10.3 Human Effects on Ecosystems

Learning Outcomes 10.3.1

• explain some of the data relating to human influences on ecosystems, including climate change and depletion of global resources, including overfishing

• explain the role of scientific journals, the peer review process and scientific conferences in validating evidence related to the debate about climate change

All over the world people are constantly taking resources from the biosphere. Global ecosystems supply food, wate1; building materials, clothing, medicines, and more, for a population of over 7 billion people. As the human population gets ever larger and we take more from the environment than we need simply for survival, biological resources are increasingly being depleted. In addition, the amount of human waste produced also has an impact on ecosystems, causing problems for other organisms. The extinction of species and loss of biodiversity in many areas of the world are clear examples of human influences on a wide range of ecosystems.

The human population explosion

As people learned to farm plants and animals to provide a reliable supply of food, more children survived and the populations grew, but on a relatively small and local scale. Later, tools and then machines enabled us to farm on a much bigger scale. Now we can change the environment with reservoirs, roads, canals, towns and cities. We have developed medicines that keep us and our children alive and allow many of us to survive to great old age. We have also developed engines that burn fossil fuels and release large quantities of exhaust gases into the atmosphere. We clear huge areas of rainforest to grow crops or rear cattle. We have developed floating factories that can clear whole areas of the oceans of fish - a long way from artisanal fishing boats that provide for a family, a village or a local market.

All of these activities have been driven by basic desires to provide ourselves with food, shelter and goods. As an unintended side effect we appear to be having a major impact on many of the ecosystems of the Earth. Scientists have increasing evidence that we are affecting the global climate, biological resources and biodiversity around the world.

Human influences on ecosystems

Human effects on ecosystems are many and far reaching. You are going to consider three in particular:

Climate change

From individual observations, to major scientific studies, there is a growing consensus that the Earth's climate is changing. Global temperatures are rising. This is seen both in overall climate patterns and in the increasing number and frequency of ;extreme weather events' all over the world.

The world's climate has changed regularly over time. The fossil record shows us how often the world has gone through ice ages and periods of tropical heat or desertification. The difference is that this time it is happening fast and there is a growing body of evidence that the changes are the direct result of human activities (see Section 10.3.2).

Depletion of biological resources

As the population of the world has grown, so has the demand for resources such as firewood, land for housing, and food. In the more economically developed parts of the world, people have gone way beyond simply fulfilling the basic needs of life. They eat far more food than they need and want a great variety of different foods. As a result, biological resources are being depleted and ecosystems destroyed, both on the land and in the seas and oceans (see Section 10.3.3).

Loss of biodiversity

As you have already learned, biodiversity is extremely important, in terms of both variety of species and genetic diversity within each species. Human influences appear to be affecting, and often reducing, biodiversity in a number of ways, through activities such as overfishing, habitat reduction and as a result of climate change.

The burden of proof

As you know scientists cannot simply state that one thing causes another. They look for correlations in data and carry out further investigations to see if there is a causal relationship or whether the correlation is simply coincidence.

When a scientist or a group of scientists has carried out research, they publish their findings. Scientific findings are not widely accepted by the scientific community unless they are published in a reputable scientific journal. This is because a paper submitted for publication in a journal goes through a process of peer review. The paper is sent to other scientists, who are experts in the field, for them to read and assess. They may even try out any techniques described. If the peer reviewers all agree that the paper is valid and reliable, it will be published.

Some journals are well known and very well regarded, while some are smaller and specialised but still respected. Some journals have a reputation for being slightly less 1igorous in the content they admit. Wherever science is published the authors have an ethical responsibility to ensure the highest standards of research design, data analysis and interpretation of data are applied. Cases where scientists are less than honest and the peer review process fails to detect this are fortunately very rare and published data is widely regarded as reliable.

Scientists who are working in the same field meet up regularly at scientific conferences. Here they share their data, discuss ideas, and listen to a number of presentations on the same area of work. Conferences give scientists somewhere they can talk, take a critical look at other work in their own field, meet up with others, collaborate and move their investigations and understanding forward.

