Atmospheric Carbon Dioxide and Temperature
Up to this point, we've primarily focused on naturally-occurring climate change that occurs over long time scales. Understanding the rates of change and time scales across which climate change processes occur is important, because it helps us to differentiate from climate change that occurs naturally and climate change that is cause by humans. Human-caused climate change is also called anthropogenic climate change.
There are many ways in which humans change global, regional, and local climates. A good example of how humans can change climate very locally (at the scale of your house) is by changing the vegetation type around a home or yard. Let's pretend you bought a house in Boise, Idaho, that has no trees or grass in the yard. Instead, the previous owners, who owned a construction company, had paved over much of the yard in order to park numerous pieces of construction equipment. Imagine all that asphalt on a sunny summer day. How hot would it be around your house?
You decide to rip out the asphalt and plant a lots of trees around the house. Within 10 years, those trees have grown tall enough that the house and the yard are mostly in the shade all day long. How different are the summer temperatures in the shade compared to when it was all asphalt? How different do you think the winter temperatures are with no asphalt to absorb the winter sunlight?
Congratulations - you have changed the microclimate of your property, just by changing the land cover! At a somewhat larger spatial scale, this is the exact opposite of what happens in cities, where the development of neighborhoods, shopping centers, and urban buildings add asphalt while displacing trees and grass. The resulting effect is called the urban heat island effect, whereby the core of a city is usually much warmer than the surrounding rural areas.
There are many ways in which humans change global, regional, and local climates. A good example of how humans can change climate very locally (at the scale of your house) is by changing the vegetation type around a home or yard. Let's pretend you bought a house in Boise, Idaho, that has no trees or grass in the yard. Instead, the previous owners, who owned a construction company, had paved over much of the yard in order to park numerous pieces of construction equipment. Imagine all that asphalt on a sunny summer day. How hot would it be around your house?
You decide to rip out the asphalt and plant a lots of trees around the house. Within 10 years, those trees have grown tall enough that the house and the yard are mostly in the shade all day long. How different are the summer temperatures in the shade compared to when it was all asphalt? How different do you think the winter temperatures are with no asphalt to absorb the winter sunlight?
Congratulations - you have changed the microclimate of your property, just by changing the land cover! At a somewhat larger spatial scale, this is the exact opposite of what happens in cities, where the development of neighborhoods, shopping centers, and urban buildings add asphalt while displacing trees and grass. The resulting effect is called the urban heat island effect, whereby the core of a city is usually much warmer than the surrounding rural areas.
Urban Heat Island
The urban heat island can be particularly pronounced on days with strong solar heating and weak winds. The lack of winds helps keep the heat "bubble" close to the urban core, rather than dispersing it. The heat island also persists into the overnight hours as concrete and asphalt surfaces hold on to heat and re-radiate it back to the surrounding environment after the sun sets. For these reasons, long term temperature records used to study global climate change typically do not use urban areas, or places that have undergone significant modification to the landscape.
At global scales, land cover change by humans still plays a role in altering the climate of the Earth. But recall that oceans make up 70% of the Earth surface -- this means that as much as we are changing the land cover and the albedo of Earth, this is only one piece of anthropogenic climate change. A much larger contributor at global scales is how humans impact Earth's atmosphere.
Recall that the Greenhouse Effect is a naturally-occurring process whereby the primary greenhouse gases in the atmosphere (carbon dioxide, water vapor, and methane) absorb radiation and hold heat energy close to Earth's surface, helping to moderate surface temperature compared to the much larger temperature ranges found in space. In the animation, what happened when you increased the amount of carbon dioxide and water vapor in the atmosphere? Did the temperature near the surface increase or decrease?
Over the last 150 years, humans have increased the amount of carbon dioxide in the atmosphere by burning fossil fuels, such as coal and oil. Just like the process of boiling water converts a liquid to gas, burning fossil fuels (which requires oxygen) converts a solid (carbon) to a gas (carbon dioxide). As the amount of carbon dioxide has increased and warmed the atmosphere, the extra heat energy has been melting ice and converting liquid water in oceans and lakes into water vapor through a positive feedback loop. Because of this feedback loop, there is even more water vapor absorb heat energy in the atmosphere, and it gets warmer even faster!
Scientists use a lot of data to understand and model climate change and to differentiate between the natural climate change that occurs very slows over thousands of years versus the rapid climate change that has occurred just over the last 150 years or so. Part of doing science is showing data and results and interpreting those results. Instead of telling you about the relationship between carbon dioxide and temperature over the last century, the next exercise allows you to look at and graph the data and come to your own conclusions.
Log into BBLearn and in Module 3, under Mastering Assignments, complete "Assignment 3.4: Climate Change."
Recall that the Greenhouse Effect is a naturally-occurring process whereby the primary greenhouse gases in the atmosphere (carbon dioxide, water vapor, and methane) absorb radiation and hold heat energy close to Earth's surface, helping to moderate surface temperature compared to the much larger temperature ranges found in space. In the animation, what happened when you increased the amount of carbon dioxide and water vapor in the atmosphere? Did the temperature near the surface increase or decrease?
Over the last 150 years, humans have increased the amount of carbon dioxide in the atmosphere by burning fossil fuels, such as coal and oil. Just like the process of boiling water converts a liquid to gas, burning fossil fuels (which requires oxygen) converts a solid (carbon) to a gas (carbon dioxide). As the amount of carbon dioxide has increased and warmed the atmosphere, the extra heat energy has been melting ice and converting liquid water in oceans and lakes into water vapor through a positive feedback loop. Because of this feedback loop, there is even more water vapor absorb heat energy in the atmosphere, and it gets warmer even faster!
Scientists use a lot of data to understand and model climate change and to differentiate between the natural climate change that occurs very slows over thousands of years versus the rapid climate change that has occurred just over the last 150 years or so. Part of doing science is showing data and results and interpreting those results. Instead of telling you about the relationship between carbon dioxide and temperature over the last century, the next exercise allows you to look at and graph the data and come to your own conclusions.
Log into BBLearn and in Module 3, under Mastering Assignments, complete "Assignment 3.4: Climate Change."