Coal
forests continued after the Carboniferous rainforest collapse. These
plant fossils are from one of those forests from about 5 million years
after the CRC. However, the composition of the forests changed from a lepidodendron-dominated forest to one of predominantly tree ferns and seed ferns.
The Carboniferous rainforest collapse (CRC) was a minor extinction event that occurred around 305 million years ago in the Carboniferous period. The event occurred at the end of the Moscovian and continued into the early Kasimovian stages of the Pennsylvanian (Upper Carboniferous).
It altered the vast coal forests that covered the equatorial region of Euramerica (Europe and North America). This event may have fragmented the forests into isolated refugia
or ecological "islands", which in turn encouraged dwarfism and, shortly
after, extinction of many plant and animal species. Following the
event, coal-forming tropical forests continued in large areas of the Earth, but their extent and composition were changed.
The rise of rainforests in the Carboniferous greatly altered the landscapes by eroding low-energy, organic-rich anastomosing (braided) river systems with multiple channels and stable alluvial
islands. The continuing evolution of tree-like plants increased
floodplain stability (less erosion and movement) by the density of
floodplain forests, the production of woody debris, and an increase in
complexity and diversity of root assemblages.
Collapse occurred through a series of step changes. First there
was a gradual rise in the frequency of opportunistic ferns in late
Moscovian times. This was followed in the earliest Kasimovian by a major, abrupt extinction of the dominant lycopsids and a change to tree fern-dominated ecosystems. This is confirmed by a 2011 study showing that the presence of meandering and anabranching streams, occurrences of large woody debris, and records of log jams decrease significantly at the Moscovian-Kasimovian boundary. Rainforests were fragmented, forming shrinking 'islands' further and
further apart, and in latest Kasimovian time, rainforests vanished from
the fossil record. Little mixing of different plant assemblages occurred
throughout this transition; floral assemblages were highly discrete and
conservative and gave way to new ones without any transitional floras
intermediate in composition with regards to the preceding one and
succeeding one.
Invertebrates
The
fossil record of insects can be difficult to study, due to the
generally smaller and more delicate nature of their bodies. One study
tabulate the rates of origination and extinction of over 600 terrestrial
and freshwater animal families. Their stratigraphic ranges spanned a
geologic interval from the middle Paleozoic biotic invasion of the land to the Permian–Triassic extinction event.
Insects comprise more than half of the sampled families, most of which
are from tropical Euramerica. This study found a Late Pennsylvanian
extinction pulse that reflects drying climates and the transition of
lycopod to tree fern-dominated land floras.
Vertebrates
Before
the collapse, vertebrate animal species distribution was very
cosmopolitan, with the same species existing across tropical Pangaea.
After the collapse, each surviving rainforest 'island' developed its
own unique mix of species. Many amphibian species became extinct, while
the ancestors of reptiles and mammals diversified into more species
after the initial crisis. These patterns are explained by the theory of insular biogeography,
a concept that explains how evolution progresses when populations are
restricted into isolated pockets. This theory was originally developed
for oceanic islands,
but it can be applied equally well to any other ecosystem that is
fragmented, only existing in small patches and surrounded by another
unsuitable habitat.
According to this theory, the initial impact of habitat fragmentation
is devastating, with most life dying out quickly from lack of
resources. Then, as surviving plants and animals reestablish themselves,
they adapt to their restricted environment to take advantage of the new
allotment of resources, and diversify. After the CRC, each pocket of
life evolved in its own way, resulting in a unique species mix that
ecologists call "endemism".
A 2018 paper challenged this theory, however, finding evidence for
increased cosmopolitanism rather than endemism following the demise of
Carboniferous rainforests.
Carboniferous rainforest collapse is sometimes treated as an extinction factor for large Carboniferous arthropods such as giant griffinflyMeganeura and millipede Arthropleura. It is common theory that high oxygen
levels have led to larger arthropods, and these organisms have been
thought to live in forests. It was said that rainforest collapse led to a
decrease in oxygen concentration and a decrease in the habitat of these
arthropods, leading them to extinction. Later study shows that both griffinflies and Arthropleura more likely lived a forest-independent life, and fossil records of both large griffinflies and Arthropleura are known after rainforest collapse.This means that rainforest collapse and reduced oxygen levels were less involved in their extinction.
Vertebrates
Terrestrially adapted synapsids, the predecessors of the mammal lineage, like Archaeothyris were among the groups who quickly recovered after the collapse.
The sudden collapse affected several large groups. Labyrinthodont amphibians were particularly devastated, while the amniotes (the first members of the sauropsid and synapsid groups) fared better, being physiologically better adapted to the drier conditions.
Amphibians can survive cold conditions by decreasing metabolic
rates and resorting to overwintering strategies (i.e. spending most of
the year inactive in burrows or under logs). However, this is not an
effective way to deal with prolonged unfavourable conditions, especially
desiccation.
