Aerosol Climate Feedbacks

Question 1

What is the CLAW hypothesis?

Answer 1

-increase of DMS emission in a warmer climate raises atmospheric DMS concs
-this means more sulfate aerosols
-this increases CCN, making clouds brighter, reflecting more sunlight back to space and cooling earth

Question 2

Where does phytoplankton growth occur the most?

Answer 2

Where both the light and nutrient concentration in sufficient

Question 3

How can phytoplankton biomass be measured?

Answer 3

By using chlorophyll concentration in the euphoric zone

Question 4

Where is the euphotic zone?

Answer 4

Layer closest to the surface that receives enough light for photosynthesis to occur

Question 5

How is DMS synthesised?

Answer 5

Phytoplankton make DMSP which can be broken into DMS by algal and bacterial enzymes

Question 6

What are plankton?

Answer 6

A combination of microscopic plants (phytoplankton) and animals (zooplankton)

Question 7

What happens to atmospheric DMS?

Answer 7

It is oxidised to sulphate aerosol precursor compounds e.g. sulfur dioxide and then to sulfuric acid
These can then condense onto existing particles or nucleate to non-sea salt sulphate particles

Question 8

Is the claw hypothesis positive or negative feedback?

Answer 8

Negative

Question 9

Why is the CLAW hypothesis negative feedback?

Answer 9

Increased DMS emission in warmer climate -> more sulfate aerosols -> clouds brighter -> less sunlight -> cools earth -> less phytoplankton and DMS

Question 10

What is the anti claw hypothesis?

Answer 10

Increasing temps -> increased ocean stratification -> decreased amount of nutrients available in euphotic zone -> less phytoplankton growth -> less DMS -> fewer CCN -> decreased albedo -> warmer oceans

Question 11

Is the claw hypothesis proven?

Answer 11

No

Question 12

What are some challenges in the assessment of the CLAW hypothesis?

Answer 12

-obtaining detailed understanding of the relative strength of different marine aerosol sources
-obtaining detailed understanding of the processes that lead to DMS production as degradation in the ocean and DMS emission to atmosphere during changing climate conditions

Question 13

What is the climate feedback from forests?

Answer 13

-increased CO2 -> increased temp and vegetation productivity -> increase biological volatile organic compounds (BVOCs) -> enhance natural aerosol formation and growth -> increase CCN -> increase albedo and decrease temp -> increase diffuse radiation which has positive influence on photosynthesis

Question 14

Is climate feedback from forests positive or negative?

Answer 14

Negative on temp

Question 15

Is the feedback mechanism for forests proven?

Answer 15

Not really but strong evidence

Question 16

Why would reducing anthropogenic emissions in warmer regions not have as bit of an effect?

Answer 16

Natural aerosol concs increase with temp so reducing anthropogenic aerosols won’t change much

Question 17

Why is quantifying the contribution of terrestrial ecosystems to secondary organic aerosols hard?

Answer 17

Anthropogenic emissions can mask natural sources

Question 18

How much have arctic temperatures warmer compared to the rest of the earth?

Answer 18

A factor of 2 or 3

Question 19

Is sea ice a positive or negative feedback?

Answer 19

Positive

Question 20

Describe the feedback of reduced sea ice

Answer 20

Reduced sea ice -> increased aerosol emissions from oceans and ships -> more CCN or ice nuclei -> impact micro physical properties of Arctic clouds -> either increase non-precipitating Arctic stratus OR increase precipitating Arctic stratus -> increase temp -> decrease ice

Question 21

How could sea salt counteract reduced sea ice?

Answer 21

Increased SSA -> more clouds -> higher albedo -> cooler temps

Question 22

What is the GLOMAP response to melted sea ice?

Answer 22

-weak response to CCN due to efficient scavenging of aerosols by extensive drizzing from stratocumulus clouds
-NPF cannot compensate for wet scavenging
-Nucleation suppressed from large condensation sink

Question 23

How have reduced European emissions impacted Arctic climate?

Answer 23

-less sulfate being transported to Arctic
-fewer CCN
-but unclear impact

Question 24

What are three Arctic feedbacks?

Answer 24

1. Marine aerosols from DMS
2. Biogenic secondary organic aerosols
3. Sea ice retreat

Question 25

Why are feedback systems difficult to model in ESMs?

Answer 25

-need for development of complex chains of models even for single feedbacks
-complex coupling between different processes