When you are evaluating a study to decide whether or not to take notice of the conclusions, there are a number of factors to take into account. You need to examine the methodology to see if it is valid, that is, properly designed to answer the questions being asked. You need to know the size of the study and to see if the measurements have been carried out with precision and accuracy It is also important to find out if other scientists have been able to repeat the methodology and have had similar results - if so, the results are considered more reliable. Knowing who carried out the research, who funded the study and where it was published can also help you decide whether anything might have affected or biased the study. You then need to evaluate the data and conclusions from the study in the light of all these factors.

In the next few pages you are going to be presented with some of the evidence scientists have been gathering on the impact of humans on the ecosystems of the world. Much of the data you will study comes from a report by the Intergovernmental Panel on Climate Change (IPCC), published in 2013. It was gathered and analysed by scientists from countries including Australia, Canada, Chile, China, France, Germany, India, Japan, New Zealand, Norway, Russia, Switzerland, the USA and the UK.

The IPCC is a body arising from the United Nations Environmental Programme and the World Meteorological Organization. This panel analyses research, from scientists all over the world, on climate change and produces regular unbiased reports based on all the available data to be used by politicians and decision makers globally. The role of the IPCC is 'to provide the world with a clear scientific view on the current state of knowledge in climate change and its potential environmental and socio-economic impacts'.

Learning Outcomes 10.3.2 Human Influences on climate change

• explain some of the data relating to human influences on ecosystems, including climate change.

Over the last few years a large body of evidence has been built up to show that:

• global temperatures are increasing, having an inevitable effect on global climate

• the levels of caroon dioxide and other greenhouse gases in the atmosphere are increasing at an unprecedented rate.

Scientists all over the world have been collecting data on the temperature changes and caroon dioxide levels associated with climate change, and looking to see if there is a causal relationship between them.

The greenhouse effect

Greenhouse gases reduce heat loss from the surface of the Earth in a way that is similar to how glass panels reduce heat loss from a greenhouse. These gases have a very important role in the atmosphere, without which life on Earth as we know it would not be possible. They maintain the temperature at the surface of the Earth at a level suitable for life. Without greenhouse gases in the atmosphere, the surface of Earth would probably be more like that of Mars, with an average surface temperature of -63 •c instead of 14 •c.

Camon dioxide is one of the 'greenhouse gases'; others include methane and water vapour When radiation from the Sun reaches the Earth, some is reflected back into space by the atmosphere and by the surface of the Earth and some is absorbed by the atmosphere. The key wavelength is infrared, the radiation that makes us feel warm. Infrared radiation that reaches the Earth's surface is of a fairly short wavelength. It is absorbed by the surface of the Earth and then radiated from the surface at a longer wavelength. Some of this radiation is absorbed and re-radiated back to the Earth's surface by greenhouse gas molecules in the atmosphere. This is known as the greenhouse effect (see fig A) and it is vital to life on Earth. In theory, if the levels of greenhouse gases increase, the 'greenhouse· becomes more effective and the temperature of the atmosphere rises.

Evidence for global temperature increases

The UK Met Office has daily weather records going back to

r

1869, but w itten evidence from diaries and ships' logs goes back over 1 DO years more. Recent weather records also suggest that the Earth's surface temperature is increasing. In 1998 the Intergovernmental Panel on Climate Change (IPCC) gathered together a lot of data to produce a graph of global temperature

(see fig B).

We have data of measured temperatures only since the mid-1800s. Scientists have used a number of techniques to produce other data that can give an indication of the temperature, but not an exact value - the temperature is inferred. These other sources of data are called temperature proxies, and when they are used on graphs, we use error lines to show how accurate these values are thought to be. To see how temperature has changed over the centuries, scientists have taken readings using temperature proxies including tree rings, corals, ice cores and peat bog data. This has resulted in a famous graph known as the 'hockey stick graph' (see fig C) - the fluctuating black line indicates the mean data.

Frozen isotopes

Antarctic and Greenland ice cores are a widely used source of temperature proxies. Scientists drill deep down into the ice and then analyse the air trapped in the different layers. This provides a record that goes back thousands of years. The oxygen isotopes in melted ice (the proportion of 180 to 160) reflect the air temperature when the ice layer was laid down. Atmospheric carbon dioxide levels can also be measured.

The results of the analysis of air from ice cores for over 300 000 years is shown in fig D. It appears that about 140 000 years ago, the surface of the Earth was about 6 •c cooler than it is today and the Earth was in an ice age. On the other hand. about 120 000 years ago the climate was 1-2 •c warmer than it is now. These warm periods are known as interglacials. Since then we have had another ice age and some more warming.

