Presentation from Workshop on Climate Change: Assumptions, Uncertainties and Surprises, 3-4 September 2020

1. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
Integrating changes in extreme events in climate and
mitigation scenario development
Sonia I. Seneviratne
Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland
sonia.seneviratne@ethz.ch
OECD Workshop «Climate change: Assumptions, uncertainties and surprises», 03.09.2020

2. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
Extremes & Scenarios
• How do we design resilient emissions pathways
consistent with the Paris Agreement?
• Role of climate extremes in affecting realism of
scenarios and resilience of society

3. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
California, 2018, 2020
Japan 2018
Recent extreme events
2018-2020 extremes
Germany 2018
Australia, 2019-2020 Siberia, 2020
Europe, 2019

4. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
Relevance of extremes for climate scenarios
• Extremes affect ecosystems:
• A single fire and/or drought event can destroy a large part
of a forest and annihilate several years of CO2 storage
• Affects production of biofuels, food
• Affects biodiversity, animals, plants

5. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
Relevance of extremes for climate scenarios
• Extremes affect ecosystems:
• A single fire and/or drought event can destroy a large part
of a forest and annihilate several years of CO2 storage
• Affects production of biofuels, food
• Affects biodiversity, animals, plants
• Extremes affect people
• Single events can kill people, affect agriculture, spread
diseases (e.g. cholera), and destroy livelihoods (flooding)
• Single events can contribute to instability, conflict,
migration (e.g. 2006-2011 Syrian drought)

6. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
Relevance of extremes for climate scenarios
• Extremes affect ecosystems:
• A single fire and/or drought event can destroy a large part
of a forest and annihilate several years of CO2 storage
• Affects production of biofuels, food
• Affects biodiversity, animals, plants
• Extremes affect people
• Single events can kill people, affect agriculture, spread
diseases (e.g. cholera), and destroy livelihoods (flooding)
• Single events can contribute to instability, conflict,
migration (e.g. 2006-2011 Syrian drought)
• Extremes affect energy production and use
• Hydropower energy production
• Lack of cooling for nuclear reactors during heatwaves
• Enhanced energy demand for cooling during heatwaves

7. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
Mitigation scenarios
(IPCC SR15, SPM.3a)
On average net-zero CO2
emissions in 2050 and negative
emissions (carbon dioxide
removal; CDR) after that
Scenarios compatible with low
or no-overshoot of 1.5ºC have
CDR at the level of about 10%
of present-day emissions:
much of it through land-based
CDR

8. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
Land-based carbon dioxide removal vs extremes
• Afforestation
• Bioenergy with carbon
capture and storage

9. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
Land-based carbon dioxide removal vs extremes
• Afforestation
• Bioenergy with carbon
capture and storage
• How about extremes?

10. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
Land use changes in Integrated Assessment Models (1.5C)
(Seneviratne et al. 2018, Phil. Trans. Roy. Soc. A)
Are these changes in land use realistic given changes in extremes?

11. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
Relevance of extremes for climate scenarios
• Models used to compute potential emissions pathways
(Integrated Assessment Models) do not include changes in
extremes as constraint for scenarios
• Impact models are found to underestimate impacts from
extreme events (e.g. Schewe et al. 2019, Nature Communications)
• Climate change literature is only starting to consider
compound events (combination of extremes leading to
oversized impacts, e.g. Zscheischler et al. 2018, Nature Climate Change): Fire
risk, concurrent impacts on breadbasket regions

12. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
How to speed up research?
An Earth System Model
emulator can allow to compute
new climate scenarios rapidly,
which could provide a
feedback on the development
of emissions scenarios
Emissions
scenarios
Global
warming
trajectories
Regional
extremes
ERC Proof-of-concept MESMER-X project (2021-2022)
(Beusch et al. 2020, Earth Syst. Dyn.)

13. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
How to speed up research?
An Earth System Model
emulator can allow to compute
new climate scenarios rapidly,
which could provide a
feedback on the development
of emissions scenarios
Emissions
scenarios
Global
warming
trajectories
Regional
extremes
ERC Proof-of-concept MESMER-X project (2021-2022)
(Beusch et al. 2020, Earth Syst. Dyn.)

14. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
Conclusions
• COVID pandemics has shown lack of preparedness of human society
to global threats

15. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
Conclusions
• COVID pandemics has shown lack of preparedness of human society
to global threats
• Extreme events, including compound events, constitute a major threat
from climate change, already now. We cannot be sure that our society
would be able to cope with extremes associated with a global warming
of >2ºC (unprecedented for homo sapiens).

16. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
Conclusions
• COVID pandemics has shown lack of preparedness of human society
to global threats
• Extreme events, including compound events, constitute a major threat
from climate change, already now. We cannot be sure that our society
would be able to cope with extremes associated with a global warming
of >2ºC (unprecedented for homo sapiens).
• Limiting global warming to 1.5ºC would imply reduced risks and less
probability of major extreme events (hot extremes in most regions,
heavy precipitation in several regions, droughts in some regions)
compared to 2ºC (IPCC SR15)

17. Sonia Seneviratne / IAC ETH Zurich03.09.2020 OECD workshop
Conclusions
• COVID pandemics has shown lack of preparedness of human society
to global threats
• Extreme events, including compound events, constitute a major threat
from climate change, already now. We cannot be sure that our society
would be able to cope with extremes associated with a global warming
of >2ºC (unprecedented for homo sapiens).
• Limiting global warming to 1.5ºC would imply reduced risks and less
probability of major extreme events (hot extremes in most regions,
heavy precipitation in several regions, droughts in some regions)
compared to 2ºC (IPCC SR15)
• Mitigation scenarios for low-emissions pathways need to be better
assessed in the light of their resilience to extreme events (e.g. European
Green Deal). Lack of consideration so far means we should be
particularly cautious and implement ambitious mitigation fast.