Transcript Ecosystem Impacts of Climate Change

Chapter 13: Climate Change and
the causes of change
OUTLINES
1. Climate and Climate System
1.1 Weather versus Climate
1.2 Climatic Controls
1.3 Climate System Components
2. Forcing, Response, Coupling and Feedback
3. Climate Change Through Time
4. Causes of Change
5. Global Warming and Greenhouse Effects
6. Climate Modeling
4.1 Coupled Ocean-Atmosphere-Land-Ice Model
4.2 Role of Forcing Factors
Natural [volcanos + sun] Variability versus Human [GHG + sulfate] Effects
7. Summary
1.1 Weather versus Climate
Weather
The condition of atmosphere at a given time and
place
 Short-term (and large) fluctuations that arise from internal instabilities
of the atmosphere
 Occurs as a wide variety of phenomena that we often experience
 Effects are immediately felt
 Social and economic impacts are great but are usually localized
 Many such phenomena occur as part of larger-scale organized systems
 Governed by non-linear chaotic dynamics; not predictable
deterministically beyond a week or two.
1.1 Weather versus Climate
Climate
 Defined as the average state of the atmosphere over a finite time
period and over a geographic region (space).
 Can be thought of as the “prevailing” weather, which includes the
mean but also the range of variations
 Intimate link between weather and climate provides a basis for
understanding how weather events might change under a
changing climate
 Climate is what you expect and weather is what you get.
 Climate tells what clothes to buy, but weather tells you what clothes
to wear.
Weather and Climate
1.2 Climatic Controls
The world's many
climates are
controlled by the
same factors as
affecting weather,
a) intensity of sunshine
and its variation
with latitude,
b) distribution of land
and water,
c) ocean temperature
and currents,
d) mountain barriers,
e) land cover,
f) atmospheric
composition.
This map shows sea-level temperatures (°F).
1.3 The Climate System Components
1.3 Climate System Components
Atmosphere
• Fastest changing and most responsive component
• Previously considered the only “changing” component
Ocean
• The other fluid component covering ~70% of the surface
• Plays a central role through its motions and heat capacity
• Interacts with the atmosphere on days to thousands of years
Cryosphere
• Includes land snow, sea ice, ice sheets, and mountain glaciers
• Largest reservoir of fresh water
• High reflectivity and low thermal conductivity
Land and its biomass
• Slowly changing extent and position of continents
• Faster changing characteristics of lakes, streams, soil moisture
and vegetation
Human interaction
• agriculture, urbanization, industry, pollution, etc.
2. Climate: Forcing and Response
Input
Machine
Output
Forcing and Response: A Bunsen Burner Experiment
Three major kinds of
climate forcing in
nature:
Tectonic processes
Earth-orbital changes
Changes in Sun’s strength
Anthropogenic forcing
Urbanization
Deforestation
Burning fossil fuels
Agriculture
Response time depends
on “materials” or
“components”.
Response Times of Various Climate System Components
Climate System
Coupling of components
Positive coupling between A & B (A  B):
A incr. => B incr.; A decr. => B decr.
Negative coupling: A —o B
A incr. => B. decr.; A decr. => B incr.
Feedbacks
A feedback is a mechanism whereby an initial change in
a process will tend to either reinforce the change
(positive feedback)
or weaken the change (negative feedback).
Correct setup
A’s body T
(–)
A’s blanket T
B’s body T
(–)
B’s blanket T
Incorrect setup
A’s body T
A’s blanket T
(+)
B’s blanket T
B’s body T
Equilibrium states
• Correct elec.
blanket setup with
negative feedback
loop => equilibrium
state.
• Stable equilibrium:
Minor perturbation
from this state will
return to the same
equilibrium.
Stable eq.
state
Stable eq.
Stable eq.
state
state
Unstable equilibrium states
• At an unstable
equilibrium state,
the smallest
disturbance moves
the system away
towards a stable
equil. state (if one
exists).
• System rarely stays
at an unstable equil.
state for long.
Example of a positive feedback
Think about the polar regions:
Example of a positive feedback
More energy
retained in system
Albedo decreases,
Less solar energy
reflected
Warm temperatures
Ice and snow melt