Increasing data reliability

Both dendrochronology (the dating of past events using tree-ring growth) and peat bog dating

(using cores taken from peat bogs that show growth patterns over hundreds or even thousands of years) are used to confirm radiocamon dating. For example, wood or peat bog samples of known age can be dated from radiocarbon measurements, using remains of plants and pollen grains, which give an indication of climatic conditions when those plants are alive, and the results compared to give a form of calibration. This gives scientists clear reference points that they can use to determine the accuracy of their estimations of age.

Data like these were used to produce the IPCC graph you saw in fig B. In 2008, scientists recalculated the figures using more than 1200 temperature proxy records going back 1300 years, without using tree-ring data, and used two different statistical methods. The hockey stick graph

(fig C) was shown to be valid, with all statistical methods used and whether tree-ring data were included or not. All of the evidence points the same way - global temperatures are rising.

Evidence for increasing levels of carbon dioxide

Scientists have found evidence for the increasing levels of carbon dioxide in the atmosphere in many different ways. Some of the most famous evidence comes from what is known as the Mauna Loa curve, a series of readings taken at regular intervals at the Mauna Loa observatory on Hawaii

(see fig E(a)). The air is sampled continuously at the top of four 7-metre tall towers and an hourly average of camon dioxide concentration is taken (along with a number of other readings). The air in the area is relatively free from local pollutants and scientists believe it is representative of the

air in the Northern Hemisphere. Measurements started in 1958 and the monitoring methods and instruments used have remained very similar throughout that time. The records show that the level of atmospheric carbon dioxide has increased from 315.98 ppmv (parts per million by volume of dry air) in 1959 to 381.74 ppmv in 2006. The annual fluctuations in the levels of carbon dioxide seem to be the result of seasonal differences in the fixation of carbon dioxide by plants, as in temperate regions plants lose their leaves in winter and take up less camon dioxide.

Ice core data also show clear changes in carbon dioxide concentration. fig E(b) shows data taken from the Law Dome ice cores - particularly pure and undisturoed ice in the Antarctic. The shape of the curve is similar to that of the temperature curves in figs Band C.

Scientists are also measuring caJbon dioxide levels in the oceans and seas, both by the amount of carbon dioxide dissolved in the surface water and the changes in pH. The more carbon dioxide is dissolved in the water, the lower the pH. Look back to Section 10.2.3 to remind yourself of the role of the oceans as a carbon sink.

The role of methane

Methane (CH4} is a potent greenhouse gas, and over a period of 20 years has a 72 times greater effect on warming the atmosphere than caJbon dioxide. However, much less of it is produced than of

CO2. Its main sources are from the decay of organic material by some species of bacteria, particularly in wet conditions, and from the digestion of ruminant heJbivores, such as deer, sheep and cows. Methane breaks down naturally high in the atmosphere in a series of reactions that eventually form carbon dioxide and water molecules.

Methane levels have risen by about 150% since 1750 for several reasons. Rice paddy fields are waterlogged during much of the time the rice is growing and bacteria in this waterlogged soil release methane as they grow. Levels of rice production have been increasing steadily to feed the ever-increasing world population, and so more methane is produced. In addition, as the human population grows, so do the numbers of animals that we depend on for food, including cattle, who release methane from their digestive systems. Scientists have calculated that up to 60% of the methane in the atmosphere is now produced as a result of human activity in some way.

Did YOU know7

Cows belch a lot and every time they burp they release methane gas. Estimates of the amount of methane produced per cow per day vary from 100 to 700 dm3. This varies depending on factors such as the breed of cow, the type of food eaten and whether the cow is giving milk. There are an estimated 1.2 billion cows in the world, so a lot of methane is being produced. The IPCC estimate that 16% of the methane produced as a result of human activities comes from livestock, and dairy cows produce the most.

A number of research teams have set out to breed or engineer new strains of grass that can be digested more easily by cows, reducing methane emissions. And an Irish research team looked at whether changing the way cows are farmed could reduce overall methane emissions. Older cows produce more milk, but less methane per pint By keeping cows alive, healthy and giving milk for longer, the average methane emissions of the entire herd can be reduced.

