Assessing Climate Change’s Threat to Biodiversity: Key Findings

Biodiversity forms the foundation of every ecosystem on Earth, from tropical rainforests to deep ocean trenches. Yet climate change is rapidly reshaping which species can survive and where they can live. The consequences are stark: shifting habitats, disrupted seasonal patterns, and growing extinction risks that threaten the intricate web of life supporting human wellbeing. Understanding how climate change affects biodiversity-and which ecosystems face the greatest danger-is essential for effective conservation action.

Observed impacts on species worldwide 🔗

Climate change has already left a measurable imprint on species across the planet. According to IPCC assessments, terrestrial, freshwater, and ocean ecosystems have undergone alterations at a global scale, with clear impacts on ecosystem structure, species geographic ranges, and the timing of seasonal life cycles. These changes are not hypothetical projections-they are happening now.

Range shifts and altered behaviour 🔗

Half of the more than 4,000 species analysed by the IPCC Sixth Assessment Report have shifted their distribution to higher latitudes or elevations in response to rising temperatures. Marine species have been particularly mobile, with plants and animals shifting poleward at an average rate of 59 kilometres per decade as ocean temperatures climb. This reorganisation of marine biodiversity has fundamentally altered ecosystem composition, especially at the ocean surface.

Beyond geographic shifts, species are changing their behaviour and seasonal activities. Breeding times are occurring earlier for many bird species, while flowering and migration patterns have shifted across numerous plant and animal groups. These phenological changes create mismatches in ecological relationships-when pollinators emerge before flowers bloom, or when predators and prey become desynchronised, entire food webs can destabilise.

Local extinctions already documented 🔗

The impacts are not merely about relocation. Local population extinctions caused by climate change have been detected in 47% of 976 species studied. The Bramble Cay melomys became the first mammal officially declared extinct due to climate change, with rising sea levels and storm surge destroying its island habitat. The IUCN reports that climate change currently affects at least 15,801 species on its Red List of Threatened Species, increasing their likelihood of extinction.

Vulnerable ecosystems facing severe threats 🔗

While all ecosystems experience climate impacts, certain habitats face disproportionately severe threats due to their sensitivity, exposure levels, or the specialised species they harbour.

Coral reefs in crisis 🔗

Coral reef ecosystems represent perhaps the most dramatic example of climate vulnerability. The world is currently experiencing its fourth global coral bleaching event, which scientists have called unprecedented. Since January 2023, bleaching-level heat stress has impacted 84% of the world’s coral reef area across at least 83 countries and territories. This far exceeds previous events-during the first global bleaching event in 1998, only 21% of reefs experienced bleaching-level stress.

The severity has escalated dramatically. NOAA’s Coral Reef Watch had to add three new alert levels (Levels 3-5) to their Bleaching Alert Scale because existing metrics could not capture the extreme heat stress corals now face. Level 5 indicates risk of over 80% of all corals on a reef dying from prolonged bleaching.

Rising ocean temperatures cause coral polyps to expel the symbiotic algae living in their tissues, leaving the coral bleached white. If conditions do not improve quickly, the coral dies. Ocean acidification further compounds the problem by reducing the ability of reef-building organisms to form their calcium carbonate structures.

Arctic and polar ecosystems 🔗

The Arctic is warming four times faster than other regions, causing rapid sea ice loss that threatens polar species. Arctic seals face challenges in breeding, raising pups, and accessing foraging areas as the ice platforms they depend on disappear. Cold-adapted species living in polar regions face particularly high extinction risk because climate impacts there are unfolding at maximum speed and extent.

Mountain ecosystems at the edge 🔗

Alpine environments present a unique vulnerability challenge. For every one-degree-Celsius increase in temperature, mountaintop species shift approximately 100 metres upslope. This creates a shrinking habitat scenario-as species move higher, the available land area decreases dramatically. Species already living at summits have nowhere left to go.

Mountain ecosystems represent islands of high-elevation habitat isolated by surrounding lowlands. Changes in environmental conditions particularly threaten endemic species confined to limited areas. The likely climate change losers among mountain plants are late successional species, those with small restricted populations, and species already confined to summits or plains.

Projected future impacts and extinction risks 🔗

Scientific projections paint a concerning picture of accelerating biodiversity loss if warming continues unchecked.

Extinction risk escalates with each degree of warming 🔗

The IPCC Sixth Assessment Report provides extinction risk estimates at different warming levels: at 1.5°C, the median estimate is 9% of species at high extinction risk; at 2°C, this rises to 10%; at 3°C, 12%; and at 5°C, 15%. However, maximum estimates are considerably higher-reaching 48% at 5°C of warming.

A 2024 study published in Science analysed over 30 years of biodiversity research encompassing more than 450 studies. The findings indicate that limiting warming to 1.5°C would put approximately 1 in 50 species (roughly 180,000 species) at extinction risk by 2100. At 2.7°C-the trajectory under current international emissions commitments-1 in 20 species would face extinction risk.

Biodiversity hotspots under pressure 🔗

IPCC assessments of biodiversity hotspots reveal that of 6,116 projections for more than 2,700 species, approximately 44% were found to be at high extinction risk and 24% at very high extinction risk from climate change. The risk intensifies dramatically for endemic species-those found nowhere else on Earth. Endemic species face approximately 10 times greater extinction risk compared to 1.5°C when warming reaches 3°C.

Regional patterns show particular concern for certain areas. Species in South America, Australia, and New Zealand face the greatest threats, while amphibians are the most threatened taxonomic group due to their sensitivity to shifting rainfall patterns and drought conditions.

