Lecture Climate ChangeLesson 3

Glaciers & Clouds

Rene Orthrene.orth@bgc-jena.mpg.de

Course webpagehttps://www.bgc-jena.mpg.de/bgi/index.php/Lectures/HydroBioClimClimateChange

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Lesson 3

Glaciers & Clouds

1) Glaciers

Basic functioning

Impact of climate change

2) Clouds

Basic functioning

Impact of climate change

3) Aerosols

4) Geoengineering

Glaciers

The cryosphere is a natural integrator of climate variability→ therefore it provides a visible signature of climate change

IPCC (2013)

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Glaciers

More than half the Earth’s land surface (seasonally) covered by ice

Ice content on land closely linked with sea level

IPCC (2013)

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Basic functioning of glaciers

Glaciers(1) grow in the accumulation area(2) flow downslope(3) shrink/melt in the ablation area

Equilibrium line altitude (ELA) determines size of glacier

IPCC (2013)

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Ice flows!

On long time scales ice behaves like a viscous liquid

https://www.youtube.com/watch?v=Za5wpCo0Sqg (from 1:08 min)

https://www.youtube.com/watch?v=hRhnLtFZxso

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Basic functioning of glaciers

On short time scales (< 50 years)

Complex glacier dynamics

→ depend on size, slope, distribution of area across elevation, amount of (dark) debris cover

On long time scales (> 50 years)

Climate as main control

→ temperature controlling the equilibrium line altitude, and precipitation amount and seasonality feeding the glacier

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Summary

● Glaciers are controlled by climate at decadal-centennialtime scales, and by a complex interplay of topography,elevation, and local conditions on shorter time scales

Lesson 3

Glaciers & Clouds

1) Glaciers

Basic functioning

Impact of climate change

2) Clouds

Basic functioning

Impact of climate change

3) Aerosols

4) Geoengineering

Impact of climate change

Climate changeshifts ELA upwards

150m per degreewarming

Precipitationchanges locally also

play a role

IPCC (2013)

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Impact of climate change

● Glacier volume has decreased in all mountain ranges across theworld during the past 150 years

● Decrease rate varies over time, accelerating in recent decades

● Glaciers take several decades to adjust to a changed climate(i.e. most glaciers will continue to shrink even if warming would stopnow)

● Small glaciers adapt faster than large glaciers, many of them willdisappear because they will have no accumulation area left

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Impact of climate change

Glacier lengths are decreasing all around the world

Known through satellite and in situ measurements

IPCC (2013)

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IPCC (2013)10

Length changes translate intomass changes

Impact of climate change

IPCC (2013)

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Glacier retreat often leaves lakes

Impact of climate change12

Runspect.com

Summary

● Glaciers are controlled by climate at decadal-centennialtime scales, and by a complex interplay of topography,elevation, and local conditions on shorter time scales

● Glaciers are shrinking in volume and length all over theworld and will continue to shrink for decades independentof human emissions; many small glaciers will disappear

Lesson 3

Glaciers & Clouds

1) Glaciers

Basic functioning

Impact of climate change

2) Clouds

Basic functioning

Impact of climate change

3) Aerosols

4) Geoengineering

Clouds- warming atmosphere through condensation- cooling Earth through reflecting short-wave radiation to space- warming Earth through reflecting long-wave radiation back to Earth→ all depending on cloud amount, height, reflectivity

IPCC (2013)

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Clouds

Low clouds

● reflect some long-wave radiation back toEarth

● reflect much short-wave radiation to space

● low clouds cool the climate

High clouds

● reflect much long-wave radiation back toEarth

● reflect much (bit less if they consist of ice)short-wave radiation to space

● both effects largely cancel out to yield lownet effect

IPCC (2013)

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Clouds

Clouds can consist of liquid or ice particles

Global cloud distribution affected by circulation

IPCC (2013)

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IPCC (2013)

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Clouds

Modelling cloud dynamics is difficultdue to limited spatial and temporal resolution of models

IPCC (2013)

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Summary

● Glaciers are controlled by climate at decadal-centennialtime scales, and by a complex interplay of topography,elevation, and local conditions on shorter time scales

● Glaciers are shrinking in volume and length all over theworld and will continue to shrink for decades independentof human emissions; many small glaciers will disappear

● Clouds have complex impacts on the Earth’s radiationbalance and climate depending on their height andcomposition; modelling (small-scale) cloud dynamics ischallenging

Lesson 3

Glaciers & Clouds

1) Glaciers

Basic functioning

Impact of climate change

2) Clouds

Basic functioning

Impact of climate change

3) Aerosols

4) Geoengineering

Impacts of climate change

Low clouds● reflect some long-wave radiation back to Earth● reflect much short-wave radiation to space● low clouds cool the climate

→ decrease in low cloud amount projected by climate models→ warming effect

High clouds● reflect much long-wave radiation back to Earth● reflect much (bit less if they consist of ice) short-wave

radiation to space● both effects largely cancel out to yield low net effect

→ are expected to get higher→ more back-reflection of long-wave radiation to Earth→ warming effect

