The big picture

What is the climate like in your area? Have you experienced any unusual weather e.g. extreme dry or wet spells?

Weather and climate has always changed and continues to do so. However current change is occurring at a much faster rate than ever known before.

Since global records began in 1880, we have recorded:

• The warmest year in 2014.

• Warmest month in July 2015.

• The ten warmest years between 1998 and 2014.

We are also experiencing more frequent extreme weather events.

Various factors influence climate from the energy emitted from the sun and reaching the earth to the amount of energy that is absorbed or reflected back into space.

There is still some debate about whether the current change is due to natural forces or as a consequence of human activity. The scientific consensus is that climate change is occurring and that human activity is a major contributor.

Has there been more or less extreme weather events in 2016-17?

Climate and weather

Climate is the ‘average’ weather over the long term (e.g. years) often at a regional level whereas weather refers to the conditions over a short time scale (e.g. day to day) at a local level. Changes to weather overtime are presented as statistics e.g. mean and variation in temperature, rainfall, sunshine, wind and humidity. Trends in weather data can be used to predict future climate.

Figure 1. Weather forecast (over the short term for a specific area).

Figure 2. Global change in surface temperature illustrating climate change.

Examiner Tip

Ensure you can distinguish between weather and climate.

Factors affecting climate

Climate is affected by factors outside the earth (extraterrestrial) and within the earth:

• Factors outside the earth:

  • Solar radiation emitted from the sun.

  • Tilting and orbit of the earth.

• Factors within the earth:

  • Atmospheric and ocean circulation systems.

  • Greenhouse gases that trap heat and warm the land, oceans and atmosphere.

  • Volcanic activity.

  • Feedback cycles.

Factors outside the earth

Solar radiation from the sun drives the earth’s climate. The amount of energy reaching the earth’s surface can vary according to the amount of energy emitted from the sun and the position of the earth in relation to the sun.

Solar radiation from the sun

The amount of solar energy emitted from the sun has changed in the past. For example, reduction in radiation as a result of low sunspot activity contributed to the Little Ice Age from around 1650 to 1850. The sun experiences an 11-year cycle with periods of low and high emissions. However this variation has a minimum impact on the earth’s climate and there have not been any significant changes in solar emissions in recent times.

Figure 3. Solar cycle of irradiation.

Tilting and orbit of the earth

The axis of the earth is currently tilted at an angle of 23.5°. This axial tilt can vary from 21.6° to 24.5° over a period of 41,000 years. The tilting of the earth influences how much solar energy is absorbed and results in seasonal changes.

When the northern hemisphere tilts (23.5°N) towards the sun:

• It absorbs more sunlight resulting in summer.

• The southern hemisphere is tilted away from the sun leading to winter there, with little light reaching the South Pole.

Conversely when southern hemisphere it tilted towards the sun:

• It absorbs more sunlight resulting in summer.

• It is winter in the northern hemisphere and it remains dark in the North Pole until the spring.

Figure 4. Seasonal variation in solar radiation.

The earth also wobbles along its axis which is known as precession, with a cycle of about 23,000 years.

Figure 5. Precession occurs because earth wobbles like a spinning top.

The orbit of the earth around the sun is not circular but is elliptical and this is known as the earth’s eccentricity. The variation in the earth's eccentricity has a cycle of about 100,000 years. The elliptical orbit means that the distance of the earth from the sun varies through the year, with the closest point currently occurring in January. Nevertheless there is little change in the amount of energy reaching the earth.

Figure 6. The earth’s orbit varies overtime.

Collectively the cycles of axial tilt, precession and eccentricity are referred to as the Milankovitch cycle and influence the amount of sunlight reaching the earth. The Milankovitch cycle contributes to the earth’s fluctuation between glacial periods (ice age) and interglacial periods.

Figure 7. Ice cores in Antarctica demonstrate changes in temperature reflecting glacial and interglacial periods over the past 420,000 years.

Causes of climate change

In addition to the energy from the sun emitted and the orientation of the earth other factors within the planet affect our climate. These include:

• Atmospheric and ocean circulation systems.

• Concentration of greenhouse gases within the atmosphere.

• Volcanic activity.

• Feedback cycles

• Atmospheric and ocean circulation systems

Due to the curvature of the earth, more radiation reaches the equator than the Polar Regions. Hence temperatures are higher in the equator and lowest at the pole. Energy from the equator is transferred toward the poles through atmospheric and ocean circulation systems. The latter is caused by winds and difference in water temperature and salinity.

