Which of the following is an example of amplifying feedback?

When Joan gets a low grade on a test, she studies harder for the next test.
When income rises, people spend more. But when they spend more, income rises.
As the oxygen in the blood declines, an animal breathes faster. As it breathes faster, the oxygen in the blood rises.
When temperature in a house rises, the air conditioner turns on and cools the house.


The subject of climate change involves many feedback loops. In fact, without positive feedback, there would be no real concern about the increasing levels of carbon dioxide in the atmosphere. Three of the following are examples of positive or amplifying feedback and one is an example of negative or dampening feedback. Which is the example of negative feedback?

More carbon dioxide in the atmosphere raises ocean temperatures; oceans can hold more carbon dioxide when they are cooler.
Warmer climate reduces snow cover; snow cover reflects sunlight, which prevents warming.
More carbon dioxide increases plant growth; plants absorb carbon dioxide from the atmosphere.
Warmer temperatures lead to more water vapor in the atmosphere; water vapor is a greenhouse gas.

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