Unchecked global warming could affect most terrestrial ecoregions. Increasing global temperature means that ecosystems will change; some species are being forced out of their habitats (possibly to extinction) because of changing conditions, while others are flourishing. Secondary effects of global warming, such as lessened snow cover, rising sea levels, and weather changes, .may influence not only human activities but also the ecosystem.
For the IPCC Fourth Assessment Report, experts assessed the literature on the impacts of climate change on ecosystems. Rosenzweig et al. (2007) concluded that over the last three decades, human-induced warming had likely had a discernible influence on many physical and biological systems (p. 81). Schneider et al. (2007) concluded, with very high confidence, that regional temperature trends had already affected species and ecosystems around the world (p. 792). With high confidence, they concluded that climate change would result in the extinction of many species and a reduction in the diversity of ecosystems (p. 792).
Studying the association between Earth climate and extinctions over the past 520 million years, scientists from the University of York write, "The global temperatures predicted for the coming centuries may trigger a new ‘mass extinction event’, where over 50 percent of animal and plant species would be wiped out."
Many of the species at risk are Arctic and Antarctic fauna such as polar bears and emperor penguins. In the Arctic, the waters of Hudson Bay are ice-free for three weeks longer than they were thirty years ago, affecting polar bears, which prefer to hunt on sea ice. Species that rely on cold weather conditions such as gyrfalcons, and snowy owls that prey on lemmings that use the cold winter to their advantage may be hit hard. Marine invertebrates enjoy peak growth at the temperatures they have adapted to, regardless of how cold these may be, and cold-blooded animals found at greater latitudes and altitudes generally grow faster to compensate for the short growing season. Warmer-than-ideal conditions result in higher metabolism and consequent reductions in body size despite increased foraging, which in turn elevates the risk of predation. Indeed, even a slight increase in temperature during development impairs growth efficiency and survival rate in rainbow trout.
Rising temperatures are beginning to have a noticeable impact on birds, and butterflies have shifted their ranges northward by 200 km in Europe and North America. Plants lag behind, and larger animals' migration is slowed down by cities and roads. In Britain, spring butterflies are appearing an average of 6 days earlier than two decades ago.
A 2002 article in Nature surveyed the scientific literature to find recent changes in range or seasonal behaviour by plant and animal species. Of species showing recent change, 4 out of 5 shifted their ranges towards the poles or higher altitudes, creating "refugee species". Frogs were breeding, flowers blossoming and birds migrating an average 2.3 days earlier each decade; butterflies, birds and plants moving towards the poles by 6.1 km per decade. A 2005 study concludes human activity is the cause of the temperature rise and resultant changing species behaviour, and links these effects with the predictions of climate models to provide validation for them. Scientists have observed that Antarctic hair grass is colonizing areas of Antarctica where previously their survival range was limited.
Mechanistic studies have documented extinctions due to recent climate change: McLaughlin et al. documented two populations of Bay checkerspot butterfly being threatened by precipitation change. Parmesan states, "Few studies have been conducted at a scale that encompasses an entire species" and McLaughlin et al. agreed "few mechanistic studies have linked extinctions to recent climate change." Daniel Botkin and other authors in one study believe that projected rates of extinction are overestimated. For "recent" extinctions, see Holocene extinction.
Many species of freshwater and saltwater plants and animals are dependent on glacier-fed waters to ensure a cold water habitat that they have adapted to. Some species of freshwater fish need cold water to survive and to reproduce, and this is especially true with salmon and cutthroat trout. Reduced glacier runoff can lead to insufficient stream flow to allow these species to thrive. Ocean krill, a cornerstone species, prefer cold water and are the primary food source for aquatic mammals such as the blue whale. Alterations to the ocean currents, due to increased freshwater inputs from glacier melt, and the potential alterations to thermohaline circulation of the worlds oceans, may affect existing fisheries upon which humans depend as well.
The white lemuroid possum, only found in the Daintree mountain forests of northern Queensland, may be the first mammal species to be driven extinct by global warming in Australia. In 2008, the white possum has not been seen in over three years. The possums cannot survive extended temperatures over 30 °C (86 °F), which occurred in 2005.
A 27-year study of the largest colony of Magellanic penguins in the world, published in 2014, found that extreme weather caused by climate change is responsible for killing 7% of penguin chicks per year on average, and in some years studied climate change accounted for up to 50% of all chick deaths. Since 1987, the number of breeding pairs in the colony has reduced by 24%.
