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greenhouse gases

the greenhouse effect

  • when visible light is absorbed by the earth’s surface, it is reradiated in the form of heat
    • this heat is trapped in the lower atmosphere by several gases and then reradiated back to earth
  • carbon dioxide (CO2) is the most prevalent greenhouse gas
    • it is being added to the atmosphere much faster than it is being removed
  • other greenhouse gases
    • methane (CH4, “natural gas”) is naturally present in bogs, rice paddies, landfills, and released from the digestive systems of animals like cattle
    • traps much more heat than CO2
    • leveled have doubled since pre-industrial revolution times
    • nitrous oxides (NOx) come from manure, burning fossil fuels, fertilizers, industrial work, cars
    • fluorinated gases
    • CFCs
    • HFCs
    • halons
    • water vapor varies greatly from day to day but has not increased much over the past 10,000 years

changes in greenhouse gas concentrations

the greenhouse effect

  • climate: an area’s long-term atmospheric conditions
    • eg. temperature, precipitation, atmospheric pressure, wind
    • different from weather
    • weather: the conditions of the atmosphere over a short period of time
  • earth’s energy budget
    • the climate is influenced by solar radiation
    • ~70% of solar radiation is absorbed by the troposphere and the earth’s surface
    • visible light and infrared radiation
  • electromagnetic spectrum: the range of wavelengths of electromagnetic energy
  • the greenhouse effect
    • greenhouse effect: when visible light is absorbed by the earth’s surface, it is reradiated in the form of heat; that heat is trapped in the lower atmosphere by several gases and then reradiated back to earth
    • the greenhouse effect is natural, we’ve known about it since about the mid-1800’s, and it is critical to the temperature on earth which allows humans to live and function as we do
  • atmospheric levels of CO2
    • in the early 1900s, Svante Arrhenius predicted that the increasing amount of CO2 being released would warm the planet
    • in 1958, Charles David Keeling took the first measurement of atmospheric CO2 levels
    • daily measurements have been taken since then at a weather station in Mauna Kea, Hawaii
    • the keeling curve
  • global temperatures have risen

changes in the atmosphere

measuring temperature

  • thermometers were invented in the 17th century
  • satellites measure infrared radiation emitted from the sea surface

proxies for temperature

  • proxy: a figure that can be used to represent the value of something in a calculation
  • O2 isotopes in water
  • density of tree rings — gives information on temperature in precipitation

ice core analysis

  • ice core — ”frozen time capsules”
  • oldest records extend 130,000 years back in Greenland, 800,000 years in Antarctica
  • ice layers hold particles and contain tiny bubbles of atmospheric air (fossil air pockets)

the CO2 increase

  • CO2 levels vary naturally but natural variations cannot explain the recent spike in CO2 concentration
  • climate change
    • the greenhouse effect is a natural phenomenon that keeps the earth warm
    • human (anthropogenic) activities are responsible for the increase in release of greenhouse gases
    • because of higher concentrations of greenhouse gases, the global temperature is increasing

climate models and predictions

  • the keeling curve
    • we cannot just extrapolate the keeling curve because there are other greenhouse gases whose concentrations are changing and the oceans will remain warm for a while
  • feedback mechanisms
    • positive feedback mechanisms
    • reinforce and amplify ongoing trends
    • eg. higher temperature → more water evaporation → more water vapor in the atmosphere → water vapor is a greenhouse gas → higher temperature
    • negative feedback mechanisms
    • diminish or reverse a particular trend and maintain the initial conditions
    • eg. higher temperature → more water evaporation → more water vapor in the atmosphere → more clouds → more reflection of sunlight → less sunlight reaching the surface → lower temperatures (cooling)

climate models

  • computational devices for solving large sets of equations
  • not perfect, but can be tested against reality over time
  • create possible “scenarios,” some more optimistic than others
  • in the context of the climate, scenarios are called representative concentration pathways (RPCs)
  • climate scenarios

tipping points

  • tipping point: the critical point in a situation, process, or system beyond which a significant and often unstoppable effect or change takes place
  • we are currently on the brink of five disastrous climate tipping points
  • spurious correlation: a false correlation or fallacy; an attempt to draw a correlation between two things which are not related