Wind occurs as a result of differences in air pressure:

• Low pressure occurs when air is warmed; it expands and rises forming clouds.

• High pressure is created when a reduction in temperature cools the air which contracts becoming denser and descends. This often results in clear skies and calm weather conditions.

The movement of air from high to low pressure (replacing rising air) creates wind.

Figure 1. The movement of air from high to low pressure.

Tricellular model

The tricellular model is used to explain transfer of heat through the atmosphere. It links to topic 2.4 Biomes, zonation and succession. To summarize, the tricellular model comprises of the Hadley cell, Ferrel cell and Polar cell.

Hadley cell

As air is heated at the equator, it rises and cools with altitude which stops it rising further. As the air moves towards the pole it is deflected (by Coriolis force caused by the rotation of the earth) towards the right in the northern hemisphere and towards the left in the southern hemisphere. The air becomes cooler and therefore denser leading to it falling at about 30°N or 30°S of the equator. Some air is transferred back to the equator, replacing rising air and some continues on its journey towards the pole. This divergence of descending air leads to a subtropical high pressure region associated with sunny and dry conditions.

Ferrel cell

As the air moves from the Hadley cell towards the pole, it enters the Ferrel cell where it picks up moisture as it crosses the sea. At about 60°N or 60°S this warm air meets cold air from the pole called the polar front and is forced upwards creating a region of low pressure associated with high rainfall. The rising air is divided with some moving back to the equator and the rest continuing toward the pole.

Polar cell

Air that moves from the Ferrel cell to the Polar cell, rises and continues moving towards the pole. As the air cools it descends creating a high pressure region and some of the air moves back towards the equator forming the polar fronts that meet the Ferrel cell (at about 60°N or 60°S).

Figure 2. Global atmospheric circulation.

Theory of Knowledge

Models are often used to help our understanding. To what extent could use of simplified model systems limit wider consideration of issues and hence restrict greater understanding?

El Niño

Climate in one part of the world can influence climate in another region via atmospheric and ocean circulation systems. For example El Niño events in the equatorial Pacific Ocean influence weather and climate in North America and Europe.

Normally in the absence of El Niño:

• In the Western Pacific Ocean, high surface water temperatures cause water to evaporate resulting in development of low pressure. This leads to heavy rainfall over East Asia and Eastern and Northern parts of Australia.

• In the Eastern Pacific Ocean upwellings bring cold deep waters to the surface, lowering the surface water temperature resulting in high pressure. Offshore winds from South America, (blowing from land to sea) further contribute to dry weather conditions in this region.

• This difference in atmospheric pressure between the Western and Eastern Pacific ocean results in air moving from the East (high pressure, descending warm air) to the West (low pressure, rising air).

Figure 3. Normal year - absence of El Niño phenomenon.

During El Niño the air flow and ocean currents change direction. El Nino events develop when:

• Warm surface water in the Western Pacific Ocean extends further eastwards and the resulting warmer temperature in the Eastern Pacific Ocean creates lower pressure above South America. The rising moist air results in greater rainfall in the region increasing the risk of flooding.

• Air flows from the Western Pacific Ocean (high pressure, descending air) to the Eastern Pacific Ocean (low pressure, rising air). The air mass in the west is now drier and East Asia and Australia experience less rainfall with the possibility of drought occurring.

Figure 4. The El Niño phenomenon.

A change in water temperature and surface winds in the Eastern Pacific results in a decline in upwelling which:

• Contributes to an increase in surface water temperatures.

• Reduces nutrients released from deep waters, adversely affecting primary production and fisheries.

El Niño events occur every two to seven years and can last from a few months to more than a year.

The following video also explains the El Niño phenomenon:

Greenhouse effect

Greenhouse gases and the role of the greenhouse effect in warming the earth. A rise in the concentration of greenhouse gases present in the atmosphere increases the amount of energy absorbed raising global temperatures. For example, carbon dioxide levels have increased from 280 parts per million prior to the industrial revolution in the eighteenth century to over 400ppm today.

Figure 5. Increase in atmospheric carbon dioxide levels correspond to an increase in the average global temperature.

Evidence of this increase in carbon dioxide levels and rise in temperature come from:

• Direct measurements, although we only have about 100 years of accurate data.

• Deep sea sediments and ice cores taken from Antarctic, Greenland and mountain glaciers.

