Download Lectures 1 and 2. - Cryospheric Processes Laboratory

Climate (definition)
• Climate encompasses the statistics of
temperature, humidity, atmospheric pressure,
wind, rainfall, atmospheric particle count and
other meteorological elemental
measurements in a given region over long
periods.
• Climate can be contrasted to weather, which
is the present condition of these elements and
their variations over shorter periods.
• A region's climate is generated by the climate
system, which has five components:
• atmosphere,
• hydrosphere,
• cryosphere,
• land surface,
• and biosphere.
Climate Classification
• Perhaps the first attempt at climate classification
was made by the ancient Greeks, who divided
each hemisphere into three zones: torrid,
temperate, and frigid.
• Since the beginning of the twentieth century,
many climate-classification schemes have been
devised.
Köppen Classification of Climate
• For decades, a climate classification devised by Wladimir
Köppen (1846–1940) has been the best-known and most used
tool for presenting the world pattern of climates.
• The Köppen classification uses easily obtained data: mean
monthly and annual values of temperature and precipitation.
• Furthermore, the criteria are unambiguous, simple to apply, and
divide the world into climate regions in a realistic way.
• Köppen believed that the distribution of natural vegetation was
the best expression of an overall climate.
• Consequently, the boundaries he chose were largely based on
the limits of certain plant associations.
Köppen’s Classification Scheme
• Köppen recognized five principal climate groups, each
designated with a capital letter:
–
–
–
–
–
–
–
A (humid tropical),
B (dry),
C (humid middle-latitude, mild winters),
D (humid middle-latitude, severe winters), and
E (polar).
Four groups (A, C, D, E) are defined by temperature.
The fifth, the B group, has precipitation as its primary criterion.
Type A Climate
• Situated along the equator, the wet tropics (Af, Am) constant high
temperatures and year-round rainfall combine to produce the most
luxuriant vegetation in climatic realm—the tropical rain forest.
• Temperatures in these regions usually average 25°C (77°F) or more
each month and the daily temperature variations characteristically
greatly exceed seasonal differences.
• Precipitation in Af and Am climates is normally from 175 to 250
centimeters (68 to 98 inches) per year and is more variable than
temperature, both seasonally and from place to place.
• Thermally induced convection coupled with convergence along the
intertropical convergence zone (ITCZ) leads to widespread ascent
of the warm, humid, unstable air and ideal conditions for
precipitation.
Type B Climate
• Dry regions of the world cover about 30 percent of Earth's
land area.
• Other than their meager yearly rainfall, the most
characteristic feature of dry climates is that precipitation is
very unreliable.
• Climatologists define a “dry climate” as one in which the
yearly precipitation is less than the potential water loss by
evaporation.
• To define the boundary between dry and humid climates,
the Köppen classification uses formulas that involve three
variables:
– (1) average annual precipitation,
– (2) average annual temperature, and
– (3) seasonal distribution of precipitation.
Type C Climate
• Humid middle-latitude climates with mild
winters (C climates) occur where the average
temperature of the coldest month is less than
18°C (64°F) but above -3°C (27°F).
• Several C climate subgroups exist.
Type D Climate
• Humid continental climates with severe
winters (D climates) experience severe winters.
• The average temperature of the coldest month is
-3°C (27°F) or below and the average
temperature of the warmest month exceeds
10°C (50°F).
• The greatest annual temperature ranges on
Earth occur here.
Type E Climate
• Polar climates (ET, EF) are those in which the
mean temperature of the warmest month is
below 10°C (50°F).
• Annual temperature ranges are extreme, with
the lowest annual means on the planet.
• Although polar climates are classified as humid,
precipitation is generally meager, with many
nonmarine stations receiving less than 25
centimeters (10 inches) annually.
Polar Climates
• Two types of polar climates are recognized.
• Found almost exclusively in North America, the tundra
climate (ET), marked by the 10°C (50°F) summer
isotherm at its equatorward limit, is a treeless region of
grasses, sedges, mosses, and lichens with permanently
frozen subsoil, called permafrost.
• The ice cap climate (EF) does not have a single
monthly mean above 0°C. Consequently, the growth of
vegetation is prohibited, and the landscape is one of
permanent ice and snow.
Highland Climates
• Highland climates are characterized by a great
diversity of climatic conditions over a small area.
• In North America, highland climates characterize the
Rockies, Sierra Nevada, Cascades, and the
mountains and interior plateaus of Mexico.
• Although the best known climatic effects of an
increased altitude are lower temperatures, greater
precipitation due to orographic lifting is also common.
• Variety and changeability best describe highland
climates.