Amphibians must return to water to lay eggs, while amniotes have eggs
that have a membrane that retains water and allows gas exchange out of
water. Because amphibians had a limited capacity to adapt to the drier
conditions that dominated Permian environments, many amphibian families
failed to occupy new ecological niches and became extinct. Amphibians also removed the scales of their aquatic ancestors, and breathed with both lungs
and skin (as long as the skin was kept wet). But amniotes re-evolved
scales, now more keratinized, allowing them to conserve water but losing
their cutaneous respiration.
Synapsids and sauropsids acquired new niches faster than amphibians, and new feeding strategies, including herbivory and carnivory, previously only having been insectivores and piscivores. Synapsids in particular became substantially larger than before and
this trend would continue until the Permian–Triassic extinction event,
after which their cynodont (mammal ancestors) descendants became smaller and nocturnal, though dicynodonts trended towards larger sizes throughout the Triassic.
Possible causes
Atmosphere and climate
There are several hypotheses about the nature and cause of the Carboniferous rainforest collapse, some of which include climate change. After the late Bashkirian glacial maximum of the Late Paleozoic Ice Age I, around 318 Ma, frequent shifts in seasonality from humid to arid times began.
The Carboniferous period is characterised by the formation of
coal deposits which were formed within a context of the removal of
atmospheric carbon. In the latest Middle Pennsylvanian (late Moscovian) a
cycle of aridification began, coinciding with abrupt faunal changes in marine and terrestrial species. This change was recorded in paleosols, which reflect a period of overall decreased hydromorphy,
increased free-drainage and landscape stability, and a shift in the
overall regional climate to drier conditions in the Upper Pennsylvanian
(Missourian). This is consistent with climate interpretations based on
contemporaneous paleo-floral assemblages and geological evidence.
At the time of the Carboniferous rainforest collapse, the climate
became cooler and drier. This is reflected in the rock record as the
Earth entered a short, intense ice age. Sea levels dropped by about 100
metres (330 ft), and glacial ice covered most of the southern continent
of Gondwana. The climate was unfavourable to rainforests and much of the
biodiversity in them. Rainforests shrank into isolated patches mostly
confined to wet valleys further and further apart. Little of the
original lycopsid rainforest biome survived this initial climate crisis.
The concentration of carbon dioxide in the atmosphere crashed to one of
its all time global lows in the Pennsylvanian and early Permian. As the climate became drier through the Late Paleozoic, rainforests were eventually replaced by seasonally dry biomes.
Volcanism
After restoring the middle of the Skagerrak-Centered Large Igneous Province using a new reference frame, it has been shown that the Skagerrakplume rose from the core–mantle boundary to its ~300 Ma position. The major eruption interval took place in very narrow time interval, of 297 Ma ± 4 Ma. The rift formation coincides with the Moskovian/Kasimovian boundary and the Carboniferous rainforest collapse.
Geography
While the CRC affected the equatorial region of Euramerica, the collapse had no effect in the region of Cathaysia
to the east (which mostly corresponds to modern China), where
Carboniferous-like rainforests persisted until the end of the Permian,
around 252 million years ago.
The Joggins Fossil Cliffs on Nova Scotia's Bay of Fundy,
a UNESCO World Heritage Site, is a particularly well-preserved fossil
site. Fossil skeletons embedded in the crumbling sea cliffs were
discovered by Sir Charles Lyell in 1852. In 1859, his colleague William Dawson discovered the oldest known reptile-ancestor, Hylonomus lyelli, and since then hundreds more skeletons have been found, including the oldest synapsid, Protoclepsydrops.
Summary
of major environmental-change categories that cause biodiversity loss.
The data is expressed as a percentage of human-driven change (in red)
relative to baseline (blue), as of 2021. Red indicates the percentage of
the category that is damaged, lost, or otherwise affected, whereas blue
indicates the percentage that is intact, remaining, or otherwise
unaffected.
Biodiversity loss happens when species disappear completely from Earth (extinction)
or when there is a decrease or disappearance of species in a specific
area. Biodiversity loss means that there is a reduction in biological diversity
in a given area. The decrease can be temporary or permanent. It is
temporary if the damage that led to the loss is reversible in time, for
example through ecological restoration.
If this is not possible, then the decrease is permanent. The cause of
most of the biodiversity loss is, generally speaking, human activities
that push the planetary boundaries too far. These activities include habitat destruction (for example deforestation) and land use intensification (for example monoculture farming). Further problem areas are air and water pollution (including nutrient pollution), over-exploitation, invasive species and climate change.
Many scientists, along with the Global Assessment Report on Biodiversity and Ecosystem Services, say that the main reason for biodiversity loss is a growing human population because this leads to human overpopulation and excessive consumption. Others disagree, saying that loss of habitat is caused mainly by "the
growth of commodities for export" and that population has very little to
do with overall consumption. More important are wealth disparities
between and within countries. In any case, all contemporary biodiversity loss has been attributed to human activities.
