determining allowable co2 emissions from regional- and ... · 14.6.2016 sonia seneviratne / iac eth...

Sonia Seneviratne / IAC ETH Zurich 14.6.2016 Ecole Polytechnique

Determining allowable CO2 emissions from regional- and impact-related climate targets Sonia I. Seneviratne

Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland [email protected]

Acknowledgements: M. Donat, A.J. Pitman, R. Knutti, R. Wilby, E. Davin, A. Hirsch, Q. Lejeune, R. Orth, M. Vogel, and M. Wilhelm Ecole Polytechnique, France, 14.06.2016


2015 Paris agreement


COP21: 1.5° vs 2°


Climate projections

(IPCC 2013)

Agreement at COP21 to hold the increase in global temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit increases to 1.5°


3 questions using climate simulations: •  Identify optimal target between 1.5°-2°: Including the impact

perspective

•  How do we reduce uncertainties: •  Example: Land surface feedbacks for temperature extremes

•  How do we reduce regional impacts?

Towards a 1.5°-2° world…


Allowable CO2 emissions based on regional targets?

(Seneviratne et al. 2016, Nature)


Link between cumulative CO2 emissions and global T°

Direct link between cumulative CO2 emissions and climate response A global T° target can be linked to cumulative emissions target

(IPCC 2013)


What are implications of global temperature changes?

“People are not killed by the global temperature”… …what matters are regional changes in extremes and impacts

How do these relate to the projected global temperature changes?


1.5°C and 2°C targets: “reasons for concern”

(IPCC 2014, WG2)


1.5°C and 2°C targets: “reasons for concern”

(IPCC 2014, WG2)

Can we be more quantitative?


Scaling relationships for extremes

Can these scaling relationships be used to relate regional changes with global T° changes and thus with cumulative CO2 emissions targets?



Relating regional climate targets with CO2 emissions


RCP8.5 RCP4.5



Interesting results: •  Almost linear scaling for

multi-model mean (see also Fischer et al. 2014, GRL)


RCP8.5 RCP4.5





•  Pattern independent of

emissions scenario!


RCP8.5 RCP4.5





•  Pattern independent of

emissions scenario!

•  Tool to define impact-based targets?


RCP8.5 RCP4.5



Rx5day Southern Asia


Also scaling found for warming of minimum temperatures

RCP8.5

RCP4.5



Rx5day Southern Asia


Also scaling found for warming of minimum temperatures and changes in heavy precipitation

RCP8.5

RCP4.5



Advantages:

1.  Provides a better quantitative understanding of relation between emissions and impacts for stakeholders

2.  Independent of emissions scenario, direct link between political decisions and impacts

3.  Help linkage between costs of emissions reduction and avoided costs of impacts



Advantages:

1.  Provides a better quantitative understanding of relation between emissions and impacts for stakeholders

2.  Independent of emissions scenario, direct link between political decisions and impacts

3.  Help linkage between costs of emissions reduction and avoided costs of impacts

Caveats:

•  Large uncertainty ranges in some cases (e.g. droughts) •  Shared model biases •  Does not consider the impact of local forcing (land use, aerosols) •  Does not include uncertainty of scaling of CO2 emissions with global T°


3 questions using climate simulations: •  Identify optimal target between 1.5°-2°: Including the impact

perspective





Uncertainties in scaling: Example from 2 regions

Contiguous US

Central Europe

IPCC SREX regions



Txx, CEU


Role of soil moisture – temperature feedbacks

T+

GHG

T++

GHG

è evidence in projections: Seneviratne et al. 2006, Nature; Diffenbaugh et al. 2007, GRL; Seneviratne et al. 2013, GRL è observational evidence: Hirschi et al. 2011, Nature Geoscience; Quesada et al. 2012, Nature Climate Change; Mueller and Seneviratne 2012, PNAS; Miralles et al. 2014, Nature Geoscience


Analysis for Southeastern Europe Quantile regression of %HD with 6-month SPI

(Hirschi et al. 2011, Nature Geoscience)