Adding concentrates to the diet also reduces methane emissions per cow, because the concentrates are easier to digest and help prolong the cow's working life. However, generating the electricity needed in the manufacture of the concentrates produces carbon dioxide, so a balance needs to be struck.

Current evidence suggests that with a combination of good husbandry, careful breeding and possible genetic engineering of food plants, people may still be able to drink milk and eat beef, and reduce the production of methane at the same time.

Correlation or causation?

According to the lPCC, atmospheric concentrations of carbon dioxide, methane and nitrogen oxides have increased to levels that have not been seen for at least 800 000 years. Carbon dioxide levels have increased by 40% since pre-industrial times, primarily from fossil fuel emissions and secondarily from changes in land use, for example deforestation. The ocean has absorbed about 30% of the emitted anthropogenic (produced by people) carbon dioxide and this has caused ocean acidification. A lot of evidence from many studies now suggests a clear correlation between

the rise in carbon dioxide and other greenhouse gases in the atmosphere and the increase in global temperatures. However, the correlation is so close (see fig B) that it can be difficult to decide whether increases in greenhouse gases are causing the rising temperatures or are the resulz of rising temperatures.

Models of global warming

To say that there is a causal relationship between rising carbon dioxide levels and rising temperatures, with their associated climate change, we need a mechanism to explain how one factor changes the other. From our understanding of the greenhouse effect and because of the timing of the changes, a logical step

is to consider that humans are responsible. Since the Industrial Revolution we have burnt increasing quantities of fossil fuels

for energy and for transport, and more recently co generate electricity, and all this produces carbon dioxide. Alternatively, some scientists have proposed a mechanism where solar activity affects cloud formation and therefore surface temperature. Some data (fig I) seems to show a correlation between solar activity and atmospheric temperature, rather than between carbon dioxide concentrations and temperature. Howeve1; after looking at all

the evidence, the IPCC reached the conclusion that sunspot and solar flare activities over the past 50 years would most likely have produced cooling rather than warming, and that any influence they have on global climate is relatively small.

All these theories about global warming and climate change are based on data that require detailed interpretation and the use of computers to model very complex systems. Proving a causal link is almost impossible. However, many studies on different aspects of global warming, such as polar ice melting and climate change in different regions of the world using a wide variety of different computer models, suggest that the increase in atmospheric carbon dioxide and other greenhouse gases is increasing surface temperature, and that human carbon dioxide emissions are responsible for at least some of the current global warming and associated climate changes. The I PCC believe there is sufficient evidence now to state that there is a causal link. However, it will almost certainly turn out that global warming is multifactorial, with many different inputs - it is not only about carbon dioxide levels.

figJ Global anthropogenic greenhouse gas emissions between 1970 and 2004.

In 2007, the IPCC looked at data and models of climate change presented by scientists from all around the world. They saw that anthropogenic carl:Jon dioxide levels increased by 80% between 1970 and 2004, mainly due to the use of fossil fuels. The IPCC decided that the balance of the evidence shows a 95% probability that human activities resulting in the build-up of greenhouse gases are at least partly responsible for the observed increase in global temperatures. In their 2013 report they state that it is ex1remely likely that human influence has been the dominant cause of global warming since the mid-twentieth century

The IPCC use language carefully designed to indicate how strongly the evidence backs up the hypothesis. They have decided that it is very likely that human activities have contributed to the rise in sea level in the second half of the twenty-first century, but only likely that they have also influenced the changes in rainfall patterns that have been observed. At the moment climate changes and environmental damage are occurring far faster than anyone imagined. It appears that some of the effects of human influences on global ecosystems through anthropogenic climate change are already irreversible.

Example Questions 10.3.2:

1 The term 'greenhouse effect' is widely used to suggest something negative. Why is this an inaccurate use of the term?

2 Discuss the evidence that global temperatures are steadily rising.

3 (a) What is the overall percentage increase in atmospheric carbon dioxide from 1959 to 2006 based on the Mauna Loa data (fig E(a))?

(b) Why is the data from Mauna Loa regarded as reliable?

4 What can the data from the Law Dome ice cores (fig E(b )) tell us that the Mauna Loa data cannot and how reliable is this data?

5 There is one very simple way of reducing the methane emissions from cattle. What is it and why do you think it is not widely suggested?

