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.
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.
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
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 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
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.