Changes in Earth's Albedo Measured by Satellite (Wielicki et al, 825) Essay

Changes in Earth's Albedo Measured by Satellite (Wielicki et al, 825) - Essay Example The global albedo is found to change with changes in the cloud cover, amount of atmospheric aerosols, and forest, snow, & ice cover on the earth’s surface. The magnitude of impact on global albedo due to events caused on earth can be demonstrated by the following example – A volcanic eruption in Mount Pinatubo in June 1991 released aerosols in the stratosphere, which raised global albedo by almost 0.007 in a span of two years. A larger increase in global albedo with unknown causes was reported to occur between 2001 and 2003. In order to investigate whether any significant changes in global albedo occurred between 2001 and 2003, Wielicki et al. examined the observations made by global satellites that measured changes in the earth’s albedo (825). These observations included those made by CERES (Clouds and Earth’s Radiant Energy System) of NASA’s Terra spacecraft. The monthly anomalies in the data caused by seasonal changes were nullified and data was plotted. The data provided by CERES covers global observations for the complete solar spectrum ranging from a wavelength of 0.3 to 4 Â µm. The observations of the global data reveals a small decrease of about 0.006 in the global albedo corresponding to about 2 W m-2 decrease in the shortwave reflected flux. These results contradict with those obtained by Palle et al, who demonstrated a large increase of about 0.017 in the global albedo corresponding to an increase of about 6 W m-2 in the shortwave reflected flux. Independent observations made by two individual CERES instruments were compared. It is believed that the 1.1 W m-2 decrease in the flux observed by one of the CERES instruments could be due to exposure to ultraviolet radiation during a hemispheric scan. When taken into consideration, this further reduces the anomaly to 0.9 W m-2. Wielicki et al. further explain the effect of change in albedo on earth’s climate (825). When changes in land surface, aerosols, and fores t, snow and ice cover is the cause for change in albedo, then increasing albedo results cooling of the earth and decreasing albedo results in warming. These changes on earth’s surface significantly influence the amount of reflected solar radiation but have comparatively minor effects on the emitted thermal infrared radiation that results in cooling. Wielicki et al. contend that if observations made by Palle et al. were correct, then there would have been global cooling double of what had been observed in the Pinatubo eruption. However, such a global cooling was not observed. Furthermore, Wielicki et al. explain another possibility that the earth’s total ocean heat storage could witness a significant reduction. It is estimated that between 2000 to 2002, the ocean heat storage has experienced an increase of 0.7 W m-2. In order to account for the global changes in reflected solar flux, the flux in ocean heat storage was scaled to global surface area from an ocean-only are a utilized by Willis et al (Wielicki et al. 825). According to Wielicki et al, if changes in global albedo were occurring, then there would be a decrease of 0.7 Â ± 0.8 W m-2 in the reflected flux. This is found to be consistent with the observations made by CERES. Until now, only the effects of change in albedo have been discussed. Cloud changes may also be affecting both the earth’s albedo and its thermal infrared cooling, and may also be a cause for albedo changes that do not