Aerosol Climate Feedbacks Flashcards
What is the CLAW hypothesis?
-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
Where does phytoplankton growth occur the most?
Where both the light and nutrient concentration in sufficient
How can phytoplankton biomass be measured?
By using chlorophyll concentration in the euphoric zone
Where is the euphotic zone?
Layer closest to the surface that receives enough light for photosynthesis to occur
How is DMS synthesised?
Phytoplankton make DMSP which can be broken into DMS by algal and bacterial enzymes
What are plankton?
A combination of microscopic plants (phytoplankton) and animals (zooplankton)
What happens to atmospheric DMS?
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
Is the claw hypothesis positive or negative feedback?
Negative
Why is the CLAW hypothesis negative feedback?
Increased DMS emission in warmer climate -> more sulfate aerosols -> clouds brighter -> less sunlight -> cools earth -> less phytoplankton and DMS
What is the anti claw hypothesis?
Increasing temps -> increased ocean stratification -> decreased amount of nutrients available in euphotic zone -> less phytoplankton growth -> less DMS -> fewer CCN -> decreased albedo -> warmer oceans
Is the claw hypothesis proven?
No
What are some challenges in the assessment of the CLAW hypothesis?
-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
What is the climate feedback from forests?
-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
Is climate feedback from forests positive or negative?
Negative on temp
Is the feedback mechanism for forests proven?
Not really but strong evidence
Why would reducing anthropogenic emissions in warmer regions not have as bit of an effect?
Natural aerosol concs increase with temp so reducing anthropogenic aerosols won’t change much
Why is quantifying the contribution of terrestrial ecosystems to secondary organic aerosols hard?
Anthropogenic emissions can mask natural sources
How much have arctic temperatures warmer compared to the rest of the earth?
A factor of 2 or 3
Is sea ice a positive or negative feedback?
Positive
Describe the feedback of reduced sea ice
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
How could sea salt counteract reduced sea ice?
Increased SSA -> more clouds -> higher albedo -> cooler temps
What is the GLOMAP response to melted sea ice?
-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
How have reduced European emissions impacted Arctic climate?
-less sulfate being transported to Arctic
-fewer CCN
-but unclear impact
What are three Arctic feedbacks?
- Marine aerosols from DMS
- Biogenic secondary organic aerosols
- Sea ice retreat
Why are feedback systems difficult to model in ESMs?
-need for development of complex chains of models even for single feedbacks
-complex coupling between different processes
