Back To CourseEarth Science 102: Weather and Climate
13 chapters | 127 lessons
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Joanne has taught middle school and high school science for more than ten years and has a master's degree in education.
Just like this rock formation, the earth's climate represents a delicate balancing act. There is a precise equilibrium between the energy coming in from the sun and the energy being reflected back into space from the planet's surface.
When an event occurs, such as humans adding greenhouse gases to the atmosphere, this equilibrium is disturbed. In response, the climate will either warm up or cool down to reset the balance. In this example, greenhouse gases prevent solar radiation from being reflected back into space. However, to keep the balance, energy must be reflected back into space from the planet. So, the climate warms up, allowing more energy to be released as heat, until the original balance has been restored.
The climate responds through what is referred to as feedback mechanisms. A feedback mechanism is a process that allows a system, such as climate, to self-regulate in response to a change, such as increasing greenhouse gases.
A common example of a feedback mechanism is the thermostat in your home. When the temperature inside becomes too cold, the heater switches on, warming up the air. Once the air reaches the correct temperature, the heater switches off, and the air starts to cool back down. This process repeats, allowing you to keep your room at a stable temperature.
The earth's climate has several feedback mechanisms, such as the ice-albedo feedback, the water vapor-cloud feedback, the atmosphere-ocean interactions, and the atmosphere-biota interactions.
Albedo is derived from the Latin term for 'whiteness' and refers to how reflective a surface is. The more ice there is on the earth's poles, the higher the earth's albedo.
When the earth is very 'white,' it becomes more reflective. You have likely noticed this effect if you have ever been skiing. When the earth has a high albedo, more of the sun's radiation is reflected back into space and less is absorbed by the planet. This has the effect of keeping our planet cooler.
Here is how the ice-albedo feedback loop operates. The amount of radiation that the earth receives from the sun does not always stay the same. When the sun sends more radiation to the earth's surface, the planet starts to heat up. This increase in temperature causes the ice at the poles to melt. Less ice means that the planet's albedo decreases. Less radiation is reflected back into space and more is absorbed, causing the earth to heat up even more. A warmer planet means more ice melting, less radiation reflected back, and more absorbed, and so on. As you can see, the ice-albedo feedback loop causes the planet to continue to heat up.
This is what is referred to as positive feedback. In positive feedback, the initial effect is enhanced or increased. In this case, the initial effect was warming caused by increased solar radiation. The positive feedback loop causes the warming to continually increase.
Lucky for us, and everything else on our planet, the ice-albedo feedback loop does not continue unchecked. This is where the water vapor-cloud feedback loop, an example of negative feedback, comes into play. In negative feedback, the initial effect is counteracted or decreased. The thermostat we discussed in the introduction is another example of negative feedback.
As you have probably noticed, on a very foggy day, water droplets in the air make it hard to see. This is because they are scattering and reflecting the sun's rays. While this can make it hard to drive your car, it also helps keep the earth cool as the sun's radiation is bounced back into space.
As the planet warms up, the oceans begin to evaporate at a higher rate. This water vapor in the atmosphere leads to the formation of clouds, or water droplets in the sky. The clouds (notice that they are white like the snow) reflect the sun's radiation away from the planet, causing the earth to cool back down. Thus, the water vapor-cloud feedback loop keeps the planet from heating up forever.
Another example of positive feedback can be found in the earth's atmosphere-ocean interactions.
The ocean serves as a giant storage vault for carbon dioxide, one of the primary greenhouse gases. Nearly half of the carbon dioxide that humans have added to the atmosphere in the last 100 years (through factories, cars, and the burning of fossil fuels) has been absorbed by the oceans.
Here is where the feedback loop comes in. Colder water can hold more carbon dioxide than warmer water. As the atmosphere heats up, so do the oceans. The warming water allows carbon dioxide to escape into the atmosphere, enhancing the greenhouse effect and further warming the planet.
We find an example of negative feedback in Earth's atmosphere-biota interactions. Biota simply refers to all of the living creatures - plant, animal, or otherwise - in a particular area. In this case, we are looking at all of the living creatures on the planet, particularly the plant life. Plants both on land and in the ocean play a very large role in the stability of our climate. They are essential in removing carbon dioxide from the atmosphere during the process of photosynthesis.
Additionally, returning to the concept of albedo, as the temperature around plants increases, they lose more water through transpiration. Transpiration refers to the evaporation of water from plants' leaves. More water in the atmosphere means more cloud cover, which reflects solar radiation back into space.
So, a warmer climate leads to more plant life. Increased plant life means that more carbon dioxide is removed from the atmosphere and more clouds are added. This leads to less greenhouse gases trapping heat and more of the sun's rays being reflected away from the planet. As a result, the climate cools down. You can see that plants are important in combating global warming!
So let's review what we have learned. The earth's climate is in a delicate equilibrium between the energy coming in from the sun and the energy being reflected back into space from the planet's surface. Whenever there is a shift in this equilibrium, the climate responds through various feedback mechanisms.
A feedback mechanism is a process that allows a system, such as climate, to self-regulate in response to a change, such as increasing greenhouse gases. Feedback can be either positive or negative. In positive feedback, the initial effect is enhanced or increased. In negative feedback, the initial effect is counteracted or decreased.
Two examples of positive feedback in the climate are the ice-albedo feedback and the atmosphere-ocean interactions. Albedo is derived from the Latin term for 'whiteness' and refers to how reflective a surface is.
Two examples of negative feedback in the climate are the water vapor-cloud feedback and atmosphere-biota interactions. Biota refers to all of the living creatures - plant, animal or otherwise - in a particular area.
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Back To CourseEarth Science 102: Weather and Climate
13 chapters | 127 lessons