6 How does the data shown in fig H support the theory that carbon dioxide levels and the temperature at the Earth's surface are linked? How reliable is the data?

7 Using figJ, calculate the percentage increase in carbon dioxide from fossil fuel use between 1970 and 2004 and compare it with the overall percentage increase in greenhouse gases from all sources over the same period.

10.3.3 The biological impact of climate change

Explain some of the data relating to human influences on ecosystems, including climate change.

Some of the biggest concerns about the impact of human activities on ecosystems center on climate change and how it will affect the distribution of species around the world.

Climate change

Weather describes the state of the atmosphere at a particular time and place, with regard to temperature, rainfall, humidity and windiness. Climate is the average weather pattern in an area over many years. Rising temperatures affect weather and rainfall patterns and can also cause long-term changes in the climate. It is impossible to link any one weather event to global warming, but

statistical evidence suggests that there is an increase in extreme weather events linked to the rise in global temperatures.

Rainfall patterns are complex, but they also seem to be changing. For example, there have been a number of years of lower than expected rainfall in Africa. In 2013, around 200 million people

(25% of the African population) were experiencing high water stress. If the current trend for low rainfall continues in Africa, it is predicted that by the year 2050 between 350 and 600 million people will be short of water for their crops and to drink. In contrast, in some areas rainfall has been both higher than average and extremely heavy, leading to flooding, which causes devastation and carries away the vital topsoil. Areas of China,

Pakistan and India have already seen a clear increase in torrential rainfall leading to severe flooding. An international group of

scientists have taken monthly recorded rainfall from around the world from 1925 to 1999 and compared what really happened to various computer models. They found that many of the changes corresponded to those expected if global warming was a factor.

Risk of flooding

Many scientists believe that the thinning of polar ice is a clear indication of global warming and could result in flooding.

In 2002, 500 billion tonnes of ice broke away from the Antarctic

peninsula and eventually melted into the sea. Also, Antarctic temperatures have increased by an average of 2.5 •c in the past 50 years - faster than anywhere else on the Earth. In the Arctic, the sea ice has been retreating by about 2. 7% each decade since 1978 and many glaciers are also retreating at a rate of about

50 metres a yeat

As the ice melts, the volume of water in the seas and oceans of the world will increase, causing sea levels to rise. Also, as the water gets warmer, its volume increases, resulting in an even bigger impact on sea levels. The implications for human life as sea levels rise are immense. Around 100 million people live less than 1 metre above current sea levels. For example, in the UK, large areas of the east coast could be lost for good, and the Netherlands might disappear completely!

The effect on organisms

Temperature has an effect on enzyme activity, which in turn affects the whole organism. There is an optimum temperature for many enzyme-controlled reactions and if the temperature increases beyond that point the enzyme starts to denature and the reaction rate falls, eventually stopping completely. Increased temperature could have different effects on processes, including the rate of growth and reproduction. If plants grow faster they will take up more carbon dioxide and may therefore reduce atmospheric carbon dioxide levels. In other places, temperature may exceed the optimum for some enzymes, and organisms there will die. The majority of plant and animal species are found in the tropics and many have very little tolerance for change, because conditions in the tropics tend to vary very little throughout the year: Experimental data suggest that a change of just 1 •c could threaten the survival of up to 10% of all species. The insects, which are vital as pollinators of the many flowering plants, are particularly vulnerable and if they go, so do the plants, followed by the animals that feed on them, in a mass extinction.

At higher latitudes, seasonal cycles affect life cycles. Global warming appears to be affecting the onset of the seasons, affecting both life cycles and the distribution of species. Warmer temperatures mean that plants grow and flower earlier and insects such as moths and butterflies become active earlier as the plant food they need for their caterpillars is available. Some birds can adapt to these changes. For example, the breeding cycle of the great tits in Wytham Woods near Oxford in the UK has moved forward, triggered by the same temperature changes that have resulted in winter moth larvae, the main food supply

for their chicks, being available. The UK great tits lay eggs about 2 weeks earlier now than they did 47 years ago. However, great tit populations in the Netherlands are not doing so well. The breeding time is getting earlier every year but the caterpillars are emerging even earlier so the birds are missing the peak population. and raising fewer chicks. For some animal species. breeding earlier in the year may mean they can fit more than one breeding cycle in. so those populations will increase.

