The Atmosphere

• The atmosphere is a layer or a set of layers of gases surrounding a planet or other material body, that is held in place by the gravity of that body. An atmosphere is more likely to be retained if the gravity it is subject to is high and the temperature of the atmosphere is low.
• Composition of the Earth's atmosphere

  • Nitrogen (about 78%)
  • Oxygen (about 21%)
  • Argon (about 0.9%)
  • Carbon dioxide (0.04%)
  • Other gases in trace amounts
• Oxygen is used by most organisms for respiration: nitrogen is fixed by bacteria and lightning to produce ammonia used in the construction of nucleotides and amino acids; and carbon dioxide is used by plants, algae and cyanobacteria for photosynthesis.
• The atmosphere helps to protect living organisms from genetic damage by solar ultraviolet radiation, solar wind and cosmic rays. The current composition of the Earth's atmosphere is the product of billions of years of blochemical modification of the paleoatmosphere by living organisms.
• Functions of the atmosphere

  • Source of gases for natural processes
  • Absorbs electromagnetic radiation from the Sun
  • Delays the escape of infrared energy
  • Creates moving air which distributes heat and water vapour
  • Provides winds over the oceans which create ocean water currents
  • Creates pressure which allows liquid water to exist
  • Source of gases for human exploitation
• Natural processes are in a state of balance which maintains the average composition of the atmosphere so that it only changes over very long timescales. This is known as dynamic equilibrium.
• Photosynthesis and aerobic respiration are particularly important processes. Although they roughly balance each other, the rates at which they occur vary over different timescales, so the concentrations of gases fluctuate around an average concentration.
• Many of the processes that affect the atmosphere are interconnected. So, if one process is changed it can change other processes. This is important because it means that human actions can trigger a sequence of events where an action changes one process which causes other processes to alter as a direct result of the first change.
• There is a lot that is yet to be discovered and understood about how atmospheric processes work, so it is not possible to accurately predict the effect of human activity on specific atmospheric processes.
• Insolation

  The amount of solar radiation reaching a given area.
• Emissions from the earth

  Greenhouse gases are those that absorb and emit infrared radiation in the wavelength range emitted by Earth. Carbon dioxide (0.04%), nitrous oxide, methane, and ozone are trace gases that account for almost 0.1% of Earth's atmosphere and have an appreciable greenhouse effect.
• Thermal stratification

  The phenomenon in which lakes develop two discrete layers of water of different temperatures: warm on top (epilimnion) and cold below (hypolimnion). Colder, denser water is on the bottom; zone of rapid change above, and warmer, less dense water at the surface of the lake.
• Chemical processes

  A chemical process is a method or means of somehow changing one or more chemicals or chemical compounds.
• Atmospheric composition


  • Carbon
  • Oxygen
  • Hydrogen
  • Nitrogen
• Atmospheric gases (N, O2, CO2, H2O) are extracted from the atmosphere to make biological molecules used by all living organisms
• Biological molecules


  • Carbohydrates
  • Lipids
  • Amino acids
  • Proteins
• Nitrogen fixation


  • Processes: Lightning
  • Haber process
  • Nitrogen fixing bacteria (leguminous plants)
• Transmission of electromagnetic light in the atmosphere


  1. Visible light largely passes (or is transmitted) through the atmosphere

  2. Atmospheric gases absorb radiation in certain wavelengths while allowing radiation with differing wavelengths to pass through
• Absorption of electromagnetic light in the atmosphere

  • Light absorption converts the light energy to internal energy of the absorbing molecules and eventually transfers it to the surrounding gas as heat
  • Atmospheric gases absorb light in distinct spectral regions usually at more or less broad bands
• Visible light is absorbed by an object

  The object converts the short wavelength light into long wavelength heat
• Greenhouse gases


  Let the short wavelength visible light pass through the atmosphere, but block much of the long wavelength (heat) infrared energy from escaping
• Photosynthesis


  1. Light energy is converted to chemical energy in the form of sugars

  2. Glucose (or other sugars) are constructed from water and carbon dioxide, and oxygen is released as a by-product
• Reflection of electromagnetic radiation

  • The Earth absorbs most of the energy reaching its surface, a small fraction is reflected
  • In total approximately 70% of incoming radiation is absorbed by the atmosphere and the Earth's surface while around 30% is reflected to space and does not heat the surface
• Delaying the escape of infrared energy