Pine forests in British Columbia have been devastated by a pine beetle infestation, which has expanded unhindered since 1998 at least in part due to the lack of severe winters since that time; a few days of extreme cold kill most mountain pine beetles and have kept outbreaks in the past naturally contained. The infestation, which (by November 2008) has killed about half of the province's lodgepole pines (33 million acres or 135,000 km²) is an order of magnitude larger than any previously recorded outbreak. One reason for unprecedented host tree mortality may be due to that the mountain pine beetles have higher reproductive success in lodgepole pine trees growing in areas where the trees have not experienced frequent beetle epidemics, which includes much of the current outbreak area. In 2007 the outbreak spread, via unusually strong winds, over the continental divide to Alberta. An epidemic also started, be it at a lower rate, in 1999 in Colorado, Wyoming, and Montana. The United States forest service predicts that between 2011 and 2013 virtually all 5 million acres (20,000 km2) of Colorado’s lodgepole pine trees over five inches (127 mm) in diameter will be lost.
As the northern forests are a carbon sink, while dead forests are a major carbon source, the loss of such large areas of forest has a positive feedback on global warming. In the worst years, the carbon emission due to beetle infestation of forests in British Columbia alone approaches that of an average year of forest fires in all of Canada or five years worth of emissions from that country's transportation sources.
Besides the immediate ecological and economic impact, the huge dead forests provide a fire risk. Even many healthy forests appear to face an increased risk of forest fires because of warming climates. The 10-year average of boreal forest burned in North America, after several decades of around 10,000 km² (2.5 million acres), has increased steadily since 1970 to more than 28,000 km² (7 million acres) annually. Though this change may be due in part to changes in forest management practices, in the western U.S., since 1986, longer, warmer summers have resulted in a fourfold increase of major wildfires and a sixfold increase in the area of forest burned, compared to the period from 1970 to 1986. A similar increase in wildfire activity has been reported in Canada from 1920 to 1999.
Forest fires in Indonesia have dramatically increased since 1997 as well. These fires are often actively started to clear forest for agriculture. They can set fire to the large peat bogs in the region and the CO₂released by these peat bog fires has been estimated, in an average year, to be 15% of the quantity of CO₂produced by fossil fuel combustion.
A 2018 study found that trees grow faster due to increased carbon dioxide levels, however, the trees are also eight to twelve percent lighter and denser since 1900. The authors note, "Even though a greater volume of wood is being produced today, it now contains less material than just a few decades ago."
In 2019 unusually hot and dry weather in parts of the northern hemisphere caused massive wildfires, from the Mediterranean to – in particular – the Arctic. Climate change, by rising temperatures and shifts in precipitation patterns, is amplifying the risk of wildfires and prolonging their season. The northern part of the world is warming faster than the planet on average. The average June temperature in the parts of Siberia, where wildfires are raging, was almost ten degrees higher than the 1981–2010 average. Temperatures in Alaska reach record highs of up to 90°F (32°C) on 4 July, fuelling fires in the state, including along the Arctic Circle.
In addition to the direct threat from burning, wildfires cause air pollution, that can be carried over long distances, affecting air quality in far away regions. Wildfires also release carbon dioxide into the atmosphere, contributing to global warming. For example, the 2014 megafires in Canada burned more than 7 million acres of forest, releasing more than 103 million tonnes of carbon – half as much as all the plants in Canada typically absorb in an entire year.
Wildfires are common in the northern hemisphere between May and October, but the latitude, intensity, and the length of the fires, were particularly unusual. In June 2019, the Copernicus Atmosphere Monitoring Service (CAMS) has tracked over 100 intense and long-lived wildfires in the Arctic. In June alone, they emitted 50 megatones of carbon dioxide - equivalent to Sweden’s annual GHG emissions. This is more than was released by Arctic fires in the same month in the years 2010 - 2018 combined. The fires have been most severe in Alaska and Siberia, where some cover territory equal to almost 100 000 football pitches. In Alberta, one fire was bigger than 300 000 pitches. In Alaska alone, CAMS has registered almost 400 wildfires this year, with new ones igniting every day. In Canada, smoke from massive wildfires near Ontario are producing large amounts of air pollution. The heat wave in Europe also caused wildfires in a number of countries, including Germany, Greece and Spain. The heat is drying forests and making them more susceptible to wildfires. Boreal forests are now burning at a rate unseen in at least 10,000 years.
The Arctic region, is particularly sensitive and warming faster than most other regions. Particles of smoke can land on snow and ice, causing them to absorb sunlight that it would otherwise reflect, accelerating the warming. Fires in the Arctic also increase the risk of permafrost thawing that releases methane - strong greenhouse gas. Improving forecasting systems is important to solve the problem. In view of the risks, WMO has created a Vegetation Fire and Smoke Pollution Warning and Advisory System for forecasting fires and related impacts and hazards across the globe. WMO’s Global Atmosphere Watch Programme has released a short video about the issue.
Mountains cover approximately 25 percent of earth's surface and provide a home to more than one-tenth of global human population. Changes in global climate pose a number of potential risks to mountain habitats. Researchers expect that over time, climate change will affect mountain and lowland ecosystems, the frequency and intensity of forest fires, the diversity of wildlife, and the distribution of fresh water.