Climate change is another threat to global biodiversity. For example, coral reefs—which are biodiversity hotspots—will be lost by the year 2100 if global warming continues at the current rate. Still, it is the general habitat destruction (often for expansion of
agriculture), not climate change, that is currently the bigger driver of
biodiversity loss. Invasive species and other disturbances have become more common in
forests in the last several decades. These tend to be directly or
indirectly connected to climate change and can cause a deterioration of
forest ecosystems.
Groups that care about the environment have been working for many
years to stop the decrease in biodiversity. Nowadays, many global
policies include activities to stop biodiversity loss. For example, the UN Convention on Biological Diversity aims to prevent biodiversity loss and to conserve wilderness areas. However, a 2020 United Nations Environment Programme report found that most of these efforts had failed to meet their goals. For example, of the 20 biodiversity goals laid out by the Aichi Biodiversity Targets in 2010, only six were "partially achieved" by 2020.
This ongoing global extinction is also called the holocene extinction or sixth mass extinction.
The current rate of global biodiversity loss is estimated to be 100 to 1000 times higher than the (naturally occurring) background extinction rate, faster than at any other time in human history,and is expected to grow in the upcoming years. The fast-growing extinction trends of various animal groups like
mammals, birds, reptiles, amphibians, and fish have led scientists to
declare a current biodiversity crisis in both land and ocean ecosystems.
In 2006, many more species were formally classified as rare or endangered or threatened; moreover, scientists have estimated that millions more species are at risk that have not been formally recognized.
Deforestation also plays a large role in biodiversity loss. More
than half of the worlds biodiversity is hosted in tropical rainforest. Regions that are subjected to exponential loss of biodiversity are referred to as biodiversity hotspots.
Since 1988 the hotspots increased from 10 to 34. Of the total 34
hotspots currently present, 16 of them are in tropical regions (as of
2006). Researchers have noted in 2006 that only 2.3% of the world is covered
with biodiversity loss hotspots, and even though only a small percentage
of the world is covered in hotspots, it host a large fraction (50%) of vascular plant species.
In 2021, about 28 percent of the 134,400 species assessed using the IUCN Red List criteria are now listed as threatened with extinction—a total of 37,400 species compared to 16,119 threatened species in 2006.
A 2022 study that surveyed more than 3,000 experts found that
"global biodiversity loss and its impacts may be greater than previously
thought", and estimated that roughly 30% of species "have been globally
threatened or driven extinct since the year 1500."
Research published in 2023 found that, out of 70,000 species,
about 48% are facing decreasing populations due to human activities,
while only 3% are seeing an increase in populations.
Biologists define biodiversity as the "totality of genes, species and ecosystems of a region". To measure biodiversity loss rates for a particular location, scientists record the species richness and its variation over time in that area. In ecology, local abundance is the relative representation of a species in a particular ecosystem. It is usually measured as the number of individuals found per sample. The ratio of abundance of one species to one or multiple other species living in an ecosystem is called relative species abundance. Both indicators are relevant for computing biodiversity.
An October 2020 analysis by Swiss Re found that one-fifth of all countries are at risk of ecosystem collapse as the result of anthropogenic habitat destruction and increased wildlife loss. If these losses are not reversed, a total ecosystem collapse could ensue.
In 2022, the World Wildlife Fund reported an average population decline of 68% between 1970 and 2016 for 4,400
animal species worldwide, encompassing nearly 21,000 monitored
populations.
An annual decline of 5.2% in flying insect biomass found in nature reserves in Germany – about 75% loss in 26 years
Insects are the most numerous and widespread class in the animal kingdom, accounting for up to 90% of all animal species. In the 2010s, reports emerged about the widespread decline in populations across multiple insect orders. The reported severity shocked many observers, even though there had been earlier findings of pollinator decline.
There have also been anecdotal reports of greater insect abundance
earlier in the 20th century. Many car drivers know this anecdotal
evidence through the windscreen phenomenon, for example. Causes for the decline in insect population are similar to those driving other biodiversity loss. They include habitat destruction, such as intensive agriculture, the use of pesticides (particularly insecticides), introduced species, and – to a lesser degree and only for some regions – the effects of climate change. An additional cause that may be specific to insects is light pollution (research in that area is ongoing).
Most commonly, the declines involve reductions in abundance,
though in some cases entire species are going extinct. The declines are
far from uniform. In some localities, there have been reports of
increases in overall insect population, and some types of insects appear
to be increasing in abundance across the world. Not all insect orders are affected in the same way; most affected are bees, butterflies, moths, beetles, dragonflies and damselflies.
Many of the remaining insect groups have received less research to
date. Also, comparative figures from earlier decades are often not
available. In the few major global studies, estimates of the total number of
insect species at risk of extinction range between 10% and 40%, though all of these estimates have been fraught with controversy.
