Species are essential components of ecosystems that support life and provide services to humanity. A reduction in greenhouse gas emissions must occur to avoid climate change impacts on species.
Limited physiological tolerance to warming temperatures are the leading cause of local extinctions; however, other proximate factors also increase extinction risk - these include changes in precipitation patterns and competition from invasive species.
The number of species at risk of extinction
Recent reports estimate that one-third of the world's species may be at risk of extinction, including plants, animals and other organisms. Global warming, deforestation, habitat destruction, pollution and climate change are identified as key threats to biodiversity; furthermore this loss threatens ecosystem services as well as human societies worldwide.
Studies have documented shifts in species' geographic ranges that appear to be tied to climate change. Unfortunately, pinpointing their causes remains difficult - many likely result from death while others could be related to factors like migration or recruitment declines or niche shifts.
Environmental planning and management often overlook these elements of climate change, but their implications should not be disregarded. Beyond forcing some species to relocate, climate change has also caused physiological and behavioral shifts among animals - for instance, warmer temperatures have resulted in earlier breeding seasons for North American tree swallows (Tachycineta bicolor). This change has had serious ramifications on population sizes of this species.
Many species at risk of extinction have yet to be assessed for their susceptibility to climate change, with evaluation limited by long-term monitoring stations available and how frequently their population parameters can be assessed by surveys. In order to make an accurate evaluation, larger databases on population trends over time will need to be created in order to make a thorough assessment.
IUCN estimates there are over two million species on Earth, comprising both animal and plant varieties. While it would be impossible to assess every individual species' risk of extinction in such a vast diversity, the IUCN strives to reevaluate each one using an objective process at least every ten years.
These efforts are critical in determining how many species are at risk of extinction due to climate change. The IUCN prioritizes four metrics when assessing risk to species: (1) its geographical range is decreasing, 2) population is small and declining, (3) growth slower than anticipated in future, 4) its population growth rate increasing.
The number of species that have already gone extinct
Many species face the danger of extinction immediately. Scientists have already revealed that more than 10,967 species listed on the IUCN Red List are already endangered with climate change threatening their populations quickly dwindling away.
Scientists are racing against time to inventory all of Earth's species, but are facing an extinction rate hundreds-to-thousands times higher than any natural average. Before humans arose, about one species per century went extinct; now, this figure hovers closer to 24 per day.
One loss of any species can have far-reaching repercussions for an ecosystem. It may disrupt delicate balance between plants and animals by eliminating pollinators or stirring up nutrients in the soil; alter river flow patterns or change sea colors; in some instances even leading to collapse of an entire system.
Over recent decades, scientists have been able to monitor these changes by studying local extinctions - the disappearance of species from particular areas - which many can trace directly back to climate change and offer key clues as to which species might adapt or survive in response to future warming conditions.
Many studies have used data compiled from historical animal and plant distribution surveys with more recent resurveys to detect shifts in species' geographic distribution (23-27). Shifting temperatures could be driving species into habitats too hot for them; while changing temperatures combined with decreased precipitation could increase water stress levels and lead to species' extinction (23-27).
As global temperatures continue to increase, global extinction rates may accelerate rapidly. A recent climate-change model study using local surveys showed that without adapting or moving into cooler climates by evolution or plasticity, between 57%-70% of 538 tropical survey species may face extinction under extreme temperature scenarios (28).
Researchers have also utilized proximate cause analysis to investigate local extinctions. Rising temperatures may increase the likelihood of wildfires (30), leading to an increase in species extinction rates (31). Alterations in precipitation patterns due to human activities could directly drive an extinction event such as that of an Australian lizard species found on Bramble Cay (32).
The number of species that could go extinct in the next 50 years
Human activities have brought on unprecedented species loss on Earth in millions of years, as human activities encroach on animal habitats, pollute the environment and worsen climate change. Scientists have warned that without swift action taken to safeguard biodiversity, we are at risk of another sixth mass extinction event, with species disappearing faster than they can be replaced; endangering food chains and setting off environmental disasters; however a new global agreement to preserve nature, signed on Dec 19 can play a part but will take time.
All species, once gone forever, leave behind genes, behaviors and interactions that have taken many generations or millennia to evolve. Their loss also deprives ecosystems of vital services provided by them - from pollinating plants to recycling nutrients in soil or controlling pest populations; all functions essential to any ecosystem's survival.
Scientists have long attempted to predict which species will survive a warming world, yet no satisfactory answers have yet been given. Key questions include whether species can adapt by dispersing upwards towards cooler habitats, shifting their climatic niches or both.
Scientists used an existing mammal species database to estimate their extinction risk and advanced computer simulations of evolution to predict how quickly new species would fill in any gaps left by those that no longer existed.
Researchers discovered that more species may become extinct than previously anticipated in a warming world. Their analysis indicates that between 57-70% of all species could become extinct if maximum temperatures increase by two degrees Celsius - similar to other estimates using various climate change scenarios. Extinction rates vary based on habitat availability as well as physiological adaptations such as desiccation stress in desert trees or oxygen shortage at high temperatures in aquatic organisms (Table 2).
The number of species that could go extinct in the next 100 years
New research indicates that animal and plant extinction rates have been steadily rising over recent years, likely continuing to do so as greenhouse gas emissions continue to accumulate at their current rates. This will have significant ramifications on both ecosystems and human societies globally.
As climate change progresses, more species will be at risk of extinction - leading to biodiversity losses and ecosystem services provided to humans by ecosystems. Furthermore, species loss increases vulnerability of plants and animals against other threats like disease transmission.
Habitat destruction and climate change are to blame. Deforestation, overuse of land for agriculture, pollution of water bodies and drying lakes and ponds all contribute to decreasing biological diversity - particularly threatening orangutans whose habitat has been greatly compromised due to forest degradation caused by production of palm oil. Bornean and Sumatran subspecies of orangutan are currently nearing extinction as a result of forest degradation for palm oil production.
One study suggests that global warming will decimate one-third of species by 2030 if current trends persist, leading to irreparable damage to biodiversity and ecological systems around the globe.
Another study reported that millions of species could vanish from Earth within 100 years, including plants, animals and microorganisms like bacteria. This would have serious ramifications for humanity as food supplies would decrease and other vital resources could dwindle significantly.
Climate change poses particular threats to species at the base of food chains, including krill - a crucial source of nutrition for whales, penguins, and seals. Rising Arctic Ocean temperatures are decreasing krill populations rapidly; as such they could eventually go extinct altogether.
Researchers of this study discovered that many species could withstand increases in maximum temperatures up to a certain threshold; after which local extinctions often took place in areas where temperatures exceeded this threshold - although their cause wasn't always immediately apparent.
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