Transcript Earth`s Climate

Earth’s Climate
and
Climate Change
Weather and Climate
What is weather?
Weather is the state of atmospheric conditions (i.e., hot/cold, wet/dry, calm/stormy,
sunny/cloudy) that exist over relatively short periods of time (hours to a couple of
days).
Weather includes the passing of a thunderstorm, hurricane, or blizzard, and the
persistence of a heat wave, or a cold snap.
What is Climate?
Climate is the weather we expect over the period of a month, a season, a decade,
or a century.
More technically, climate is defined as the weather conditions resulting from the
mean state of the atmosphere-ocean-land system, often described in terms of
"climate normals" or average weather conditions.
Climate Change is a departure from the expected average weather or climate
normals.
Factors That Determine Climate
The Earth is cold at the poles and warm at the equator
Sun light is incident on the Earth at steeper angles in the polar regions.
Sunlight falling at an angle is spread out over a greater area and therefore
causes less heating.
Factors That Determine Climate
Tilt of the Earth’s axis
•23.5 towards the sun in summer
•23.5 away from the sun in winter
Polar regions become extremely cold in winter.
Even though the poles get constant sun in
summer, the solar angle is so low that the
heating is small. Also, polar ice reflects sunlight,
further reducing the effect of constant sun.
Solar energy absorption
Solar energy reflection
Factors That Determine Climate
Latitude:
Warm and moist at the equator, cold and dry at the poles
Altitude:
Higher altitudes are colder and dryer
Proximity to oceans:
Oceans moderate temperature and increase humidity
Local terrain:
Mountains can cause clouds an precipitation on the windward side,
and dry conditions on the leeward side
The climate where you live
Climate Data
Direct Measurements:
Observations of air & water temperature, precipitation amount,
etc… have been made routinely with accurate instruments for
about 150 years
Historical Records:
Clues left in written documents from the past
Paleoclimate:
Properties of the Earth and Atmosphere are determined from
clues hidden in the Earth, a kind of forensic science.
Sources of paleoclimate information:
•Ice Cores
•Tree Rings
•Ocean Sediment
Ice Cores
•Ice cores are samples of ice taken from glaciers .
•Air bubbles, dust, and oxygen isotopes get
trapped in glacial ice, and can be used to analyze
past climate.
•Glaciers become thicker over time, so the deeper
you drill the older the ice is.
Glaciers obtain one layer each year, so
counting layers is like counting years.
Ice core data can extend back hundreds of
thousands of years
•Ice cores can reveal temperature, precipitation,
and gas composition of the lower atmosphere
•They also can indicate volcanic eruptions, solar
variability, sea-surface productivity and a variety of
other climate indicators.
Ice Cores
Deuterium (a hydrogen isotope)
can be used to reconstruct past
temperature changes.
In Antarctica, a cooling of 1°C
results in a 9 ppm decrease in
deuterium.
The ratio of oxygen isotopes,
O18/O16, in ice is an indication of
temperature change.
Smaller values of O18/O16
indicate warmer temperatures.
Changes over 200 millennia from
Greenland ice cores
Climate related parameters
determined from ice cores
Ice Core
Property
Climate Parameter
CO2, CH4
Greenhouse gasses
SO2, ash
Volcanic eruptions
Be10, Cl36
Solar activity
O18/O16 ,
deuterium
Temperature
thickness
Precipitation
Tree Rings
In temperate regions where there is a distinct growing season, trees
generally produce one ring a year
Since tree growth is influenced by climatic conditions, patterns in treering widths, density, and isotopic composition reflect variations in
climate.
Trees can grow to be hundreds to thousands of years old and can
contain annually-resolved records of climate for centuries to millennia.
If a tree is fossilized, the age of the tree (how long ago it died) can be
determined by examining isotopes.
Isotope ratios are also indicative of temperature change.
Ocean Sediments
Billions of tons of sediment accumulate in the ocean and lake
basins each year.
Scientist drill cores of sediment from ocean and lake floors.
Ocean and lake sediments include tiny fossils and chemicals that
are used to interpret past climates.
The Greenhouse Effect
The Earth receives ultraviolet (UV) radiation from the sun,
absorbs it, and then radiates the energy out as infrared radiation
If the Earth behaved as a simple blackbody then the Earth’s
average temperature would be –18 C
However, the Earth’s average temperature is
15 C.
The Earth is warmer because our atmosphere
traps some of the outgoing IR radiation. This
is a natural process known as the greenhouse
effect.
The greenhouse effect is a good thing, without
it the Earth would become too cold for life to
exist.
However, man’s activities appear to be
altering the natural balance.
The Greenhouse Effect
Greenhouse Gasses
Greenhouse gases are atmospheric gases that trap infrared
radiation emitted from the earth.
Most of the significant greenhouse gases are long-lived and well-mixed:
•Long-lived means they are chemically stable and therefore last years in
the atmosphere
•Well-mixed means they are evenly distributed in the atmosphere.
•This family includes carbon dioxide, methane, oxides of nitrogen, and
halocarbons.