Changes in temperature could have an even more drastic effect on some organisms. For example, the embryos of some reptiles are sensitive to temperature as they develop. Male crocodiles develop only if the eggs are incubated at 32-33 °C. If the eggs are cooler or warmer, females develop. If global warming results in only female crocodiles developing, it could be the end of a species that has survived virtually unchanged for millions of years.

Changes in species distribution

A change in climate could affect the range of many different organisms. For example, alpine plants in mountainous parts of the UK are becoming rarer. Most animals can move more easily than plants. so they can often survive change more easily As areas become warmer, some animals may be able to extend their ranges northwards. but may become extinct at the southern end of their current range. Others may be able to colonise a bigger area. In a study by Parmesan et al. in 1999 of 35 species of non-migratory European butterflies, the ranges of 63% of the species had shifted northwards by 35-240 km in the past 100 years and only 3% (one species) had shifted south. The shift in butterfly populations paralleled a 0.8 •c warming over Europe during this time.

If organisms involved in the spread of disease are affected, patterns of world health could change as well. The World Health Organization (WHO) has warned that global warming could be responsible for a major increase in insect-borne diseases in Britain and Europe. The prediction is that by 2100. conditions could be ideal for disease-carrying organisms such as mosquitoes, ticks and rats. The WHO is urging countries to make plans so that preventative measures can be put in place as the climate changes.

10.3.4 Managing Biological Resources.

As the human population grows, so does our influence on ecosystems. All around the world, biological resources are being depleted at a very rapid rate.

Depletion of resources - farming

When we farm we remove the crop before the plants die and decompose and therefore break the natural cycles that return minerals to the soil. As a result, soil mineral concentrations can decrease rapidly, especially when a monoculture (where one crop is grown over a large area) absoros large quantities of particular minerals. In some regions, monocultures are the mainstay of farming, from huge wheat fields to massive oil palm and banana plantations. In many other parts of the world, small-scale and family farms are common, but these too can deplete biological resources in the soil and in the surrounding ecosystems.

Artificial fertilisers can replace the minerals used by plants, but they do not support the structure of the soil. Once soil biodiversity is lost, the soil structure breaks down and it becomes infertile even when fertilisers are used.

Science and practical experience provide evidence of the impact of different farming methods and suggest ways in which land can be sustainably managed, but each way has cost and ethical implications. Science cannot dictate which is the best way for a particular community to farm; that is for each society to choose and the choice will depend on the needs and priorities of the people involved. Maximum yield from the land may be the priority for financial reasons or because without it a family will starve.

Depletion of resources - fishing

Fishing, the harvesting of fish and other aquatic organisms such as crustaceans from coastal areas, seas and inland waters, provides food and employment for around 820 million people worldwide. Sadly, the fish stocks of the ocean are fast becoming one of the most depleted biological resources. If we take too many fish,

or fish at the wrong times of year, the fish cannot breed and replenish the populations, and fishing becomes unsustainable. The problem is particularly acute in coastal areas, but is also seen in deeper oceans and in inland waters. The Food and Agriculture Organization of the United Nations (UN FAO) has published data showing that up to 25% of the major marine fish stocks are being depleted or over-exploited, putting the fish populations at risk of extinction. Another 44% are being fished right up to their safe biological limit.

More Peruvian anchovies are caught than any other fish in the world, but in 2012 catches were down by 46%. Often fishing is local. carried out on a relatively small scale by local people, but it is also carried out on an industrial scale by large fishing fleets. Atlantic cod was traditionally caught by the UK fishing fleet and widely eaten in the UK. but the development of factory fishing fleets by other countries, and overfishing by the UK fleet, has seen such a dramatic decline in cod numbers that the population may never fully recover.

A number of factors appear to be causing the large-scale depletion of fish stocks around the world. These include:

• the size of the global fishing fleet - the fleet is currently almost twice the size that would be needed to take a sustainable supply of fish

• open-ocean factory ships that take huge catches of fish, often including many species that are not wanted as food

• techniques such as bottom trawling, where nets are dragged along the seabed, damaging the vulnerable seabed habitat and catching a wide variety of species, many of which are not wanted

enormous drift nets that are almost invisible and catch and kill many species accidentally

• nets with small mesh sizes that catch immature fish as well as adult fish

• fishing through the breeding seasons.

