---
title: "Positive Feedback — AP Enviro Definition & Exam Guide"
description: "Positive feedback is a loop where a change amplifies itself, like melting ice lowering albedo and causing more warming. Key to AP Enviro Unit 9 climate change."
canonical: "https://fiveable.me/ap-enviro/key-terms/positive-feedback"
type: "key-term"
subject: "AP Environmental Science"
unit: "Unit 9"
---

# Positive Feedback — AP Enviro Definition & Exam Guide

## Definition

In AP Environmental Science, positive feedback is a mechanism where an initial change triggers effects that amplify that same change, accelerating it in the same direction (for example, melting Arctic ice lowers albedo, which causes more warming and more melting).

## What It Is

Positive feedback is a self-reinforcing loop. A change happens, that change causes effects that push in the *same* direction, and the whole thing snowballs. "Positive" doesn't mean good here. It means *amplifying*. A [positive feedback loop](/ap-enviro/key-terms/positive-feedback-loop "fv-autolink") accelerating [climate change](/ap-enviro/unit-5/clearcutting/study-guide/z93clkKj7xsyG7zZPAtG "fv-autolink") is bad news, not a win.

The classic AP example is the **ice-albedo feedback**. Bright ice and snow reflect [sunlight](/ap-enviro/unit-2/ecological-tolerance/study-guide/dLeq5qqhYeCboAOsuBiz "fv-autolink") back to space (high albedo). When warming melts that ice, it exposes dark ocean or land underneath, which absorbs more heat, which causes more warming, which melts more ice. Each turn of the loop makes the next turn stronger. Compare that to negative feedback, which pushes *against* a change and stabilizes the system. Positive feedback destabilizes it.

## Why It Matters

This lives in **[Unit 9](/ap-enviro/unit-9 "fv-autolink"): Global Change**, specifically topic 9.5 Global Climate Change. It supports learning objective **[AP Enviro](/ap-enviro "fv-autolink") 9.5.A**, explaining how short- and long-term climate changes impact ecosystems. The essential knowledge points (STB-4.F.3 through STB-4.F.5) cover how shifting sea levels, atmospheric circulation like Hadley cells and the jet stream, and ocean currents like the conveyor belt all respond to and reshape climate. Positive feedback is the engine that turns a small initial change into a large one, so it's the conceptual glue connecting all those mechanisms. If you can explain *why* warming speeds itself up, you can answer most Unit 9 climate questions.

## Connections

### [Ice and Snow Albedo Feedback (Unit 9)](/ap-enviro/key-terms/ice-and-snow-albedo-feedback)

This is the textbook positive feedback loop. Less ice means lower [albedo](/ap-enviro/key-terms/albedo "fv-autolink"), which means more absorbed heat, which means more melting. It's the example AP loves because you can trace the loop in one sentence.

### Ocean Conveyor Belt and Hadley Cells (Unit 9)

Currents and [atmospheric circulation](/ap-enviro/unit-4/global-wind-patterns/study-guide/eVG86e42B0MvmzUs3FYI "fv-autolink") move heat around the planet. When warming disrupts them (STB-4.F.4 and STB-4.F.5), the new circulation pattern can lock in more warming, turning a heat-transport system into a feedback amplifier.

### Glacier Melt and Sea Level Rise (Unit 9)

Melting glaciers raise sea levels, which floods continental shelves and creates new marine habitats while drowning others (STB-4.F.3). The melt also feeds the albedo loop, so glacier loss is both an effect of warming and a driver of more of it.

### Soil Carbon and Permafrost (Units 5 & 9)

Warming thaws frozen soil and speeds [decomposition](/ap-enviro/key-terms/decomposition "fv-autolink"), releasing stored carbon as CO2 and methane. That extra greenhouse gas warms the planet more, which thaws more soil. It links land use and soil science from earlier units to climate feedback in Unit 9.

## On the AP Exam

Multiple-choice stems ask you to pick the mechanism that creates a positive feedback loop, like "which climate-driven change would create the strongest positive feedback loop accelerating further climate change?" The classic data setup gives you a stat (such as Arctic sea ice dropping 40% since 1979) and asks for the most significant consequence. The answer is usually the albedo loop. On FRQs, you may need to describe a feedback loop step by step (initial change, effect, how the effect amplifies the original change). The 2018 SAQ used an Arctic food web, the kind of ecosystem where these loops play out. When asked, make the loop explicit and show that each step pushes in the same direction.

## positive feedback vs Negative feedback

Both are feedback loops, but they do opposite things. Positive feedback amplifies a change and pushes the system further from where it started (melting ice causes more melting). Negative feedback opposes a change and pulls the system back toward stability (sweating cools you when you overheat). Remember: "positive" means amplifying, not beneficial.

## Key Takeaways

- Positive feedback means a change amplifies itself and accelerates in the same direction; it does not mean the outcome is good.
- The ice-albedo feedback is the go-to example: melting ice lowers albedo, dark surfaces absorb more heat, and that melts even more ice.
- It belongs to Unit 9 topic 9.5 and supports learning objective AP Enviro 9.5.A on how climate change impacts ecosystems.
- Negative feedback is the opposite; it resists change and stabilizes the system, while positive feedback destabilizes it.
- On the exam, be ready to trace a feedback loop step by step and show each step reinforces the original change.
- Disrupted ocean currents and atmospheric circulation can flip from heat-distributing systems into climate amplifiers.

## FAQs

### What is positive feedback in AP Environmental Science?

It's a self-reinforcing loop where an initial change triggers effects that push the system further in the same direction, accelerating the change. The Arctic ice-albedo loop is the standard example: melting ice exposes dark surfaces that absorb more heat and cause more melting.

### Does positive feedback mean a good outcome?

No. "Positive" here means amplifying, not beneficial. A positive feedback loop in climate change usually makes things worse by speeding up warming, like melting permafrost releasing carbon that causes even more warming.

### How is positive feedback different from negative feedback?

Positive feedback amplifies a change and drives the system away from where it started, while negative feedback opposes the change and stabilizes the system. Melting ice causing more melting is positive; sweating to cool an overheated body is negative.

### Why does melting Arctic sea ice create a positive feedback loop?

Ice has high albedo, so it reflects sunlight back to space. When ice melts, it exposes darker ocean that absorbs heat instead of reflecting it, which warms the area and melts more ice. With Arctic sea ice down about 40% since 1979, this loop is a major driver of accelerated warming.

### How do I explain a positive feedback loop on the FRQ?

Name the starting change, describe the effect it causes, and then show how that effect pushes the original change even further. For example: warming melts ice, the exposed dark surface absorbs more heat, that extra heat causes more warming and more melting.

## Related Study Guides

- [9.5 Global Climate Change](/ap-enviro/unit-9/global-climate-change/study-guide/7uD60uqTmhzrFIlNVpw9)

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