Water vapor is a greenhouse gas that is neither well-mixed nor long-lived.
Because of this, its overall effect on global warming is the least understood.
Greenhouse Gasses
Factors that determine the importance of a greenhouse gas:
•Atmospheric abundance
•The wavelengths of radiation absorbed
•The efficiency of radiation absorption
Greenhouse Gas Concentrations
Greenhouse Concentration Concentration
gas
1750
1995
Percent
Change
Carbon
dioxide, CO2
280 ppmv
360 ppmv
29%
Methane,
CH4
0.7 ppmv
1.7 ppmv
143%
Nitrous oxide,
N2O
280 ppbv
310 ppbv
11%
Carbon Dioxide (CO2)
CO2 accounts for 55% of the global warming effect.
Natural sources of CO2:
•Respiration: all living organisms respire and give off carbon dioxide.
•Decomposition of organic material
Anthropogenic sources of CO2:
•Fossil fuel burning (65%)
•deforestation and burning of rain forest
•land-use conversion
•cement production
Anthropogenic sources account for most of the CO2 produced annually.
Carbon Dioxide (CO2)
CO2 in the atmosphere is increasing dramatically
Methane (CH4)
CH4 accounts for 20% of the global warming effect.
Natural sources of CH4:
produced as a result of microbial activity in the absence of oxygen.
•Natural wetlands or bogs
•Termites
Anthropogenic sources of CH4:
•Rice paddies
•Cattle
•Drilling for oil
•Landfills
•Biomass burning
•Coal mining.
Anthropogenic sources account for 70% of the methane produced annually.
methane oxidizes with OH to become water: CH4 + OH > CH3 + H2O
Methane (CH4)
CH4 concentration in the atmosphere are increasing dramatically
Global Temperature Change
From Direct Measurements
Temperature change is often reported as the “temperature anomaly,” which
is the temperature compared to the average over some time period.
Below, global average temperatures are compared to the average
temperature during 1951 – 1980.
Global average
temperatures, relative to
the 1951-1980 average
(about 14°C)
Global Temperature Change
From Direct Measurements
•1998 saw the 20th straight year of above-normal surface temperatures.
•1998 was the hottest year since the mid-1800s, global temperatures
were 1.04 degrees F above average.
•The 10 warmest years in the 150-year history of recorded temperatures
have all occurred since 1983.
•In Alaska and other polar regions, the permafrost is melting and whole
forests are dying due to an increase of insects associated with warming
temperatures.
Global Temperature Change
From Proxy Measurements
Global temperatures determined from ice cores and other paleoclimate
records indicate that the Earth’s temperature was fairly constant until
recently
Global Climate Models (GCM)
GCMs are computer models that simulate the Earth’s climate:
They calculate a variety of things including:
• Air temperature
• Sea level
• Sea temperature
• Glacier size and thickness
GCMs consider the Earth’s surface, oceans, and atmosphere:
How they behave and how they interact with each other
Why use GCMs?
The Earth-Ocean-Atmosphere system is extremely complex
• Understand current climate
• Predict future climate
How well do GCMs perform?
One test is to see if GCMs
can simulate what has
already happened
Global Temperature Change Past - Future
GCMs predict
drastic warming if
nothing changes
Indications of Global Warming
Melting of polar ice
Glaciers in southeastern Greenland are thinning by more than
3 feet a year
Rise in sea level
Water expands as it warms
Melting glaciers
Enhanced plant growth
Plants need CO2 for photosynthesis
Warmer temperatures
Longer growing seasons
The End
Extra slides follow
Ice Cores
Ice cores can reveal temperature, precipitation, and gas composition of
the lower atmosphere
They also can indicate volcanic eruptions, solar variability, sea-surface
productivity and a variety of other climate indicators.
More on the relationship between glacier depth and time
Depth is related to time, glacial ice accumulates one layer per year.
Accumulation rates inferred in this way are supported by measurements of
beryllium 10 (Be10).
Be10 is an isotope produced by the interaction of cosmic rays and the
upper atmosphere.
The deposition rate of Be10 can be assumed constant.
Therefore, the amount of Be10 in ice is related directly to time.
Global Climate Models (GCM)
GCMs come in a variety of types:
Atmosphere general circulation models (AGCMs): consist of a three-dimensional
representation of the atmosphere coupled to the land surface and cryosphere
AGCMs coupled to a 'slab' ocean: This type of model predicts changes in seasurface temperatures and sea-ice by treating the ocean as though it were a layer
of water of constant depth (typically 50 metres)
Ocean general circulation models (OGCM): a three-dimensional representation
of the ocean and sea-ice
Carbon cycle models: describe several important climate feedbacks on carbon
dioxide concentration, for instance fertilization of plant growth by carbon dioxide
and uptake or out gassing of carbon dioxide by the oceans
Atmospheric chemistry models: calculate chemical reactions that determine the
production or destruction of important species such as ozone and methane
Coupled atmosphere-ocean general circulation models (AOGCMs): the most
complex models in use, consisting of an AGCM coupled to an OGCM. AOGCMs
can be used for the prediction of future climate.