If this were the only mechanism acting, we’d get a runaway temperature increase
Snow and ice
albedo
feedbacks in
the polar regions
are to blame for
the large
changes already
observed.
1997
Ninnis Glacier Tongue
Antarctica
2000
Example of a negative feedback
More energy
retained in system
Albedo decreases
Less solar energy
reflected
Warm temperatures
More evaporation
More clouds
Example of a negative feedback
More energy
retained in system
Albedo increases
More solar energy
reflected
Warm temperatures
More evaporation
More clouds
• 3. Climate Change Through Time
Holland in 1565 (Little Ice Age)
Climate Change Since the Last Glacial Maximum
Data important for estimating past climate include:
lake bottom sediment, ice cores, fossil evidence, written documents,
coral isotopes, calcium carbonate layers in caves, borehole
temperature, and dendrochronology or tree ring data.
These data have helped identify several important climate change
events in the past 18,000 years.
The Earth’s Climate History
1.
Over the last century, the earth’s surface temperature has increased by about 0.75°C (about
1.35°F).
2.
Little Ice Age = Cooling during 1,400 A.D. – 1,900 A.D. (N.H. temperature was lower by 0.5°C,
alpine glaciers increased; few sunspots, low solar output)
3.
Medieval Climate Optimum (Warm Period) = Warming during 1,000 A.D. – 1,300 A.D. in Europe
and the high-latitudes of North Atlantic (N.H. warm and dry, Nordic people or Vikings colonized
Iceland & Greenland)
4.
Holocene Maximum = 5,000-6,000 ya (years ago) (1°C warmer than now, warmest of the current
interglacial period)
5.
Younger-Dryas Event = 12,000 ya (sudden drop in temperature and portions of N.H. reverted
back to glacial conditions)
6.
Last Glacial Maximum = 21,000 ya (maximum North American continental glaciers, lower sea
level exposed Bering land bridge allowing human migration from Asia to North America)
7.
We are presently living in a long-term Icehouse climate period, which is comprised of shorterterm glacial (e.g., 21,000 ya) and interglacial (e.g., today) periods. There were four periods of
Icehouse prior to the current one.
8.
For most of the earth’s history,
the climate was much warmer than today.
Proxy Records of Climate
• Recent times:
instrumental
• More recent times:
historical, tree rings, ice
cores
• Proxies for more ancient
climates are found in
sediments or inferred from
fossils and land forms.
• Can generally only
resolve changes that occur
over 100 years or greater
Yearly Temperature Change for the Last 1000 Years
Small
climate
changes
(0.5°C)
Data from tree rings, corals, ice cores, and historical records are
shown in blue. Data from thermometers are shown in red.
About 1000 y.a., the N.H. was cooler than now (e.g., 1961-1990
average). Certain regions were warmer than others. Warm and dry
summers in England (1000-1300): vineyards flourished and wine was
produced. Vikings colonized Iceland and Greenland.
Global temperature over the last 1000 years.
Global temperature over
the past 1000 years.
The past 140 years
Yearly Temperature Change for the Last 140 Years
Data over the globe (land and sea).
Warming periods: 1900-1945 (by 0.5°C), the mid-1970s to present.
The warmest decade: the 1990s. The warmest year: 1998. 2001
second warmest year on record. Over last 25 years warming ~ 0.5 C
Over past century warming ~ 0.75 C
Cooling periods: 1945-1975.
Surface air temperature trends over the past century
The warming has been greatest at night over land in the mid-to-high latitudes
of the northern hemisphere. The warming during the northern winter and
spring has been stronger than at other seasons. In some areas, primarily over
continents, the warming has been several times greater than the global
average. In a few areas, temperatures have actually cooled, e.g., over the
southern Mississippi Valley in North America.
www.gcrio.org/ipcc/qa/02.html
An increasing body of observations gives a
collective picture of a warming world and
other changes in the climate system
• Global mean surface temperature increase
(NH, SH, land, ocean)
• Melting of glaciers, sea ice retreat and thinning
• Rise of sea levels
• Decrease in snow cover
• Decrease in duration of lake and river ice
• Increased water vapor, precipitation and
