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(a)
C
c
W
c
More sunlight reflected
back into space
More evaporation
Altered climate
More water in the
atmosphere
More clouds
More water
vapour condensing
More water vapour
greenhouse gas
(b)
C
c
W
c
More sunlight reflected
back into space
Smaller ice caps
Altered climate
Less sunlight
reflected
Larger ice caps
More precipitation
freezing
More energy/heat
absorbed
(c)
C
c
W
c
Smaller algal population
with less photosynthesis but still
drawing down atmospheric CO
2
More evaporation
hence more rain
Altered climate
Less erosion and iron
washed into oceans
More erosion and iron
washed into oceans
Iron encourages algae whose
photosynthesis reduces CO
2
Less evaporation
hence less rainfall
Fig. 1.8
Examplesofinteractingpositive-andnegative-feedbackmechanismsafectingclimatechange.Seealso
Figure4.13foranexampleofanotherfeedbackcycle:therearemany.
magnitude of this natural effect may not be as large as some might wish, hence
the discussion as to whether we should deliberately fertilise the oceans with iron or
take some other measure (although it would be unwise to tinker with the planet's
biosphere mechanisms without a thorough understanding of them). Given that there
are feedback processes that amplify change and those that stabilise the climate, it is
not surprising that changes in the global climate are not always gentle. For example,
we do not see a gentle segue from a glacial to an interglacial. Instead, we see a sharp
transition between the two (see Figure 1.6). It is as if positive feedback encourages
sharp changes while negative feedback encourages stable states and that either one
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