  • Incoming visible light is absorbed, converted to heat, and re-emitted as infrared energy
  • Naturally occurring atmospheric gases absorb this infrared energy, convert it to heat and increase the temperature of the atmosphere
• Warm atmosphere


  • Emits infrared energy which is absorbed by the Earth's surface
  • Reduces heat loss by conduction from land and the oceans
• Heat distribution


  1. Most of the energy from the Sun, absorbed at the Earth's surface, is absorbed in tropical regions

  2. The warm surface heats the atmosphere above and this heat is distributed to higher latitudes by warm winds
• Ocean currents


  1. Winds blowing over the oceans create currents that distribute heat by carrying warm water from tropical areas to higher latitudes

  2. These currents can also distribute dissolved nutrients which is vital for the health of our oceans around the world
• Transport of water vapour

  1. Winds transport water vapour to areas that would otherwise get little or no precipitation

  2. Over millions of years life has come to rely on these annual rhythms
• Global climate change

  • Changes to the composition of the atmosphere that alter energy processes, the climate and the physical and biological processes they control
  • Changes resulting from human activity are known as anthropogenic
• Anthropogenic sources of greenhouse gases

  • CO2
  • CH4
  • NOX
  • Tropospheric ozone
  • CFCs
• Global warming potential (GWP) table shows pre-industrial concentrations, 2018 concentrations, lifetimes and main human activity sources for various greenhouse gases
• Water vapor is not included in the GWP table
• Consequences of global climate change

  Relatively small temperature increases may have a range of direct and indirect impacts on the abiotic and biotic conditions on Earth
• Ecological changes from global climate change

  • Changes in species survival caused by altered abiotic factors such as temperature and water availability
  • Species may be affected directly by the temperature, by changes to other species they rely on, or by changes to natural processes that affect them
• Temperature rise and CO2

  • May cause plants to grow faster, providing more food for herbivores
  • However, plants growing too fast may mean certain species miss out on the early feeding on the fresh young shoots and may die off due lack of food or the plants producing toxins later in the growth cycle which affects the herbivores
• Precipitation

  • Rising temperatures will intensify the Earth's water cycle, increasing evaporation
  • Increased evaporation will result in more frequent and intense storms but will also contribute to drying over some land areas
  • Storm-affected areas are likely to experience increases in precipitation and increased risk of flooding, while areas located far away from storm tracks are likely to experience less precipitation and increased risk of drought
• Disturbance of hibernation patterns

  Can endanger the species and mess up entire ecosystems
• Hibernation disturbance

  • Yellow-bellied marmots emerging 38 days earlier from hibernation in Rocky Mountains, USA
  • Late spring snowfalls have delayed the Rocky Mountain ground squirrels' emergence from hibernation by 10 days over the last 20 years in Rocky Mountains, USA
  • Hedgehogs emerging up to three weeks earlier from hibernation in United Kingdom
  • Hibernation of bats affected as they emerge from hibernation earlier if spring temperatures are higher in United Kingdom
  • Hibernation among polar bears has reduced, the amount of energy pregnant females normally store up before hibernation has significantly come down in Canada, USA (Alaska)
  • Brown bears in the Spanish Cantabrian Mountains have not been hibernating at all in Spain
  • Himalayan brown bear and the Asiatic black bear, which would normally go into hibernation right through winter, are no longer doing so in India
  • Spotted Snout Burrower's reliance on seasonal rainfall tends to break periods of hibernation in Southern Africa
  • Climate change is affecting hibernation cycles of many of Australia's frog species, including the endangered Baw Baw frog in Australia
• This will alter wetland habitats to enlarge or shrink, tree species e.g in the UK Oak trees have deep roots and will be able to survive droughts better than beech trees that have shallower roots
• Timing of ecological events

  • The timing of ecological events such as flowering, migration and nesting may change
  • Survival of interdependent species may be reduced, for example, if pollinating insects are not present when flowers are produced
  • The distribution of species may change as conditions change and they colonise areas that have become suitable
  • Species may not be able to colonise new areas as quickly as they disappear from their old range, especially for slow-growing species like trees
  • Suitable new areas may not be available
  • Human land use may block movement
  • Species live in inter-dependent communities, all the species will not be able to move at the same speed