The Carbon Dioxide (CO2) Problem
The carbon dioxide problem can be stated relatively simply:
- More than six and a half billion people burn fuel to keep warm, to
provide electricity to light their homes and to run industry, and to
move about using cars, buses, boats, trains, and airplanes.
- The burning of fuel produces carbon dioxide, which is released to
- The burning of fuels adds about 6 gigatons of carbon to the atmosphere
- Carbon dioxide concentrations in the atmosphere have risen from about
270 parts per million (0.026%) before the industrial age to about 380
parts per million (0.038%) by 2006, a 41% increase over pre-industrial
values, and a 31% increase since 1870.
- Carbon dioxide is a greenhouse gas, and the increased concentration
of carbon dioxide in the atmosphere must influence earth's radiation
Measurements of Temperature and Carbon Dioxide
Measurements of carbon dioxide can be made at any location on earth
remote from nearby local sources because the
atmosphere is well mixed over periods of a few years. The two most
famous sets of measurements were made at Mauna Loa in Hawai'i and at
Vostok station in Antarctica.
- Charles Keeling began collecting flasks of air from an observatory
at the summit of Mauna Loa in Hawai'i in 1959. Keeling,
the first to confirm the rise of atmospheric carbon dioxide by very
precise measurements that produced a data set now known widely as the "Keeling
Curve." Prior to his investigations, it was unknown whether the
carbon dioxide released from the burning of fossil fuels and other
industrial activities would accumulate in the atmosphere instead of
being fully absorbed by the oceans and vegetated areas on land. From
Charles David Keeling: Climate Science Pioneer.
Carbon dioxide concentration in the atmosphere measured by David Keeling
and colleagues at Mauna Loa, Hawai'i and from polar ice cores, with
average global surface temperature of earth.
Image from Woods
Hole Research Center, presentation by Director John P. Holdren, The
- The Vostok
ice core is a cylinder of ice collected by drilling from the surface
to near the bottom of the Antarctic ice sheet. Total length was 2083
meters, brought back in 4-6 meter sections. The core shows annual layers,
which can be used to date the air bubbles trapped in the ice. Analysis
of the gas content of the bubbles gives the concentration of carbon
dioxide in the atmosphere when the ice formed. Ratios of oxygen isotopes
and deuterium gives air temperature at the station at the time ice
Atmospheric carbon dioxide concentration calculated from air
bubbles trapped in the Antarctic continental glacier and cored
at the Vostok ice Station. Notice that present carbon dioxide
concentrations far exceed all values for the past 400,000 years,
and that the concentration is high when temperature is high.
This does not imply cause or effect. Both carbon dioxide and
temperature are linked through feedback loops. Both variables
change over periods of around 100,000 years due to slow variations
in earth's orbit and spin axis. To learn more about the relation
between carbon dioxide and temperature, we need other data and
Image from UNESCO Introduction
to Climate Change, GRID-Arendal.
- The page on Evidence for Global
Warming has more information on ice cores and other sources of
Sources of Anthropogenic (Human-Produced) Carbon
Anthropogenic (human-produced) carbon dioxide is mostly from the burning
of fossil fuel: coal, oil, and natural gas. The burning of forests to
produce agricultural land, and the burning of forest wood for heating
and cooking add smaller amounts. The following information comes mostly
from the Statistical
Review of World Energy 2005 by British Petroleum.
- Global energy use from fossil fuels was approximately 8,260 million
metric tons oil equivalent, which is approximately 9,623 X 109 m3 =
a cube of oil 2.12 km on a side.
- Global oil consumption in 2003 was 76,800,000 barrels of oil per
day. Most of the remainder of our energy comes from natural gas and
- Per capita consumption of energy in the United States is about
57 barrels of oil equivalent per year. The energy is used to heat and
light homes, offices, and stores, to power trucks and automobiles,
and to operate machinery. 57 barrels of oil at $50/barrel = $2,850.
