Will climate change cause more disease epidemics?

The age of industry

The development of human societies has been accompanied by the destruction of natural ecosystems and rapid extinction of species: Compared to the long-term extinction rate, species are now disappearing 100 to 1,000 times faster. The main cause is the destruction and fragmentation of habitats. In the past 500 million years there have been five major mass extinctions - we humans cause the sixth extinction.

In 2006, scientists from six nations searched the Yangtze for six weeks using state-of-the-art equipment for traces of the Chinese river dolphin (also called Baiji). Vain. Since then it has been considered “functionally extinct” (if there are still specimens, they have no chance of survival). In the 1950s, the Yangtze, its only habitat, was still home to thousands of dolphins; since then the number has declined due to river dikes, heavy shipping and excessive fishing. For several years it has been considered one of the most endangered animal species in the world.

 Chinese river dolphin. Fig .: Alessio Marrucci, from >> wikipedia commons,
License: >> GNU FDL 1.2, accessed January 21, 2009.

The Chinese river dolphin (more at www.baiji.org; in English) is just one example, with it a whole genus of large mammals disappeared from the earth. The whole tragedy is hidden behind statistics and figures like the following:

The loss of biodiversity 1970-2000

The Living Planet Index is one of the possible ways the decline in biological
Measure diversity: It shows the decline in populations (>> more) of vertebrates.
From the base year 1970 to 2000, diversity fell by a total of 40 percent.
Illustration from Millennium Ecosystem Assessment, Biodiversity Synthesis,
own translation.

Life on earth developed in the course of time an almost unmanageable variety (see here). The term biodiversity includes the diversity of species on earth, the genetic diversity within species and the diversity of ecosystems (The Diversity of Life - Biodiversity). Today this diversity is declining at a dramatic rate: natural ecosystems are being destroyed by human activities, the species living in them are becoming rarer or are dying out. Some ecosystems are particularly hard hit by the destruction, around 35 percent of them are Mangroves and 20 percent of the Coral reefs has been destroyed by man. Freshwater habitats and species are also particularly endangered, as these habitats fall victim to human water consumption: of the approximately 10,000 freshwater fish species, a good 20 percent have become extinct or endangered in the last few decades. Of the fish species that only occur in the Mediterranean region, 56 percent are endangered, more than every second species. The particular endangerment of freshwater habitats is also shown by the WWF's Living Planet Index (figure above), which shows the decline in populations - i.e. the number of of a kind of inhabited area. With the decline in populations, the genetic diversity decreases, so it is also a kind of advance warning for a future endangerment of the species. 2017 a study by the Entomological Association Krefeld showed that in German protected areas the number of flightinsects decreased by 76 percent from 1989 to 2016 [1010]. In 2019, the results were supplemented by a study carried out at the Technical University of Munich: According to this, the total mass of insects had decreased from 2008 to 2017 in the meadows by 67 percent and in the forests by about 40 percent, the number of species by about a third [ 1012]. Similar results were also obtained in other countries: For example, in a protected forest in the US state of New Hampshire, the number of insects has decreased by more than 80 percent since the mid-1970s and the number of species by almost 40 percent [1014]. The tropics are also affected, where around 80 percent of all known insect species live: In the La Selva research station in Costa Rica, the biodiversity of the regularly collected insect caterpillars has decreased by around 40 percent since 1997 [1014]. Globally, around 40 percent of insects are considered threatened with extinction [1016]. Since the total number of species on earth is not known, no one knows how many species have become extinct.

We are witnessing the sixth mass extinction

The extinction of species has always existed - it is part of natural selection. But what happened today has nothing to do with it. These show fossils, molecular clocks and birds. The fossils can be used to find out how long a species lives on average. Molecular clocks, the study of changes in DNA that have accumulated over time, further refine the result. The result: The lifespan of species is very different (as also shown by the “living fossils” still occurring today, see for example here), but on average a species lives one to two million years. Birds are among the best known living beings - also thanks to a special kind of people "birdwatcher ”or in German called bird watcher. They often spend their vacation in search of rare birds (the author of this site has a few days in one with birdwatchers popular hotel on Tobago - and will never forget the excitement about the birds that were spotted before breakfast and that woke him up regularly). Thanks to these activities, we now know about 10,000 species of birds in the world.

