Climate Roles of H2O, CH4 and CO

Water Vapor

Water vapor is the most important greenhouse gas. Not only are its infrared absorption features widespread and strong, but it displays a significant continuum absorption. Thus, while not one of the “gases of concern” in the sense of anthropogenic modification, the feedbacks engendered by the higher water content of a warmer atmosphere (and, potentially, greater cloud cover) are a vital element of these studies. Furthermore, water vapor, through continua centered at 100 and 1600 cm-1, is a crucial element in the radiative balance of the upper troposphere. TES routinely measures humidity (water vapor) profiles with a precision better than 10%.

Methane

Although the abundance of methane (CH4) is tiny compared with carbon dioxide, it is a far more potent warming agent. Methane also contributes to tropospheric ozone production. Monitoring of methane (CH4) is a secondary goal for TES.

It has been shown that TES is sensitive to the methane column. The column that can be derived has the most sensitivity between 300 and 400 mb. TES has a relatively small footprint size – meaning more homogeneous pixels allowing for higher probability of cloud-free pixels, and TES's infrared wavelengths allow some CH4 retrievals to occur even in the presence of clouds. In addition, TES does not require a high surface albedo to detect CH4, and does not need to assume an air mass factor based on CO2, which may vary with CH4. Finally, TES profiles contain some vertical information for CH4 (rather than containing only column averaged information).

Carbon Monoxide

Carbon monoxide (CO) is only a very weak direct greenhouse gas, but has important indirect effects on global warming. Carbon monoxide is an ozone precursor, and also reacts with the hydroxyl (OH) radicals in the atmosphere, reducing their abundance. As OH radicals reduce the lifetimes of many strong greenhouse gases (such as methane), CO indirectly increases the global warming potential of these gases.

Back: Global Climate Change

Greenhouse gases contribute to global warming by trapping some of the energy that Earth radiates after being warmed by the sun. TES scientists are currently able to calculate how much energy is trapped at various altitudes by ozone and they’re in the process of doing the same with water vapor, the most abundant greenhouse gas. Upcoming work with TES data may similarly reveal the effects of methane.