If the energy were used entirely as electricity, it would cost about
$7,300 per person per year.
- Consumption of energy in the United States was approximately:
- 89.4% from burning fossil fuels.
- 39.1% oil
- 25.9% natural gas
- 24.4% coal
- 8.1% from nuclear energy
- 2.5%from hydroelectric power plants
- The United States used approximately 24% of all the world's energy,
although we are only 4.6% of the world's population.
Anthropogenic sources are a small part of the global
carbon system. Their production mixes with carbon dioxide released
by the respiration of plants and animals, and through the decay of
carbon-based material from plants and animals.
Other Greenhouse Gases
Carbon dioxide is one of several greenhouse gases released in large
quantities by human activities. The important gases are:
- Water vapor. This is by far the most important greenhouse gas. It
evaporates mostly from the ocean, and it causes earth's surface to
be about 30°C warmer (out of the 33°C of warming caused by
all greenhouse gases combined). See Ocean
and Climate for a discussion of how much water warms the atmosphere.
- Carbon dioxide.
It is produced by
bacteria in wetlands and bogs, cattle, rice paddies, termites, landfills,
and coal mining. About two thirds of the emissions into the atmosphere
come from human activity, mostly in the northern hemisphere. Methane
concentration was 1783 parts per billion in 2004, which was 155%
larger than pre-industrial concentrations. The rise in methane appears
to have leveled off, and concentrations have increased only 5 parts
per billion since 1999. Methane does not remain long in the atmosphere,
about 8 years (Fischer et al, 2008), so emissions and sinks are already
close to balance. One pound of
methane is 22 time more effective in absorbing infrered radiation
than is a pound of carbon dioxide. The Department of Meteorology
at the University of Maryland College Park has a web page listing the amounts
emitted by various sources.
Average methane mixing ratios in the boundary
layer (the layer of the atmosphere in immediate contact with Earth's
surface) in 2003, calculated with a chemistry–transport model.
The atmospheric lifetime of methane is almost a decade, so it disperses
globally. Regions of strong emissions are nevertheless manifest,
leading to the largest variability in the northern hemisphere and
an inter-hemispheric difference of 5–10%. The recently proposed
release of methane by terrestrial vegetation is not included, as
its magnitude is still uncertain. Figure and text are from Lelieveld
(2006), who redrew the figure from Houweling (1999).
- Nitrous oxide,
from microbes in the soil and the ocean, and from burning fossil fuels
at high temperatures, such as car engines. About one-third of the emissions
into the atmosphere come from human activity. N2O concentrations
were 319 parts per billion in 2004, which was 18% larger than pre-industrial
concentrations. Its lifetime in the atmosphere is similar to that of
carbon dioxide, about a century.
- Halocarbons such
as refrigerants used in air conditioners .
- Tropospheric ozone, produced in smog.
For more information on greenhouse gases, see the expert's
page on greenhouse gases written by the Atmospheric Radiation Measurement
(ARM) Program of the U.S. Department of Energy (DOE).
For more information on climate change, read the US Global Change Research
Information Office's pages
on global warming. Or, read the section on Climate at
the Environmental Protection Agency's Climate
Change Web Site. You may also wish to visit other pages at the Department
of Energy's Atmospheric Radiation Measurement Program site. Or
The different sites provide different viewpoints and information written
at different technical levels.
Houweling, S., T. Kaminski, F. Dentener, J. Lelieveld, and M. Heimann
(1999). Inverse modeling of methane sources and sinks using the
adjoint of a global transport model. Journal
of Geophysical Research 104 (D21): 26,137–26,160.
Fischer, H., M. Behrens, et al. (2008). Changing boreal methane sources
and constant biomass burning during the last termination. Nature 452
Lelieveld, J. (2006). Climate change: A nasty surprise in the greenhouse.
Nature 443 (7110): 405–406.
16 February, 2009