CLIMATE
Learning Objectives:
Weather is the temperature, humidity, pressure and precipitation for a regional area over a period of a few days. It is variable and dynamic.
Climate is the summary of weather conditions for an area over a period of several years. It is an average of temperature, humidity, pressure and precipitation for an area.
Global Climate Change is a concern of environmentalists and politicians alike. To fully understand future climate change climate patterns of the past must be studied.
I) Patterns of Climate Change:
HOW DO YOU TAKE THE EARTH'S TEMPERATURE AND HOW DO YOU KNOW IF IT IS GETTING HOTTER?
Climate of the past is studied through a variety of methods.****
**** refer to class discussion for graphs of climate data (sorry, copyright problem)
Historical Temperature Records:
Historical temperature records over the last century show an increase in temperature, there are problems with this data however.
-Methods of measurement of temperature did not become uniform until after 1945. This could lead to wide errors in the temperature recorded from station to station.
-Most weather stations that report regional temperature data are located in urban areas. The temperature that is reported for Norfolk comes from the airport. Urban Heat Island Effect: urban areas are warmer than surrounding areas due to combustion engines, concrete pavement and other numerous heat sources. With increased urban sprawl this century is the historical data reflecting a warming climate or urban heat island effect.
-Temperature readings come from weather stations....large areas of the globe are never measured. The temperature over oceans, in large wilderness areas and over desolate sections of the global are never recorded or reported from isolated stations located in population centers. (Urban Heat Island)
SOLUTION: Nasa's Mission to Planet Earth has launched a series of satellites that measure climatic data including temperature. These readings are taken in a grid fashion over the entire globe. Urban areas are measured as well as areas outside of the urban areas. Thousands of readings taken daily give a much more accurate picture of global temperature. Not enough data has been collected to determine if climate is warming or cooling or stable but it is a first step in unraveling the climate puzzle.
Historical Documents:
Fossil Records:
Fossil records show that the climate on Earth has been warmer in the past and colder in the past. By studying the distribution of species geologists can estimate the range of climate (colder than today, much colder, slightly colder or warmer than today, much warmer, slightly warmer.) This method is non quantitative but does give an estimate of climate trends in the past. Also oxygen isotope ratios can be measured from carbonate shells found in sea floor sediment cores.
Lithology:
Through studying the sediment deposits and rock records in an area geologists can make a gross estimate of climate through time. Again this is non quantitative and gives a VERY gross estimate. Example: Evidence of glacial deposits suggest a climate colder than today's.
Ice Core Data:
Glacial ice in Antarctica, Greenland and Siberia provide an accurate picture of climate over the last 250,000 years. Air bubbles trapped within the ice contain a record of "paleoair" that can be examined. Information determined includes: carbon dioxide concentration in the atmosphere, oxygen isotope ratios and particulate concentrations.
Carbon Dioxide: ice core data shows that carbon dioxide levels have varied considerably over the past 250,000 years.
Oxygen isotope ratios: two common oxygen isotopes are O-16 and O-18. The ratio of O-16 to O-18 varies with climate. (This is due to evaporation of lighter isotope with water and deposition as ice) In air samples the more O-18 present the cooler the climate. This can be quantified by comparing today's O-16/O-18 ratio. Data from ice cores show that temperature over the last 250,000 years has been variable. It has been warmer than today and it has been cooler.
Study of climate in the past shows that the Earth has been warmed during some periods and cooler during some periods. Climate is variable over time.
II) Causes of Climate Change:
Greenhouse Effect:
The Greenhouse Effect is the theory that greenhouse gases trap heat in the atmosphere and increasing greenhouse gases will increase global temperature. Water vapor is the most abundant greenhouse gas in the atmosphere, others include methane and carbon dioxide. Greenhouse gases are an essential component of the atmosphere and act to retain heat at night making the Earth habitable. Methane is present in minute amounts and will not be discussed here. Carbon dioxide is the second most abundant greenhouse gas. The greenhouse theory proposes that increased amounts of carbon dioxide in the atmosphere (from burning of fossil fuels) will trap more heat in the atmosphere and the Earth's climate will warm.
When the ice core data for temperature (O-16/O-18 ratios) is compared with ice core data for carbon dioxide concentrations there is an undeniable correlation between carbon dioxide concentrations and temperature. During periods of warm temperature coincide with periods of increased carbon dioxide.
BUT.... which is the cause and which is the effect.... Are carbon dioxide levels controlling temperature OR is temperature controlling carbon dioxide levels?
Burning of fossil fuels is blamed for increasing carbon dioxide levels over the last 100-200 years. Man could be altering the climate and this SHOULD be addressed but... what about the other 250,000 years? Why are carbon dioxide concentrations variable? One idea is the population of carbonate shelled microorganisms. More carbonate shells means more carbon dioxide removed. There is no supporting evidence for this. Some scientists have suggested that the Earth's climate changes over time and that carbon dioxide levels change in response to change in temperature. The gas laws state that gas is more soluble in cold fluids than warm fluids. If climate is changing independently it is reasonable to assume that carbon dioxide could go into and out of solution with changing temperature. If climate is changing independently, why is it changing?
Milankovitch Cycles:
An astronomer, Milutin Milankovitch, determined that variations in the Earth-Sun relationship affect the amount of solar radiation received on the Earth and this in turn affects climate. The eccentricity (shape of the orbit), precession (wobble of the orbit) and obliquity (tilt of the Earth's axis) vary in cycles ranging from 19,000 years to 400,000 years. Each parameter affects the distribution of incoming solar radiation altering the seasonal variation. The effect of this variation can be calculated to determine if it has a cooling or warming effect on Earth's climate. A composite of the cycles over which these parameters occur determines the relative cooling or warming the effect of the Milankovitch Cycles over time. There is a very close correlation between ice core temperature data and composite Milankovitch Cycles.
Other Possible Causes for Climate Change:
Volcanism: Particulates in the upper atmosphere from volcanic eruptions act to reflect solar radiation having a cooling effect on climate. This was evidenced after the eruption of Mount Pinatubo. Generally it is not thought that volcanism alone could account for the variability seen in the climate record.
Tectonism: Continental movements and orogenic uplifts act to block ocean and atmospheric flow altering climate. It is not thought that tectonism alone could account for variability in the climate record.
III) Conclusions:
Climate is variable. The variability is documented in the historical, fossil, lithologic and ice core records. The cause of climate change is debatable and more research is needed. Currently there is an effort to reduce carbon dioxide emissions. This is commendable...it can only have a positive effect on climate and certainly will not act to harm the ecosystem since man is emitting the carbon dioxide initially. BUT..... Some radical and scary solutions to global warming have been proposed. (Spread iron over the oceans to increase photosynthesis, launch mirrors into space to reflect radiation, put particulates in the upper atmosphere to reflect radiation) We need to protect our Earth not add more substances into the ecosystem!!!
See Earth Magazine, Oct. 1996 issue!
