Dealing with global climate change - Ecological Applications: Toward a Sustainable World - page 305

Observed changes to atmospheric composition and climate
We know that the atmospheric concentration of carbon dioxide increased from 280 ppm (registered
for the period 1000-1750) to 368 ppm in the year 2000, representing an increase of 31 ± 4%. Other

greenhouse gases have also increased, most notably methane, with a 151 ± 25% increase over the

same period. Associated climate changes have included an increase of 0.6 0.2˚C in global mean

surface temperature during the twentieth century, an increase in the number of hot days and a
decrease in frosty days, an increase in heavy precipitation events at mid- and high northern lati-
tudes, an increase by 5-10% in precipitation in much of the Northern Hemisphere but a decrease
in other areas (e.g. north and west Africa), and an increase in summer drought in some areas (such
as parts of Asia and Africa).

±

Observed physical environmental consequences
In response to these changes, there is good evidence in recent decades of degradation of the per-
mafrost (permanently frozen soil in polar and mountainous areas), loss of snow cover (10% since
1960), reduction by 2 weeks in the period of ice cover of mid-high latitude lakes, glacial retreat,
and thinning (by 40%) and reduction in extent (by 10-15%) of late summer/autumn Arctic sea ice.
Ocean temperatures have increased and, because of thermal expansion of water together with
inputs from melting ice, global mean sea level has risen at an annual rate of 1-2 mm during the
twentieth century. Rather more surprising, the increased inputs of meltwater may be reducing the
strength of the Gulf Stream (an ocean current that moves between Africa and the east coast of
North America) (Bryden et al., 2005).

Observed ecological consequences
Alterations to mean, minimum and maximum temperature and to precipitation patterns have been
responsible for a plethora of ecological changes. The growing season, the characteristic period of
net primary production by vegetation, has lengthened by up to 4 days per decade in the last 40
years, especially at high latitudes in the Northern Hemisphere. In addition, the ranges of various
plants, insects, birds and fi sh have shifted towards the poles and higher in altitude. Thus, various
butterfl y species have expanded northward by up to 200 km. And some alpine plants have been
moving higher at a rate of 1-4 m per decade. Meanwhile plants are fl owering, insects emerging,
amphibians breeding and migratory birds arriving earlier, by several days per decade over the past
60 years (Walther et al., 2002).
Profound ecological changes have also been happening in the oceans. Repeated surveys of
zooplankton species (small, passively drifting animals) provide a particular insight. Note in Figure
11.1 how, in response to warmer temperatures, the distribution of species that are typical of warm
temperate situations has shifted polewards in the North Atlantic, while the cold-loving subarctic
species have become more confi ned to the far north.

Predicted changes to climate in the twenty fi rst century
Depending on the precise assumptions that are made (about how the climate system functions,
how global human population size changes, the energy policy choices that are made, and any
technological advances to reduce or resorb greenhouse gases, etc.) the concentration of CO 2 is
predicted to rise from 368 ppm (in 2000) to between 540 and 970 ppm by 2100, with a concomitant
rise in average global surface temperature of between 1.8 and 4.0˚C, but with considerable variation
from place to place (Figure 11.2a). Predictions are also available for precipitation (Figure 11.2b),
sea level rise (Figure 11.2c), glacial retreat and polar ice loss.

Translating future climate change into ecological consequences
Maps like those in Figure 11.2 provide ecologists with templates of temperature and precipitation
(and other climatic features) onto which can be mapped future distributions of the world's biomes
(tropical rain forest, savanna, arid deserts, etc; Figure 11.3) as well as agriculture and forestry.
Maps of future climate are also available at regional levels. You have already seen how bioclimatic
modeling of current distributions can be used to produce climate envelopes for individual species
(Box 2.1). These envelopes can be superimposed onto the regional templates of predicted climate
to indicate where species may occur in future (Figure 11.4).