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HABYTIME MINI LECTURE 81:
THE GEOLOGIC EARTH: CLIMATE CHANGE

METEOROLOGIST JEFF HABY

This writing expands on the previous global temperature change writing at:

http://www.theweatherprediction.com/habyhints3/751/

The climate is a function of the relationships and interdependence of many variables that will be covered in this writing. It is not generally as simple as one cause leads to one effect since a cause can lead to many effects and multiple causes combine together to produce an effect. Long term climate science is tricky but enough is known to formulate many generalities. This list is by no means comprehensive and with so many variables being present it is difficult to state certainties. It is also important to note that the relationships discussed are primarily for long term climate change and not day to day weather changes.

Climate is the long term average of weather events. Weather records of 30 to 50 years can be used to get a good idea of the climate of a location. This climate though does change over 100ís, 1000ís and 10s of thousands of years and longer. The reasons that climate change includes factors such as the Milankovitch Cycles, volcanism, positioning of continents on Earth, percent of Earth covered by water, abundance of life, abundance of clouds/particulates in the atmosphere, greenhouse gas levels in the atmosphere (H20, CO2, methane, etc.), the sunís energy output, and asteroid impacts. Each of these will be analyzed for how they impact the climate change on Earth.

Milankovitch Cycles: These include the tilt of the earth, the precession of Earthís orbit, and the eccentricity of the Earthís orbit. These are explained at the link below:

http://www.theweatherprediction.com/habyhints2/608/

Volcanism: Volcanism releases gasses and particulates into the atmosphere. This can result in either a cooling or warming of climate. A cooling can occur when enormous amounts of particulates such as dust and ash are released high into the atmosphere. Once high in the atmospheres these particulates can stay suspended for many years. The particulates help reflect incoming solar radiation and this can result in a cooling of climate. If an enormous amount of greenhouse gasses are released from volcanism, the increase in these gases can contribute to warming the climate over longer time scales. Thus volcanism can generally cool the climate at first and then warm the climate over the long term. Volcanism was much higher in the early Earth than it is now. The temporary cooling effect from dust and ash emissions that reach the upper atmosphere are the major effect of volcanic eruptions in this day in age.

Positioning of continents: The positioning of continents helps control where the ocean currents are located. The size of the continents will determine how much land area is landlocked and thus not as influenced by the oceans. A huge climate control is the ocean water. The positioning of cold and warm ocean currents has a strong influence on the climates of locations, especially near the water. Continental drift explains how the continents move over geologic time due to molten rock circulations beneath the Earthís crust. Over time the continents slowly change position and this impacts the position and strength of ocean currents. The positioning of ice caps and glaciers can also have an influence on ocean currents.

Percent of Earth Covered by Water: Water has a high heat capacity and can thus store huge volumes of energy. Climate is modified by the ocean surface. A higher percent of land area can result in greater temperature extremes during the year while a higher percent of water area can result in lesser temperature extremes during the year. Currently the Earth is covered with about 70% water. The climate would be different if this value was changed to 65% or 75%. Rising sea level increases the water percentage coverage. This is typically accompanied with warming temperatures. Lowering sea level decreases the water percentage coverage but can result in a greater ice coverage since ice caps and glaciers tend to expand when temperatures cool globally.

Abundance of Life: Plant life uses solar energy to make and store sugars. Abundant life also changes the albedo of the land surface. Plant life produces a lower albedo that results in more solar energy being absorbed. Abundant plant life also takes in an abundance of CO2 while animals through respiration release CO2, which is a greenhouse warming gas. Regions abundant in plant life tend to have more H2O. H2O is a greenhouse gas and water on the surface is good at absorbing abundant amounts of solar radiation. Huge land areas that are covered in rich vegetation will tend to warm the planet.

Abundance of Clouds/Particulates in the Atmosphere: A wetter climate will add more water vapor to the atmosphere. Water vapor is a greenhouse gas that contributes to atmospheric warming thus the addition of evaporation and transpiration will tend to warm the climate. An abundance of vegetation will help produce a steady supply of H2O to the atmosphere. Wet soils from rain will also help a steady supply of H2O to the air. An increase of H2O can lead to more clouds. An increase of clouds can help reflect away more incoming solar radiation. Thus, although H2O leads to greenhouse warming, it can be kept in check by less solar radiation reaching the surface due to reflection off of clouds.

Particulates such as from dust storms and pollution will add substances to the atmosphere that can reflect some incoming solar radiation. This can cause cooler temperatures at the surface.

Greenhouse Gas Levels in the Atmosphere (H20, CO2, methane, etc.): An increase in greenhouse gases will lead to warmer temperatures. The two main greenhouse gasses are H2O (Water Vapor) and CO2 (Carbon Dioxide). H2O is an important greenhouse gas due to its abundance while CO2 is important since it is a strong greenhouse gas even though it is a small percentage of the overall air in the atmosphere. An increase in plant life will cause more H2O to be emitted into the atmosphere which contributes to warming. The burning of fossil fuels increases CO2 in the atmosphere which contributes to warming. Methane being released from warmer soils can contribute to warming. As a general rule, the higher the concentration of greenhouse gases in the atmosphere, then the warmer the temperature.

Sunís Energy Output: The sun has a dramatic influence on climate. The distance from the sun and the solar output are both very important factors. The Earth being 1% closer or farther from the sun or the sun producing 1% less or more output will have a significant influence on the Earthís climate. Sun spot cycles slightly alter the solar output. Over geologic time the solar output from the sun changes.

Asteroid Impacts: Large asteroid impacts will have a catastrophic impact on climate. They can produce a dramatic cooling over a short period of time. This occurs due to the enormous amount of dust that is emitted into the atmosphere after impact. Some of the dust will stay in the atmosphere for months and years. This significantly reduces the solar radiation that is able to reach the surface. This can result in much colder temperatures that puts stress on life forms. Dramatic changes to the species on Earth can result from asteroid impacts. Albedo changes on Earth following a large asteroid impact will also alter climate.