Which one of the following is an example of positive feedback in the context…

Concept — A climate feedback is the loop that appears when a change in the climate sets off a process that then acts back on that same change. The loop is called positive (self-reinforcing) when the response amplifies the original change and carries the system further from where it started, and negative (self-correcting) when the response opposes the original change and pulls the system back toward its starting state. The sign describes reinforcement versus opposition only; it carries no judgement about whether the outcome is desirable.

Application — Start from an initial warming and follow the melting-ice branch one step at a time:

1. Warming raises temperatures over snow cover and ice shelves, so part of that snow and ice melts.

2. Snow and ice have a very high albedo — fresh snow reflects up to about 90% of the sunlight falling on it — while the ocean and bare land they expose have a low albedo and absorb most of it.

3. With less bright surface left, the reflection of sunlight falls and the absorption of solar energy at the surface rises.

4. That extra absorbed energy warms the surface further, which melts still more snow and ice.

5. Step 4 hands the system back to step 1 with a larger warming than it began with, so each pass around the loop feeds the next.

Each pass around the loop leaves the system warmer than the one before it, so the process reinforces the very change that started it. This chain is known as the ice–albedo feedback.

Cross-check — Each of the other three processes closes its loop in the opposing direction:

• “Warmed earth radiates more infrared energy (heat) into space”: by the Stefan–Boltzmann law the emitted flux climbs as T4, so a warmer Earth sheds heat to space faster and is pulled back down in temperature. This Planck response is the strongest negative feedback in the climate system.

• “Plants remove carbon dioxide from the air”: photosynthetic uptake draws down the very greenhouse gas that is driving the warming, weakening the forcing behind it — a negative carbon-cycle feedback.

• “Oceans remove carbon dioxide from the air”: dissolving CO2 into surface seawater likewise strips the forcing agent out of the atmosphere and damps the warming — again a negative feedback.

Note — A warming ocean does hold less dissolved CO2, and thawing permafrost releases methane; those are genuine positive feedbacks. But the option as worded describes oceans removing CO2 from the air, which is the damping direction, so it does not qualify here.

Result — Of the four processes listed, only “Snow cover and ice shelf melting reduce reflection of sunlight” feeds its own effect back into the warming that produced it, so that is the example of a positive feedback in the context of climate change.