Studies suggest a warmer climate in the United States would cause lower-elevation habitats to expand into the higher alpine zone. Such a shift would encroach on the rare alpine meadows and other high-altitude habitats. High-elevation plants and animals have limited space available for new habitat as they move higher on the mountains in order to adapt to long-term changes in regional climate.
Changes in climate will also affect the depth of the mountains snowpacks and glaciers. Any changes in their seasonal melting can have powerful impacts on areas that rely on freshwater runoff from mountains. Rising temperature may cause snow to melt earlier and faster in the spring and shift the timing and distribution of runoff. These changes could affect the availability of freshwater for natural systems and human uses.
Ocean acidification poses a severe threat to the earth's natural process of regulating atmospheric C02 levels, causing a decrease in water's ability to dissolve oxygen and created oxygen-vacant bodies of water called "dead zones." The ocean absorbs up to 55% of atmospheric carbon dioxide, lessoning the effects of climate change. This diffusion of carbon dioxide into seawater results in three acidic molecules: bicarbonate ion (HCO3-), aqueous carbon dioxide (CO2aq), and carbonic acid (H2CO3). These three compounds increase the ocean's acidity, decreasing its ph by up to 0.1 per 100ppm (part per million) of atmospheric CO2. The increase of ocean acidity also decelerates the rate of calcification in salt water, leading to slower growing reefs which support a whopping 25% of marine life. As seen with the great barrier reef, the increase in ocean acidity in not only killing the coral, but also the wildly diverse population of marine inhabitants which coral reefs support.
Another issue faced by increasing global temperatures is the decrease of the ocean's ability to dissolve oxygen, one with potentially more severe consequences than other repercussions of global warming. Ocean depths between 100 meters and 1,000 meters are known as "oceanic mid zones" and host a plethora of biologically diverse species, one of which being zooplankton. Zooplankton feed on smaller organisms such as phytoplankton, which are an integral part of the marine food web. Phytoplankton perform photosynthesis, receiving energy from light, and provide sustenance and energy for the larger zooplankton, which provide sustenance and energy for the even larger fish, and so on up the food chain. The increase in oceanic temperatures lowers the ocean's ability to retain oxygen generated from phytoplankton, and therefore reduces the amount of bioavailable oxygen that fish and other various marine wildlife rely on for their survival. This creates marine dead zones, and the phenomenon has already generated multiple marine dead zones around the world, as marine currents effectively "trap" the deoxygenated water.
Climate change can increase the frequency and the magnitude of algal bloom. In 2019 the biggest Sargassum bloom ever seen, create a crisis in the Tourism industry in North America. The event was probably caused by Climate Change and Fertilizers. Several Caribbean countries, even considered declare am emergency state because of the impact on tourism. The bloom can benefit the marine life, but, can also block the sunlight necessary for it.
Eventually the planet will warm to such a degree that the ocean's ability to dissolve water will no longer exist, resulting in a worldwide dead zone. Dead zones, in combination with ocean acidification, will usher in an era where marine life in most forms will cease to exist, causing a sharp decline in the amount of oxygen generated through bio carbon sequestration, perpetuating the cycle. This disruption to the food chain will cascade upward, thinning out populations of primary consumers, secondary consumers, tertiary consumers, etc., as primary consumers being the initial victims of these phenomenon.
Fresh water covers only 0.8% of the Earth's surface, but contains up to 6% of all life on the planet. However, the impacts climate change deal to its ecosystems are often overlooked. Very few studies showcase the potential results of climate change on large-scale ecosystems which are reliant on freshwater, such as river ecosystems, lake ecosystems, desert ecosystems, etc. However, a comprehensive study published in 2009 delves into the effects to be felt by lotic (flowing) and lentic (still) freshwater ecosystems in the American Northeast. According to the study, persistent rainfall, typically felt year round, will begin to diminish and rates of evaporation will increase, resulting in drier summers and more sporadic periods of precipitation throughout the year. Additionally, a decrease in snowfall is expected, which leads to less runoff in the spring when snow thaws and enters the watershed, resulting in lower-flowing fresh water rivers. This decrease in snowfall also leads to increased runoff during winter months, as rainfall cannot permeate the frozen ground usually covered by water-absorbing snow. These effects on the water cycle will wreak havoc for indigenous species residing in fresh water lakes and streams.
