What this lesson teaches
I can explain the natural causes of climate change and their feedback loops.
Syllabus 8834, Topic 1.2, 1. The Science of Climate Change. Can natural factors fully account for contemporary climate change?
Make a guess
A slight cooling lets more snow survive the summer. How can that make the cooling bigger?
- Snow reflects more sunlight, cooling further.
- It cannot; a small cooling fades away.
- Snow makes the Sun give off less energy.
- Snow traps heat underneath, warming the ground.
Show the answer
Snow reflects more sunlight, cooling further.
More snow and ice raise albedo, so less energy is absorbed. That cools things further and more ice grows: a positive, amplifying feedback.
A change in incoming energy can start a climate shift, and growing or melting ice can then make that shift bigger.
Solar output is the energy the Sun gives off. It varies over a cycle of about 11 years, changing the energy Earth receives. Its effect must be judged by the measured size and direction of the energy change.
Orbital changes are different. They do not change the Sun's output. Instead, changes in Earth's orbit shape, tilt and wobble move sunlight between latitudes and seasons. Over tens of thousands of years, they helped set the timing of glacial cycles. Cooler northern summers let snow survive and ice sheets grow.
Albedo is how much sunlight a surface reflects. More snow and ice raise albedo, so less energy is absorbed. This cools things further, so more ice grows. This is a positive feedback, because it amplifies the first change. It also works in reverse: melting ice exposes darker ground, which absorbs more heat.
Positive feedback does not mean good or warmer. It means amplifying. A negative feedback reduces the first change. For example, a warmer Earth gives off more heat to space. So an amplifying cooling loop is also a positive feedback.
Slow orbital cycles and small solar changes cannot explain today's rapid warming. Natural mechanisms matter for past climate change, but their existence is not evidence that human greenhouse gases have little effect.
- Solar output
- Energy the Sun gives off; varies on an 11-year cycle.
- Albedo
- The share of sunlight a surface reflects.
- Positive feedback
- Amplifies the first change, warming or cooling.
Step by step
Find the first change
Solar output, or orbital shifts in sunlight.
Follow the surface
Cooling grows ice; warming melts it.
Close the loop
Albedo changes absorption and boosts the first change.
Real examples to use
Arctic sea ice
Summer Arctic sea ice has shrunk by about 13% per decade since satellite records began in 1979. Darker open water absorbs more sunlight, adding to warming.
Worked example: A cooling loop that is positive
Less summer melting leaves more snow. Higher albedo means less sunlight is absorbed, so summers stay cool and more snow survives. Every step boosts cooling, so this is a positive feedback even though temperature falls.
Watch out for this
Positive feedback always makes things warmer.
It strengthens the first change, whether that is warming or cooling.
Check your understanding
Which sequence is a positive ice-albedo feedback?
- A cold afternoon is followed by a warmer afternoon the next day.
- Warming melts ice, more heat is absorbed, warming grows.
- Warming increases heat lost to space and reduces the warming.
Show the answer
Warming melts ice, more heat is absorbed, warming grows.
Yes. The loop amplifies the warming.