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)
3
IPCC (2013)
4
Modelling Clouds
IPCC (2013)
5
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
6
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)
9
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
14
Aerosols-cloud interactions (aci)
IPCC (2013)
15
As net effect from aerosol-climate feedbacks, most models project cooling, but with different magnitude
Aerosols are changing the climate
IPCC (2013)
16
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
17
IPCC (2013)
18
Very rapid climate change as solar radiation management is
stopped
Unintended changes in precipitation
Global modelling of solar radiation management
IPCC (2013)
19
Geoengineering
Difficulties● methods can not counter all effects of climate change
(e.g. precipitation changes) ● risk of unforeseen side effects● political, ethical, practical issues
20
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