What does this have to do with extinction? Quite simply, if a group of people lived to be an average of 70 years old, we would expect that an average of 70 people would die each year. When a species lives one to two million years old, we would expect 10,000 species to become extinct every 100 to 200 years. In fact, around one species of bird is currently going extinct every year. In other words, the rate of extinction in birds is about 100 to 200 times the long-term, natural rate of extinction. Other well-known species are even more extinct than birds; overall is the Extinction rate 100 to 1000 times higher today than the long-term extinction rate. This means that the extinction rate is only comparable to that today Big Five, the five major mass extinctions in the last 500 million years; such as the meteorite impact that made the dinosaurs extinct. Therefore, the current extinction is also called sixth mass extinction designated.


Accelerated Extinction in the Future?

The omens are even worse for the future. Of the 10,000 bird species, 1,100 were on the Red List of Threatened Species in 2000, i.e. more or less threatened with extinction. An endangered species can live for decades, maybe even a century, maybe one or the other species can still be saved - but especially in species-rich countries, the Red Lists' results are not particularly encouraging. So let's assume that hundreds of species are saved: If nothing else changes, a further 1,000 bird species could be exterminated in the future just by continuing today's trends - if this extinction continues until the end of this century, it would be all over again compared to today Accelerated by a factor of 5 to 10. Here, too, the birds are unfortunately no exception, as the following illustration shows:

The rate of extinction has accelerated extremely in the recent past.
Image from Millennium Ecosystem Assessment: Biodiversity Synthesis,
own translation.

Depending on the category, up to 52 percent of the well-known species are threatened with extinction (this is documented in the “Red Lists” of the IUCN and the individual countries). If we extrapolate the above assumptions with the higher extinction rate and endangerment of all these species and not just birds, we come to the conclusion that 30 to 50 percent of the species living today could become extinct by the end of the century.

What we can learn from islands

Can this order of magnitude be correct? The biologists have also chosen other approaches to determine possible future extinction rates. One of these approaches is based on the findings of the study of living things on islands ("island biogeography"): There it turned out that the number of species depends on the size of the island. The bigger the island, the more species. However, the relationship is not linear (island twice as large = twice the number of species), but rather forms a "Species-area relationship"Well-known curve, where the relationship between area and number of species depends on the region and group of organisms examined. A typical relationship looks like this: an island half the size still has around 85 percent of the species of a large island; a small island 5 percent the size the big island still has about half its number of species.

What does this mean for the extinction rate? Since the main cause is habitat destruction, habitats are getting smaller and smaller, and they become a kind of island for their living beings, surrounded by an environment in which they cannot live. Many examples have shown that laws similar to those on islands actually apply in other habitats. Let's take the birds again: By 1870, around half of North America's eastern forests had been cut down (further information). Even then there was already birdwatcher, in America, John James Audubon had described and drawn the birds of America. About 30 endemic bird species lived in these forests, of which four have now become extinct and a fifth species is highly threatened. So let's calculate with 4.5 extinct species: Exactly the 15 percent that would be expected according to the numbers of the islands. (Species are actually resilient - it takes decades for the number of species to adapt to the size of a habitat (there is also a technical term for this: the "blame for extinction").extinction debt") of a habitat - therefore one can only recognize the extent of the loss of biological diversity where the change was so long ago that the" blame for extinction "has already been paid, to stay in the jargon.)

For an estimate of the possible global extinction of species through the destruction of habitats, there is something else that has to do with the distribution of species diversity (>> more): There are areas that are particularly species-rich and particularly endangered, the “hotspots”.

Priorities of species protection: "Hotspots"

As the fish species in the Mediterranean area show, the threat to biodiversity is particularly pronounced in some areas: namely where a high number of endemics that only occur here meet with changes in habitat, intensive hunting or other causes of species extinction. This is often the case in the tropics: high biodiversity comes together with the ongoing destruction of habitats in order to gain arable and pasture land, and in the forests there is often intensive hunting. In 1988, British environmentalist Norman Myers suggested 10 tropical rainforest areas that should be protected as a top priority. The list was expanded to include other regions over time, and in 1996 the environmental protection organization began Conservation International together with Myers to revise the concept and put it on an objective footing: As a focus of species protection ("Hot spots”) She proposed areas in which at least 1,500 species of vascular plants (ie ferns and seed plants, which include conifers and flowering plants) are endemic and in which at least 70 percent of the natural vegetation has already been destroyed. This inventory resulted in 25 hot spots, which in the event of further revisions to 34 hot spots and are shown in the following figure.

