July 15, 2004 — The NOAA Climate Monitoring and Diagnostics Laboratory collects atmospheric data and conducts research on atmospheric constituents (or elements) that are capable of forcing climate change and may contribute to global ozone depletion. CMDL accomplishes its mission by collecting long-term gas (i.e., carbon dioxide, methane, carbon monoxide, halocarbons, nitrous oxide, tropospheric (lower atmosphere) and stratospheric (upper atmosphere) ozone), aerosols and solar/infrared radiation measurements at sites around the globe. Measurements are conducted from five manned CMDL Atmospheric Baseline Stations (Pt. Barrow, Alaska; Trinidad Head, Calif.; Mauna Loa, Hawaii; Cape Matatula, American Samoa and Amundsen-Scott South Pole Station, Antarctica), and from 60 other globally distributed cooperative measurement locations, including regular aircraft profiles, ship transects, balloons and trains. At some stations, CMDL atmospheric data records date back to 1958 and have continued unbroken to this day. One of the most significant of these is the carbon dioxide record from the NOAA Mauna Loa Baseline Observatory in Hawaii.

“By tracking long-term measurements of gases and aerosols that contribute to climate change, CMDL supports one of NOAA’s primary mission goals — to understand climate variability and change to enhance society’s ability to plan and respond,” said retired Navy Vice Adm. Conrad C. Lautenbacher, Ph.D., undersecretary of commerce for oceans and atmosphere and NOAA administrator. "Its record of atmospheric measurements will also serve as a component in the emerging global observing system." he added.

Carbon Dioxide
The annual saw-tooth pattern in the carbon dioxide graph to the right is produced by growing vegetation that consumes carbon dioxide in the spring and summer, and releases it in the fall and winter. The long-term upward trend results from carbon dioxide that is released by the combustion of fossil fuels. Carbon dioxide is the most important climate-forcing gas in the atmosphere and is growing at a rate of about 1.5 parts-per-million per year (Click on NOAA image to the right for a larger view of the Mauna Loa carbon dioxide record).

Methane
Methane is the second most important climate forcing gas, but its growth rate in the global atmosphere has stabilized over the last four years. This may indicate that methane is reaching a steady state (i.e., sources equal sinks) and/or lower leak rates in the recent production of natural gas in the former Soviet Union (Click on NOAA image to the right for a larger view of the CMDL methane measurements).

Halocarbons
Halocarbons make up the third largest group of climate-forcing gases. These include chlorofluorocarbons (CFCs), halogenated (contain Cl and Br) solvents — like methyl chloroform (CH₃CCl₃) and carbon tetrachloride (CCl₄) — and their replacement compounds, hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). While halocarbon concentrations are only in the parts-per-trillion (one molecule in a trillion air molecules) range, these gases are extremely efficient at climate forcing (some about 10,000 times that of carbon dioxide per individual molecule), and absorb radiation in the “atmospheric window” where other major atmospheric gases do not.

Halocarbons also catalyze the destruction of ozone in the stratosphere and are responsible for the annual Antarctic springtime phenomenon known as the Antarctic Ozone Hole. In an international effort to protect the ozone layer, production of most halocarbons are now prohibited or restricted by international agreement — the Montreal Protocol on Substances that Deplete the Ozone Layer. Only limited production of CFCs for essential uses (e.g., medical inhalers) and in developing countries (e.g., China, India, etc.) is currently permitted. Because of the Montreal Protocol, the total atmospheric amount of chlorine (and its bromine equivalent) has decreased by about six to seven percent since 1992. Continued monitoring of halocarbons will provide the fundamental data needed to better understand stratospheric ozone observations, especially during the recovery expected over the next few decades (Click on NOAA image to the right for a larger view of the global trends in controlled ozone depleting chemicals).

Water Vapor
Water vapor concentrations in the stratosphere are much smaller than those in the troposphere, but changes in stratospheric water vapor may play a significant role in altering the temperature in both layers of the atmosphere. Global climate model results show that due to energy redistribution in the stratosphere, increases in water vapor can lead to cooling in the upper atmosphere, while these same increases can lead to a warming near the surface. The 22-year record of stratospheric water vapor observations collected from Boulder, Colo.— the only one of its kind — has been derived from monthly balloon soundings. The record shows significant year-to-year variations, but over the longer term, the one percent annual increase in water vapor throughout the entire stratosphere is very significant. Approximately 30 percent of the recently observed water vapor increase may be attributed to increases in atmospheric methane that reacts with the hydroxyl radical (OH) to form carbon dioxide and water. However, the source for the remaining 70 percent of the increase is not well established. (Click on NOAA image to the right for a larger view of increased water vapor in the stratosphere).