Earthworms
Earthworm on plant
Scientists have studied loss of earthworms
from several long-term agronomic trials. They found that relative
biomass losses of minus 50–100% (with a mean of minus 83%) match or
exceed those reported for other faunal groups. Thus it is clear that earthworms are similarly depleted in the soils of fields used for intensive agriculture. Earthworms play an important role in ecosystem function, helping with biological processing in soil, water, and even greenhouse gas balancing. There are five reasons for the decline of earthworm diversity: "(1) soil degradation
and habitat loss, (2) climate change, (3) excessive nutrient and other
forms of contamination load, (4) over-exploitation and unsustainable
management of soil, and (5) invasive species".
Factors like tillage practices and intensive land use decimate the soil
and plant roots that earthworms use to create their biomass. This interferes with carbon and nitrogen cycles.
Knowledge of earthworm species diversity is quite limited as not even 50% of them have been described. Sustainable agriculture methods could help prevent earthworm diversity decline, for example reduced tillage. The Secretariat of the Convention on Biological Diversity is trying to take action and promote the restoration and maintenance of the many diverse species of earthworms.
Amphibians
The golden toad of Monteverde, Costa Rica, was among the first casualties of amphibian declines. Formerly abundant, it was last seen in 1989.
Since the 1980s, decreases in amphibian populations, including population decline and localized mass extinctions,
have been observed in locations all over the world. This type of
biodiversity loss is known as one of the most critical threats to global
biodiversity. The possible causes include habitat destruction and modification, diseases, exploitation, pollution, pesticide use, introduced species, and ultraviolet-B
radiation (UV-B). However, many of the causes of amphibian declines are
still poorly understood, and the topic is currently a subject of
ongoing research.
Modeling results found that the current extinction rate of amphibians could be 211 times greater than the background extinction rate. This estimate even goes up to 25,000–45,000 times if endangered species are also included in the computation.
The decline of wild mammal
populations globally has been an occurrence spanning over the past
50,000 years, at the same time as the populations of humans and
livestock have increased. Nowadays, the total biomass of wild mammals on
land is believed to be seven times lower than its prehistoric values,
while the biomass of marine mammals had declined fivefold. At the same
time, the biomass of humans is "an order of magnitude
higher than that of all wild mammals", and the biomass of livestock
mammals like pigs and cattle is even larger than that. Even as wild
mammals had declined, the growth in the numbers of humans and livestock
had increased total mammal biomass fourfold. Only 4% of that increased
number are wild mammals, while livestock and humans amount to 60% and
36%. Alongside the simultaneous halving of plant biomass, these striking
declines are considered part of the prehistoric phase of the Holocene extinction.
Since the second half of the 20th century, a range of protected areas and other wildlife conservation efforts (such as the Repopulation of wolves in Midwestern United States) have been implemented. These have had some impact on preserving wild mammal numbers. There is still some debate over the total extent of recent declines in wild mammals and other vertebrate species. In any case, many species are now in a worse state than decades ago. Hundreds of species are critically endangered.Climate change also has negative impacts on land mammal populations.
Some pesticides, like insecticides, likely play a role in reducing the populations of specific bird species. According to a study funded by BirdLife International, 51 bird species are critically endangered and eight could be classified as extinct or in danger of extinction. Nearly 30% of extinction is due to hunting and trapping for the exotic pet trade. Deforestation,
caused by unsustainable logging and agriculture, could be the next
extinction driver, because birds lose their habitat and their food.
While plants are essential for human survival, they have not received the same attention as the conservation of animals. It is estimated that a third of all land plant species are at risk of
extinction and 94% have yet to be evaluated in terms of their
conservation status. Plants existing at the lowest trophic level require increased conservation to reduce negative impacts at higher trophic levels.
In 2022, scientists warned that a third of tree species are
threatened with extinction. This will significantly alter the world's
ecosystems because their carbon, water and nutrient cycles will be affected. Forest areas are degraded due to common factors such as logging, fire, and firewood harvesting. The GTA (global tree assessment) has determined that "17,510 (29.9%)
tree species are considered threatened with extinction. In addition,
there are 142 tree species recorded as Extinct or Extinct in the Wild."
Possible solutions can be found in some silvicultural methods of forest management that promote tree biodiversity, such as selective logging, thinning or crop tree management, and clear cutting and coppicing. Without solutions, secondary forests recovery in species richness can take 50 years to recover the same amount as the primary forest, or 20 years to recover 80% of species richness.
Flowering plants
Viola calcarata, a species highly vulnerable to climate change.
Relatively few plant diversity assessments currently consider climate change, yet it is starting to impact plants
as well. About 3% of flowering plants are very likely to be driven
extinct within a century at 2 °C (3.6 °F) of global warming, and 10% at
3.2 °C (5.8 °F). In worst-case scenarios, half of all tree species may be driven extinct by climate change over that timeframe.
Freshwater species
Freshwater ecosystems
such as swamps, deltas, and rivers make up 1% of earth's surface. They
are important because they are home to approximately one third of vertebrate species. Freshwater species are beginning to decline at twice the rate of
species that live on land or in the ocean. This rapid loss has already
placed 27% of 29,500 species dependent on fresh water on the IUCN Red List.
