NASA:Clouds and Earth's Radiation Budget

Credit:NASA

Energy from the Sun reaching the Earth drives almost every known physical and biological cycle in the Earth system. The energy that keeps the earth's surface warm originates from the sun. The primary source of energy to drive our global climate system (including atmospheric and, to a lesser extent, oceanic circulation) is the heat we receive from the Sun, termed solar insolation. The amount of insolation which reaches the Earth's surface depends on site latitude and season. The insolation into a surface is largest when the surface directly faces the Sun. As the angle increases between the direction normal to the surface and the direction of the rays of sunlight, the insolation is reduced in proportion to the cosine of the angle. This is known in optics as Lambert's cosine law. 

These false-color images show the average solar insolation, or rate of incoming sunlight at the Earth's surface, over the entire globe for the months of January and April. The colors correspond to values (kilowatt hours per square meter per day) measured every day by a variety of Earth-observing satellites and integrated by the International Satellite Cloud Climatology Project (ISCCP). NASA's Surface Meteorology and Solar Energy (SSE) Project compiled these data--collected from July 1983 to June 1993--into a 10-year average for that period. Credit Image courtesy Roberta DiPasquale, Surface Meteorology and Solar Energy Project, NASA Langley Research Center, and the ISCCP Project

This 'projection effect' is the main reason why the polar regions are much colder than equatorial regions on Earth. On an annual average the poles receive less insolation than does the equator, because at the poles the Earth's surface is angled away from the Sun.

 Although the energy that is emitted from the sun is almost constant, even small changes can have noticeable effects. When the Sun's energy reaches the Earth it is partially absorbed in different parts of the climate system. The absorbed energy is converted back to heat, which causes the Earth to warm up

 There are three main factors that directly influence the energy balance of the earth and it's temperature: 

• The total energy influx, which depends on the earth's distance from the sun and on solar activity

• The chemical composition of the atmosphere

• Albedo, the ability of the earth's surface to reflect light. 

Solar Variability: Striking a Balance with Climate Change NASA Video

 The Earth's climate system is a compilation of the following components and their interactions-

•  The atmosphere
  

•  The hydrosphere, including the oceans and all other reservoirs of water in liquid form, which are the main source of moisture for precipitation and which exchange gases, such as CO2, and particles, such as salt, with the atmosphere.
   

• The land masses, which affect the flow of atmosphere and oceans through their morphology (i.e. topography, vegetation cover and roughness), the hydrological cycle (i.e. their ability to store water) and their radiative properties as matter (solids, liquids, and gases) blown by the winds or ejected from earth's interior in volcanic eruptions.
   

• The cryosphere, or the ice component of the climate system, whether on land or at the ocean's surface, that plays a special role in the Earth radiation balance and in determining the properties of the deep ocean.
   

• The biota - all forms of life - that through respiration and other chemical interactions affects the composition and physical properties air and water.

The Earth has periods of time when the temperature rises (warming cycles) and periods when the temperature drops (cooling cycles) it is a series of natural cycles of our planet. The Sun and it's level of solar activity has an major influence on these cycles. 

Today climate change and global warming are receiving unprecedented attention due to the possibility that human activity on Earth during the past couple hundred years will lead to significantly large and rapid changes in environmental conditions. 

The first step in addressing the issue of global warming is to recognize that the warming pattern, if it continues, will probably not be uniform. The term "global warming" only tells part of the story; our attention should be focuses on "global climate change." The real threat may not be the gradual rise in global temperature and sea level, but the redistribution of heat over the Earth's surface. Some spots will warm, while others will cool; these changes, and the accompanying shifts in rainfall patterns, could relocate agricultural regions across the planet.

The Greenhouse Effect

The greenhouse effect is a natural occurrence that maintains Earth's average temperature at approximately 60 degrees Fahrenheit.

Under normal conditions some of the sun's heat is radiated back into space

The 'Greenhouse Effect' occurs when heat is trapped in the atmosphere by gases 

 The greenhouse effect is a necessary phenomenon that keeps all Earth's heat from escaping to the outer atmosphere. Without the natural greenhouse effect it is certain that life on Earth would be difficult to sustain. 

Temperatures on Earth would be much lower than they are now, and the existence of life on this planet would not be possible. The global average temperature would drop precipitously 33 degrees from its current 15° to -18°C. The Earth would become an ice planet.

 However, too many greenhouse gases in Earth's atmosphere could increase the greenhouse effect.

 This could result in an increase in mean global temperatures as well as changes in precipitation patterns. 

The Earth's atmosphere, a thin blanket of gases, protects the planet from the harshest of the sun's ultraviolet radiation. The atmosphere, by trapping the Earth's warmth, keeps rivers and oceans from freezing. Carbon dioxide and water vapor are the most important gases in creating the insulating or "greenhouse effect" of the atmosphere. 

EPA Diagram

Global Warming: How Humans are Affecting Our Planet 

Over the last 400,000 years the Earth's climate has been unstable, with very significant temperature changes, going from a warm climate to an ice age in as rapidly as a few decades. These rapid changes suggest that climate may be quite sensitive to internal or external climate forcings and feedbacks. As can be seen from the blue curve, temperatures have been less variable during the last 10 000 years. Based on the incomplete evidence available, it is unlikely that global mean temperatures have varied by more than 1°C in a century during this period. The information presented on this graph indicates a strong correlation between carbon dioxide content in the atmosphere and temperature. A possible scenario: anthropogenic emissions of GHGs could bring the climate to a state where it reverts to the highly unstable climate of the pre-ice age period. Rather than a linear evolution, the climate follows a non-linear path with sudden and dramatic surprises when GHG levels reach an as-yet unknown trigger point.

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This image was created with data acquired by the Atmospheric Infrared Sounder, AIRS,instrument on NASA's Aqua spacecraft during July 2008. The image shows large scale patterns of carbon dioxide concentrations that are transported around the Earth by the general circulation of the atmosphere.

Polar Ice

Melting Arctic sea ice has shrunk to a 29-year low, significantly below the minimum set in 2005, according to preliminary figures from the National Snow and Ice Data Center, part of the University of Colorado at Boulder. NASA scientists, who have been observing the declining Arctic sea ice cover since the earliest measurements in 1979, are working to understand this sudden speed-up of sea ice decline and what it means for the future of Earth's northern polar region.

NASA JPL Video: The Big Thaw October 01, 2007 A thick chunk of Arctic sea ice the size of two states has disappeared. Is it global warming or normal causes? A new NASA-led study found a 23-percent loss in the extent of the Arctic's thick, year-round sea ice cover during the past two winters. Between winter 2005 and winter 2007, the perennial ice shrunk by an area the size of Texas and California combined. This drastic reduction of perennial winter sea ice is the primary cause of the fastest-ever sea ice retreat on record this summer. Scientists say the rapid decline in winter perennial ice was caused by unusual winds. For more information go to: www.jpl.nasa.gov

credit:NASA

Polar ice reflects light from the sun. As this ice begins to melt, less sunlight gets reflected into space. It is instead absorbed into the oceans and land, raising the overall temperature, and fueling further melting. This results in a positive feedback loop called ice albedo feedback, which causes the loss of the sea ice to be self-compounding. The more it disappears, the more likely it is to continue to disappear. -full story click here