Climate
Change
Temperature – A Critical
Environmental Variable
 Life
can be described very simply as a
series of well-regulated biochemical
reactions.
 Most of the reactions are controlled by
specialized proteins called enzymes.
 Temperature is critical to biochemical
reactions, because it determines the
effectiveness of the enzymes controlling
the reactions.
Temperature – A Critical
Environmental Variable
 When
temperature
is either too low or
too high, enzyme
activity is reduced.

Goldilocks
principle
Temperature – A Critical
Environmental Variable


Temperature can
similarly affect the
performance of entire
organisms.
A Goldilocks-like
relationship between
temperature and
performance is often
seen in ectotherms,
organisms whose body
temperature depends
on the surrounding
environment.
Temperature – A Critical
Environmental Variable


Temperature also
affects groups of
organisms.
Population growth
rates and thus
population dynamics
may also follow the
Goldilocks Principle,
with growth rates
maximized at some
optimal temperature.
Temperature – A Critical
Environmental Variable
 At
global scales,
species richness—the
number of species in a
given area—tends to
be highest in the
tropics and lowest
near the poles.
 Much of this variation
can be explained by
temperature.
Detecting
Climate
Change
Detecting Climate Change
 The
climate on Earth is continually
changing.
 Several ice ages have come and gone.
 The lower temperatures and altered rain
patterns during the ice ages produced a
world very different than today's.

Northern forests were replaced by large
expanses of tundra as cool, dry air rolling off
the ice sheets pushed tree habitats
southward.
Detecting Climate Change
 Climate
continues to change today as it
has always done in the past.
 We can use statistics to monitor changes.
 We need to know whether the changes
are due to the same factors as in the past.

Attribution
Climate vs Weather
 Weather
describes short-term behavior of
the atmosphere.

Time scale: minutes to months
 Climate
describes a region's average
weather conditions over a long time
period, and how much those conditions
vary.

Time scale: 30 years +
Detecting Trends
 To
investigate climate change, we need
to detect trends in the climate.
 Detecting such trends in climate, even
when they are known to exist, is difficult
because of weather.
 Variability (i.e "noise" in the data) can
make it difficult to detect trends ("signal").
Detecting Trends
 Sometimes

p < 0.0001
the trends are easy to see.
Detecting Trends
 Sometimes

p = 0.0025
they are a bit harder to detect.
Detecting Trends
 It
is easier to detect a trend with a larger
signal.
 When the signal was small (0.005 °C/year),
the trend was difficult to detect even
though we know it was there, while larger
signals were easier to detect with simple
regression analysis.
Detecting Signals
 The
amount of noise also affects our
ability to see the trends.
5 Components of Earth’s
Climate System
 Atmosphere
- air
 Hydrosphere - water
 Cryosphere – frozen water
 Lithosphere – rocks & soil
 Biosphere – living organisms
Trends in the 5 components



If Earth's climate is changing then we should
find predictable, directional changes in all
five components of the climate system.
If the data show that each component is
changing in a way that is consistent with a
warming (or cooling) climate, we have more
faith in concluding that Earth's climate as a
whole is changing.
Conversely, if each component is changing
independently and in different directions, we
will conclude that the Earth is not, on
average, warming or cooling.
Measuring Temperature Over
Time - Atmosphere
 This
animation suggests that Earth has
warmed and that this warming is not
regional but has occurred across much of
the globe.
Measuring Temperature Over
Time - Atmosphere
 The
IPCC climatologists found that Earth's
mean annual temperature increased
about 0.74 °C over the past 100 years
(1906-2005).
Measuring Temperature Over
Time - Biosphere
 Because
the growth and population
dynamics of many organisms—including
trees and other plants, corals, plankton,
and insects—vary predictably in response
to changing climates, in a sense, these
organisms record ancient climates.
Measuring Temperature Over
Time - Biosphere



As trees grow, new wood is
laid down just under the bark
in annual layers that can be
seen as tree growth rings.
In good years, the tree grows
faster, giving a wider ring for
that year.
By measuring the variation in
tree ring width, it's possible to
reconstruct how temperature
and precipitation have varied
over the life of a tree.
Measuring Temperature Over
Time - Cryosphere
 If
the Earth is warming, we would expect
that the Earth's snow and ice should melt
faster each year.
Measuring Temperature Over
Time - Cryosphere
 The
dramatic reduction in the Arctic's
annual sea ice minimum has been
accompanied by a decline in perennial
sea ice, the thick, year-round ice cover.
 Many mountain glaciers retreated over
the past 50 years or so.
Measuring Temperature Over
Time - Cryosphere
1941
2004
Measuring Temperature Over
Time - Hydrosphere
 Climatologists
have hypothesized that the
amount, intensity, frequency and type
of precipitation will change.
 At much larger scales, warmer
temperatures may be affecting the
behavior of critical climate phenomena
like El Niño and La Niña, which can affect
precipitation patterns across much of the
globe.
Measuring Temperature Over
Time - Hydrosphere
 Warmer
temperatures
can simultaneously
produce both more
intense storms in places
where the air is saturated
and more extreme
droughts where it is not,
even if the total amount
of precipitation is not
changing.
Sea Level Rise
 Changes
in
precipitation,
evaporation, storage
and runoff—in
particular from
melting ice sheets
and glaciers—can
change the amount
of water in the
ocean.
Earth’s Climate
and Climate
Models
Greenhouse Gases
 Atmosphere
is important in determining a
planet’s temperature.
 Earth is now warm enough to have large,
unfrozen oceans because its atmosphere
acts like a blanket, trapping heat and
thereby raising surface temperatures.
 This is the greenhouse effect, which makes
life possible here on Earth.
Greenhouse Gases
 The
key to the greenhouse effect lies in
the difference in wavelength between
incoming and outgoing radiation.
Greenhouse Gases