Volcanic activity

Volcanic activity can have a short term effect on climate. Emissions from volcanic activity include ash and gases such as sulphur dioxide. The latter reacts in the atmosphere forming a sulphate aerosol that reflects solar radiation back into space and causes global cooling. Scientists have estimated that the eruption of Mt. Pinatubo, in the Philippines on 15 June 1991 led to a cooling of the earth for about three years.

Climate feedback

Positive and negative feedback mechanisms can either enhance or reduce global warming respectively.

Figure 1. Climate feedback mechanism can be positive or negative.

Positive feedback

Water vapour

If temperatures rise, more water evaporates. Water is a greenhouse gas and therefore further increases temperature resulting in positive feedback.

Figure 2. Positive feedback mechanism affecting climate change.

Ice albedo

Ice and snow have a reflective surface and therefore a high albedo. If temperatures increase, ice and snow melts reducing the amount of solar radiation reflected back into space. Dark surfaces which replace the ice and snow increase absorption of sunlight and contribute to global warming. Higher temperatures result in more ice and snow melting.

Permafrost

Increase in temperature results in melting of permafrost which releases methane. Methane is a greenhouse gas which further increases global temperatures.

Figure 3. Permafrost - soil subsurface layers are thawing releasing methane.

Carbon dioxide solubility

If temperatures increase, the solubility of carbon dioxide in the oceans decreases, the release of carbon dioxide into the atmosphere results in further warming of the planet.

Negative feedback

Plant photosynthesis

If temperatures increase, levels of plant photosynthesis can rise and more carbon dioxide is absorbed. This reduction in overall atmospheric levels of carbon dioxide results in a reduction in global temperature.

Figure 4. Negative feedback mechanism affecting climate change.

Cloud cover

Cloud cover can lead to either negative feedback or positive feedback depending on temperature of cloud (i.e. altitude) and optical properties (i.e. particle size and whether solid or liquid form):

• Negative feedback tends to dominate in low clouds that reflect some of the incoming solar radiation back into space increasing heat loss and causing global cooling.

• Positive feedback tends to dominate in high cloud cover that acts as a blanket retaining heat radiated from the earth’s surface which increases the temperature.

Figure 5. Examples of cloud feedback.

Examiner Tip

Ensure you are able to explain feedback mechanisms and illustrate them using positive and negative feedback examples.

Watch the following video which provides an overview on key aspects of climate 'How does the climate system work':

Impacts of climate change I

Rising concentrations of greenhouse gases (such as water vapour, carbon dioxide, methane and nitrous oxide) in the atmosphere have led to higher average global temperatures.

Higher temperatures

From 1880 to 2013, atmospheric carbon dioxide levels went up by over 40% and the global temperature increased by 0.85°C. The Intergovernmental Panel on Climate Change (IPCC) using different scenarios have suggested various changes in global temperatures for 2100 e.g.:

• If GHG emissions are reduced and there are negative emissions (e.g. carbon dioxide absorption through forestation schemes) the average global temperature will increase by 0.3 to 1.7°C.

• If high GHG emissions continue, temperatures could rise by 2.6 to 4.8°C.

Higher temperatures will affect the hydrological cycle. With a rise in temperature, more water will evaporate resulting in some regions experiencing greater rainfall. However this rainfall will not be distributed equally and some already water stressed areas are likely to receive even less rainfall. In general there is an increase probability that:

• The annual amount of precipitation will increase in high altitudes, equatorial Pacific and other already wet regions of the subtropics. (Wet subtropical regions typically have between 80 to 165 cm of rainfall per year compared to dry subtropical regions that have between 30 to 90 cm of rainfall per year).

• The annual amount of precipitation will decrease in the mid latitudes and dry regions of the subtropics.

Figure 1. Predicted change in precipitation by the end of the 21st century.

Extreme weather patterns are likely to become more frequent, longer in duration and more intense. There may be more episodes of longer periods of drier hot weather (heat waves) or more intense storm events with high rainfall, thereby increasing the risk of drought or floods respectively.

Warming of the oceans may also affect ocean circulation systems which are driven by temperature and salinity differences, further influencing weather and climate around the world.

Sea level rise

With the increase in global temperature, sea levels rose by an average of 19 cm between 1901 and 2013. Increase in temperature leads to:

• Thermal expansion of the oceans (water absorbs heat and expands).

• Increased melting of snow and ice. Loss of glaciers (e.g. Mount Kilimanjaro in East Africa and in Andes in South America), ice sheets (e.g. Greenland and Antarctic) and snow cover is expected to continue.

Figure 2. Melting of Greenland ice sheet.

