Chapter 15: The Climate System and Climate Change

The Climate System

  • The geography of net radiation and heat flow: fuelling the weather engine
  • Radiation controls: the spectrum and various trace gases
  • Beyond control: about all those absorbers and the greenhouse effect

What is Global Change?

  • Global change refers to the impacts that are global in extent. Cumulative or synergistic effects of local/regional actions.
  • These impacts are long-lasting or potentially permanent
  • Atmospheric change:
  • Stratospheric ozone depletion
  • Global climatic change due to greenhouse gases for example

Especially Global Warming!

  • Global warming is climate change beyond what nature can do, which is due to our own contribution (Anthropogenic causes)
  • Natural periods of warming and cooling will continue, as they have done throughout time
  • Earth today is very warm today, unlike before when it was much cooler
  • Global warming adds to nature by enhancing the warm periods and suppressing the cool periods

Global Change Affects the "Global Commons”

  • Common property resources are collectively owned or communally accessed or utilized
  • The Tragedy of the Commons: Everyone involved but none responsible
  • Global commons: outside national jurisdiction
  • Deep ocean
  • Antarctica
  • Atmosphere

To Understand Climatic Change, We Need to Understand Earth’s Energy Cycle

  • We can take a systems approach to Earth’s energy cycle:
  • Sources of energy (where energy comes from- incoming)
  • Sinks of energy (where energy goes - outgoing)
  • Reservoirs (where energy is stored within the Earth) - various reservoirs of heat and carbon are in Earth
  • Fluxes (how energy moves around in the cycle)
  • Our planet absorbs solar radiation in W (watts)
  • The Earth warms up from short-wave solar radiation. Before we can get long-wave radiations, we need to have the earth warming by the sun, in order for Earth to radiate long-wave temperatures. This way the sun doesn’t overheat by long-waves
  • The greenhouse effect is a good thing as we would be unable to live without it, since it provides warm temperature for the planet

Earth’s Energy Cycle


  • Source of energy for Earth is mainly from solar energy
  • Other sources
  • Terrestrial Energy: Decay of naturally occurring radioactive elements; compression heating; residual heat; etc.
  • Tidal Energy

Storage Reservoirs

  • OCEAN + CRYOSPHERE – biggest concern right now is the weakening of the cryosphere because it melts in heating conditions, in which Earth today is very warm.
  • BIOSPHERE - mainly plants

Fluxes and Processes (In)

  • Photosynthesis
  • Convection
  • Tides

Fluxes and Processes (Out)

  • Reflection (which is a short-wave energy term). Reradiation (is a long-wave energy term. Like explained before, before Reradiation takes place, Earth needs to be warm and heated)
  • Degradation
  • Transpiration
  • Radiation

To Understand Climate Change, We Need to Understand Radiative Forcing

  • Factors that change Earth’s net Irradiance
  • Net Irradiance: balance of incoming and outgoing energy
  • Net Irradiance is measured at the boundary between the troposphere and stratosphere. What concern us are the changes that occur at the top of the troposphere. Changes at that point are considered radiative forcing
  • Earth’s climate system experiences both internal and external radiative forcing:
  • Internal forcing: greenhouse effect- caused by human activity
  • External forcing: astronomical factors- the Sun for example

Contribution of Gilbert Plass

  • Water vapour (which is a very powerful greenhouse gas) is confined (restricted) to the troposphere but carbon dioxide is well mixed through both the troposphere and the stratosphere. Water vapour is active both in long and short-waves radiation
  • STRATOSPHERIC COOLING is linked to Tropospheric warming

Radiative Forcing can be Positive or Negative

  • Positive forcing warms the surface
  • Negative forcing cools the surface
  • Net irradiance has changed (++) since pre-industrial times- enough to alter the climate
  • Need for figure out much of this change is caused by human activity

Internal Radiative Forcing Results from the Greenhouse Effect

  • Trace gases in the atmosphere are radiatively active: absorb energy in certain wavelengths:
  • These are the “Greenhouse Gases”
  • They are mainly in the troposphere
  • Where do greenhouse gases come from?
  • Some naturally occurring (Ex. CO2,CH4,H23,O3)
  • Some are Anthropogenic (Ex. CFCs)
  • Some are naturally occurring but remobilized by human activity (Ex. CO2 and CH4 are the greatest concern)

Radiation Absorption Gases

  • Nitrogen
  • Oxygen
  • Carbon dioxide
  • Methane
  • Ozone
  • Hydrogen
  • Helium
  • Nitrous oxide

Trace gases in the atmosphere act as selective radiation filters (“Blinds”) - Trace gases absorb radiations. The greenhouse effect is when the long-wave filter (hotter than short-wave) has a greater effect than short-wave filter. The temperature on Earth is neutral due to trace gases, however, it adds on to the long-wave filter.

