Climate change triggers species migration

In 2021, the World Bank's Groundswell report estimated that up to 216 million people could migrate due to climate change by 2050. The causes include repeated heatwaves, fires, droughts, decreasing agricultural yields, rising waters, and coastal retreats.

Species distribution shifts

These factors are expected to affect all life, with observable changes in the distribution areas of thousands of animal and plant species. A recent meta-analysis has shown that at least 10 percent of known butterfly species are experiencing geographic distribution changes.

Butterflies as climate indicators

Since the 1990s, butterflies have served as climate sentinels, with their northward movement in Europe and North America representing the first biological footprint of climate change. The northward movement is due to colder temperatures toward the poles and higher altitudes, with an average decrease of 0.6 °C per 100 meters of elevation gain, which is 6 °C per kilometer.

Widespread species movement

A study published in 2026 found that more than half of 1,888 observed species, ranging from insects to plants, through birds and fish, are moving north to escape the heat on the "warm" edges of their distribution areas. Species living outside their thermal tolerance zones experience physical effects, such as slowed movement in frogs below 0 °C, insect torpor, and plant water loss in extreme heat.

Thermal stress on ectotherms

Thermal stress is particularly challenging for ectothermic species, whose internal temperatures vary with external temperatures, making it difficult for insects and reptiles to regulate their body heat.

Geographical barriers to migration

The movement toward peaks and poles is not uniform and is influenced by geographical features such as seas and mountains. In Europe, species moving toward small peaks risk falling into climate traps, a phenomenon observed in the Alpine, Carpathian, and Pyrenean massifs.

Differential migration patterns

In contrast, in the Americas, species moving upward in altitude also move north or south in latitude. The concept of "extinction debt" suggests that if the mortality rate of certain populations exceeds their birth rate, extinction will occur in the future. For example, younger oak trees cannot withstand heatwaves, leading to the potential extinction of the species if heatwaves persist.

Forest movement influenced by pollution

European forests are also migrating, relying on reproduction and the dispersal of diaspores via wind, water, and animal vectors, including humans. Contrary to expectations, European forests are moving westward, influenced by historical industrial activity and nitrogen pollution from the 1980s.

Climate traps in Western Europe

This movement is observed in former industrial regions of northern France, the Benelux, and Lombardy, where nitrogen inputs in the soil benefit "nitrophile" plant species. However, this could lead to climate traps in the future with rising temperatures in Western Europe.

Island species face invasive threats

Island species are particularly vulnerable to invasive exotic species, which are expanding rapidly in the era of global warming and human globalization. In French Polynesia, the miconia plant suffocates local vegetation, while in New Caledonia, electric ants proliferate at the expense of local species.

Invasive species impact on islands

On many islands, cats and rats decimate chick populations. Some species adapt to new environmental conditions by changing their reproductive cycles, with several plant species flowering earlier and birds nesting earlier.

Genetic diversity and survival

Genetic diversity also plays a role in adaptation, with species like the golden-crowned kinglet and certain bumblebee species resisting invasive species due to high genetic diversity. In contrast, species with low genetic diversity, such as the Tasmanian devil, are vulnerable to new pathogens.

Habitat corridors and invasive spread

Protected natural areas and green corridors can help species by preventing habitat fragmentation and preserving migration abilities. However, green corridors can also serve as highways for invasive species, necessitating habitat diversification.

Adaptation limits and climate speed

Scientists observe both the adaptive capacities of life and the challenges posed by the speed of climate change. While some species can adapt, the rapid pace of climate change may outstrip these abilities, as seen in the case of corals, which once lived in polar regions but now lack the time to return.