Anthropogenic changes in the ocean

Changes in fish populations are not only related to the amount and method of fishing. There was a marked fall in the cod populations around 1975 and a peak around 1980, followed by steady decline. A number of studies suggested that these changes were the result of changes in environmental conditions as much as in the human fishing quotas. Global water temperatures, levels of pollution and numbers of natural predators such as seals can all vary considerably. Sea temperatures are affected by global warming through the cooling effect of melting sea ice. Rises and falls in sea temperature can affect the amount of phytoplankton, which are the producers in most marine food chains, and this can affect the food available for fish higher up the food chain. Another factor is that many fish spawn in relatively shallow coastal waters, which are more affected by temperature changes than the deep ocean.

The conservation conundrum

The scientific evidence is growing steadily to show that the sustainability of biological resources is dependent on human beings changing their behaviour It is easy for a country with plenty of food, readily available education and healthcare and

a strong infrastructure to condemn the felling of a rainforest. However, when people have very little, the drive to make money to buy the food, healthcare and education they so badly need for themselves and their children is understandably more important. Farming on an industrial scale, or fishing the oceans, provide food and a way of earning a living for many millions of people.

We need to find ways to halt the depletion of biological resources before it is too late. As you saw in Book 1 Section 3.3.4, a

great deal of work is being done to conserve the biodiversity of individual species and of ecosystems and there is more on this in Section 10.3.5.

People are becoming increasingly aware that the sustainability of our resources depends on the effective management of the conflict between human needs and conservation. Sustainability demands a decent standard of living for everyone now, without compromising the needs of future generations or of the ecosystems around us. This is not easy to achieve. There are too many human needs, vested interests and conflicts of interest to make this a simple problem to solve.

The evidence is building all the time for the effect of human activities on climate change. You have looked at some of the evidence showing how carbon dioxide levels in the atmosphere and the oceans are increasing steadily and the planet is getting warmer When you look at fig D, you can see that the biggest producers of greenhouse gas emissions are not the cars on the road or the farmer, but the companies producing electricity; the industries that support the economic stability of the world, and forestry - especially deforestation and burning. The problem

is that we all want electricity, industries are needed for global economic success and the countries that are cutting down rainforests need the resources to move above the basic survival line. It will take a lot of international cooperation as well as the effort of millions of individuals to make the changes needed to slow the production of greenhouse gases and replace as much of the lost vegetation as possible.

Conserving fish stocks

Various methods of protecting fish populations have been introduced and are already having a small but measurable impact on fish numbers:

• controlling the size of the mesh in the fishing nets, so only the largest fish are caught

• banning fishing during the breeding seasons of different fish

• imposing very strict quotas on fishing fleets and individual fishing vessels

• encouraging the use of fishing methods that are less damaging to the ecosystems

• banning the catching of severely endangered species of fish altogether

However, these controls need to be policed and introducing them deprives people of their livelihoods. In the UK alone, many fishing communities have been badly hit by unemployment, as the fishing boats have been forced to stay at home to protect our stocks.

Fish farming and aquaculture

Another way of protecting the wild fish stocks in our coastal, ocean and lake ecosystems is to farm fish and other seafood such as mussels, prawns and other crustaceans. Fish farming, or aquaculture, is becoming a very successful way of providing people with the fish they want and therefore the protein that they need. More fish are eaten in China than anywhere else in the world, and around two-thirds of all commercial fish farming in the world takes place there - it is a successful business. In Africa people are increasingly farming fish like Tilapia in a new but growing industr y In countries such as the UK and USA, fish such as salmon, trout and shellfish, including mussels, are farmed.

In 2012, around 47% of all the fish eaten by people worldwide was produced in aquaculture. This will have an impact on protecting the wild stocks of fish in global ecosystems. Fish farms are not carbon neutral, they use electricity and produce greenhouse gases. Fish farms also feed their fish. Unfortunately their food is often made from other fish. So fish farming does nor necessarily prevent overfishing. Increasingly, alternative foodstuffs based on ingredients such as marine algae are being used in fish farms to reduce their environmental impact. Fish farms are not an ideal answer, but they are certainly an important part of the solution, producing sustainable fish stocks for the future and preserving the biological resources in our coastal waters and oceans.