Climate Change

Climate Change

1. Climate

   • There is a difference between weather and climate.
     • Weather is a description of the current conditions of the atmosphere: temperature, pressure, humidity
     • Climate is a description of typical atmospheric conditions - typical weather
       • 30 years of data should be used to describe climate
         • Can be used to predict weather patterns
   • What factors include climate
     • Lattitude
       • It affects the angle of incidence of sunlight.
         • The part of the Earths surface which is perpendicular to sunlight receives the greatest amount of radiation per unit of surface area
           • The angle of incidence changes with seasons due to axial tilt of the earth
     • Global Circulation
       • Prevailing winds can have effects on weather conditions
       • Jet streams overhead can affect climate by controlling the frequency of storms
       • Ocean currents affect local climates by transporting warm water at the equator
     • Air Masses
       • Transport of warm or cold moist or dry air
     • Geography
       • Features such as mountains can affect local climates
     • Land Cover
       • Urban heat islands are caused by changes in surface albedo, evapotranspiration, heat capacity and topography
   • Historical Climate Change
     • Mt Pinatubo 1991 launched dust and sulphuric acid into the stratosphere
       • These aerosols remain in the air for years because they cannot be washed out by rain and are too light to fall quickly
         • This reflects sunlight and makes the earth cooler
   • Solar Variation
     • Cycles have been observed
     • A slight change in solar strength coincided with the sunspot cycle warming phase at the start of 20th century
   • Milankovic theory of ice
     • Timing of gradual changes in the shape of the earths orbit and the tilt of its axis
       • It alters seasonal temperature differences between summer and winter
         • Timescale is 21000, 41000 and 10000 years
   • Interannual variability
     • Any given year can be warmer or colder than the last
       • Affected by ENSO NAO and PDO
         • ENSO is a periodic change in the atmosphere and ocean circulation of the tropical Pacific region

2. Global Warming

   • First Law of Thermodynamics
     • Energy cannot be created or destroyed, energy going into a system is equal to the energy coming out of the system
   • Stefan-Botlzmann Law
     • All matter emits energy in the form of radiation
   • Application to Earths Climate
     • E in = radiation coming from the sun
       • E out = radiation emitted by the Earth
         • E stored = determines Earths temperature
     • There is always a balance between E in and E out
   • Wiens Law
     • Wavelength of radiation emitted by a mass is inversely proportional to its temperature
   • Greenhouse gasses are transparent to visible radiation but absorb infrared radiation.
     • In the atmosphere greenhouse gasses have no effect on the sun but absorb radiation from the earth.
     • It keeps the Earth 33 Degrees warmer than it would be otherwise
   • Enhanced Greenhouse effect and global warming
     • Since the industrial revolution human activities have had an effect of increasing the concentration of greenhouse gasses into the atmosphere
       • Increased greenhouse effect warming of global temperatures
     • Carbon Dioxide is released through combusting fossil fuels. Which is an important greenhouse gas
     • Methane caused by sewage treatment and landfills
     • Ozone is helped formed by car exhausts
     • Holocarbons
   • A feedback is a process that reacts to an initial change by causing further change in the same quantity
     • For global warming a positive feedback responds to warmer temperatures by causing additional warming
       • Most important climate feedback is water vapor
         • Warmer air holds more water and it is a greenhouse gas which can cause further warming
         • Another is Cloud Cover which can absorb radiation from the earth and reflect it from the sun
   • Effect of air pollution
     • S02 and N0x form aerosols that reflect sunlight and have a cooling effect. But it gets washed out by the rain
   • Evidence
     • Warming trent with average global temperature increasing from 0.6-0.8 Degrees
     • proxy measurements of change, tree rings snow packs, indicate that temperature change is ocuring fast
     • Retreat of Ice and Snow, all mountain glaciers have been in retreat.
       • Snow cover has reduced by 10% and reduced permafrost in the southern boundary
     • Biological indicators
       • Length of the growing season north of 45 increased by 12 days in the 1990s, the timing of flowering egg laying and migration has moved to earlier points in the year
       • Distribution of plant and animal species has changed.
   • Modeling climate change
     • Using the Atmosphere-Ocean General Circulation Model.
     • Global warming of 3-5 Degrees by 2100
       • lag behind the change in radiative forcing due to the thermal inertia of the oceans
     • Sea Level rise
     • Greater warming at higher latitudes and continents
     • Increased evaporation and precipitation and heavy rain
     • Drier soils.