 Greenhouse Gases Differ in their Ability to Cause Global Warming

  • Global warming potential (or radiative forcing potential): relative ability of a given greenhouse gas to contribute to greenhouse warming
  • Expressed in relation to carbon dioxide (potential= 1) over the atmospheric lifetime of the gas, or 100 years
  • Methane is 25 times as powerful as carbon dioxide
  • Nitrous oxide is 296 times as powerful as carbon dioxide
  • Short-wave’s job is to warm the surface of the Earth and create radiator, through which after long-wave radiation can occur

Greenhouse Gases Warm the Lower Atmosphere

  • As the surface absorbs solar UV (ultraviolet) radiation it increases in temperature and releases IR radiation
  • Greenhouse gases absorb this outgoing IR radiation
  • Water vapour, carbon dioxide, nitrous oxide, methane, ozone, chlorofluorocarbons (CFCs)
  • After absorbing outgoing IR energy, greenhouse gases release it again
  • Some is lost to pace
  • Some is re-radiated downward, warming the troposphere and the planet’s surface

External Radiative Forcing Results from Astronomical Variations

  • External radiative forcing processes outside the Earth system
  • Variations in solar output (Ex. Sunspot cycles, etc.)
  • Variations in Earth’s orbit
  • These processes result in cyclical variations in insolation (solar energy reaching the top of Earth’s atmosphere)
  • We have no real control over these processes
  • Orbital variations cause cyclical variations in insolation and therefore in climate, including glacial cycles

The Climate System is Even More Complicated, Because of Feedbacks:

  • Positive feedback cycles (self-reinforcing)
  • (Ex: Warming - evaporation of seawater - more water vapour in atmosphere - more warming)
  • Negative feedback cycles (self-limiting)
  • (Ex: Warming - evaporation of seawater - more cloud cover - blocks incoming radiation - cooling)
  • These feedbacks inter in complex ways:
  • (Ex: Aerosols and clouds can have either a warming or cooling effect)

Climatic Change is Recorded in Different Ways, On Different Time Scales

  • Tools for the study of climate change :
  • Historical (observed, measures) records of climate (temp, precipitation) have been kept since 1860s
  • Paleoclimatology - Study of past climates
  • (Ex. Rock record and fossil assemblages for example)
  • Climate proxies: Natural events that are controlled by - and closely mimic - some aspect of climate
  • Records kept either by people or by nature

Direct Atmospheric Sampling Tells us About the Present Situation

  • Most types of direct measurement of atmospheric conditions have not been kept for very long (not stayed same for very long)

Climate Proxies Provide a Record of Past Climates

  • Long-term climate proxies: Climate-controlled variations in the composition of
  • Groundwater in aquifers
  • Deep-sea sediments
  • Shells of marine organisms
  • Ice cores from glaciers
  • Natural processes cause stable isotopes to become separate or fractioned, and differentially concentrated

Correlations Between Atmospheric Dust, CO2, CH4, o18O, and Temperature

  • Globally cold year: More light water locked up in ice caps, so ocean water starts out heavier(+).
  • Globally warm year: More light water released from ice caps, so ocean water starts out lighter (-)
  • Therefore, more CO2 causes warmer temperatures

Models are Another Fundamentally Important Tool for Climate Study

  • General circulation models (GCMs): They are three dimensional (3D) dynamic models of climate system
  • GCMSs link atmospheric, oceanographic, hydrospheric, and biospheric processes with geography and altitude
  • Purposes for GCMs models
  • Improve weather forecasting
  • Run simulations of present-day climate patterns as a way of testing climate models.
  • Predict future global climatic changes
  • Model building is useful as it helps understand how the climate system works
  • They help us understand climate

Sources of Uncertainty in GCMs

  • They have Short time length of instrumental records
  • Complexity and feedbacks in climate system
  • Role of clouds
  • Impacts of vegetation and soil moisture changes on moisture content of atmosphere
  • Response of ice, soil to warming
  • Relationship of soil variations to climate
  • Casual relationships between atmospheric GHGs and surface temperature
  • Computer limitations are another reason why GCMs may not be as accurate
  • Future anthropogenic contributions to GHGs

Anthropogenic forcing refers to human contributions to global warming.

According to IPCC IV, the average surface temperatures have been rising since 1906, with most of the increase occurring in the last few decades. This is mainly due to anthropogenic contributions.

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