Where nature is particularly endangered


The Hot spots biodiversity according to information from Conservation International. Own illustration.

The distribution of diversity in the world's oceans and their endangerment is less well known. But the Pacific in the area of ​​Indonesia and the Philippines is particularly rich in species. Coral reefs have a high level of biodiversity, for example up to 1,000 species of fish can be found in a reef.

Example Indonesia

Indonesia is one of the most biodiverse countries in the world: On land the biodiversity is only surpassed by Brazil, in the sea the Philippines are on par. With a land area of ​​1.3 percent, it is home to around 10 percent of the rainforest and 20 percent of all animal and plant species, including 17 percent of all bird species and 25 percent of all fish species; 14 percent of all coral reefs on earth are in the Indonesian archipelago and are home to over 2,000 species of fish. About 6 percent of all birds, mammals and flowering plants on earth are found on the island of Borneo alone. At the same time, the country suffers the percentage highest rate of deforestation in the world (more). Indonesia has two hotspots: the western half belongs to the Sundaland hotspot, the eastern half to Wallacea (the reason for this separation: Both are separated by the Wallace Line, a dividing line discovered by Alfred Russel Wallace (more) between Asian and Australian flora and fauna ). Orangutans live in Sundaland, whose populations are declining due to the destruction of the rainforest for rubber and oil palm plantations and for paper production; Wallacea is home to numerous endemic bird species and the Komodo dragon, the largest species of lizard on earth. Here the rainforest is also being destroyed as a result of a major government program in which the population of overpopulated regions was relocated to sparsely populated islands. The coral reefs are being destroyed by the warming of the water (more), by the discharge of untreated sewage and by fishing with dynamite and cyanide.

Additional Information:
>> Sundaland (Conservation International, in English)
>> Wallacea (Conservation International, in English)

An investigation of the hotspots showed that here of 17 million square kilometers of original area only about 2 million square kilometers were in a more or less unchanged condition; only 800,000 square kilometers were protected.Just a look at the map shows that the hotspots are often located in areas that people particularly like and densely populate, such as the coast - that is also the reason for their particular endangerment. Only the 800,000 protected square kilometers are protected from further destruction (this is optimistic: some of the areas are only protected on paper). This area corresponds to about 5 percent of the original area. According to experience on islands, only half of the species can therefore survive here in the long term; the other half is expected to be lost. Similar calculations for other areas, such as the rainforests, also ended up with one future extinction rate from one third to one half of all species - confirming the above estimates of the future extinction rate.

By the way: An extinction rate of a third to a half corresponds exactly to the magnitude in which we humans use the earth's resources for ourselves (>> here). That is also plausible: we are exterminating species to the extent that we are taking away their resources. The following section shows the reasons in detail.

The causes of extinction

Main historical cause on the mainland: The hunt

Until the 20th century, hunting was the main cause of extinction, and in the seas it still is today (in the form of fishing, see below). In prehistoric times, the large species of mammals and birds were decimated; So with the colonization of North America the pigeon was exterminated, and the bison almost, so in Central Europe the big predators like wolf and brown bear were driven out. Hunting still plays a role (for example, tigers are poached in order to process its components into medicines, which are valued in Asian countries).

Most important cause today on the mainland:
Destruction of habitats

Today, the main cause of biodiversity loss on the mainland is the destruction of natural habitats: the destruction of freshwater habitats; the conversion of forests into arable and pasture land (see industrial agriculture) or the use of land for settlements. Of the 130 million square kilometers of the earth that are ice-free are over 100 million square kilometers redesigned by man [1060] - above all on arable land and commercial forests, but also on - after all, 1.3 million square kilometers - on settlement area. While the conversion of forests into arable land in the temperate latitudes has largely been completed, it is currently affecting the tropical rainforests, which are particularly rich in species: they have now shrunk to half their original area, and the decline continues almost unchecked - every year rainforests fall from the one and a half times the size of Switzerland. The remaining rainforests are also often fragmented, as their settlement goes hand in hand with the construction of roads (on the edges of which the deforestation then continues) and other disturbances; and fragmentation also leads to a loss of biodiversity due to the species-area relationship.