Global populations of freshwater fish are collapsing due to water pollution and overfishing.
Migratory fish populations have declined by 76% since 1970, and large
"megafish" populations have fallen by 94% with 16 species declared
extinct in 2020.
Marine biodiversity encompasses any living organism that resides in the ocean or in estuaries. By 2018, approximately 240,000 marine species had been documented. But many marine species—estimates range between 178,000 and 10 million oceanic species—remain to be described. It is therefore likely that a number of rare species (not seen for
decades in the wild) have already disappeared or are on the brink of
extinction, unnoticed.
Human activities have a strong and detrimental influence on
marine biodiversity. The main drivers of marine species extinction are
habitat loss, pollution, invasive species, and overexploitation.Greater pressure is placed on marine ecosystems near coastal areas because of the human settlements in those areas.
Overexploitation has resulted in the extinction of over 25 marine species. This includes seabirds, marine mammals, algae, and fish.Examples of extinct marine species include Steller's sea cow (Hydrodamalis gigas) and the Caribbean monk seal (Monachus tropicalis). Not all extinctions are because of humans. For example, in the 1930s, the eelgrass limpet (Lottia alveus) became extinct in the Atlantic once the Zostera marinaseagrass population declined upon exposure to a disease. The Lottia alveus were greatly impacted because the Zostera marina were their sole habitats.
Land use intensification (and ensuing land loss/habitat loss); a significant factor in loss of ecological services due to direct effects as well as biodiversity loss
Earth's 25 terrestrial hot spots of biodiversity. These regions contain a high number of plant and animal species and have been subjected to high levels of habitat destruction by human activity, leading to biodiversity loss.Deforestation and increased road-building in the Amazon rainforest in Bolivia
cause significant concern because of increased human encroachment upon
wild areas, increased resource extraction and further threats to
biodiversity.
Habitat destruction (also termed habitat loss or habitat reduction) occurs when a natural habitat is no longer able to support its native species. The organisms once living there have either moved elsewhere, or are dead, leading to a decrease in biodiversity and species numbers. Habitat destruction is in fact the leading cause of biodiversity loss and species extinction worldwide.
The direct effects of urban growth on habitat loss are well
understood: building construction often results in habitat destruction
and fragmentation. This leads to selection for species that are adapted to urban environments. Small habitat patches cannot support the level of genetic or taxonomic
diversity they formerly could while some more sensitive species may
become locally extinct. Species abundance
populations are reduced due to the reduced fragmented area of habitat.
This causes an increase of species isolation and forces species toward
edge habitats and to adapt to foraging elsewhere. Additionally, edge effects often result in altered light, temperature,
and humidity conditions that change vegetation structure and
microhabitat suitability, further reducing biodiversity in fragmented
urban patches. Urban environments also favor fast-reproducing, mobile species,
contributing to biotic homogenization and the global decline of
ecological uniqueness.
Infrastructure development in Key Biodiversity Areas (KBA) is a major driver of biodiversity loss, with infrastructure present in roughly 80% of KBAs. Infrastructure development leads to conversion and fragmentation of
natural habitat, pollution and disturbance. There can also be direct
harm to animals through collisions with vehicles and structures. This
can have impacts beyond the infrastructure site. For example, chronic noise from roads can interfere with bird song used
in mating and territory defense, reducing reproductive success. Artificial lighting can disrupt nocturnal foraging patterns,
predator-prey interactions, and migratory navigation in species such as
bats, amphibians, and sea turtles. Infrastructure can also create ecological traps, where animals are
drawn to altered environments that ultimately reduce their fitness or
survival. Furthermore, road mortality and bird collisions with buildings
and power lines cause direct harm to wildlife, with cascading impacts
across trophic levels. These impacts often extend well beyond the
development footprint and may disrupt landscape connectivity critical
for migration and climate adaptation. Fragmented landscapes also impede
species' range shifts in response to climate change, making it harder
for populations to track suitable environmental conditions and
increasing extinction risk.
Humans are changing the uses of land in various ways, and each can lead to habitat destruction and biodiversity loss. The 2019 Global Assessment Report on Biodiversity and Ecosystem Services found that industrial agriculture is the primary driver of biodiversity collapse. The UN's Global Biodiversity Outlook 2014 estimated that 70% of the projected loss of terrestrial biodiversity is caused by agriculture use.This is supported by more recent findings from the 2022 Global Land Outlook
report by the UN Convention to Combat Desertification, which states
that over 50% of agricultural land is moderately or severely degraded. According to a 2005 publication, "Cultivated systems [...] cover 24% of Earth's surface". The publication defined cultivated areas
as "areas in which at least 30% of the landscape is in croplands,
shifting cultivation, confined livestock production, or freshwater
aquaculture in any particular year".As
of 2023, approximately 38% of the Earth's terrestrial surface is used
for agriculture, including grazing and crop production, making it the
dominant land use globally.