Nitrogen and oxygen (N2 and O2), gases
constituting the bulk of Earth's atmosphere,
are transparent to both long and short
wavelengths.
But greenhouse gases like CO2, CH4, and H2O,
absorb the longwave radiation that is
radiated from Earth's surface.
The energy these gases absorb is eventually
re-radiated in all directions, including back
toward Earth, where it raises the average
surface temperature from -19 °C to 15 °C.
Modeling Climate Change
 Models
reflect our current understanding
of climate and allow scientists to test
hypotheses about factors affecting it.
Modeling Climate Change

A planet's equilibrium surface temperature can be
predicted from a simple climate model that
accounts for:




Solar output, the energy warming a planet, which
varies over time.
Distance from the Sun, which determines the
amount of solar radiation intercepted by a planet.
Albedo, describing what proportion of incident
solar radiation is reflected.
Greenhouse gases produce the "greenhouse
effect," further warming the surface of planets with
atmospheres containing them.
Modeling Climate Change
 More
complex models describe nonequilibrium systems and incorporate
climate feedbacks like the ice-albedo
feedback loop.
 Global circulation models (GCMs) are
even more complex, incorporating a
layered atmosphere, 3-dimensional
spinning sphere structure, complex
topography, and layered oceans.
Modeling Climate Change
 Current
GCMs can accurately reproduce
recent large-scale patterns in average
temperature. They are increasingly able
to simulate smaller-scale phenomena like
El Niño.
Humans and
Climate
Change
Attribution of Recent Climate
Change
 Natural
climate forcings typically
include aerosols from volcanic eruptions,
plus changes in solar irradiation resulting
from variation in the Earth's orbit or in solar
output.
 Anthropogenic climate forcings result
from human actions and include
greenhouse gas and man-made aerosol
emissions, changes in land use, and
exhaust from jet airplanes.
Attribution of Recent Climate
Change
 Although
solar
output varies,
changes are too
small to account
for observed
increases in
average surface
temperature on
Earth.
Attribution of Recent Climate
Change

Since the 1850s,
concentrations of
CO2 and other
greenhouse gases have
increased markedly,
primary from fossil fuel
combustion. Evidence
comes from
measurements made
directly (e.g., Keeling's)
and indirectly (e.g., from
air bubbles trapped in
ice).
Attribution of Recent Climate
Change
 Models
suggest that observed warming is
probably a direct result of increases in
greenhouse gases.
Attribution of Recent Climate
Change
 Climate
models are used to forecast how
Earth's climate will respond to different
IPCC emission scenarios.
 These models predict an increase of
between 1.8 °C and 4.0 °C by 2100.
Future Climate Change

The IPCC estimated
the likely climate
response to Increasing
Affluence (A1B),
Regionality (A2), and
Green Growth (B1)
scenarios with 20
GCMs. They also
added a baseline
scenario that
assumed,
optimistically, that CO2
concentrations were
held constant after
2000.
How Will Climate Change
Affect Us?
 Likely,
high latitudes will warm more than
mid-latitudes, land surfaces will warm
more than oceans, and precipitation
patterns will change.
How Will Climate Change
Affect Us?
 Heat
waves, droughts
and severe storms are
likely to increase.
 Ecosystems will be
affected by ocean
acidification and
altered patterns of
primary production and
respiration.
How Will Climate Change
Affect Us?
 Further
changes may occur abruptly and
unexpectedly. Human populations are
likely to be strongly and negatively
affected.
Biological
Consequences
of Climate
Change
How Can Species Avoid
Extinction Due to Climate
Change?
 Species
may move.
 Species may acclimate.
 Species may evolve.
Effect on Timing


Climate change may
affect phenology, the
timing of life-history
events.
Springtime events like
flowering are expected
to occur earlier while
autumnal events like

migration or hibernation
are expected to occur
later.
Increased
temperature leads to
faster development
times in butterflies.
Mismatches in Timing
 Altered
phenologies
may produce
mismatches between
predators and prey or
flowers and pollinators,
reducing the
population growth
rate of one or both
species.
Fitness Varies with
Temperature
 An
individual's
fitness can vary with
temperature, often
summarized using
a temperature
performance curve.
Range Shifts
 Species
distributions are
expected to shift
poleward or uphill
in response to
climate change.
Changes to Community
Dynamics
 Because
species
distributions change
independently,
climate change may
alter both
community
composition and
community
dynamics.
 Pine
bark beetles
survive better in
milder winters –
spread disease in
coniferous forests.
Acclimation to New
Conditions
 Another
possible response is
to acclimate to the new climate.
 An individual may be able to adjust so
that its temperature performance curve
changes and is better suited to the new
temperature.
Adaptation to New Conditions
 Species
may
adapt to climate
change through
evolution by
natural selection,
which can alter
the species'
temperature
performance
curve.
Time elapsed: 100 years
Adaptation to New Conditions
A
species' ability to evolve adaptations to
climate change depends on the rate of
climate change and the species' genetic
variation and generation time.
Adaptation to New Conditions


Caribou of Greenland
mature slowly, can live 10
years or longer, and do not
begin to reproduce until they
are 3-4 years old.
This difference in generation
time means that, for any
given rate of warming,
caribou and other long-lived
species experience more
warming per generation
than do insects and other
short-lived organisms.