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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, O 18/O 16, in ice is an indication of temperature change. Smaller values of O 18/O 16 indicate warmer temperatures. Changes over 200 millennia from Greenland ice cores Climate related parameters determined from ice cores Ice Core Property Climate Parameter CO 2, CH 4 Greenhouse gasses SO 2, ash Volcanic eruptions Be 10, Cl 36 Solar activity O 18/O 16 , 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 gas Concentration 1750 1995 Percent Change Carbon dioxide, CO 2 280 ppmv 360 ppmv 29% Methane, CH 4 0. 7 ppmv 143% Nitrous oxide, N 2 O 280 ppbv 310 ppbv 11%
Carbon Dioxide (CO 2) CO 2 accounts for 55% of the global warming effect. Natural sources of CO 2: • Respiration: all living organisms respire and give off carbon dioxide. • Decomposition of organic material Anthropogenic sources of CO 2: • Fossil fuel burning (65%) • deforestation and burning of rain forest • land-use conversion • cement production Anthropogenic sources account for most of the CO 2 produced annually.
Carbon Dioxide (CO 2) CO 2 in the atmosphere is increasing dramatically
Methane (CH 4) CH 4 accounts for 20% of the global warming effect. Natural sources of CH 4: produced as a result of microbial activity in the absence of oxygen. • Natural wetlands or bogs • Termites Anthropogenic sources of CH 4: • 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: CH 4 + OH > CH 3 + H 2 O
Methane (CH 4) CH 4 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 20 th straight year of above-normal surface temperatures. • 1998 was the hottest year since the mid-1800 s, 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 CO 2 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 (Be 10). Be 10 is an isotope produced by the interaction of cosmic rays and the upper atmosphere. The deposition rate of Be 10 can be assumed constant. Therefore, the amount of Be 10 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.