ACARA v9 CONTENT DESCRIPTION “use models of energy flow between the geosphere, biosphere, hydrosphere and atmosphere to explain patterns of global climate change”
Builds on earlier work picturing Earth as four connected spheres and on the idea that matter and energy are conserved. Here those ideas carry the climate story: the planet runs on an energy budget, and energy moving between the spheres sets the patterns of global climate.
Earth runs on an energy budget
Almost all of the energy that drives Earth’s climate arrives as sunlight. The surface absorbs that energy, warms up, and radiates it back out as infrared. When the energy leaving as infrared matches the energy arriving as sunlight, the average surface temperature stays steady. Scientists call this an energy balance, and it is the starting point for any model of climate.
Earth as an energy budget
Sunlight warms the surface and the surface radiates infrared back to space. Slide to change how much infrared escapes and watch whether the planet stays in balance.
Energy in equals energy out, so the average surface temperature stays the same. This steady state is what scientists call energy balance.
The greenhouse effect
The atmosphere is not empty: it holds gases such as carbon dioxide and water vapour that absorb outgoing infrared and re-emit some of it back toward the surface. This greenhouse effect keeps Earth far warmer than it would be otherwise, warm enough for liquid water and life. Adding more greenhouse gas means more infrared is held back, so the surface settles at a higher temperature.
The greenhouse effect
Greenhouse gases in the air absorb outgoing infrared and send some of it back toward the surface. Add or remove gas and watch the surface temperature respond.
With more greenhouse gas, more outgoing infrared is absorbed and returned to the surface, so the surface settles at a higher temperature. A natural greenhouse effect keeps Earth warm enough for liquid water; without any greenhouse gases the surface would be far colder.
Energy flows between the spheres
Energy and carbon do not stay in one place. The ocean absorbs heat and carbon dioxide from the air, plants take carbon dioxide out of the atmosphere as they grow, and over long times carbon is locked into rock. Each of these is a flow between two of the four spheres, and together they shape how the climate responds to a change in the energy budget.
Energy and carbon flow between the spheres
Climate depends on how energy and carbon move between the four Earth systems. Pick a flow to see which two spheres it links and which way it runs.
Atmosphere to hydrosphere: the ocean absorbs much of the extra heat, storing energy and slowing surface warming.
The enhanced greenhouse effect
When extra greenhouse gas is added to the air, mainly carbon dioxide from burning fuels that were stored in the geosphere, the greenhouse effect strengthens. More outgoing infrared is held back, so the energy balance tilts toward warming and the surface settles at a higher temperature. This is often called the enhanced greenhouse effect to separate it from the natural one.
The enhanced greenhouse effect
Adding greenhouse gas to the air strengthens the greenhouse effect. Step through to see the energy balance shift toward warming.
Steady greenhouse level: energy in and out are matched.
Reading the patterns in the data
Models of energy flow make predictions, and scientists test those predictions against measurements. Records of the carbon dioxide level and of the average surface temperature both rise over the same period, and the two move together. Reading data like this is how a pattern of climate change is described and how the energy-flow models are checked against the real world.
Reading a climate trend
Step through the years to plot two illustrative series, carbon dioxide level and average temperature change, and see how they move together.
Across these illustrative figures the two lines climb together: as the carbon dioxide level rises, the average temperature rises too. Reading data like this is how scientists describe patterns of climate change and test the models of energy flow against the real record.
Putting the model together
A single picture ties it together: sunlight in, infrared out, greenhouse gases holding back part of that infrared, and energy moving between the geosphere, biosphere, hydrosphere and atmosphere. Change one part of the budget and the whole system shifts to a new balance. That is the model scientists use to explain the patterns of global climate and how they change over time.
Quick self-check
1. What keeps Earth in a steady average temperature?
2. What do greenhouse gases do to outgoing infrared?
3. When the ocean absorbs heat, energy flows between which two spheres?
4. What is the enhanced greenhouse effect?
5. In the climate data, how do carbon dioxide level and temperature move over time?