Climate system

Climate system

1. Components

   • Atmosphere
     • Trace/Greenhouse gases: CO2, CH4,N2,O3,
       • Absorb infrared radiation and emit it up and down. Warm surface temperature
     • H20 vapor also GHG
     • aerosols (liquid particles)
     • clouds
     • nitrogen (N2, 78.1%), oxygen (O2, 20.9% argon (Ar, 0.93%)
   • Hydrosphere
     • Oceans
       • Large thermal inertia
       • Regulator of climate and source of climate variability
     • fresh water
     • Hydrological cycle
   • Cryosphere
     • Ice sheets: Greenland, Antartica
       • Storage of water, potencial source of sea level variations
     • sea ice, permafrost
     • continental glaciers and snow fields
     • High albedo, low thermal conductivity and drives deep ocean circulation
   • Lithosphere
     • soil
   • Biosphere
     • Vegetation
       • Controls how energy from sun it's return to atmosphere
       • Photosynthesis: CO2
     • Uptake and release GHGs
     • Carbon cycle
     • Release Volatile organic compounds (VOC)-affect aerosols

2. Climate change

   • External Forcing (outside climate system
     • Solar energy
     • Volcanic Eruptions
     • Antropogenic (Human)
       • Large scale since mid-18th century
       • Aerosols
         • Short-lived (rain wash)
         • mineral dust, sulphates and nitrates and soot.
         • Human industrial, energy related, and land-use activities
         • Complex effect on RF
           • Direct Neg RF
           • Some, s.a. soot, absorb SR-P RF
           • affect Clouds
         • Vary a lot regionally but w/ global effects
       • GHGs
         • Well-mixed (long lives in atmo)
           • CO2
             • Increase +30% since pre-industrial
             • Isotopic composition betrays fossil fuel origin
           • N2O
           • Methane
             • Agricultural and industrial activities
           • Cloroflourocarbon
             • Don't appear naturally in atmosphere
             • Depletion of ozone layer, partly compensate their GHG effect
         • Short-lived
           • Tropospheric O3
         • Enhanced GH effect
           • +opacity atm. +altitute to emit , -energy emit, positive RF warming
       • Other gases
         • Nitrogen oxides (NO and NO2)
         • Carbon monoxide
           • change atmosphere chemistry
             • generate tropospheric O3, a GHG (+40% since pre-ind)
       • Land use
         • albedo
         • feedbacks-vegetation-carbon cycle
   • No linear effects, chaotic behaviour
   • Energy balance
     • Global mean 14°C
     • Solar energy
       • 31% reflected immediatly
     • GHGs
     • Clouds
     • Radiative forcing
       • Change in energy flux, capacity to affect energy balance
   • Internal variability
     • ENSO
     • NAO
   • Feedbacks
     • Positive
       • Water vapour
         • More important feedback for amplification of T°
     • Negative
       • radiative damping
     • Physical
       • Clouds
     • Biogeochemical
       • atmosp. CO2 and C uptake in oceans
   • Evidence Detection
     • last 1000 year cooling, following strong warming 20th century

3. Modelling

   • General circulation models
     • Atmospheric General Circulation Models (AGCMs)
       • Grid: H: 250km and V;: 10-30 levels
     • Physical laws dynamics atmos. and oceans
     • Non linear eqs solved numerically
     • Ocean General Circulation Models (OGCMs))
       • Grid:H:125-250 km V:200-400m
     • Coupled models
       • More complex
       • AOGCMs
         • Important to simulate cliimate variability as atmosp-oceans determine energy budged
         • difficult to avoid drifting from observed climate
     • Parametrization
       • Processes in smaller spatial and temporal scales than model grid
       • e.g. individual clouds, convection
     • More recent include
       • carbon cycle
       • aerosols
       • maybe atmosph. chemistry
     • SCM (simple climate models
       • IPCC:use to compute consequences of GHG emission scenarios
       • good to study one or a specific # of elements of climate system
   • Diferences in models
     • spatial dimensions, extend physical process are represented,level of parametrization, computational cost to run
   • Quality Evaluation of models
   • Projections
     • Equilibrium method
       • Double C02
         • New equilibirum vs original=CC correspondig to doubled CO2 and sensitivity of CC to RF
       • Reduce systemic errors
       • Cheap, doent require long run to reach equil.
       • Doesn't provide insight in the time dependence of CC
     • Transient method
       • GHG and aerosol scenario. CO2 gradually increased
         • Simulation vs baseline =Time-dependent projection of CC
       • Requires time-dependent profile of GHG and aerosol concentrations
         • Emissions scenarios
           • IPCC
           • Assumptions future socio economic and demographic developments
       • Also run idealized scenarios
         • Insight effects of mitigation policies