Principles of terrestrial ecosystem ecology.pdf

40 2. Earth’s Climate System
Low
pressure
Weak winds
Moderate
high
pressure
Low
pressure
Westerly aloft
Thermocline
factors that initiate these large-scale climate
features are poorly understood, the patterns
themselves and their ecosystem consequences
are becoming more predictable. Future climatic
changes will likely be associated with changes
in the frequencies of certain phases of these
large-scale climate patterns rather than any
simple linear trend in climate. Climate
warming, for example, might increase the fre-
Easterly trades
Thermocline
Figure 2.19. Walker circulation of the ocean and
atmosphere in the tropical Pacific between South
America and Indonesia during “normal” years and
during El Niño years. In normal years, strong easterly
trade winds push surface ocean waters to the
west, producing deep, warm waters and high precipitation
off the coast of Southeast Asia and cold,
"Normal " conditions
~
(La Nina event)
~
El Nino event
Low
pressure
Weak winds
High
pressure
Cold
upwelling
Moderate
high
pressure
Warm
upwelling
upwelling waters and low precipitation off the coast
of South America. In El Niño years, however, weak
easterly winds allow the surface waters to move from
west to east across the Pacific Ocean, leading to
cooler surface waters and less precipitation in Southeast
Asia and warmer surface waters and more precipitation
off South America.
quency of ENSO events and positive phases of
the NAO.
Seasonal and Daily Variations
Seasonal and daily variations in solar input
have profound but predictable effects on
climate and ecosystems. Perhaps the most
obvious variations in the climate system are the