intensity of precipitation over the NH
• Less extreme low temperatures, more
extreme high temperatures
Recent Range Shifts due to Warming
Species Affected
Location
Observed Changes
Alaska
Expansion into shrub-free areas
39 butterfly spp.
NA, Europe
Northward shift up to 200 km in 27 yrs.
Lowland birds
Costa Rica
Advancing to higher elevations
12 bird species
Britain
19 km northward average range extension
Red & Arctic Fox
Canada
Red fox replacing Arctic fox
Treeline
Europe, NZ
Advancing to higher altitude
Plants & invertebrates
Antarctica
Distribution changes
California, N.
Atlantic
Increasing abundance of warm water spp.
Arctic shrubs
Zooplankton, fish &
invertebrates
Walther et al., Ecological responses to recent climate change, Nature 416:389 (2002)
Modes of Climate Variation
Periodic variation
Abrupt shift in climate
state
Warming or cooling to new
climate state
Changes in amplitude or
frequency of climate
oscillations
4. Mechanisms of Climate Variability and
Change: External versus Internal Forcing
External
 Changes in the Sun and its output, the Earth’s rotation rate,
Sun-Earth geometry, and the slowly changing orbit
 Changes in the physical make up of the Earth system, including
the distribution of land and ocean, geographic features of the land,
ocean bottom topography, and ocean basin configurations
 Changes in the basic composition of the atmosphere and ocean
from natural (e.g., volcanoes) or human activities
Internal
 High frequency forcing of the slow components by the more rapidly
varying atmosphere
 Slow variations internal to the components
 Coupled variations: Interactions between the components
Factors that influence the Earth's climate
The Milankovitch Hypothesis
Milutin Milankovitch first proposed the following
idea in the 1930s.
Changes in climatic cycles of glacial-interglacial
periods were initiated by variations in the Earth’s
orbital parameters (Earth-Sun geometry factors)
Eccentricity: Earth’s orbit around the sun
Orbit = Ellipse
Orbit = Circle
(Eccentricity = 0)
(Eccentricity = 0.05 shown
0.0167 today
0.0605 maximum)
Varies from near circle to ellipse with a period of 100,000 years
Distance to Sun changes  insolation changes
Obliquity: Tilt of the Earth’s rotational axis
• Cycle of ~ 41,000 years
• Varies from 22.2 to 24.5°
(The current axial tilt is
23.5°)
• Greater tilt = more intense
seasons
If Earth’s orbit were circular,
No tilt = no seasons
90° tilt = largest seasonal differences at the
poles (6 mon. darkness, 6 mon. overhead sun)
Precession: positions of solstices and equinoxes in
the eccentric orbit slowly change
Wobbling
of the axis
Turning of
the ellipse
Period of about 23,000 years
Earth’s Orbit Changes Through Time
Warming from the last glacial interval to the present was interrupted by
several large and abrupt plunges back into cold periods. Evidence points
the oceanic thermohaline conveyor belt as the mechanism for these rapid
climate changes
Climate Change and Variations in Solar Output
More sunspots, stronger solar emissions from
the Sun.
Sunspot History from Telescopes
The telescope records
show:
11-year sunspot cycle.
5. Global Warming and Greenhouse Effects
Natural or Anthropogenic?
Atmospheric CO2 Concentrations Are Increasing as a
Result of of Human Emissions
Atmospheric CO2 concentrations--past 1000 years.
Global average temperatures are increasing with
increases in CO2.
Global
Average
Temperature
CO2 (ppm)
1000
CH4 (ppb)
N2O (ppb)
2000
6. Climate Modeling
• Climate models
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Use quantitative methods to simulate
the interactions of the atmosphere,
oceans, land surface, and ice.
Climate models are mainly used for
predictions and simulations.
• Dynamical/physical models
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Using physical principles to describe the
relationship among different components of
climate system in the form of mathematical
equations. These mathematical equations are called
dynamical models. By solving the
equations, we can simulate and predict the
components of the earth climate system.
Climate Model – what does it do?
• Starts with known physical laws – conservation of momentum, energy, &
mass.
• Views atmosphere, oceans, land as a continuum (i.e. all spatial scales