• Because atmospheric conditions fluctuate with
altitude and exposure to the Sun's rays, a nearly
limitless variety of local climates occur in
mountainous regions.
What changes climate?
• Changes in:
– Sun’s output
– Earth’s orbit
– Drifting continents
– Volcanic eruptions
– Greenhouse gases
Increasing greenhouse
gases trap more
heat
“Greenhouse
effect”
Visible Radiation
Infrared Radiation
The Earth’s annual and global mean energy balance. Of the incoming solar radiation, 49% is absorbed by the
surface. The heat is returned to the atmosphere as sensible heat, as evapotranspiration (latent heat) and as
thermal infrared radiation. Most of this radiation is absorbed by the atmosphere, which in turn emits radiation
both up and down. The radiation lost to space comes from cloud tops and atmospheric regions much colder than
the surface. This causes a greenhouse effect.
Global Climate Change
David D. Houghton
19
Greenhouse gases
Nitrous oxide
Carbon dioxide
Methane
Water
Sulfur hexafluoride
Global Climate System
Global Climate Change
Schematic view of the components of the global climate system (bold), their processes and
interactions (thin arrows)
andD.
some
aspects that may change (bold arrows).
David
Houghton
22
Shortwave
Radiation
Layer 3
Layer 2
Layer 1
Surface
Shortwave
Radiation
Layer 3
Layer 2
Layer 1
Surface
Shortwave
Radiation
Layer 3
Layer 2
Layer 1
Surface
Shortwave
Radiation
Layer 3
Layer 2
Layer 1
Surface
Shortwave
Radiation
Layer 3
Layer 2
Layer 1
Surface
Shortwave
Radiation
Lost to Space
Layer 3
Layer 2
Layer 1
Surface
Shortwave
Radiation
Lost to Space
Layer 3
Layer 2
Layer 1
Surface
Radiation Budget W/m 2
350
300
250
200
Incoming
150
Outgoing
100
50
0
90
60
30
0
Warming
Cooling
Radiative Forcing (Watts per square metre)
The Global Mean Radiative Forcing of the Climate System
For the year 2000, relative to 1750
Level of Scientific Understanding
Global Climate Change
David D. Houghton
31
Feedback processes. Positive: a portion of the output is fed back to
the input and acts to further simulated the process. Negative: the
prtion of the output is subtracted from the input and acts to dampen
the process.
Ice = high albedo
Water = low albedo
http://www.unep.org/geo/geo_ice/images/full/5_albedofeed
back.png
http://www.donperovich.com/images/feedback.jpg
The ice-albedo feedback loop
Effects: Snow and ice
Grinnell Glacier, Glacier National Park
1900 and 2008
Pleistocene glaciation
Milankovitch Cycles
• Mathematical theory of how orbital variations
affect climate.
• Earth’s exposure to the Sun:
– Insolation: 1) Exposure of an object to the Sun. 2)
Intensity of incoming solar radiation incident on a unit
horizontal surface at a specific level.
• High insolation leads to warmer summers and
melting of winter snowpack
• Low insolation leads to cooler summers and
survival of the winter snowpack.
Review of Kepler’s Laws
• First law: The orbit of each planet is an ellipse
with the Sun at one focus, i.e. they are eccentric
– Earth’s orbit is nearly circular. Currently, e = 0.017
• A line joining a planet to the Sun sweeps out
equal areas in equal times.
– When the Earth is close the the Sun it moves faster.
Northern winters are milder, summers are longer.
• The square of a planet’s orbital period is
proportional to the cube of its semimajor axis
– The period is the amount of time it takes for the
Earth to go around the Sun.
What does all this have to do with
Climate Change?
• Earth’s orbit is changing.
• Milankovitch parameters:
– Precession – the direction of Earth’s spin axis;
direction in which the poles are oriented
changes over time. Modifies relationship
between seasons and distance from the sun.
– Obliquity – Wobble of the Earth along its spin
axis, does not change total insolation but affects
the extent of seasonal contrasts.
– Eccentricity – Varies between 0 and 0.06; affects
total amount of sunlight hitting the Earth
http://www.globalwarmingart.com/wiki/Wikipedia:Milankovitch%20cycles
Milankovitch Cycles
• Obliquity:41,000
• Precession:
26,000 year
cycle

Eccentricity:
100,000 to
400,000 year
cycle
year cycle
e = 0 vs.
e = 0.5
Milankovitch Cycles, cont.
• Earth receives 0.2% more sunlight during
maximum eccentricity than at minimum
eccentricity. Too small to affect climate!
