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