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Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties
ments in coastal waters (Yoder et al., 2001). Bacteria, viruses, colloids, and small bubbles are also possible contributors.
Shell et al. (2003) used a global climate model to assess the role of ocean color in the sea surface temperature and other aspects of the climate system. They found that phytoplankton warm the surface by about 0.05°C on a global average basis. They also found that the large-scale atmospheric circulation is significantly affected by regional alterations of ocean color. These results suggest that the radiative effects of phytoplankton should not be overlooked in studies of climate change.
Frouin and Iacobellis (2002) also determined that absorption of sunlight by phytoplankton must be included in the global radiation budget. They estimated that, compared to pure seawater, the globally and annually averaged outgoing radiative flux is decreased by 0.25 W m−2 due to ocean phytoplankton. In coastal and high-latitude regions, the forcing can reach around 1.5 W m−2. They also found that the amount absorbed was species dependent.
TELECONNECTIONS AND RADIATIVE FORCING
Linkages between weather or climate changes occurring in widely separated regions of the globe are referred to as teleconnections. The extent to which regionally concentrated radiative forcing can affect climate via teleconnections is a matter of current research. Determining the importance of regional forcings, such as those from aerosols or land-use change, requires an understanding of the role of teleconnections that can lead forcings in one region to have effects on other regions far away. Teleconnections are most commonly thought of with respect to the transport of energy by atmospheric waves (Tsonis, 2001). For example, regional and global weather patterns have been associated with sea surface temperature anomalies (e.g., Hoerling and Kumar, 2003). Radiative and nonradiative forcing due to regional land-use change can also result in large differences in atmospheric circulation patterns at large distances from the landscape disturbance. For example, land-use change can alter deep cumulonimbus patterns, which affect atmospheric circulation in distant regions (Chase et al., 2000a).
Avissar and Werth (2005) found that deforestation of tropical regions, through teleconnections similar to those produced during El Niño events, has a significant impact on the rainfall of other regions. In particular, they found that the U.S. Midwest is the continental region the most negatively affected by the deforestation of Amazonia and Central Africa during spring and summer, when rainfall decrease could severely damage agricultural productivity in that region. These results are summarized in Figure 2-9. Avissar and Werth (2005) conclude that tropical deforestation considerably