Poleward and upslope range shifts

Ecosystems (Continuity and change) · Climate change · note 4 of 7

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Poleward and upslope range shiftsSpec D4.3.6

In short

Poleward and upslope range shifts happen when warming makes the edges of a species' range too hot, while cooler areas become suitable. Tropical-zone montane bird species in New Guinea have shifted their ranges upslope. Some North American tree species show range contraction at their warm edge and northward spread at their cool edge.

Each species can only live within a range of temperatures. As the climate warms, the warm edge of a range becomes too hot and areas beyond the cool edge become suitable. So species ranges shift towards the poles and upslope, to higher altitudes.

Evidence-based examples
Example	Evidence
Tropical-zone montane birds in New Guinea	Surveys repeated on the same mountain slopes decades apart found that many bird species now live higher up than before, with their upper and lower limits moved upslope.
North American tree species	Surveys of forest plots show some species with range contraction at their southern, warmer edge and northward spread at their cooler edge. Trees disperse slowly, so many ranges are shrinking faster than they spread.

Species on mountain tops and near the poles have nowhere further to move, so they are at particular risk of extinction.

Left: a mountain with bars showing a montane bird range in the past and now, the range now higher up (range shifts upslope). Right: bars on a latitude axis showing a North American tree range shifted north, with contraction at the warm edge and spread at the cool edge. — Warming shifts ranges upslope and towards the poles (schematic).

Written and checked against the IB Biology HL 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.

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