Understanding Global Climate Change
Greenhouse Gasses


Discovery of Global Warming - February 2016 version

The Carbon Dioxide Greenhouse Effect

  In the 19th century, scientists realized that gases in the
  atmosphere cause a "greenhouse effect" which affects the
  planet's temperature. These scientists were interested
  chiefly in the possibility that a lower level of carbon
  dioxide gas might explain the ice ages of the distant past.
  At the turn of the century, Svante Arrhenius calculated that
  emissions from human industry might someday bring a global
  warming. In 1938, G.S. Callendar argued that the level of
  carbon dioxide was climbing and raising global temperature,
  but most scientists found his arguments implausible. It was
  almost by chance that a few researchers in the 1950s
  discovered that global warming truly was possible. 

  In the early 1960s, C.D. Keeling measured the level of carbon
  dioxide in the atmosphere: it was rising fast. Researchers began
  to take an interest, struggling to understand how the level of
  carbon dioxide had changed in the past, and how the level was
  influenced by chemical and biological forces. They found that the
  gas plays a crucial role in climate change, so that the rising
  level could gravely affect our future.


Atmospheric Transmission

    An Infrared (IR) photon is absorbed by a CO2 molecule 
        CO2 + hv <==> CO2* 
        CO2* + N2 ==> N2* + CO2 
        N2* + H2O ==> H2O* + N2 
        H2O* ==> H2O + hv

Evaluating and Explaining Climate Science

  Audience -- People interested in the science behind the
  climate stories we read about every day. People who want to
  learn. People who want to contribute to other people
  learning about climate science.

James Hansen: Why I must speak out about climate change (17+ min)

  Top climate scientist James Hansen tells the story of his
  involvement in the science of and debate over global climate

Earth's Energy Imbalance
  The earth is absorbing more energy from the sun than it's
  giving up due to increasing greenhouse gas concentrations.
  The excess energy that the planet is absorbing is enormous.
  The total energy imbalance now is 0.58  0.15 W/m^2.

  From the Laws of Thermodynamics earth must warm until it
  reaches a new equilibrium (Ein = Eout) at higher temperature.
  Given current concentrations of greenhouse gasses, the earth
  will continue to warm for centuries.

Global Temperature

  This graph illustrates the change in global surface
  temperature relative to 1951-1980 average temperatures. The
  10 warmest years in the 136-year record all have occurred
  since 2000, with the exception of 1998. The year 2015 ranks
  as the warmest on record. (Source: NASA/GISS). This research
  is broadly consistent with similar constructions prepared by
  the Climatic Research Unit and the National Oceanic and
  Atmospheric Administration.

Carbon Dioxide

  Carbon dioxide (CO2) is an important heat-trapping
  (greenhouse) gas, which is released through human activities
  such as deforestation and burning fossil fuels, as well as
  natural processes such as respiration and volcanic
  eruptions. The first chart shows atmospheric CO2 levels in
  recent years, with average seasonal cycle removed. The
  second chart shows CO2 levels during the last three glacial
  cycles, as reconstructed from ice cores.

Sea Level

  Sea level rise is caused primarily by two factors related to
  global warming: the added water from melting land ice and
  the expansion of sea water as it warms. The first chart
  tracks the change in sea level since 1993 as observed by

Land Ice

  Data from NASA's GRACE satellites show that the land ice
  sheets in both Antarctica and Greenland are losing mass. The
  continent of Antarctica has been losing about 134 gigatonnes
  of ice per year since 2002, while the Greenland ice sheet
  has been losing an estimated 287 gigatonnes per year.
  (Source: GRACE satellite data)

Berkeley Earth Reports

  The "margin of uncertainty" represents the 95% confidence
  limit, obtained principally by comparison of results from
  subdividing the data into independent sets. The global
  temperature estimate is compiled as combination of a
  land-only temperature estimate constructed by Berkeley Earth
  directly, and an ocean temperature estimate produced by the
  Hadley Centre in the UK and modified by Berkeley Earth.