The greenhouse Earth: A view from space

Abstract

The natural greenhouse effect of the Earth is strongly influenced by the radiative effects of water vapour and clouds in the atmosphere, which control the energy absorbed from the sun, and that lost through thermal emission to space. Any perturbations to the climate balance, for example through so-called 'radiative forcing' due to increasing CO? amounts, variations in solar constant, or other causes, can be amplified by the feedback processes that involve water in its various phases. The radiative cooling of the Earth in the absence of clouds has recently been shown to be dominated by emission from upper-tropospheric water vapour, in the far infrared portion of the spectrum, and this is illustrated: observations of this radiative flux, and of the distribution of water vapour in the upper troposphere, are urgently needed. The role of clouds is discussed, and it is noted that their response to global warming is not presently unambiguously determined with available models, due to the complexity of competing processes: again, as in the cloud-free case, more accurate global observations are needed. The paper is illustrated by data from satellite experiments, most notably the Earth Radiation Budget Experiment sponsored by NASA.

Evaluation of upper tropospheric water vapor in the NCAR Community Climate Model (CCM3) using modeled and observed HIRS radiances

“…UTWV contributes to OLR most significantly in the pure rotation band of the far infrared spectral region (>18 mm) and to a lesser extent in the vibration-rotation bands (5 -8 mm). Several studies have examined the important role of the far infrared water vapor absorption [Clough et al, 1992;Clough and Iacono, 1995;Sinha and Harries, 1995], and others have addressed the importance of the spectral aspect of the greenhouse effect to GCMs and climate simulations [Harries, 1996;Slingo and Webb, 1997].…”

Upper‐tropospheric inversion and easterly jet in the tropics

“…Tropical convective regions are often surrounded by extensive, clear-sky regions on synoptic to planetary scales [e.g., Salby et al, 1991]. It has been pointed out that these clear-sky regions may also be important for Earth's energy balance because much of the Earth's radiation is emitted from the middle and upper tropospheric water vapor in these regions [e.g., Pierrehumbert, 1995;Harries, 1996]. Investigation of both convective and nonconvective regions is, therefore, needed for a better understanding of the tropical atmosphere.…”

Measurement of the water vapour vertical profile and of the Earth's outgoing far infrared flux

“…This is because, through the hydrological cycle, it is involved in all phenomena from energy transport to radiative effects governing the climate system (Pierrehumbert, 2002). Atmospheric water, in the form of both vapour and clouds, is the most important greenhouse component that traps the outgoing longwave radiation (OLR) (Harries, 1996). Its main contribution to climate changes is through feedback processes that occur as a consequence of a man-induced temperature variation driven by the increased CO 2 concentration.…”