GPHY 314 Chapter 9: Impacts of Climate Change

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29 Dec 2020
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CHAPTER 9: Impacts of Climate Change
Although temperature in any single place can vary considerably by season, day, and even within a
day, variations tend to cancel when averaged over entire globe
o Large temperature variations are nearly completely canceled by opposite variations
somewhere else on Earth
Due to cancellation, global average temperature of Earth very stable
o Seemingly small changes in global average temperature associated with significant shifts
in Earth’s climate i.e. during last ice age was about 5°C colder than present
Rate of change matters because the faster warming occurs, the less time people and natural
ecosystems have to adapt to changes
Modern human society is only a century or so old, over which Earth’s climate has been stable,
varying by less than 1°C, so the argument that we have experienced this type of warming before
is fundamentally misleading
Both humans and ecosystems have adapted to our environment
o Any changes in climate either warming or cooling will result in overall negative
outcomes for humans
Not every single change in every region will be negative, but positive effects are expected to be
outweighed by more pervasive negative effects
Physical Impacts
Temperature
o Continents warm more than oceans because of larger heat capacity of oceans
Warming in northern North America and Eurasia projected to be more than 40%
greater than global average warming
o High latitudes will warm more than tropics, primarily due to ice-albedo feedback
Models predict more warming in Arctic than Antarctic
o In general, adding GHGs tends to reduce temperature contrasts, and expect more
warming in winter than summer, and more warming at night than day
As abundance of GHGs increases, heating of surface from GHGs becomes
stronger while heating from sunlight remains about the same
Thus, variations in solar heating with latitude, time of day, and season become a
smaller component of the total heating of the surface, and will therefore lead to
smaller temperature variations
o In middle of 21st C, all RCP scenarios show about same amount of warming but by end of
21st C, global average warming for RCP8.5 is x4 larger than RCP2.6 and x2 RCP4.5
o Can be confident temperatures will continue to increase in future and that general
distribution of warming will be in accord with these model predictions
Precipitation
o As GHGs increase, energy in for surface increases because of increased infrared radiation
from atmosphere falling on surface, which leads to increase in evaporation from ocean
Since precipitation must balance evaporation, precipitation also increases
More quantitatively, total global precipitation projected to increase by few
percent for every degree Celsius of global average warming
o Although total rainfall expected to increase, won’t be distributed evenly
Large-scale shift to higher latitudes, causing decrease in many parts of tropics
General rule of thumb that wet places get wetter while dry places get drier
o Less wintertime precipitation will fall as snow and more will fall as rain
Very important -> When snow falls, water doesn’t run off until snow melts in
spring but rain runs off immediately
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