Irvine and schaefer 2021 solar geoengineering

1. Solar geoengineering: an
emerging scientific and
political challenge
Dr. Pete Irvine
p.irvine@ucl.ac.uk
Twitter: @peteirvine
1

2. Temperature and Cumulative CO2 emissions
Global temperatures rise linearly
with cumulative CO2 emissions.
To limit warming limit total
cumulative CO2 emissions.
Temperature targets can be
converted into carbon budgets
2

3. Temperature and Climate Risks
3

4. 4
CO2 T Risks Greater
Climate
Risks
Greater
Mitigation
Costs

5. The Paris Climate Agreement 2015
World’s first global climate agreement aimed to limit warming below 1.5 °C.
5

6. Paris Commitments vs. Paris Target
6

7. Meeting 1.5 °C will be really hard even with NETs
7

8. Components of long-term climate policy
8
2000 2100 2200
Global-mean
Temperature
No Policy
Emissions
Cuts
+ NETs
+ Solar
Geoengineering?

9. Volcanic eruptions cool the climate
Volcanic eruptions have a cooling effect that persists for years
They emit Mts of sulphates which create a global aerosol layer
9

10. Stratospheric Aerosol Geoengineering Deployment
High-flying jets could deliver Mts
of SO2 to stratosphere.
New designs needed but existing
technology sufficient
For 1Mt per year to stratosphere:
• 180 sorties per day
• 60 aircraft, 3 sorties per day
• $1.4 Billion per Mt per year
Bingamann et al. (2020), AIAA, DOI:
10.2514/6.2020-0618
10

11. Stratospheric Aerosol Geoengineering Cannot Solve
Climate Change
1) SA Geo cannot perfectly offset climate change
2) It only masks warming
3) Direct CO2 effects persist
• Physiological effects on plants
• Ocean acidification
4) It has side-effects
• Scatters light downwards too
• Stratospheric heating
• Stratospheric ozone loss
• Injected aerosols reach surface
11
But could it help?

12. Temperature response to solar geoengineering
Significant differences between forcings
But temperature restored within ~10%
12
Figure: Kravitz et al. (2011), ASL
GeoMIP G1
4xCO2 - ~4% solar
Figure: Irvine et al. (2017), Earth’s Future
4xCO2
4xCO2 - ~4% solar (100% Geo)
(50% Geo)

13. Hydrological response to solar geoengineering
Restoring temperatures weakens
hydrological cycle
Significant regional reductions in
precipitation
13
Precipitation Anomaly
4xCO2 - Control
G1 - Control
Figure:
Tilmes
et
al.
(2013),
JGR
Figure:
Kravitz
et
al.
(2013),
JGR
… are optional?

14. These plots show a case
where warming is halved
with solar geoengineering
Solar geoengineering is
highly effective at
offsetting both the
positive and negative
hydrological anomalies
14

15. 15
CO2 T Risks
Greater
Climate
Risks
Greater
Mitigation
Costs
Solar Geoengineering would Transform Climate Change
Greater
CO2 Risks
Greater
Solar Geo
Risks

16. 16
Would solar geoengineering undermine emissions cuts?
Greater
Climate
Risks
Greater
CO2 Risks
Greater
Solar Geo
Risks
Less
action on
emissions
cuts?

17. Solar geoengineering experiments planned
Marine Cloud Brightening SCOPEX planned for this year
- Test strat aerosol chemistry,
microphysics and plume
dynamics
17

18. Conclusions
Gulf between goals (1.5 °C) and emissions commitments (3 °C)
Negative emissions technologies necessary but insufficient
Solar geoengineering feasible and may help reduce risks
Observation challenges
Characterizing current climate, esp. stratosphere + clouds
Observing natural analogues – esp. volcanic eruptions
Supporting meso-scale perturbative field tests
Detecting illicit deployments?
Monitoring an ongoing deployment
18

19. FIN
19

20. Political challenges of solar
geoengineering
Dr. Stefan Schäfer
ESA, January 22nd, 2021

22. 2015 Paris Agreement aims to limit climate change by
“Holding the increase in the global average temperature
to well below 2°C above pre-industrial levels and
pursuing efforts to limit the temperature increase to
1.5°C above pre-industrial levels” (Article 2)

23. Remaining CO2-Budget in 2011 for these goals, according
to the IPCC:
• For 1,5°C: 400 Gt(CO2)
• For 2°C: 1.000 Gt(CO2)
Current annual emissions: ca. 40 Gt(CO2) per year

24. To achieve the 1.5°C goal, emissions would have to be
reduced at much higher rates than foreseen in the
Nationally Determined Contributions (NDCs).
In case the NDCs are met until 2030, emissions post-2030
would have to be reduced by about 5% per year—for a
66% chance at 2°C.

25. Lawrence et al. 2018, Nature Communications

26. Lawrence et al. 2018, Nature Communications

27. Reference
values defined
on the basis of
the difference
between 1.5
and 2°C of
warming:
650 Gt(CO2) or
0,6 W/m2.
Lawrence et al. 2018, Nature Communications

28. “Based on present knowledge, climate
geoengineering techniques cannot be relied on
to significantly contribute to meeting the Paris
Agreement temperature goals.”
Lawrence et al. 2018, Nature Communications

29. Mitigation deterrence
Can we be sure that solar geoengineering won‘t
first and foremost work to support those
interests that want to prolong widespread use
of fossil fuels?

30. Slippery slope
Can we ensure independent assessment and
decision-making that takes alternatives into
account and is not captive to vested interests?

31. Termination shock
If solar geoengineering were halted,
temperatures would rise rapidly to the level that
they were being suppressed from.
Can we expect this never to happen over the
lifetime of a solar geoengineering intervention,
a minimum of many decades?

32. Blame game
Blameworthy weather events: a new source of
conflict?
Who would take responsibility?
Compensation schemes? How much is a human
life worth, where?

33. Democratic decision-making
Who gets to participate, and who has final
decision-making powers over deployment?
What forms of justice would be taken into
account (distributive, intergenerational,
corrective, ecological, procedural)—if any?
Who would be able to voice criticism, and have
that criticism be heard and responded to?

34. Climate Engineering in Context: Critical Global Discussions
October 5-8, 2021

35. Thank you!
stefan.schaefer@iass-potsdam.de