Invasive alien species and climate change

What is the issue ? 

An alien species is an animal, plant, or other organism that is introduced by humans, either intentionally or unintentionally, into places outside its natural range.

Globalisation has increased the movement of people and goods around the world, leading to a rise in the number of species introduced to areas outside their natural ranges. Some alien species – classed as “invasive” – become established and negatively impact native biodiversity and ecosystems, and in some cases nature’s contributions to people and good quality of life.

A 2017 study found that over one-third of all introductions in the past 200 years occurred after 1970, and the rate of new introductions is showing no sign of slowing down. In fact, a 2020 study predicts that under a “business as usual” scenario the number of established alien species will increase by 36% through 2050. Current predictions suggest that the situation will be much worse as climate and land- and sea-use change are worsening (IPBES, 2023). Examples of IAS are below:

The Water hyacinth (Eichhornia crassipes) forms a dense cover on the surface of freshwater bodies. Its populations are known to double in as little as 12 days, blocking waterways, limiting boat traffic, and affecting fishing and trade. In Lake Victoria in Eastern Africa, it can grow to such densities that ships are unable to leave docks.

Rats are frequently identified with catastrophic declines of birds on islands, and transmit the plague bacterium via fleas in certain areas of the world.

The Argentine ant (Linepithema humile) is the greatest threat to the survival of various endemic Hawaiian arthropods, including insects and crustaceans. It displaces native ant species, some of which may be important seed-dispersers or plant-pollinators, leading to the disruption of native ecosystems.

The Emerald Ash Borer beetle (Agrilus planipennis) is decimating some of the most prominent ash tree species in North America. It has the potential to destroy over eight billion ash trees.

Interactions amongst drivers of environmental change, including climate change, exacerbate and compound the problem. Extreme climatic events such as hurricanes, floods, and droughts can transport IAS to new areas and increase their spread by decreasing the resistance of habitats to biological invasions. Climate change is also opening up new pathways of introduction of IAS. For example, emerging Arctic shipping passages due to melting ice caps will greatly reduce the time taken for ships to travel from Asia to Europe, increasing the risk of alien species surviving the journey. 

Many IAS have the ability to expand rapidly to higher latitudes and altitudes as the climate warms, outpacing native species. Alien species that are regularly introduced by humans but have so far failed to establish themselves may succeed in doing so as a consequence of climate change creating more favourable conditions for some of these species. 

Some habitats, such as temperate forests and freshwater systems that currently have thermal barriers limiting the establishment of IAS, will become more suitable for alien species as the climate changes.  

Why is it important ?

The increase in the number and spread of IAS will have major and diverse societal and environmental impacts. Invasive alien species are a major threat to global food security and livelihoods. People with the greatest direct dependence on nature may be disproportionately affected by IAS. Developing countries that have high levels of subsistence and smallholder farming are highly vulnerable because they often lack the capacity to prevent and manage biological invasions.

IAS reduce the resilience of natural habitats, making them more vulnerable to the impacts of climate change. For example, some grasses and trees that have become IAS can significantly alter fire regimes, especially in areas that are becoming warmer and drier. This increases the frequency and severity of wildfires and puts habitats, urban areas, and human life at risk. IAS can also impact agricultural systems by reducing crop and animal health. 

The economic costs of IAS and their management are estimated to be $423 billion annually. Of these costs, which are a gross underestimate because of the difficulties in accessing information, 92% are associated with impacts of the IAS and only 8% to their management.

Invasive alien species are among the top drivers of biodiversity loss and species extinctions across the world (IPBES, 2019). Indeed, IAS are responsible either solely or as a contributing factor for 60% of all global extinctions (IPBES, 2023). The majority of known global extinctions (90%) with invasive alien species as one of the major causes have been reported from islands.

What can be done?

The impacts of IAS are amplified and compounded by our changing climate. Policy responses addressing both biological invasions and climate change are critical.

Climate change policies can incorporate IAS by including IAS prevention and control, and by ensuring that measures to address climate change do not increase the threat of IAS. For example, native tree species should be used for carbon sequestration or erosion control rather than introduced species such as Acacia or Eucalyptus occurring outside their native range. Climate change should be also explicitly incorporated into prioritisation approaches for IAS, including risk assessments, to robustly identify those alien species that could become a threat in the future. Those species – known as “sleeper species” – need to be identified and prioritised for eradication or control before they spread and become invasive.

Prevention is the most effective approach to mitigating the impacts of invasive alien species. Managing the pathways of introduction for IAS, including strictly enforced pre-border quarantine, import controls, and border biosecurity is critical to slowing the rate of IAS arriving and establishing globally.

Island ecosystems are particularly vulnerable to climate change and IAS. Measures to prevent the introduction and establishment of IAS on islands, and other vulnerable ecosystems, include effective biosecurity to manage priority pathways of introduction, supported by early warning and rapid eradication to tackle alien species before they become invasive. Cross-border collaboration and international cooperation across sectors is key.

And finally, adequate and sustained resourcing, including capacity building, is critical to ensuring the effectiveness of management programmes. The success of eradication programmes depends on the support and engagement of relevant stakeholders and Indigenous Peoples and local communities.

More information:

IUCN Species Survival Commission

IUCN Global Invasive Species Database (GISD)  

IUCN SSC Invasive Species Specialist Group (ISSG)

Global Register of Introduced and Invasive Species (GRIIS)

IPBES thematic assessment on invasive alien species and their control

Honolulu Challenge on Invasive Alien Species 

Environmental Impact Classification Scheme of Alien Taxa (EICAT)

Kunming-Montreal Global Biodiversity Framework Target 6 on invasive alien species

CBD and IUCN. (2024). Invasive Alien Species Toolkit for Target 6 of the Kunming-Montreal Global Biodiversity Framework

IAS section in the IPCC report, Climate Change 2014: Impacts, Adaptation, and Vulnerability