More than 17,000 species are at risk of losing habitat by 2050 as
agriculture continues to expand to meet future food needs (as of 2020). A global shift toward largely plant-based diets would free up land to allow for the restoration of ecosystems and biodiversity. In the 2010s over 80% of all global farmland was used to rear animals. Recent FAO data shows that livestock systems occupy about 77% of
agricultural land while providing less than 20% of the global calorie
supply — highlighting an imbalance between land use and nutritional
output.
As of 2022, 44% of Earth's land area required conservation attention, which may include declaring protected areas and following land-use policies. Additionally, a 2023 analysis in Science Advances
concluded that at least 30% of land must be actively protected and
ecologically restored by 2030 to meet global biodiversity goals,
aligning with the Kunming-Montreal Global Biodiversity Framework agreed
upon at COP15.
Industrial processes contributing to air pollution through the emission of carbon dioxide, sulfur dioxide, and nitrous oxide.
Air pollution adversely affects biodiversity. Pollutants are emitted into the atmosphere by the burning of fossil fuels and biomass, for example. Industrial and agricultural activity releases the pollutants sulfur dioxide and nitrogen oxides. Once sulfur dioxide and nitrogen oxide are introduced into the atmosphere, they can react with cloud droplets (cloud condensation nuclei), raindrops, or snowflakes, forming sulfuric acid and nitric acid. With the interaction between water droplets and sulfuric and nitric acids, wet deposition occurs and creates acid rain.
A 2009 review studied four air pollutants (sulfur, nitrogen, ozone, and mercury) and several types of ecosystems. Air pollution affects the functioning and biodiversity of terrestrial as well as aquatic ecosystems. For example, "air pollution causes or contributes to acidification of lakes, eutrophication of estuaries and coastal waters, and mercury bioaccumulation in aquatic food webs".
Noise generated by traffic, ships, vehicles, and aircraft can affect
the survivability of wildlife species and can reach undisturbed
habitats. Noise pollution is common in marine ecosystems, affecting at least 55 marine species. One study found that as seismic noises and naval sonar increases in marine ecosystems, cetacean diversity decreases (including whales and dolphins). Multiple studies have found that fewer fishes, such as cod, haddock, rockfish, herring, sand seal, and blue whiting, have been spotted in areas with seismic noises, with catch rates declining by 40–80%.
Noise pollution has also altered avian communities and diversity.
Noise can reduce reproductive success, minimize nesting areas, increase
stress response, and reduce species abundance. Noise pollution can alter the distribution and abundance of prey species, which can then impact predator populations.
Pollution from fossil fuel extraction
Potential for biodiversity loss from future fossil fuel extraction: Proportions of oil and gas field area overlapping with Protected Areas
(PAs) (gray polygons) of different IUCN Protected Area management
categories by UN regions: North America (a), Europe (b), West Asia (c),
LAC (d), Africa (e), and Asia Pacific (f). Absolute area of overlap
across all IUCN management categories is shown above histograms.
Location of fields overlapping with PAs are shown in (g). Shading is
used so that points can be visualized even where their spatial locations
coincide, so darker points indicate higher densities of fields
overlapping PAs.
Fossil fuel extraction and associated oil and gas pipelines have major impacts on the biodiversity of many biomes due to land conversion, habitat loss and degradation, and pollution. An example is the Western Amazon region. Exploitation of fossil fuels there has had significant impacts on biodiversity. As of 2018, many of the protected areas with rich biodiversity were in areas containing unexploited fossil fuel reserves worth between $3 and $15 trillion. The protected areas may be under threat in future.
Many commercial fishes have been overharvested: a 2020 FAO report classified as overfished 34% of the fish stocks of the world's marine fisheries. By 2020, global fish populations had declined 38% since 1970.
The changing distribution of the world's land mammals in tonnes of carbon. The biomass of wild land mammals has declined by 85% since the emergence of humans.
The world's population numbered nearly 7.6 billion as of mid-2017 and
is forecast to peak toward the end of the 21st century at 10–12 billion
people. Scholars have argued that population size and growth, along with overconsumption, are significant factors in biodiversity loss and soil degradation. Review articles, including the 2019 IPBESreport, have also noted that human population growth and overconsumption are significant drivers of species decline. A 2022 study warned that conservation efforts will continue to fail if
the primary drivers of biodiversity loss continue to be ignored,
including population size and growth.
Other scientists have criticized the assertion that population growth is a key driver for biodiversity loss. They argue that the main driver is the loss of habitat, caused by "the
growth of commodities for export, particularly soybean and oil-palm,
primarily for livestock feed or biofuel consumption in higher income economies." Because of the wealth disparities between countries, there is a
negative correlation between a country's total population and its per
capita footprint. On the other hand, the correlation between a country's
GDP and its footprint is strong. The study argues that population as a metric is unhelpful and counterproductive for tackling environmental challenges.
The term invasive is poorly defined and often very subjective. The European Union defines invasive alien species as those outside their natural distribution area that threaten biological diversity. Biotic invasion is considered one of the five top drivers of global biodiversity loss and is increasing because of tourism and globalization. This may be particularly true in poorly regulated fresh water systems, though quarantines and ballast water rules have improved the situation.