The most important today and foreseeable future Drivers of decline
of biodiversity
in the different habitats on earth. Reading example:
So far, climate change has mostly had a low to moderate importance in the
polar areas already have a high. Its influence will increase rapidly in the future.
Image from >> Millenium Ecosystem Assessment, own translation.

How fast do the rainforests die?

The remoteness and the still enormous extent of the tropical rainforests make it very difficult to provide precise information on the destruction of the rainforests, especially since most of the countries in which the forests are located are reluctant to disclose data due to international attention. Not even satellite images always help: Different forest types (see below) cannot be distinguished there, and smaller deforestation areas, for example for manioc cultivation, can hardly be discovered. However, these are often the harbingers of large-scale forest destruction.

The available data also differ in that “tropical rainforest” can be defined very differently: Strictly speaking, they are evergreen forests in which it rains all year round - but with this definition even a large part of the Amazon rainforest does not belong to the tropical rainforests (Around Manaus, for example, some of the trees lose their leaves every year due to the season). In Australia, there are forests outside the tropics that are humid and evergreen. Depending on the definition adopted, there were 14 to 18 million square kilometers of tropical rainforests before the industrialization of the world (Figure); of which around 7 million square kilometers had already been burned down and / or deforested by 1990:

region original expansionAs of 1990
Southeast Asian mainland 3 million square kilometers0.3 million square kilometers
Southeast Asian Islands2 million square kilometers1 million square kilometers
Central Africa2 - 3 million square kilometers1.5 - 2.5 million square kilometers
West africa1.25 million square kilometers0.14 million square kilometers
Mexico and Central America1 million square kilometers0.3-0.4 million square kilometers
South America9 million square kilometers6.6 million square kilometers

The largest rainforest in 1990 with 6.6 million square kilometers was the tropical rainforest in the Amazon / Orinoco basin (in addition, in South America there is the Atlantic coastal rainforest that was once 1 million square kilometers and has now shrunk to a few percent). How fast is this largest rainforest disappearing? The area fluctuates from year to year - more forest is burned down in dry years than in wet ones; the “official” values ​​of the Brazilian “Instituto Nacional de Pesquisas Espaciais” are between 9,000 and 30,000 square kilometers per year. Almost as high - according to some estimates even higher - is the rate in Indonesia. According to the FAO, an average of 120,000 square kilometers of tropical rainforest were destroyed every year from 1990 to 2000 (and not to forget: 40,000 square kilometers of other tropical forests are added to this every year, so that a total of 160,000 square kilometers of tropical forest are destroyed every year). The destruction of these forests also contributes significantly to climate change (more); it ensures that Indonesia and Brazil make the third and fourth largest contributions to climate change on earth, after China and the USA. Indonesia is ahead of Brazil, as particularly carbon-rich peat forests are being destroyed here, which also release carbon from the peat soil.

The protection of tropical forests is also important for the protection of climate change, because not only is a lot of carbon released during slash and burn, but the forest is also lost as a carbon sink through the subsequent use of the area as cattle pasture (as on 80 percent of the area cleared in the Amazon region) - this reduces the ability of land ecosystems to bind carbon.

(All figures, unless otherwise stated, from Stuart Pimm: The World According to Pimm)

Other tropical ecosystems, such as the mangroves, which protect coastlines from floods and are nurseries for many fish species, have also declined sharply - they are still being converted into shrimp farms.

Most important cause in the seas: fishing

In marine ecosystems, fishing is primarily responsible for the extinction of species: 86 million tons of fish are caught in the oceans every year; In addition, there is an estimated 30 million tonnes of bycatch that does not appear in the catch statistics. According to the World Fisheries Report of the World Food Organization FAO, over three quarters of all stocks are overfished or exploited to the limit; a quarter is in acute danger. Endangered stocks also include well-known species such as cod. Thanks to bottom trawls, which also destroy coral reefs, deep-sea fish are also affected (the overfishing of the seas; see also A Brief History of Whaling).