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Impacts of climate change

Large model uncertainty, but consistent sign of changes

IPCC (2013)

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Impacts of climate change

Other cloud impacts

● northward shift of cold-season north hemisphere stormtracks

→ less short-wave radiation reflected in darker areas→ warming effecthttps://www.youtube.com/watch?v=m2Gy8V0Dv78

● impacts of changes in evaporation and transpiration fromland on cloud amount

● shifts in cloud composition from liquid to ice or vice versa

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Impacts of climate change

IPCC (2013)

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Impacts of climate change

As net effect from cloud-climate feedbacks, most models project warming, but with different magnitude

IPCC (2013)

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Summary

● Glaciers are controlled by climate at decadal-centennialtime scales, and by a complex interplay of topography,elevation, and local conditions on shorter time scales

● Glaciers are shrinking in volume and length all over theworld and will continue to shrink for decades independentof human emissions; many small glaciers will disappear

● Clouds have complex impacts on the Earth’s radiationbalance and climate depending on their height andcomposition; modelling (small-scale) cloud dynamics ischallenging

● Cloud impacts on climate will change in various ways in achanging climate, with a projected net warming ofuncertain magnitude

Lesson 3

Glaciers & Clouds

1) Glaciers

Basic functioning

Impact of climate change

2) Clouds

Basic functioning

Impact of climate change

3) Aerosols

4) Geoengineering

Aerosols● liquid or solid particles smaller than cloud or precipitation particles● come from natural (dust, sea spray) and anthropogenic sources

(sulphate, smoke)● lifetime 1 day – 2 weeks, vary greatly in size, chemistry, and shape

IPCC (2013)

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Aerosols-radiation interactions (ari)

● Aerosols scatter (→ cooling effect) and absorb(→ warming effect) short-wave radiation

● Cooling effect outweights the warming effect

→ aerosol-radiation interactions cool the climate

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Aerosols-radiation interactions (ari)

IPCC (2013)

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Aerosols-cloud interactions (aci)

● aerosols serve as condensation nuclei where water and icedroplets can form

● this does not lead to more clouds

● rather clouds consist of more, but smaller, droplets, which letsthem reflect more short-wave radiation

● aerosols can also influence precipitation locally,but globally no significant net change is detectable

→ aerosol-cloud interactions cool the climate

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Aerosols-cloudinteractions (aci)

IPCC (2013)

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As net effect from aerosol-climate feedbacks, most models project warming, but with different magnitude

Aerosols are changing the climate

IPCC (2013)

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Summary

● Glaciers are controlled by climate at decadal-centennial timescales, and by a complex interplay of topography, elevation, andlocal conditions on shorter time scales

● Glaciers are shrinking in volume and length all over the world andwill continue to shrink for decades independent of humanemissions; many small glaciers will disappear

● Clouds have complex impacts on the Earth’s radiation balance andclimate depending on their height and composition; modelling(small-scale) cloud dynamics is challenging

● Cloud impacts on climate will change in various ways in a changingclimate, with a projected net warming of uncertain magnitude

● Aerosols cool the climate (and thereby partly mask greenhousegas-related warming) through interactions with radiation and clouds

Lesson 3

Glaciers & Clouds

1) Glaciers

Basic functioning

Impact of climate change

2) Clouds

Basic functioning

Impact of climate change

3) Aerosols

4) Geoengineering

Geoengineering

Alter the climate system to alleviate impacts of climate change

Solar radiation management ● increasing reflectivity of the Earth● Short-term effect on climate● only impact on daytime temperature, changes daily temperature cycle● needs to be continued once in place to avoid abrupt climate change● Global upscaling difficult

Carbon dioxide removal ● Removing CO2 from atmosphere

● Long-term effect on climate

● CO2 storage needs to be permanent

● Global upscaling difficult

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IPCC (2013)

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Very rapid climate change assolar radiation management is

stopped

Unintended changes inprecipitation

Global modelling of solar radiation management

IPCC (2013)

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Geoengineering

Difficulties

● methods can not counter all effects of climate change(e.g. precipitation changes)

● risk of unforeseen side effects

● political, ethical, practical issues

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Summary

● Glaciers are controlled by climate at decadal-centennial time scales, and bya complex interplay of topography, elevation, and local conditions on shortertime scales

● Glaciers are shrinking in volume and length all over the world and willcontinue to shrink for decades independent of human emissions; manysmall glaciers will disappear

● Clouds have complex impacts on the Earth’s radiation balance and climatedepending on their height and composition; modelling (small-scale) clouddynamics is challenging

● Cloud impacts on climate will change in various ways in a changing climate,with a projected net warming of uncertain magnitude

● Aerosols cool the climate (and thereby partly mask greenhouse gas-relatedwarming) through interactions with radiation and clouds

● There are approaches to alleviate climate change through (additional)human intervention into global climate, e.g. through solar radiationmanagement or CO2 removal; related political, ethical and practical issues