Invasive species may drive local native species to extinction via competitive exclusion, niche displacement, or hybridisation
with related native species. Therefore, alien invasions may result in
extensive changes in the structure, composition and global distribution
of the biota at sites of introduction. This leads to the homogenisation
of the world's fauna and flora and biodiversity loss.
Climate change
The relationship between the magnitude of climate variability and change (including both large increases and decreases in global temperature) and the extinction rate, over the past 450 million years. This graph does not include the recent human made climate change.
Climate change is another threat to global biodiversity. But habitat destruction, e.g., for the expansion of agriculture, is currently a more significant driver of biodiversity loss.
A 2021 collaborative report by scientists from the IPBES and the IPCC
found that biodiversity loss and climate change must be addressed
simultaneously, as they are inextricably linked and have similar effects
on human well-being. In 2022, Frans Timmermans, Vice-President of the European Commission, said that people are less aware of the threat of biodiversity loss than they are of the threat of climate change.
The interaction between climate change and invasive species is complex and not easy to assess. Climate change is likely to favour some invasive species and harm others, but few authors have identified specific consequences of climate change for invasive species.
Invasive species and other disturbances have become more common in forests
in the last several decades. These tend to be directly or indirectly
connected to climate change and have negative consequences for forest
ecosystems.
Decline in arctic sea ice extent (area) from 1979 to 2022
Decline in arctic sea ice volume from 1979 to 2022
Climate change contributes to destruction of some habitats, endangering various species. For example:
Climate change causes rising sea levels which will threaten natural habitats and species globally.
Melting sea ice destroys habitat for some species. For example, the decline of sea ice in the Arctic
has been accelerating during the early twenty‐first century, with a
decline rate of 4.7% per decade (it has declined over 50% since the
first satellite records). One well known example of a species affected is the polar bear, whose habitat in the Arctic is threatened. Algae can also be affected when it grows on the underside of sea ice.
Warm-water coral reefs are very sensitive to global warming and ocean acidification. Coral reefs provide a habitat for thousands of species. They provide ecosystem services such as coastal protection and food. But 70–90% of today's warm-water coral reefs will disappear even if warming is kept to 1.5 °C (2.7 °F). For example, Caribbean coral reefs – which are biodiversity hotspots – will be lost within the century if global warming continues at the current rate.
Extinction risks
Relative
to now, key areas for wildlife will retain less of their biodiversity
under 2 °C (3.6 °F) of global warming, and even less under 4.5 °C
(8.1 °F).
There are several plausible pathways that could lead to plant and animalspeciesextinction from climate change. Every species has evolved to exist within a certain ecological niche, but climate change leads to changes of temperature and average weather patterns. These changes can push climatic conditions outside of the species' niche, and ultimately render it extinct. Normally, species faced with changing conditions can either adapt in place through microevolution
or move to another habitat with suitable conditions. However, the speed
of recent climate change is very fast. Due to this rapid change, for
example cold-blooded animals (a category which includes amphibians, reptiles and all invertebrates) may struggle to find a suitable habitat within 50 km of their current location at the end of this century (for a mid-range scenario of future global warming).
Biodiversity loss has bad effects on the functioning of ecosystems. This in turn affects humans, because affected ecosystems can no longer provide the same quality of ecosystem services, such as crop pollination, cleaning air and water, decomposing waste, and providing forest products as well as areas for recreation and tourism.
Two key statements of a 2012 comprehensive review of the previous 20 years of research include:
"There is now unequivocal evidence that biodiversity loss
reduces the efficiency by which ecological communities capture
biologically essential resources, produce biomass, decompose and recycle
biologically essential nutrients"; and
"Impacts of diversity loss on ecological processes might be
sufficiently large to rival the impacts of many other global drivers of
environmental change"
Permanent globalspecies loss (extinction) is a more dramatic phenomenon than regional changes in species composition. But even minor changes from a healthy stable state can have a dramatic influence on the food web and the food chain, because reductions in one species can adversely affect the entire chain (coextinction). This can lead to an overall reduction in biodiversity, unless alternative stable states of the ecosystem are possible.
For example, a study on grasslands
used manipulated grassland plant diversity and found that ecosystems
with higher biodiversity show more resistance of their productivity to
climate extremes.
On food and agriculture
An infographic describing the relationship between biodiversity and food.
In 2019, the UN's Food and Agriculture Organization (FAO) produced its first report on The State of the World's Biodiversity for Food and Agriculture.
It warned that "Many key components of biodiversity for food and
agriculture at genetic, species and ecosystem levels are in decline."
The report also said, "Many of the drivers that have negative
impacts on BFA (biodiversity for food and agriculture), including
overexploitation, overharvesting, pollution, overuse of external inputs,
and changes in land and water management, are at least partially caused
by inappropriate agricultural practices"
and "transition to intensive production of a reduced number of species,
breeds and varieties, remain major drivers of loss of BFA and ecosystem
services."