• Eccentricity influences climactic effect of
precession:
– Large eccentricity and summer at aphelion –
Northern Hemisphere glaciation is favored
– Half a precession cycle passes, the situation
is reversed.
Currently:
low eccentricity decreasing to a minimum in 30,000
years. Ice sheet growth will not occur. Interglacial will be longlived: 1.5 to 2.5 precession cycles.
Combining Orbital Forcing and
Climactic Response - d18O
Obliquity
Eccentricity
Longitude of
perihelion
Precession index
Insolation
Oxygen isotopes
from forams and
ice cores.
http://www.globalwarmingart.com/wiki/Wikipedia:Milankovitch%20cycles
Milankovitch Conclusions
• Periodicity of each orbital factor is manifested
within the oxygen isotope record.
• However, the change in insolation is very small
(10%) but effect is large.
• The eccentricity forcing is weak. Needs to be
amplified in order to create a major climactic
response.
How do we know?
Vostok Ice Cores
• Longest continuous ice core
recovered in Antarctica: 2 km
• Represents 200,000 of ice
accumulation.
• Has since been extended to 3.6
km representing 420,000 years.
• Air bubbles frozen in the ice.
Can use to estimate past CO2
content in the atmosphere.
•
http://www.sciencedaily.com/image
s/2008/11/081117103653-large.jpg
Vostok Ice Core – Findings
• Firm link between global climate change and
variations in the quantity of greenhouse gases in the
atmosphere.
• Correlation between local temperature from
hydrogen isotopes in the ice, and global changes in
temperature from oxygen isotopes and ice sheet size.
• Very fast changes in CO2 levels from glacial
concentrations of 190 ppm to nearly contemporary
240 ppm in 4,000 years
Vostok Ice Core – Findings
Present day observations
Definition of climate data record (CDR)
A Climate Data Record (CDR) is a specific definition of a
climate data series, developed by the Committee on Climate
Data Records from NOAA Operational Satellites of the
National Research Council at the request of NOAA in the
context of satellite records[1]. It is defined as "a time series
of measurements of sufficient length, consistency, and
continuity to determine climate variability and change." [2].
Climate models
• Climate models use quantitative methods to simulate the
interactions of the atmosphere,oceans, land surface and
ice.
• They are used for a variety of purposes from study of the
dynamics of the weather and climate system to projections
of future climate.
• All climate models balance, or very nearly balance,
incoming energy as short wave (including visible)
electromagnetic radiation to the earth with outgoing
energy as long wave (infrared) electromagnetic radiation
from the earth.
• Any imbalance results in a change in the average
temperature of the earth.
•
The simplest way is looking at the Earth’s climate
in terms of its global energy balance
• Over 70 % of the incoming energy is absorbed at
the surface surface albedo plays a key role ,
being the ratio between outgoing and incoming
radiation
• The output of energy is controlled by
1) Earth’s temperature
2) Transparency of the atmosphere to this outgoing
thermal radiation
The Climate Modelling Pyramid.
a) Performance of the most
powerful computers between
1953 and 2003 (MIPS =
Million of Instructions Per
Second until 1975 , MFLOPS
= Million of Floating point per
second after)
b) Interdependency of computer
power and model capability
McGuffie and Henderson-Sellers, 2005
Basic characteristics of
a 3D climate model,
showing how the
atmosphere and ocean
are split into columns.
Both ocean and
atmosphere are
modeled as a set of
interacting columns
distributed across the
Earth’s surface.
Resolutions of ocean
and atmosphere are
usually different.
•
There are two forms of EBM:
1) Zero-dimensional model
The Earth is considered as a single point with a mean
effective temperature
1) First-order model
The temperature is latitudinally resolved
Zero-dimensional EBM
One-dimensional EBM
(1-a (Ti))*S(Ti)/4= R↑(Ti)+F(Ti)
Intermediate complexity models
• Models which are like
comprehensive models in
aspiration but their developers
make specific decisions to
parametrize interactions so that
the models can simulate tens to
hundreds of thousands of years
•
•
The atmosphere is divided
into a number of layers not
necessarily of equal thickness.
Layering can be defined with
respect to height or pressure
but it is more common to
introduce the nondimensional vertical
coordinate s , not to be
confused with the StefanBotlzmann constant)
s = (p-pT)/(ps-pT)
With p being the pressure, pT the
(constant) top of the
atmosphere pressure and ps
the (variable) pressure at the
Earth’s surface.
• The top of the atmosphere
has s = 0 where the surface
has always s = 1.
Computer models
Aspen, CO Forecast:
Partly cloudy today
High : 28°F
Low: 13°F
Increasing clouds
over night. Colder
tomorrow.