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Course webpagehttps://www.bgc-jena.mpg.de/bgi/index.php/Lectures/HydroBioClimClimateChange
Lesson 4Glaciers & Clouds
1) CloudsBasic functioningImpact of climate change
2) Aerosols
3) 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)
1
Clouds
Low clouds● reflect some long-wave radiation back to
Earth● reflect much short-wave radiation to space● low clouds cool the climate
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
IPCC (2013)
2
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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Modelling Clouds
IPCC (2013)
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Modelling cloud dynamics is difficult due to limited spatial and temporal resolution of
models
Summary
● Clouds have complex impacts on the Earth’s radiation balance and climate depending on their height and composition; modelling (small-scale) cloud dynamics is challenging
Lesson 4Glaciers & Clouds
1) CloudsBasic functioningImpact of climate change
2) Aerosols
3) 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)
7
Impacts of climate change
Other cloud impacts● northward shift of cold-season north hemisphere storm
tracks [https://www.youtube.com/watch?v=m2Gy8V0Dv78]
→ less short-wave radiation reflected in darker areas → warming effect
● impacts of changes in evaporation and transpiration from land 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)
10
Summary
● Clouds have complex impacts on the Earth’s radiation balance and climate depending on their height and composition; modelling (small-scale) cloud dynamics is challenging
● Cloud impacts on climate will change in various ways in a changing climate, with a projected net warming of uncertain magnitude
Lesson 4Glaciers & Clouds
1) CloudsBasic functioningImpact of climate change
2) Aerosols
3) 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)
11
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)
13
Aerosols-cloud interactions (aci)
● aerosols serve as condensation nuclei where water and ice droplets can form
● this does not lead to more clouds● rather clouds consist of more, but smaller, droplets, which lets
them 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-cloud interactions (aci)
IPCC (2013)
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As net effect from aerosol-climate feedbacks, most models project cooling, but with different magnitude
Aerosols are changing the climate
IPCC (2013)
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Summary
● Clouds have complex impacts on the Earth’s radiation balance and climate depending on their height and composition; modelling (small-scale) cloud dynamics 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-related warming) through interactions with radiation and clouds
Lesson 4Glaciers & Clouds
1) CloudsBasic functioningImpact of climate change
2) Aerosols
3) Geoengineering
GeoengineeringAlter 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 as solar radiation management is
stopped
Unintended changes in precipitation
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
● Clouds have complex impacts on the Earth’s radiation balance and climate depending on their height and composition; modelling (small-scale) cloud dynamics 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-related warming) through interactions with radiation and clouds
● There are approaches to alleviate climate change through (additional) human intervention into global climate, e.g. through solar radiation management or CO2 removal; related political, ethical and practical issues