To reduce biodiversity loss related to agricultural practices,
FAO encourages the use of "biodiversity-friendly management practices in
crop and livestock production, forestry, fisheries and aquaculture".
On health and medicines
The
WHO has analyzed how biodiversity and human health are connected:
"Biodiversity and human health, and the respective policies and
activities, are interlinked in various ways. First, biodiversity gives
rise to health benefits. For example, the variety of species and
genotypes provide nutrients and medicines." The ongoing drivers and effects of biodiversity loss has the potential to lead to future zoonotic disease outbreaks like the COVID-19 pandemic.
Medicinal and aromatic plants are widely used in traditional medicine as well as in cosmetic and food industries. The WHO estimated in 2015 that about "60,000 species are used for their medicinal, nutritional and aromatic properties". There is a global trade in plants for medicinal purposes.
Biodiversity contributes to the development of pharmaceuticals. A significant proportion of medicines are derived from natural products, either directly or indirectly. Many of these natural products come from marine ecosystems. However, unregulated and inappropriate over-harvesting (bioprospecting) could potentially lead to overexploitation, ecosystem degradation and loss of biodiversity. Users and traders harvest plants for traditional medicine either by
planting them or by collecting them in the wild. In both cases,
sustainable medicinal resource management is important.
Red List Index
(2019): The Red List Index (RLI) defines the conservation status of
major species groups, and measures trends in the proportion of species
expected to remain extant in the near future without additional
conservation action. An RLI value of 1.0 equates to all species being
categorised as 'Least Concern', and hence that none are expected to go
extinct in the near future. A value of 0 indicates that all species have
gone extinct.
Scientists are investigating what can be done to address biodiversity
loss and climate change together. For both of these crises, there is a
need to "conserve enough nature and in the right places". A 2020 study found that "beyond the 15% land area currently protected,
35% of land area is needed to conserve additional sites of particular
importance for biodiversity and stabilize the climate."
Additional measures for protecting biodiversity, beyond just
environmental protection, are important. Such measures include
addressing drivers of land use change, increasing efficiency in agriculture, and reducing the need for animal agriculture. The latter could be achieved by increasing the shares of plant-based diets.
Many governments have conserved portions of their territories under the Convention on Biological Diversity (CBD), a multilateral treaty signed in 1992–3. The 20 Aichi Biodiversity Targets are part of the CBD's Strategic Plan 2011–2020 and were published in 2010. Aichi Target Number 11 aimed to protect 17% of terrestrial and inland water areas and 10% of coastal and marine areas by 2020.
Of the 20 biodiversity goals laid out by the Aichi Biodiversity Targets in 2010, only six were partially achieved by 2020.The 2020 CBD report highlighted that if the status quo does not change,
biodiversity will continue to decline due to "currently unsustainable
patterns of production and consumption, population growth and
technological developments". The report also singled out Australia, Brazil, Cameroon and the Galapagos Islands (Ecuador) for having had one of its animals lost to extinction in the previous ten years.
Following this, the leaders of 64 nations and the European Union pledged to halt environmental degradation
and restore the natural world. The pledge was not signed by leaders
from some of the world's biggest polluters, namely China, India, Russia,
Brazil and the United States. Some experts contend that the United States' refusal to ratify the
Convention on Biological Diversity is harming global efforts to halt the
extinction crisis.
Scientists say that even if the targets for 2020 had been met, no
substantial reduction of extinction rates would likely have resulted. Others have raised concerns that the Convention on Biological Diversity
does not go far enough, and argue the goal should be zero extinctions
by 2050, along with cutting the impact of unsustainable food production
on nature by half. That the targets are not legally binding has also been subject to criticism.
In December 2022, every country except the United States and the Holy See signed onto the Kunming-Montreal Global Biodiversity Framework at the 2022 United Nations Biodiversity Conference. This framework calls for protecting 30% of land and oceans by 2030 (30 by 30).
It also has 22 other targets intended to reduce biodiversity loss. At
the time of signing the agreement, only 17% of land territory and 10% of
ocean territory were protected. The agreement includes protecting the
rights of Indigenous peoples
and changing the current subsidy policy to one better for biodiversity
protection, but it takes a step backward in protecting species from
extinction in comparison to the Aichi Targets. Critics said the agreement does not go far enough to protect biodiversity, and that the process was rushed.
The United Nations' Sustainable Development Goal 15
(SDG 15), "Life on Land", includes biodiversity targets. Its fifth
target is: "Take urgent and significant action to reduce the degradation
of natural habitats, halt the loss of biodiversity and, by 2020, protect and prevent the extinction of threatened species." This target has one indicator: the Red List Index.
Nearly three-quarters of bird species, two thirds of mammals and more than half of hard corals have been recorded at World Heritage Sites,
even though they cover less than 1% of the planet. Countries with World
Heritage Sites can include them in their national biodiversity
strategies and action plans.
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