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