Species of fish living in cold or cool water can see a reduction in population of up to 50% in the majority of U.S. fresh water streams, according to most climate change models. The increase in metabolic demands due to higher water temperatures, in combination with decreasing amounts of food will be the main contributors to their decline. Additionally, many fish species (such as salmon) utilize seasonal water levels of streams as a means of reproducing, typically breeding when water flow is high and migrating to the ocean after spawning. Because snowfall is expected to be reduced due to climate change, water runoff is expected to decrease which leads to lower flowing streams, effecting the spawning of millions of salmon. To add to this, rising seas will begin to flood coastal river systems, converting them from fresh water habitats to saline environments where indigenous species will likely perish. In southeast Alaska, the sea rises by 3.96 cm/year, redepositing sediment in various river channels and bringing salt water inland. This rise in sea level not only contaminates streams and rivers with saline water, but also the reservoirs they are connected to, where species such as Sockeye Salmon live. Although this species of Salmon can survive in both salt and fresh water, the loss of a body of fresh water stops them from reproducing in the spring, as the spawning process requires fresh water. Undoubtedly, the loss of fresh water systems of lakes and rivers in Alaska will result in the imminent demise of the state's once-abundant population of salmon.
In general, as the planet warms, the amount of fresh water bodies across the planet decreases, as evaporation rates increase, rain patterns become more sporadic , and watershed patterns become fragmented, resulting in less cyclical water flow in river and stream systems. This disruption to fresh water cycles disrupts the feeding, mating, and migration patterns of organisms reliant on fresh water ecosystems. Additionally, the encroachment of saline water into fresh water river systems endangers indigenous species which can only survive in fresh water.
In 2010, a gray whale was found in the Mediterranean Sea, even though the species had not been seen in the North Atlantic Ocean since the 18th century. The whale is thought to have migrated from the Pacific Ocean via the Arctic. Climate Change & European Marine Ecosystem Research (CLAMER) has also reported that the Neodenticula seminae alga has been found in the North Atlantic, where it had gone extinct nearly 800,000 years ago. The alga has drifted from the Pacific Ocean through the Arctic, following the reduction in polar ice.
In the Siberian subarctic, species migration is contributing to another warming albedo-feedback, as needle-shedding larch trees are being replaced with dark-foliage evergreen conifers which can absorb some of the solar radiation that previously reflected off the snowpack beneath the forest canopy. It has been projected many fish species will migrate towards the North and South poles as a result of climate change, and that many species of fish near the Equator will go extinct as a result of global warming.
Migratory birds are especially at risk for endangerment due to the extreme dependability on temperature and air pressure for migration, foraging, growth, and reproduction. Much research has been done on the effects of climate change on birds, both for future predictions and for conservation. The species said to be most at risk for endangerment or extinction are populations that are not of conservation concern. It is predicted that a 3.5 degree increase in surface temperature will occur by year 2100, which could result in between 600 and 900 extinctions, which mainly will occur in the tropical environments.
In November 2019 it was revealed that a 45 year study indicated that climate change had affected the gene pool of the red deer population on Rùm, one of the Inner Hebrides islands, Scotland. Warmer tempratures resulted in deer giving birth on average three days earlier for each decade of the study. The gene which selects for earlier birth has increased in the population because does with the gene have more calves over their lifetime. Dr Timothée Bonnet, of the Australian National University, leader of the study, said they had "documented evolution in action".
The livelihoods of nature dependent communities depend on abundance and availability of certain species. Climate change conditions such as increase in atmospheric temperature and carbon dioxide concentration directly affect availability of biomass energy, food, fiber and other ecosystem services. Degradation of species supplying such products directly affect the livelihoods of people relying on them more so in Africa. The situation is likely to be exacerbated by changes in rainfall variability which is likely to give dominance to invasive species especially those that are spread across large latitudinal gradients. The effects that climate change has on both plant and animal species within certain ecosystems has the ability to directly affect the human inhabitants who rely on natural resources. Frequently, the extinction of plant and animal species create a cyclic relationship of species endangerment in ecosystems which are directly affected by climate change. .
Droughts have been occurring more frequently because of global warming and they are expected to become more frequent and intense in Africa, southern Europe, the Middle East, most of the Americas, Australia, and Southeast Asia. Their impacts are aggravated because of increased water demand, population growth, urban expansion, and environmental protection efforts in many areas. Droughts result in crop failures and the loss of pasture grazing land for livestock.
Droughts are becoming more frequent and intense in arid and semiarid western North America as temperatures have been rising, advancing the timing and magnitude of spring snow melt floods and reducing river flow volume in summer. Direct effects of climate change include increased heat and water stress, altered crop phenology, and disrupted symbiotic interactions. These effects may be exacerbated by climate changes in river flow, and the combined effects are likely to reduce the abundance of native trees in favor of non-native herbaceous and drought-tolerant competitors, reduce the habitat quality for many native animals, and slow litter decomposition and nutrient cycling. Climate change effects on human water demand and irrigation may intensify these effects. By 2012, North American corn prices had risen to a record $8.34 per bushel in August, leaving 20 of the 211 U.S. ethanol fuel plants idle.