24
Ecosystem Climate Manipulations
Karin P. Shen and John Harte
Introduction
Human activities such as fossil fuel burning and
deforestation are expected to cause global climate
change of a rate and magnitude unmatched in the
historical record. Results from climate modeling
studies indicate that the earth is likely to experience
an increase in global average temperature of several
degrees Celsius by the end of the next century
(IPCC 1995). This temperature increase, and other
associated climate changes, will have far-reaching
effects on the natural environment and human
society.
Impending climate change will affect ecosystems, and ecosystem responses can in turn exert
strong feedbacks to climate. Mathematical modeling and paleoclimatic studies have explored potential ecosystem response to climate change. Since
the early 1980s, there have been hundreds of laboratory investigations of climate change impacts on
soil and plants. Field manipulation studies of global
warming have been fewer in number, and of these
only a small fraction have been on an ecosystem
level.
In this chapter, we discuss laboratory and field
manipulation methods for studying ecosystem response to global climate change. We focus our discussion on whole-ecosystem methods, and our emphasis on terrestrial ecosystems reflects the general
emphasis of past work. We begin with a brief review of global warming and model predictions, discuss the use of paleoclimatology and simulation
models, and then review ecosystem climate manipulation methods. We conclude with recommendations for successful manipulation studies.
Global Climate Change
and Ecosystems
Greenhouse gases, while relatively transparent to
incoming solar radiation, warm Earth's surface by
trapping outgoing infrared radiation. Such gases include water vapor, carbon dioxide (C0 2 ), methane
(CH 4 ), nitrous oxide (N 2 0) , and chlorofluorocarbons (CFCs). Decades-long records of atmospheric
measurements from sampling stations around the
world reveal steady increases in the tropospheric
concentrations of all of these gases (Keeling and
Whorf 1998; Ross and Elliott 1996; Schimel et al.
1995). These increases are unambiguously attributable to human activities.
Concomitant with the increasing greenhouse gas
concentrations, global average temperature has increased 0.3 to 0.6°C within the last century (IPCC
1995). Mathematical models of global climate
(general circulation models, GCMs) allow prediction of the magnitude and distribution of climate
change due to anthropogenic greenhouse gas and
aerosol emissions. Comparison of model output
with the past 100-year climate record indicates that
observed patterns of change are generally consistent with predictions. As anthropogenic greenhouse
gas emissions are unlikely to abate in the coming
decades, it is almost certain that the earth will experience continued global warming.
General circulation model studies indicate that
continuing emissions will likely increase global
mean average temperature by between 1 and 3SC
by the year 2100 (IPCC 1995), with the major
source of uncertainty being the estimation of cli353
Ecosystem Climate Manipulations
Karin P. Shen and John Harte
Introduction
Human activities such as fossil fuel burning and
deforestation are expected to cause global climate
change of a rate and magnitude unmatched in the
historical record. Results from climate modeling
studies indicate that the earth is likely to experience
an increase in global average temperature of several
degrees Celsius by the end of the next century
(IPCC 1995). This temperature increase, and other
associated climate changes, will have far-reaching
effects on the natural environment and human
society.
Impending climate change will affect ecosystems, and ecosystem responses can in turn exert
strong feedbacks to climate. Mathematical modeling and paleoclimatic studies have explored potential ecosystem response to climate change. Since
the early 1980s, there have been hundreds of laboratory investigations of climate change impacts on
soil and plants. Field manipulation studies of global
warming have been fewer in number, and of these
only a small fraction have been on an ecosystem
level.
In this chapter, we discuss laboratory and field
manipulation methods for studying ecosystem response to global climate change. We focus our discussion on whole-ecosystem methods, and our emphasis on terrestrial ecosystems reflects the general
emphasis of past work. We begin with a brief review of global warming and model predictions, discuss the use of paleoclimatology and simulation
models, and then review ecosystem climate manipulation methods. We conclude with recommendations for successful manipulation studies.
Global Climate Change
and Ecosystems
Greenhouse gases, while relatively transparent to
incoming solar radiation, warm Earth's surface by
trapping outgoing infrared radiation. Such gases include water vapor, carbon dioxide (C0 2 ), methane
(CH 4 ), nitrous oxide (N 2 0) , and chlorofluorocarbons (CFCs). Decades-long records of atmospheric
measurements from sampling stations around the
world reveal steady increases in the tropospheric
concentrations of all of these gases (Keeling and
Whorf 1998; Ross and Elliott 1996; Schimel et al.
1995). These increases are unambiguously attributable to human activities.
Concomitant with the increasing greenhouse gas
concentrations, global average temperature has increased 0.3 to 0.6°C within the last century (IPCC
1995). Mathematical models of global climate
(general circulation models, GCMs) allow prediction of the magnitude and distribution of climate
change due to anthropogenic greenhouse gas and
aerosol emissions. Comparison of model output
with the past 100-year climate record indicates that
observed patterns of change are generally consistent with predictions. As anthropogenic greenhouse
gas emissions are unlikely to abate in the coming
decades, it is almost certain that the earth will experience continued global warming.
General circulation model studies indicate that
continuing emissions will likely increase global
mean average temperature by between 1 and 3SC
by the year 2100 (IPCC 1995), with the major
source of uncertainty being the estimation of cli353