Almost every discussion of global warming begins or ends with carbon dioxide. Because of its molecular structure, carbon dioxide is a greenhouse gas: while visible sunlight can pass through the atmosphere, CO₂ absorbs and re-emits infrared energy. In balance, greenhouse gases act like insulation and help keep Earth's climate temperate; the source notes that without them Earth's average temperature would be around −18°C. Since the Industrial Revolution, however, fossil-fuel combustion and deforestation have increased atmospheric CO₂, adding to the greenhouse effect and raising global temperatures. [source] [source]
Because climate and the carbon cycle are closely connected, monitoring atmospheric CO₂ is important. The article discusses the Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite, an early space-based instrument able to make extensive measurements of atmospheric carbon dioxide under a wide range of conditions. [source]
 |
NOAA Earth System Research Laboratory
|
A map reproduced in the original article shows CO₂ concentrations in the troposphere, the atmospheric layer extending from Earth's surface to roughly 10–20 kilometres altitude, where temperature generally decreases with height and most weather occurs. The data correspond to May 2013, when atmospheric CO₂ was reported at levels unprecedented in at least 800,000 years. [source]
The highest concentrations in that seasonal snapshot appeared mainly in the Northern Hemisphere. The article relates this partly to the timing of the northern growing season: in May, vegetation had only recently begun its major seasonal uptake of carbon. In the Southern Hemisphere, seasonal vegetation patterns contributed to lower concentrations in many areas. [source] [source]
How AIRS detects carbon dioxide
AIRS measures 2,378 infrared spectral channels. Carbon dioxide absorbs and emits infrared radiation at characteristic wavelengths, creating a spectral “fingerprint.” By measuring radiation in these bands, AIRS allows scientists to estimate atmospheric CO₂ concentrations over broad areas of the globe.
AIRS observations also showed that carbon dioxide is not distributed perfectly evenly through the atmosphere. Jet streams, large-scale weather systems, and other atmospheric circulations transport gases horizontally and vertically, producing regions of relatively higher and lower concentration. These observations raised further questions about how CO₂ moves through the atmosphere.
The source then discusses NASA's Orbiting Carbon Observatory program, describing a satellite launched in 2014 specifically to observe atmospheric carbon dioxide with greater precision than instruments whose primary missions were broader atmospheric observation. [source]
 |
NASA Earth Observatory Rob Simmon Jesse Allen AIRS
|
The NASA Earth Observatory image cited in the article was produced by Rob Simmon and Jesse Allen using data supplied by the AIRS science team.
From Mauna Loa to the satellite era
Much of the foundational knowledge about atmospheric CO₂ came from measurements begun by Charles David Keeling at Mauna Loa, Hawaiʻi, in 1958. The graph discussed in the article shows measurements from May 2013, when the concentration reached approximately 399.76 parts per million. The source contrasts this with a pre-industrial concentration of about 278 ppm. [source]
The article closes by pointing readers to the IPCC Fifth Assessment Report for discussion of the effects associated with rising greenhouse-gas concentrations, including warming, changes in weather patterns and ecosystems, and loss of polar ice. The measurements and report references here are preserved in their original historical context. [source] [source]