Lecture 14

• internal climate variability = year-to-year or decade-to-decade variability
• Human = GHGs and aerosols

  Internal climate variability= year to year variation in climate caused by internal climate processes

  Detection when Climate change signal > Climate variability
• North Atlantic Oscillation
• Ella died in 2013; in 2020, a coroner's court found air pollution 'made a material contribution' to hear death - a long time for science to produce impact
• air pollution listed as cause of death of death certification for the first time ever
• air pollution linked to Asthma
• concluded: Ella was exposed to excessive amounts of nitrogen dioxide from road traffic
• New WHO guidelines challenging especially for PM2.5. Nowhere in London below limit of the annual average of 5μgm
• short term effects of pollution:

  • exacerbation of asthma
  • cough, wheezing and shortness of breath
• long term effects of pollution:

  • stroke
  • cancer
  • respiratory conditions
  • cardiovascular disease
• anticyclones cause favourable pollution episodes:

  • high pressure leads to light winds and little mixing
  • reduced vertical dispersion - mostly air descending from above, temperature inversion at the top of the boundary layer limits vertical mixing
  • no precipitation to aid 'wet' removal of aerosol pollution
  • strong sunshine allowing photochemical reactions e.g. to form ozone
• Global emissions of CO2 and of air pollutant emissions or precursors, also called near-term climate forcers (NTCF)

  Most scenarios show a reduction in global emissions although there is a large diversity between scenarios

  Future methane shows large variation between scenarios –important for ozone formation
• Particulate Matter (PM); usually PM 2.5 referred to (PM with aerodynamic diameter < 2.5 µm) – solid or liquid
• PM2.5 refers to size- its composition varies: inorganic (nitrate, sulfate, ammonium), organic (black carbon, organic carbon, dust, sea salt); has multiple anthropogenic and natural sources
• Either emitted as primary PM, or formed in the atmosphere (from gases) as secondary PM
• Ozone (O3)- a major oxidant (gas) species in our atmosphere; a secondary pollutant as formed in the atmosphere in the presence of sunlight and precursor emissions
• Nitrogen dioxide (NO2) - also a gaseous oxidant; forms from nitrogen oxide (mainly anthropogenic sources)
• PM2.5 and NO2 often co-emitted (traffic); as well as with CO2
• O3 and NO2 in urban environments usually inversely related
• O3 is a Greenhouse gas