Heat

List of Talking Points:

 * 1) Greenhouse Effect
 * 2) Global Warming
 * 3) Ozone Depletion

Contributing Factors
Over geologic time (some 4.5 billion years), Earth has naturally experienced a variable climate. These natural climate changes are caused by ongoing "internal" changes to the Earth's climate system (atmosphere, ice sheets, oceans, land, and biosphere) and by factors "external" to the Earth's climate system (changes in the Earth's orbit, changes in energy output from the sun, meteorite impacts). These changes alter the global energy balance, thereby changing Earth's surface temperatures and leading to overall global climate change. However the great majority of professional climate scientists believe that today's climate variability is now moving well outside the range of [|natural climate change], due to human influence. While changes in some of these factors occur independently, others are part of [|system feedback loops] that can act positively or negatively to affect the climate. The table below summarizes some of the main factors that cause natural climate change.

//Factors that contribute to natural climate change How it works// The [|Milankovitch theory] identifies three types of variation in the Earth's orbit around the sun that could influence global climate: For more information see: [|web.ngdc.noaa.gov] Variations in solar energy output exist over longer time scales. These variations have included number of sunspots. It is difficult to say how significant changes in solar energy output are to global climate change because experiments to measure these factors are relatively recent. For more information: [|earthobservatory.nasa.gov] The process called [|plate tectonics] moves continents around the world. Continents only move a few centimetres each year, but over millions of years the movement can be substantial. Scientists believe the arrangement of land masses significantly affects the ocean currents, in turn affecting the global climate system. As well the climate of a particular land mass might have changed dramatically over a hundred million years as that continent drifted from a location at the equator to the polar regions. A change in the greenhouse gas content of the atmosphere will affect the amount of energy trapped in the atmosphere. Variations in greenhouse gases can occur naturally or be caused by human activity. Additions of other substances, such as [|aerosols] and emissions from volcanoes, can reduce heating from solar radiation. Volcanoes release huge amounts of dust and gases into the upper atmosphere, including sulphur dioxide. The sulphur dioxide quickly turns into sulphuric acid aerosols and sulphate particles, which remain in the upper atmosphere for several years. Because they are highly reflective, they reduce the amount of sunlight reaching the Earth. Oceans affect the climate in three main ways: Areas of the Earth's surface vary in terms of how much energy they absorb and reflect, with some naturally [|more reflective] than others. Activity beneath the Earth's surface is also an important factor. Volcanic eruptions release dust and sulphur dioxide that block incoming solar radiation, resulting in a sulphur [|**aerosol cooling effect**] on global temperatures. Normal metabolic and life cycle process of plants, animals and microbes have contributed to maintaining the global energy balance as part of the natural [|carbon cycle]. [|Photosynthesis] by green plants is a key process for removing and storing CO2 from the atmosphere. Natural events such as large forest fires can remove large areas of vegetation, reducing forest capacity to pull CO2 out of the air, and also contribute CO2 from burning. The growth and decline of ice sheets affect the amount of solar energy absorbed and reflected. Light-coloured surfaces have a high [|albedo]and reflect light, while dark surfaces have a low albedo and absorb light, changing it to heat energy. This affects the overall global energy balance. Change in albedo of land surfaces is an important element of system feedback loops.
 * What causes natural climate change?**
 * Changes in Earth's orbit**
 * 1) changes in the tilt of the Earth's axis,
 * 2) changes in the shape of the Earth's orbit, and
 * 3) the shifting of equinoxes. Each variation changes the amount of solar energy reaching the Earth's surface.
 * Changes in output of energy from the sun**
 * Continental drift**
 * Composition of the atmosphere (including concentration of various greenhouse gases)**
 * Ocean circulation**
 * 1) They are the main source of atmospheric water vapour - a greenhouse gas - which is the largest single heat source for the atmosphere;
 * 2) They have an enormous heat capacity, which means that a large amount of heat is needed to raise ocean temperatures just slightly; and
 * 3) Ocean currents redistribute heat from low to high latitudes. [|2]
 * Surface and sub-surface qualities of the lithosphere, including large volcanic eruptions**
 * Changes in the biosphere**
 * Changes in the cryosphere (icesheets)**

[|Stanford Solar Center] This site presents a collection of fun educational activities based on Solar Oscillations Investigation and [|Solar and Heliospheric Observatory] data. Students can explore the Sun's tangled magnetic field, its turbulent surface motions, the dramatic sunspot cycle, and even what magic happens in the solar interior where instrumental eyes cannot penetrate. [|Aerosols and climate change]
 * //For more information and activities://**