Introduction and Problem Statement

• Climate scientist presenting on unintended consequences of air pollution cleanup
• Humans emit greenhouse gases AND particulate pollution (aerosols)
• Aerosols kill 4-10 million people annually globally
• Major public health crisis driving cleanup efforts
• Unintended consequence: accelerating climate warming as aerosols are removed

Aerosols' Climate Cooling Effects

• Most aerosols actually cool climate
• Two mechanisms:
  • Direct scattering of sunlight back to space
  • Making clouds brighter/more reflective when mixed in
• Current estimate: human aerosols cooling climate by ~0.5°C
• Without this cooling, climate impacts would be significantly worse
• Uncertainty range: cooling could be up to almost 1°C

The Conundrum

• Cleaning air for health removes climate cooling source
• Aerosols last only ~1 week in atmosphere
• Cooling effect disappears almost immediately after emissions stop
• Unlike greenhouse gases that warm for decades to centuries
• Don't know exact cooling magnitude = don't know warming to be unmasked

How Aerosols Cool Climate - Ship Tracks Example

• Aerosols increase cloud reflection of sunlight
• Ship tracks: visible satellite evidence off North America west coast
• Ocean clouds normally have few aerosols = small number of large droplets
• Ships add aerosols = large number of smaller droplets
• Smaller droplets increase cloud reflectivity
• Effect happens globally where pollution mixes with clouds

Complexity and Uncertainty

• Cloud-aerosol interactions are complex and constantly evolving
• Adding aerosols changes droplet size AND cloud evolution
• Depending on atmospheric conditions, aerosols can:
  • Make clouds more reflective
  • Make clouds less reflective
  • Not change reflectivity at all
• Right conditions can make clouds "quite a bit brighter"

Marine Cloud Brightening Concept

• Rapid climate warming reduction by mimicking pollution effects
• Use natural sea salt aerosols instead of pollution
• Target: clouds over ocean where sea salt already seeds droplets
• Computer models show promise:
  • Brightening fraction of ocean clouds rapidly reduces warming
  • Global climate models indicate feasibility

Research Challenges and Approach

• Global models lack detailed aerosol-cloud interaction resolution
• Need localized models with more aerosol/cloud detail
• Require better real-world data to test/inform models
• Most uncertainty involves small-scale air motions in clouds (few square kilometers)
• Solution: systematic study of single aerosol plume effects

Controlled Aerosol Studies Method

• Add single sea salt aerosol plume to small cloud area
• Create "single clean ship track"
• Use research aircraft with specialized instruments
• Measure atmospheric conditions, aerosols, clouds in detail
• Compare clouds with different aerosol concentrations but same conditions
• Quantify aerosol-caused reflectivity changes vs other factors

Technological Challenge

• Generating proper sea salt aerosol plume is significant challenge
• Need correct size and quantity for consistent cloud brightening
• No one has demonstrated required capability to date
• Aerosols must be ~1/1000th width of human hair (ideal size for marine cloud brightening)

New Research Instrument and Facility

• Team developing new Cloud Aerosol Research Instrument
• Generates large numbers of tiny sea salt aerosols
• Started first scientific studies 2 weeks ago
• Coastal Atmospheric Aerosol Research and Engagement (CARE) facility
• Located on USS Hornet flight deck, Alameda, California
• Multiple measurement locations along flight deck
• Studies aerosol evolution during transport to clouds
• Tests instrument delivery of proper aerosol characteristics

Public Engagement and Accessibility

• Museum location for public accessibility
• Open to education sector and other researchers
• Openness as important program component
• Goal: broader international engagement
• Particularly targeting historically marginalized communities
• These communities most vulnerable to climate change
• Direct engagement critical for equitable, informed discussions

Important Limitations and Clarifications

• Marine cloud brightening will NOT reverse greenhouse gas effects
• NOT a solution to climate crisis (emphasized repeatedly)
• Treats symptom (excess heat) not root cause
• Potential component of safer climate future approach
• World needs best information for decision-making

Future Research Importance

• Better understand evolving aerosol role in climate system
• Avoid "flying blind" into coming decades of climate change
• New capabilities for studying important climate questions
• Invitation for public to join research at facility