Anthropogenic causes and positive feedback

Ecosystems (Continuity and change) · Climate change · note 1 of 5

Spec D4.3.1, D4.3.2Download all Climate change notes (PDF)Download all notes (PDF)6 pages

Anthropogenic causes and positive feedbackSpec D4.3.1, D4.3.2

In short

Anthropogenic climate change is caused by human increases in atmospheric concentrations of carbon dioxide and methane, which enhance the greenhouse effect. Positive feedback cycles then accelerate warming: release of carbon dioxide from the deep ocean, loss of reflective snow and ice, faster decomposition and methane release in thawing permafrost, and more droughts and forest fires.

Carbon dioxide and methane are greenhouse gases: they absorb and re-emit longer-wave infrared radiation from the Earth's surface, warming the atmosphere. Anthropogenic (human-caused) increases in their concentrations enhance the greenhouse effect.

Gas	Main anthropogenic sources
Carbon dioxide	Combustion of coal, oil and natural gas; deforestation and burning of forests; cement production
Methane	Livestock such as cattle (fermentation in the gut); flooded rice fields; landfill; leaks from fossil fuel extraction

The Sun sends short-wave radiation through a layer of greenhouse gases (CO₂ and methane) to the Earth's surface; some infrared radiation escapes to space and some is trapped by the greenhouse gases and warms the Earth. — Increased CO₂ and methane trap more infrared radiation, warming the Earth.

Positive feedback cycles

In positive feedback, warming causes changes that cause further warming.

Release of CO₂ from the deep ocean: warmer water holds less dissolved CO₂, and changing circulation brings CO₂-rich deep water to the surface, where it is released.
Loss of reflective snow and ice: dark land and sea absorb more solar radiation than white ice, so warming speeds up.
Decomposition of peat and permafrost: thawing allows faster decomposition of peat and of previously undecomposed organic matter, releasing CO₂.
Methane from melting permafrost: anaerobic decomposition in waterlogged thawed soil releases methane.
Droughts and forest fires: fires release CO₂, and drought-stressed plants absorb less CO₂.

Two positive feedback loops marked +: global temperature rises, snow and sea ice melt, darker surface exposed, more solar radiation absorbed; and temperature rises, permafrost thaws, decomposition of organic matter releases CO₂ and methane, enhanced greenhouse effect. — Two positive feedback cycles: loss of reflective ice and thawing permafrost both speed up warming.

Written and checked against the IB Biology SL specification · Updated October 2026

Frequently asked questions

What are positive feedback loops in climate change?

Positive feedback loops are cycles in which warming causes changes that cause more warming. Examples are loss of reflective snow and ice, so more solar radiation is absorbed; thawing permafrost releasing CO₂ and methane; CO₂ released from the deep ocean; and more droughts and forest fires releasing carbon.

How does climate change affect coral reefs?

Climate change threatens coral reefs in two ways. Increased carbon dioxide causes ocean acidification, which suppresses calcification so corals build skeletons more slowly. Higher water temperatures cause coral bleaching, when corals expel their symbiotic algae and may die. Loss of corals causes collapse of the whole reef ecosystem.

Why are species moving to higher altitudes and towards the poles?

Species are moving because warming makes the warm edge of their range too hot, while cooler places further upslope or poleward become suitable. Tropical montane birds in New Guinea have shifted upslope, and some North American trees show contraction at their warm edge and northward spread.