Species and climate change

Threats and responses

Current global mean warming of less than 1ºC above pre-industrial levels has already significantly impacted the Earth’s climate system and the majority of the world’s ecosystems and species.
• The majority of this warming is caused by fossil fuel-generated CO2 which is also causing ocean acidification to occur at an unprecedented rate, with profound ramifications for biodiversity and humanity.
• Observed species-level impacts include exposure to rapidly shifting climate zones, increased extreme weather events, rising sea levels and changes in the distribution and seasonal activities of a wide range of species.
Conserving and restoring terrestrial, freshwater and marine ecosystems – and their component species – need to be recognised as an essential part of climate change mitigation and adaptation policy.
• Urgent mitigation action to stabilise and reduce CO2 levels is essential if catastrophic biodiversity impacts are to be avoided.
• Essential adaptation action needs to include ecosystem protection to ensure as much species resilience as possible and to maintain natural carbon sinks.

What is the issue ?

The combined effects of human-induced global warming and ocean acidification constitute an unprecedented threat to biodiversity and humanity alike. The Intergovernmental Panel on Climate Change (IPCC) confirms that the current global mean warming of less than 1ºC above pre-industrial levels has already significantly impacted the Earth’s climate system and the majority of terrestrial, freshwater and marine ecosystems and species. Observed species-level impacts include exposure to rapidly shifting climate zones, increased extreme weather events, rising sea levels and changes in the distribution and seasonal activities of a wide range of species, including many invasive pest and disease vector species.

The true impact of current warming and ocean acidification levels is being masked by a combination of climate system inertia (it will take many more decades for the full impacts of current carbon dioxide (CO2) levels to be experienced) and biodiversity response lags. The possibility that current climate sensitivity – commonly defined as the amount of warming that results from the doubling of atmospheric CO2 levels – is greater than generally assumed needs to be seriously considered. Greater climate sensitivity severely increases impact risks, and lowers the ‘safe’ target CO2 level, as well as the response time remaining for reaching target levels.

An additional threat factor is the rate at which global warming and ocean acidification are occurring. This is important because the current unparalleled rate of climate change severely limits the ability of species and ecosystems to adapt, increasing their risk of extinction.

Why is it important ?

The widespread species impacts observed to date highlight the major biodiversity impacts associated with projected distribution of novel and disappearing climates by 2100, including current biodiversity hotspot regions. Increasingly severe impacts are certain, and are likely to include disruption and collapse of food webs (e.g. from changes in plankton abundance). Increases in extreme weather events such as hurricanes, droughts and floods will increase the vulnerability of many species. Even relatively modest additional temperature increases are sufficient to compromise many reptiles – along with some bird and fish species – whose sex is temperature-determined. Higher temperatures can increasingly result in feminisation of populations of a wide range of species, compromising breeding success. Extremes in temperature will also affect many species, especially freshwater species, as they are more restricted in their movement and the smaller water bodies they inhabit heat up more rapidly. Species reliant on low-lying coastal habitats, including many migratory species and important fisheries species, will be severely compromised as sea level rise and other environmental stressors affect their viability. Ocean acidification will increasingly directly and indirectly impact a wide range of species reliant on aragonite and calcite concentrations, including corals, molluscs and krill, with serious consequences for entire ecosystems.

Vulnerability of species to climate change

The combination of climate system inertia and the fact that fossil fuel emissions are still tracking IPCC’s high emissions trajectory scenario greatly increases the risk of climate-change driven ‘tipping points’ for major systems. These include the Greenland ice-sheet melt, dieback of the Amazon rainforest and shift of the West African monsoon. Such regional tipping-point sensitivities, and their amplifying feedback risks, need to be taken into account when defining the level of dangerous anthropogenic interference with the climate system. It is the scientific rationale for considering 350 ppm CO2 as the safe planetary boundary for climate change.

Ecoregional global concentration of terrestrial and marine climate change vulnerable species (Pacifici et al. 2015)

What can be done?

The key climate change mitigation action for biodiversity and humanity alike is to stabilise and reduce CO2 levels if truly catastrophic impacts are to be avoided. Conserving and restoring terrestrial, freshwater and marine ecosystems, and their component species, needs to be recognised as essential climate change mitigation and adaptation policy. Ecosystems play a key role in the global carbon cycle (including the sequestration of vast amounts of carbon), conferring adaptive resilience to climate change whilst providing a wide range of ecosystem services essential for human well-being.

Improving threat evaluation and associated response policy is an ongoing challenge, but the severity of threat is already evident, along with the essential mitigation and adaptation actions. It is therefore essential that the latest climate change science and its implications for policy are considered.

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