Soil moisture – temperature feedbacks: Observations

Impact of soil moisture on hot extremes


Analysis for Southeastern Europe Quantile regression of %HD with 6-month SPI

(Hirschi et al. 2011, Nature Geoscience)

Impact of soil moisture on hot extremes

Conditional probability: Higher probability of occurrence with drier springs



(Mueller and Seneviratne 2012, PNAS)

NHD: # hot days SPI: Standardized Precipitation Index



(Mueller and Seneviratne 2012, PNAS)

NHD: # hot days SPI: Standardized Precipitation Index


Generally strong lag relationship between precipitation deficits and temperature extremes in transitional regions between dry and wet climates


Soil moisture-temperature feedbacks in global climate models

Soil moisture (point in Central Europe)

GLACE-CMIP5 investigates the impact of decadal changes in soil moisture on climate 5 CMIP5 models (CESM, EC-EARTH, GFDL, IPSL, MPI-ESM)

(Seneviratne et al. 2013, GRL)

GLACE-CMIP5 experiment


(GLACE-CMIP5 experiments, Seneviratne et al. 2013, GRL)

Mean drying of the soil is explaining added warming in extremes in several land regions

Role of soil moisture feedbacks


(GLACE-CMIP5 experiments, Seneviratne et al. 2013, GRL)

Mean drying of the soil is explaining added warming in extremes in several land regions

Role of soil moisture feedbacks

Regions with strong soil moisture effects in projections correspond well to those showing a stronger warming of extremes


Txx, CEU

By how much can we reduce the uncertainty in projections (e.g. using ground and remote sensing observations of land variables)?

ERC DROUGHT-HEAT project



(Mueller and Seneviratne 2014, GRL)

Evidence of systematic biases in current climate models

Systematic biases in climate models


3 questions using multi-model climate simulations: •  Identify optimal target between 1.5°-2°: Including the impact

perspective





Reducing impacts

RCP8.5 RCP4.5


RCP2.6 scenario

(VanVuuren et al. 2011, Clim. Change)


RCP2.6 scenario

(VanVuuren et al. 2011, Clim. Change)

Present simulations do not include biophysical impacts of land use (will be investigated in CMIP6 LUMIP experiment)

e.g. reforestation leading to warming in high-latitudes!


Impact of land use and land cover changes on climate

Impact of land cover type on surface fluxes during heatwaves Forests lead to a warming compared to grasslands!

(Teuling et al. 2010, Nature Geoscience)



Impact of land cover type on surface fluxes during heatwaves Forests lead to a warming compared to grasslands!


NB: Behaviour may reverse under long droughts




NB: Behaviour may reverse under long droughts


Changes in albedo induced by agricultural management

Differences in surface albedo from no-till farming

Photograph by Jim Richardson (National Geographic) (Davin et al. 2014, PNAS)


Crop distribution (%)

(Davin et al. 2014, PNAS)

Summer mean temperature changes


Changes in albedo induced by agricultural management

(Davin et al. 2014, PNAS)

Preferential cooling of hot extremes when considering combined albedo and evaporation effects!


Reducing impacts

Regional scale increases in temperature could also be reduced through regional measures (e.g. irrigation, changes in surface reflectivity): Regional “land climate engineering”

RCP8.5 RCP4.5


Reducing impacts

Regional scale increases in temperature could also be reduced through regional measures (e.g. irrigation, changes in surface reflectivity): Regional “land climate engineering” But no/little effects on ocean acidification, sea level rise

RCP8.5 RCP4.5


ERC DROUGHT-HEAT project

ERC consolidator grant (2014-2019)


Conclusions and outlook •  Scaling of regional changes in extremes with changes in global

temperature (and cumulative global CO2 emissions) •  Relationship can be used to:

•  Inform choice of global temperature targets •  Reduce uncertainties in projections •  Link costs of adaptation and mitigation •  Design strategies for regional adaptation

•  Soil moisture and land albedo effects are important for land climate and in particular for temperature extremes èrelevant for projections, mitigation and adaptation

Contact: [email protected]

determining allowable co2 emissions from regional- and ... · 14.6.2016 sonia seneviratne / iac eth...

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