present satisfying same laws).
• Find and uses numerical approximations to the continuum physical laws.
• Integrate in time to develop climate statistics same as observedevaluate success by extent of agreement.
• On global scale, this agenda very successful.
Climate
Model
Scaling/parameterization
Need to describe details
within the grid boxes
• Global climate model
• These models are the most complex. The models
divide atmosphere or ocean into a horizontal grid
with a typical resolution of 2-4 degree latitude by 2-4
degree longitude and 10-20 layers in the vertical.
They directly simulate winds, ocean currents and
many other processes. Feedback processes are
simulated in the coupled atmosphere and ocean
GCMs - water vapor, clouds, seasonal snow and ice.
Scheme of a coupled atmosphere ocean model
and supplementary models.
• Ideal gas
• Newton's law
• Navier Stokes Equations
• Coriolis force
• First law of thermodynamics
Model Grid:
The 21st century predicted by the HadCM3 climate model (one of those used by the IPCC) if
a business-as-usual scenario is assumed for economic growth and greenhouse gas emissions.
The average warming predicted by this model is 3.0°C.
• Time evolution of
globally averaged
temperature change
relative to the
period 1961-1990.
The top graph
shows the results of
greenhouse gas
forcing, the bottom
graph shows the
results of
greenhouse gas
forcing plus aerosol
forcing.
• Time evolution
of globally
averaged
precipitation
change relative
to the period
1961-1990. The
top graph
shows the
results of
greenhouse
gas forcing, the
bottom graph
shows the
results of
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The Intergovernmental Panel on Climate Change (IPCC) was established
in 1988 by two United Nations organizations, the World Meteorological
Organization (WMO) and the United Nations Environment Programme
(UNEP) to assess the "risk of human-induced climate change".
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IPCC: first assessment report in 1990
second assessment report in 1995
third assessment report in 2001
fourth assessment report in 2007
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Intergovernmental Panel on Climate Change (http://www.ipcc.ch)
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IPCC reports should be the most authoritative
reports on climate change, and are widely cited in
almost any debate related to climate change. The
reports have been influential in forming national and
international responses to climate change.
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A small but vocal minority (less than 1.5%) of the
scientists involved with the report have accused the
IPCC of bias.
• Evidence of some uncertainties:
• (1) The individual models often exhibit
worse agreement with observations.
• (2) All models have shortcomings in their
simulations of the present day climate of the
stratosphere, which might limit the accuracy
of predictions of future climate change.
• (3) There are problems in simulating natural
seasonal variability.
• (4) Coupled climate models do not simulate
with reasonable accuracy clouds and some
Confidence in the ability of models to project
future climate has increased
Simulated Annual Global Mean Surface Temperatures
Global warming

Heating 

Temperature  & Evaporation 

water holding capacity 

atmospheric moisture 


greenhouse effect  & rain intensity 

Floods
&
Droughts
Growing Cooperation Between
Modelers and Field-Scientists
“Your tools are terribly
antiquated and imprecise”
Climate Modeler
“You produce junk and
waste a lot of money”
Field-Geologist
Solution: interdisciplinary collaborations!
Requirement: understanding each others ‘language’
7. Summary
1. Climate change occurs through all time scales.
2. Climate conditions at a given period are a result of complex
interactions among components of the climate system
driven by specific forcing factors.
3. Climate modeling is a powerful approach to studying the
cause-effect relationships.
4. Observed data (proxy and instrumental) are critical for
calibrating climate models.
5. Understanding the causes and effects of global warming is
one of the grandest challenges facing today’s scientists and
the public.
Thank You!