Other important causes

In addition to the destruction of habitats and fishing, the spread of alien species that displace native species play a role (see box); the overexploitation of natural resources and chemical pollution play an important role. More than air and water pollution, overfertilization (again agriculture) contributes to chemical pollution. In the case of insects, the use of pesticides, which cannot distinguish between harmful and beneficial insects, also plays a role in many cases. Recently, climate change has also increased the loss of biological diversity (see also the endangerment of biological diversity by climate change); it is considered, for example, to be the main cause of the decline in tropical insects (which are particularly adapted to a stable climate). In the hotspots, areas with particularly high biological diversity, a quarter of all species could become extinct by climate change alone by the middle of the century [1080]! The various factors can mutually reinforce each other: Whereas in the past organisms could colonize new habitats in the event of climate change, this is made more difficult today by the isolation and destruction of habitats - often suitable habitats cannot be reached; instead, the species live in areas surrounded by human cultures or settlements “Islands”.

Climate change and species extinction are mutually reinforcing:
Climate change endangers biological diversity (see text above),
and the main causes of species extinction such as the extinction of
Rainforests aggravate climate change by adding carbon dioxide
release and change the albedo of the earth's surface (here).

The coral reefs are mainly damaged by rising temperatures (the consequences of climate change), by harvesting and fishing, by nutrient input and by mechanical destruction (also by tourists).

The consequences of introduced species

Humans have also brought many species from one country to another, from one continent to another throughout history - not just crops and
- animals, but also many other species, most of them unintentionally as a result of world trade and long-distance travel. Ecologically, existing geographic isolations that have arisen since the disintegration of the supercontinent Pangea are broken by human activities - a kind of reversal of geological history. As a result, the local biodiversity has sometimes increased, but with the loss of local species and with the consequence of a global adjustment and a global loss of biological diversity. In many cases, deliberately introduced or unintentionally introduced species (also called "invaders" by biologists) are a natural part of our environment today: nothing in Germany shows this better than the potato from South America.

In some cases, however, these species have also caused great damage because they lacked natural enemies in the new habitat and they could spread uncontrollably. So were Wild rabbit, originally brought to Australia as hunted game, where they plagued the country and destroyed large areas of the vegetation - not even the construction of the famous 1,830 kilometer long rabbit fence across Australia could stop their advance. Recently got caught Giant toads (Agas, Bufo marinus), which were introduced from South America to control pests in sugarcane fields, are out of control - they eat all kinds of small animals and poison monitor lizards and snakes when they eat them. They have now colonized the entire northeast of Australia. How much invaders can reduce biodiversity is shown by the one introduced in Hawaii at the end of the 1950s Rosy wool snail: it eats domestic snails and has led to almost ninety percent of the formerly over 700, sometimes very colorful, native snail species that only occur in Hawaii, have become extinct. In the Great Lakes of North America, those from the Black and Caspian Seas have settled Migrating clams, which probably got into the St. Lawrence River with ballast water in ships from Europe, developed into a plague: they deprive the native mussels and fish of food and clog the structures for cooling and drinking water; combating them costs $ 5 billion a year.

Currently they are Amphibians - These include the frog amphibians (frogs, toads, toads), tail amphibians (newts, salamanders) and the sneak amphibians that occur in the tropics and subtropics - the most critically endangered class of animals on earth. This is also due to a potty mushroom called Batrachochytrium dendrobatidis, short BD or Chytrid mushroom called. This fungus occurs naturally on African clawed frogs (which it does not harm); and these became popular around the world in the 1950s and 1960s as they were used for pregnancy tests (injecting urine into a pregnant woman causes the frogs to spawn). There has been a global BD epidemic since the 1980s that has destroyed numerous amphibian populations and led to the disappearance of several species from the wild. The fact that BD is so destructive is probably also due to a previous exposure to other factors, such as the destruction of habitats and climate change.

