Lesson 1 Energy Flow in Global Systems
Net Radiation Budget
Not all the solar energy that reaches Earth is used by Earth.
D1.15 Solar energy is reflected and absorbed
When
solar energy reaches Earth, it can either be reflected or absorbed by the particles of
matter.
Solar energy is short wave radiant energy. As it passes through the atmosphere it can be reflected by clouds and bounced back into space. A small amount may be absorbed by dust and converted into thermal energy.
some is used by plants for photosynthesis. As solar energy arrives at the surface, some is reflected by snow and water back into space, but about half is absorbed.
Solar energy absorbed at the Earths surface heats the the surface. In other words, increases the amount of kinetic energy (motion) of the particles that make up the Earth. Any warm matter will radiate infrared radiation. Infrared radiation is long wave radiation that interacts with gases in the atmosphere differently that solar radiation does. Greenhouse gases, like carbon dioxide, water vapour and methane, can absorb infrared radiation and gain kinetic energy. These warm molecules then emit radiation in all directions. Overall, half will radiate upwards into space and be lost from Earth, but half will radiate downwards and send energy back to Earth.
So Earths atmosphere does not much affect solar radiation arriving on Earth, but it does affect infrared radiation leaving it.
Solar radiation and the infrared radiation sent back to earth by greenhouse gases is incoming radiation. Solar radiation reflected by clouds and snow, and Infrared radiation escaping to space are outgoing radiation. The net radiation budget is the difference between the amount of incoming solar radiation and outgoing radiation emitted from the biosphere. The incoming solar energy includes all the solar energy that reaches Earth’s surface, while the outgoing radiation includes the energy that has been re-emitted by the earth’s surface and atmosphere.
Some of this outgoing radiation will be reabsorbed by the gases in the atmosphere and will become part of the incoming solar energy again.
Solar energy is short wave radiant energy. As it passes through the atmosphere it can be reflected by clouds and bounced back into space. A small amount may be absorbed by dust and converted into thermal energy.
some is used by plants for photosynthesis. As solar energy arrives at the surface, some is reflected by snow and water back into space, but about half is absorbed.
Solar energy absorbed at the Earths surface heats the the surface. In other words, increases the amount of kinetic energy (motion) of the particles that make up the Earth. Any warm matter will radiate infrared radiation. Infrared radiation is long wave radiation that interacts with gases in the atmosphere differently that solar radiation does. Greenhouse gases, like carbon dioxide, water vapour and methane, can absorb infrared radiation and gain kinetic energy. These warm molecules then emit radiation in all directions. Overall, half will radiate upwards into space and be lost from Earth, but half will radiate downwards and send energy back to Earth.
So Earths atmosphere does not much affect solar radiation arriving on Earth, but it does affect infrared radiation leaving it.
Solar radiation and the infrared radiation sent back to earth by greenhouse gases is incoming radiation. Solar radiation reflected by clouds and snow, and Infrared radiation escaping to space are outgoing radiation. The net radiation budget is the difference between the amount of incoming solar radiation and outgoing radiation emitted from the biosphere. The incoming solar energy includes all the solar energy that reaches Earth’s surface, while the outgoing radiation includes the energy that has been re-emitted by the earth’s surface and atmosphere.
Some of this outgoing radiation will be reabsorbed by the gases in the atmosphere and will become part of the incoming solar energy again.
The net radiation budget of Earth can be written as the following word equation:
Net Radiation Budget = Incoming Radiation – Outgoing Radiation
Net Radiation Budget = Incoming Radiation – Outgoing Radiation
Figure D1.16 shows how different parts of the biosphere affect the net radiation budget. You will notice that these percentages are slightly different than the ones in your textbook, because this is a more up-to-date image.
When solar energy enters Earth’s atmosphere,
When this thermal energy is emitted,
The net radiation budget for Earth is always very close to zero. Incoming radiation always closely matches the outgoing radiation. This helps keep Earth’s overall temperature stable and unchanging. Net radiation budgets that are not zero mean that the average amount of energy on Earth is changing, and that means climate change.
Changes in climate are natural. Species evolve or become extinct as climate changes. Human civilization is based on the relatively mild climate that we now enjoy. We fear that if climate change is too rapid for our civilization to adapt to, many people would suffer as our human systems, like agriculture, struggle to adapt.
It is important to note while Earth as a whole has a net radiation budget of zero, different regions of Earth will not. These differences in regions will equal out to create an overall net radiation budget of zero.
When solar energy enters Earth’s atmosphere,
- 48% of it is absorbed by the surface
- 23% of it is absorbed by the atmosphere
- 29% of it is reflected back into space
- 23% of this is reflected by the clouds and atmosphere.
- 6% is reflected by Earth’s surface.
When this thermal energy is emitted,
- 70% is re-emitted from the atmosphere and Earth’s surface
- 9% is re-emitted by clouds.
- 50% is re-emitted by the atmosphere.
- 11% is re-emitted by Earth’s surface.
- 25% is emitted by phase changes in the hydrosphere (water changing from liquid to solid to gas)
- 5% is emitted by global winds
The net radiation budget for Earth is always very close to zero. Incoming radiation always closely matches the outgoing radiation. This helps keep Earth’s overall temperature stable and unchanging. Net radiation budgets that are not zero mean that the average amount of energy on Earth is changing, and that means climate change.
Changes in climate are natural. Species evolve or become extinct as climate changes. Human civilization is based on the relatively mild climate that we now enjoy. We fear that if climate change is too rapid for our civilization to adapt to, many people would suffer as our human systems, like agriculture, struggle to adapt.
It is important to note while Earth as a whole has a net radiation budget of zero, different regions of Earth will not. These differences in regions will equal out to create an overall net radiation budget of zero.
Did You Know?
D1.17 Atmospheric dust off Africa
The most common theory around the extinction of the dinosaurs says that a large asteroid collided with Earth. This collision sent a large amount of dust into the atmosphere, severely altering the climate. The dust blocked the sun for weeks, possibly months, killing plants and disrupting the food chain. What would be the effect on the global temperature if sunlight was blocked and prevented from reaching the earth’s surface?
Read This
Please read pages 367 and 368 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on what the net radiation budget is. Remember, if you have any questions or do not understand something, ask your
teacher!
Practice Questions
Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice
questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.
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What value should Earth’s net radiation budget have? What happens if that value changes?
Earth’s net radiation budget should have a value of zero. If that value changes from zero, then the global temperature of Earth will either increase (when the value is positive, there is more incoming radiation) or decrease (when the value is negative, there is less incoming radiation) until the net radiation budget becomes zero again.
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What happens to solar energy that is absorbed by the biosphere? What happens to the solar energy that is reflected by the biosphere?
Solar energy that is absorbed by the biosphere will either be converted into food energy through photosynthesis or it will be converted into thermal energy (which is the kinetic energy of the substance’s particles). It will also be re-emitted as thermal energy.
Solar energy that is reflected by particles in the biosphere will be either absorbed by other particles in the biosphere or reflected back into space.
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Which part of the biosphere re-emits the most thermal energy back into space?
The atmosphere re-emits the most thermal energy back into space. It re-emits 50% of all the thermal energy being re-emitted.