Forcing, Feedback and Climate Sensitivity

This unit uses the flows of energy through the climate system to explain what climate feedbacks are and how to draw them as system diagrams. Energy arrives from the Sun and leaves back to space, and anything that shifts that balance starts a chain of responses. Some responses push the change further, and some push back against it. You work through short tasks during the session, building a system diagram step by step so you can see how one push ripples through the whole climate. The unit also looks at volcanic eruptions, which are a handy natural example: a big eruption throws particles into the air that block sunlight and cool the planet for a while. That is a clear case of a push from outside the system, which makes it easier to tell the difference between the push itself and the reactions that follow. Finally, the class builds a bigger diagram showing how climate policy connects to the science, which shows how many parts of society are tied into the same system.

This activity lets you play with a simple computer model of the whole planet's energy balance, built in Stella. You can change things like the strength of sunlight, how reflective the surface and atmosphere are, the amount of water vapour and carbon dioxide in the air, volcanic eruptions, and how deep the ocean's warm top layer is. Then you watch how the surface temperature responds. The best part is that you can switch feedbacks on or off. Turn on the water vapour feedback and warming grows stronger, because warmer air holds more water vapour and water vapour traps heat. Turn on the ice-albedo feedback and melting ice makes the surface darker, so it absorbs more sunlight and warms even more. By comparing runs with feedbacks on and off, you can see for yourself how much they amplify an initial push, which is exactly the idea behind climate sensitivity.

This video explains the water vapour feedback loop and how it connects to weather patterns around the world. When the air warms, it can hold more water vapour. Water vapour is itself a greenhouse gas, so the extra vapour traps more heat and the air warms further. That is an amplifying loop, and it is one of the strongest feedbacks in the climate system. The video has working scientists and clear graphics that show how water vapour, clouds, and the jet stream are all tied together. Clouds are the tricky part: depending on their height and type, they can cool the planet by reflecting sunlight or warm it by trapping heat, and that tug of war is the main reason scientists give a range rather than one exact number for how much warming a given push will cause. A teacher guide with extra links is included.

This module follows a glacier basin over long stretches of time to see how it responds when the climate shifts. You start by looking at how ice margins have retreated in the past and what processes, like rising air temperatures and changes at the ice surface, drive that retreat. Then the module separates natural climate wiggles from pushes caused by people, such as adding greenhouse gases to the atmosphere. That split matters because a push from outside, called a forcing, is what starts the change, while the system's own responses decide how big the final effect will be. Finally, you examine how the ice margin might respond to future climate change. It is a real world case study of a forcing working its way through a sensitive part of the Earth system, with the ice reacting and feeding back through changes in reflectivity.