From space, daily snapshot of CO2 levels and the feedback role of water vapor

We have blogged a bit about the techniques and precision of atmospheric CO2 measurements (see here).  Now a new space-based instrument, the Atmospheric Infrared Sounder (AIRS), is enhancing our ability to measure CO2 concentration and to forecast it’s implications, including the feedback associated with increasing water vapor.

TEXAS A&M—Researchers studying climate now have a new tool at their disposal that yields daily global measurements of carbon dioxide and water vapor in a key part of Earth’s atmosphere.

The data are courtesy of the Atmospheric Infrared Sounder (AIRS) instrument on NASA’s Aqua spacecraft and confirm the mainstream scientific view that large changes in the climate are likely over the next century.

Moustafa Chahine, the instrument’s science team leader at NASA’s Jet Propulsion Laboratory in Pasadena, unveiled the new measurements at a briefing on recent breakthroughs in greenhouse gas, weather, and climate research from AIRS at the recent American Geophysical Union meeting in San Francisco.

The new data have been extensively validated against both aircraft and ground-based observations. They give users daily and monthly measurements of the concentration and distribution of carbon dioxide in the mid-troposphere—the region of the atmosphere located between 5 and 12 kilometers, or 3 to 7 miles, above Earth’s surface and track its global transport.

Users can also access historical AIRS carbon dioxide data spanning the mission’s entire seven-plus years in orbit. The product represents the first-ever release of global daily carbon dioxide data that are based solely on observations.

One interesting findings and value of the AIRS data is that it is helping atmospheric scientists better understand (or confirm) the feedbacks between CO2, temperature and water vapor.

From John Cook @ SkepticalScience:  Water vapour is the most dominant greenhouse gas. Water vapour is also the dominant positive feedback in our climate system and amplifies any warming caused by changes in atmospheric CO2. This positive feedback is why climate is so sensitive to CO2 warming.

As water vapour is directly related to temperature, it’s also a positive feedback – in fact, the largest positive feedback in the climate system (Soden 2005). As temperature rises, evaporation increases and more water vapour accumulates in the atmosphere. As a greenhouse gas, the water absorbs more heat, further warming the air and causing more evaporation.

How does water vapour fit in with CO2 emissions? When CO2 is added to the atmosphere, as a greenhouse gas it has a warming effect. This causes more water to evaporate and warm the air more to a higher (more or less) stabilized level. So CO2 warming has an amplified effect, beyond a purely CO2 effect.

Read more about the positive feedback caused by water vapor here and here.

…scientists using AIRS data have removed most of the uncertainty about the role of water vapor in atmospheric models. The data are the strongest observational evidence to date for how water vapor responds to a warming climate.

“The argument that the scientific community does not understand water vapor is one of the most durable urban legends in the climate change debate,” says Andrew Dessler, a climate scientist at Texas A&M University.

“AIRS temperature and water vapor observations have corroborated climate model predictions that the warming of our climate produced by carbon dioxide will be greatly exacerbated—in fact, more than doubled—by water vapor.”

Dessler says that most of the warming caused by carbon dioxide does not come directly from carbon dioxide, but from effects known as “feedbacks.” Water vapor is a particularly important feedback. As the climate warms, the atmosphere becomes more humid. Since water is a greenhouse gas, it serves as a powerful positive feedback to the climate system, amplifying the initial warming.

AIRS measurements of water vapor reveal that water greatly amplifies warming caused by increased levels of carbon dioxide. Comparisons of AIRS data with models and re-analyses are in excellent agreement.

“The implication of these studies is that, should greenhouse gas emissions continue on their current course of increase, we are virtually certain to see Earth’s climate warm by several degrees Celsius in the next century, unless some strong negative feedback mechanism emerges elsewhere in Earth’s climate system,” Dessler adds.

Read the full story here

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