Warming beyond 2°C brings irreversible changes 🔗

Beyond 2°C of warming, risks of extirpation, extinction, and ecosystem collapse escalate rapidly. With 4°C warming by 2100, mass mortalities and extinctions are expected that would irreversibly alter globally important areas, including tropical coral reefs, cold-water kelp forests, and the world’s rainforests. Under projected warming of approximately 3.2°C, multiple regions across land and sea risk becoming inhospitable to up to 100% of species currently living there.

Endemic and montane species at heightened risk 🔗

Species with narrow climatic ranges, limited dispersal abilities, or restricted geographic distributions face the greatest extinction pressure from climate change.

Why endemic species are especially vulnerable 🔗

Endemic species in biodiversity hotspots face very high extinction risk projections: approximately 100% of endemic species on islands, 84% on mountains, and 54% in marine environments (notably the Mediterranean) are projected to be threatened with extinction from climate change. Their restricted ranges mean they often cannot migrate to suitable habitat when conditions change.

Island species face particular challenges because they literally have nowhere to go. Mountain species experience a similar constraint-as temperatures rise, they can move upslope, but eventually run out of mountain. Climate change causes contraction of elevational ranges for mountain plants, accelerating local extinction threats for alpine endemic species.

Montane species facing habitat squeeze 🔗

The IPCC’s mountain assessment concludes that up to 84% of endemic mountain species may be at extinction risk. Species unable to move to higher elevations or cooler locations face increasing extinction probability, with risks from extreme events like wildfire potentially worsening the situation.

Endemic high mountain species become more vulnerable to local extinction as their distribution is pushed higher. Even if species possess adaptations for extreme conditions, continued range contraction at mountaintops leads to diminishing habitat and population sizes. Alpine plants are adapted to survive extended periods under snow and ice and rely on snowmelt for moisture during short growing seasons. Warmer, drier summers and earlier snowmelt directly challenge their survival.

Uncertainties and research gaps 🔗

Despite substantial scientific understanding of climate impacts on biodiversity, significant uncertainties remain that complicate prediction and management efforts.

Thresholds for irreversible loss 🔗

One of the most challenging questions is identifying precise tipping points beyond which biodiversity loss becomes irreversible. Research synthesising hundreds of studies notes that adding biological complexity to climate models can both enhance or diminish predicted impacts, leading to better estimates for individual species but producing an overall balance in global extinction risk projections. The many unidentified and rare species typically cannot be modelled due to insufficient data, yet they likely face greater-than-average threats-meaning current estimates represent a lower bound on climate change extinctions.

Interaction between climate and other stressors 🔗

Climate change impacts are compounded by other human pressures including habitat loss and fragmentation, hunting, overfishing, pollution, and invasive species introduction. All of these reduce climate resilience, making it difficult to isolate and attribute observed changes solely to climate factors. Understanding how these stressors interact remains an active research frontier.

Adaptive capacity and species responses 🔗

Predicting how individual species will respond involves substantial uncertainty. Some species unexpectedly move their ranges downslope rather than upslope, highlighting how complicated responses to climate change can be. While average patterns may be predictable, individual species responses remain challenging to forecast. This uncertainty underscores the importance of protecting historical data and long-term monitoring programmes that establish baselines for detecting change.

Pathways forward 🔗

Research increasingly points to integrated approaches combining rapid emissions reductions with targeted conservation action. Increasing ecosystem resilience requires minimising additional stresses, reducing habitat fragmentation, expanding natural habitat extent and connectivity, and protecting refugia where microclimates allow species to persist. Restoration efforts offer co-benefits for both biodiversity and climate mitigation when deployed appropriately.

Conservation experts estimate that coral spending needs to increase sevenfold, while limiting global warming to as close to 1.5°C as possible is necessary to give coral conservation measures a chance to succeed. Current climate plans put the world on track for approximately 2.7°C of warming-far above the threshold needed for reef survival.

What do you think? Given that climate change impacts are already measurable across ecosystems worldwide, how should conservation priorities shift to protect species with the narrowest survival margins? And as warming continues, what responsibility do we have to species that cannot adapt quickly enough to survive?

References

1. https://www.ipcc.ch/report/ar6/wg2/downloads/outreach/IPCC_AR6_WGII_FactSheet_Biodiversity.pdf
2. https://en.wikipedia.org/wiki/Extinction_risk_from_climate_change
3. https://www.ipcc.ch/report/ar6/wg2/about/frequently-asked-questions/keyfaq2/
4. https://iucn.org/resources/issues-brief/species-and-climate-change
5. https://www.noaa.gov/news-release/noaa-confirms-4th-global-coral-bleaching-event
6. https://icriforum.org/4gbe-2025/
7. https://coralreefwatch.noaa.gov/satellite/research/coral_bleaching_report.php
8. https://oceanservice.noaa.gov/facts/coralreef-climate.html
9. https://www.sciencedaily.com/releases/2018/09/180910093526.htm
10. https://rm.coe.int/1680746a42
11. https://today.uconn.edu/experts/expert-spotlight/10331/new-study-shows-alarming-rate-of-potential-species-extinction-due-to-climate-change/
12. https://www.ipcc.ch/report/ar6/wg2/chapter/ccp1/
13. https://www.zsl.org/news-and-events/feature/what-does-latest-ipcc-report-mean-wildlife
14. https://www.intechopen.com/chapters/1179664
15. https://www.ipcc.ch/report/ar6/wg2/chapter/ccp5/
16. https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.925296/full
17. https://botanicgardens.uw.edu/about/blog/2023/04/13/climate-change-vulnerability-in-the-alpine/
18. https://www.science.org/doi/10.1126/science.adp4461