Earth’s Climate and

Climate Change

Weather and ClimateWhat 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

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.

The Earth is cold at the poles and warm at the equator

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

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

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.

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 tree-ring 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

Greenhouse Gas Concentrations

Greenhouse gas

Concentration 1750

Concentration 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%

Factors that determine the importance of a greenhouse gas:

•Atmospheric abundance

•The wavelengths of radiation absorbed

•The efficiency of radiation absorption

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)

Carbon Dioxide (CO2)

CO2 in the atmosphere is increasing dramatically

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)

Methane (CH4)

CH4 concentration in the atmosphere are increasing dramatically

Global Temperature ChangeFrom Direct Measurements

Global average temperatures, relative to the 1951-1980 average (about 14°C)

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 Temperature ChangeFrom 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 ChangeFrom 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 WarmingMelting 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 EndExtra 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 sea-surface 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.