-15 year event by the end of the 21st century

IPCC 2011, SREX SPM.4B

IPCC Special Report on Managing Extreme Events and Disasters to Advance Climate Change Adaptation

IPC

C 2

013,

Fig

. SPM

.7b

[...], a nearly ice-free Arctic Ocean in September before mid-century is likely for RCP8.5 (medium confidence).

Northern Hemisphere September sea ice extent

© IP

CC

201

3

RCP2.6 RCP8.5

IPC

C 2

013,

Fig

. SPM

.8

RCP2.6 (2081-2100), likely range: 26 to 55 cmRCP8.5 (in 2100), likely range: 52 to 98 cm

IPC

C 2

013,

Fig

. SPM

.9

IPC

C 2

013,

TFE

.2, F

ig. 2

+19 cm

+98 cm

It is very likely that the Atlantic Meridional Overturning Circulation will weaken over 21st

century.

IPCC 2013, TS TFE.5 Fig.1.

Ocean circulation changes:

Climate change will affect carbon cycle processes in a way that will exacerbate the increase of CO2 in the atmosphere (high

confidence). Further uptake of carbon by the ocean will increase ocean acidification.

IPC

C 2

013,

Fig

. SPM

.7c

Lecture 4:IPCC AR5: The Physical Science Basis (Part 2)

1. Effective communication: A duty for scientists

2. Projecting anthropogenic climate change

3. Achieving climate stabilization, climate targets

14th International Seminar on Climate System and Climate Change, Zhuhai

Warming of 0.8 to 2.5°C

1000 billion tons of carbon

Any climate target impliesa limited carbon budget

IPC

C 2

013,

Fig

. SPM

.10

790 Bill. t C

Budget for the 2°C target: 790 bil t CCO2 emissions until 2016*: −565 bil t C

remaining emissions: 225 bil t C

The CO2 budget will be exhausted by about 2040.

CO2 emissions in 2016*: 10 bil t C* updated from IPCC 2013

By 2040, the 2°C target will be lost.

( mod

ified

from

Pet

ers

et a

l., 2

013)

CO2 Emissions: Nearly exponential increase

~ e+1.8 %/yr ∙ t

2040

2020 20

30

2°C scenarios assuming no net negative emissions

(Sto

cker

, 201

3)

Clim

ate

Targ

et (°

C)

Starting Year of Emissions Reduction

The closing door of climate targets

(Sto

cker

, 201

3)

UnachievableClimate Targets

Clim

ate

Targ

et (°

C)

Starting Year of Emissions Reduction

(Sto

cker

, 201

3, A

llen

& St

ocke

r, 20

14)

Mitigation delay: Peak temperature rises fast

Warmingduring delay

Delay in mitigation

Mitigation delay sensitivityT/ t

Mitigation delay: Peak temperature rises fast

20th century warming: 0.08 °C per decade

1998 to 2012 warming: 0.05 °C per decade

Mitigation Delay Sensitivity

T / t 0.4 °C per decade

Committed peak warming rises 2.5 to 6times faster than observed warming

1951 to 2012 warming: 0.12 °C per decade

(Pfis

ter &

Sto

cker

, 201

6)

Mitigation delay: Steric sea level rise

(bas

ed o

n Pf

iste

r & S

tock

er, 2

016)

Mitigation delay: Committed steric sea level rises fast

20th century total sea level rise: 17 mm per decade

1971 to 2010 steric sea level rise: 8 mm per decade

Mitigation Delay Sensitivity

MDSSSLR3000 100 mm per decade

Committed steric sea level rise increases 7 to 25 times faster than observed sea level rise

1971 to 2010 total sea level rise: 20 mm per decade

Climate Change is a Resource Problem

Warming: Resource Health

Drying: Resource Water

Sea Level: Resource Land

Knut

ti et

al.,

201

5

2°C

Knut

ti et

al.,

201

5

1.5°C

Lecture 4: Take-home messages

• IPCC WGI has a new form of effective communication through approved headline statements.

• Multimodel simulations are the backbone of the WGI contribution to AR5. They quantify the changes that are projected under four scenarios (Representative Concentration Pathways).

• The cumulative carbon budget is the most policy-relevant finding of the WGI contribution. It has direct implications for the requirements to limit climate change.

• With continuing emissions climate targets become unachievable at an accelerating speed. Emissions reductions are therefore urgent if climate change and its impacts are to be limited.