Why we should be interested in biodiversity

Biodiversity is the basis for that Earth ecosystem serviceswe all live on:

  • plants provide us with oxygen, nutrients and energy (our entire diet is based on the performance of plants, even if it is in the form of animal feed), they provide "renewable raw materials" and many remedies are based on active ingredients whose model comes from nature (see above Aspirin is based on an active ingredient from willow bark);
  • Woods regulate the climate and store the greenhouse gas carbon dioxide, they filter and store water (and thus protect against erosion and flooding, for example), they provide wood as a building material and firewood as an energy source and valued (local) recreational areas;
  • Farm animals give us their labor and supply meat, wool, milk ...;
  • insects pollinate (bumblebees, bees, ...) around three quarters of all flowering plants (including our fruit trees), are food for many freshwater fish, reptiles, birds and even some mammals (anteater, ...), help with the decomposition of organic waste (dung beetles , Termites), improve the soil in hot and dry climates (termites, ants) and fight pests as beneficial insects (thus reducing the use of pesticides in agriculture and horticulture) Insects estimated at 57 billion US dollars annually [1014];
  • Microorganisms decompose our waste and bring its minerals back into the cycle, they clean our rivers and waters;
  • Landscapes and the animals, plants and peoples living in them represent an ethical and aesthetic value that makes them, for example, holiday destinations.

Nobody knows whether the ecosystems will still be able to provide these services when 30 to 50 percent of the species have become extinct or when the performance of the systems will be noticeably restricted. We know that simple ecosystems are more vulnerable (the best example is agriculture - few species increase the likelihood of pest and disease epidemics). The components of an ecosystem may play similar roles, but different environmental conditions favor one element and another. Diverse ecosystems are therefore more flexible and adaptable. A loss of biodiversity makes ecosystems more difficult to cope with changes; and since no one knows what changes the future will bring, no one can know what flexibility in ecosystems we still need. Nobody also knows which unknown remedies or other usable chemicals may still be found in little-studied or even unknown species. If we destroy ecosystems or their components (species, populations, genetic diversity), we also impair their ability to provide useful services for us. It's like removing parts from a car and throwing them away whose meaning we don't know.

It is not just about species that we are in danger of losing, but about all levels of biodiversity:

Genetic diversityPrerequisite for the adaptation of living beings to changing environmental conditions, resistance to pathogens, etc.
Area populated by a species (populations)Local populations can ensure the preservation of genetic diversity and the contribution of the species to the services of ecosystems.
species The services of the ecosystems are essentially provided by the species occurring in them.
EcosystemsA multitude of ecosystems secures a multitude of different services.

The destruction of biological diversity is irreversible. Therefore, precautionary measures alone would make it necessary to protect biodiversity. In terms of diversity, in 2007 the Zoological Society London proposed a system for assessing the importance of endangered species: the EDGE score. It is calculated from the biological peculiarity (ED stands for evolutionary distinct) the species and its global endangerment (GE stands for globally endangered), which is taken from the red lists. More information on this: www.edgeofexistence.org.

Further information on the topic:

The pillage of the world's oceans
A little history of whaling
A green planet earth - On the future of ecosystems and biodiversity

Recommended websites:

Green Facts on Biodiversity: Clear Summary of the Millennium
Ecosystem Assessment (in English). The overview is also available >> here

Red List of the World Conservation Organization >> IUCN (International Union for
Conservation of Nature and Natural Resources
) [in English]

Hot spots (Conservation International) - Detailed information about the hotspots
of species protection (in English)

Federal Agency for Nature Conservation:
Biodiversity and
Red lists in Germany

Continue with:
Global environmental change or: A large-scale experiment with the earth's ecosystem

© Jürgen Paeger 2006 - 2020

The Chinese river dolphin is one of four species of river dolphins that originated independently from early whales in China, India and South America - before the sea dolphins. The other three species live in the Ganges, on the South American Atlantic coast as well as in the Amazon and Orinoco. The Amazon dolphin, which lives in the Amazon and Orinoco, is the most common species today with 100,000 animals.

The Insect death all older motorists know from their own experience: in the past there were many more insects on the front and on the windshield of cars.

“If, over the course of eons, the biosphere has produced elements that we ... have not learned to understand, then only a fool would give up apparently dispensable parts. Keeping every gear and screw is a smart hobbyist's first precaution. ” (Aldo Leopold, American conservationist)