Aerosols
Aerosols are another climate forcing parameter that is measured extensively by CMDL. These small particles floating in the atmosphere cool the surface of the Earth by absorbing sunlight and reflecting sunlight back into space.The net effect of aerosols on the Earth's energy budget can be positive or negative, depending on the optical properties of the particles and the brightness of the underlying surface. For example, diesel soot particles above a snow-covered surface have a net positive forcing (warming), while sulfate particles from coal combustion over the dark ocean have a net negative forcing (cooling). The uncertainty of the sign and magnitude of aerosol climate forcing is high, yet CMDL measurements are helping to reduce this uncertainty. One of the more pronounced aerosol trends observed at CMDL comes from the Barrow, Alaska, baseline station where a springtime concentration of aerosols and anthropogenic gases known as “Arctic Haze” is associated with air pollution from Russia and Eastern Europe. Springtime haze concentrations had a factor of four downward trend between 1982 and 1997, but has climbed in recent years. This pattern is thought to mirror (in part) the economic activity and fossil fuel combustion in the former USSR, which is now recovering (Click on NOAA image to the right for a larger view of the 25 year record of springtime aerosol measurement at the CMDL Barrow, Alaska, baseline station).

Solar Radiation
Changes in solar radiation reaching the Earth's surface can have dramatic effects on climate forcing. CMDL solar radiation measurements dating back to 1957 at the Mauna Loa Observatory — now the Earth’s longest record of solar radiation transmission — show the effects of two large volcanic events, El Chichon in 1982 and Mount Pinatubo in 1991. These eruptions deposited aerosol particles in the stratosphere that interfered with solar radiation reaching the Earth’s surface, thus cooling it. Also apparent in the Mauna Loa solar transmission record are the annual peaks in the dust and anthropogenic aerosol from Asia that flow to Mauna Loa each spring. The record also suggests that background atmospheric aerosol concentrations over Mauna Loa are increasing, possibly due to increasing anthropogenic effluent flows out of Asia (Click on NOAA image to the right for a larger view of Mauna Loa solar beam transmission).

Ozone
Ozone can have either a positive or negative climate forcing depending on where it is located in the atmosphere. Increases of ozone in the troposphere, or lower atmosphere, may cause atmospheric warming. On the other hand, decreases in stratospheric ozone may contribute to cooling in the lower atmosphere due to the infrared absorbing properties of ozone. Apart from the well known Antarctic ozone hole, total column stratospheric ozone has decreased about three percent over the United States in the past 20 years. On the other hand, CMDL measurement show that surface ozone has increased at several urban sites in the northern hemisphere over the past two decades, but there has been no significant change in the global tropospheric background ozone levels over the same period.

Trans-Siberian Observations Into the Chemistry of the Atmosphere
The TROICA experiment provides a novel means of measuring gases and aerosols across much of the northern hemisphere with one set of instruments over a relatively short period of time. The TROICA project consists of coupling a highly instrumented railway carriage with regular passenger trains traveling across Russia from Moscow to far eastern Siberia and back — a thirteen-day journey covering about 17,000 km. The main advantage of this platform is that overhead electrical lines power all of the locomotives so there is little pollution from the train itself. Reactive gases such as ozone, nitrogen dioxide and carbon monoxide can also be measured with little influence from passing trains.

Future of Climate Monitoring and Diagnostics Laboratory Monitoring Programs
CMDL plans to increase its number of ground-based stations and aircraft sites to refine the nation’s understanding of North American sources and sinks of carbon cycle gases. In addition to the compounds already measured, CMDL scientists will add a new group of compounds, called perfluorocarbons, to their measurement database. PFCs have extremely long lifetimes in the atmosphere and may contribute significantly to climate forcing towards the end of this century. CMDL will also continue to provide atmospheric monitoring data and scientific analyses for future international assessments in its three principle areas of the research (i.e., climate forcing, ozone depletion and air quality) and plans for its atmospheric observations to continue into the next century, and beyond.

Relevant Web Sites
ATMOSPHERIC TRANSMISSION OF DIRECT SOLAR RADIATION AT MAUNA LOA, HAWAII

Carbon Cycle and Greenhouse Gas Group (CCGG) of CMDL

Halocarbons and other Trace Atmospheric Species Group (HATS) of CMDL

Ozone and Water Vapor Group (OZWV) of CMDL

Aerosol Group of CMDL

Solar & Thermal Atmospheric Group of CMDL

Climate Change for Educators

NOAA/CMDL South Pole Ozone Page

Media Contact:
Jana Goldman, NOAA Research, (301) 713-2483