The IPCC projections suggestion that by 2100, sea levels could further rise by between 26 cm to 82 cm.

Impact on water resources

Increase in global temperatures, sea level rise and changes in precipitation patterns could affect the quantity and quality of water available.

Reduced water resources

The availability of water could be influenced by:

• A reduction in precipitation in semi-arid and arid regions will reduce available water resources and this could be further exacerbated by higher temperatures increasing evaporation rates. The frequency and intensity of drought conditions is expected to increase.

• Reduction in glacier or snow water storage leading to reduced water resources downstream during spring and summer time. Loss of glacial melt in the Andes Mountains is expected to have devastating effects in Peru, a country already considered to be the most water stressed in South America. The reduction in river flow will effect both water resources and production of hydroelectric power.

• A rise in sea level may increase saline intrusion of groundwater near coastal areas. Seawater contamination of coastal aquifers can render the water too salty for domestic, agricultural and industrial uses.

Reduced water could lead to:

• Lakes and river beds drying out, adversely affecting the aquatic ecosystems and biota such as fish.

• Increase in arid areas and desertification.

• Loss of crops or reduction in yield.

• Loss of livestock due to lack of sufficient fodder, pasture areas and water to drink.

• Migration of wildlife in search of water.

• Increase mortality of wildlife.

• Increased risk of wildfires due to dry environmental conditions resulting in loss of habitats and biodiversity.

• Conflict between people over the limited water resources.

• Migration of people to other areas for employment and basic resources (i.e. water and food).

• Reduced electricity generation from hydroelectric power schemes.

Figure 3. Wildfires can result in loss of wildlife.

Flooding

Increase frequency and intensity of precipitation is likely to increase the risk of flooding in the middle and high latitude regions. Floods can cause:

• Sewers to overflow.

• Contamination of drinking water supplies and increase risk of disease.

• Landslides

• Injury or death by drowning.

• Damage to homes and possessions.

• Displacement of people.

Figure 4. Flooding of large settlement.

Impact on agriculture and fisheries

Agriculture

Some regions are expected to become more favourable for agriculture due to increase temperature and precipitation and other regions will be adversely affected by climate change. As illustrated in the figure below, crop yields are expected to:

• Increase in mid to high latitudes regions.

• Decrease in low latitude regions.

Figure 5. Projected impact of climate change on agriculture yield between 2003 and 2080s.

Increase levels of atmospheric carbon dioxide may increase the rate of photosynthesis of some plants although this may be limited by water and nutrient levels. Studies have found that climate change reduces overall global yields of wheat and maize but has less of an impact on rice and soya bean yields.

Increase in extreme events such as heatwaves, droughts or floods will have a detrimental effect on crop and livestock productivity. Dry conditions can increase the risk of wild fires that can have an adverse effect on habitats and overall biodiversity.

The change in environmental conditions may become more favourable for pests. An increase in temperature may result in some diseases spreading from low to mid latitudes. E.g. spread of corn earworm across the USA and the Colorado potato beetle that has moved north across Europe.

Fisheries

Higher water temperature can lead to:

• Death of some species unable to cope with higher temperature range leading to loss of biodiversity.

• Migration of some fish towards the poles in search of cooler waters.

• Increase in range of distribution of fish adapted to warmer waters.

• Change in spawning period, potentially expanding the growth season for some fish.

• Coral bleaching in which the coral expels zooxanthellae, a symbiotic algae. Zooxanthellae live inside the coral polyp and provide the polyp with food. Without the algae, the coral becomes more susceptible to disease. The loss of coral can lead to reduced shelter and food for many organisms and can have a detrimental effect on fisheries.

Figure 6. Zooxanthellae give coral polyp its colour and therefore when the algae is expelled the coral becomes white.

Coral reefs are also vulnerable to:

• Damage by increase occurrence of severe storms.

• Increase in ocean acidity as a result of higher atmospheric carbon dioxide levels. Dissolved carbon dioxide reacts with water to form carbonic acid which then dissociates to form hydrogen ions and bicarbonate ions. The hydrogen ion increases water acidity which can affect biological processes (e.g. reproduction, growth and photosynthesis). The bicarbonate ions reduce available carbonate ions required by corals, shrimp, oysters and other animals for the formation of their skeleton or shells. Ocean acidification results in decline in reproduction and reduction in growth and development of many marine organisms.

Figure 7. Ocean acidification reduces ability of marine organism to form calcium carbonate shells or skeletal features.

Impacts of climate change II

In addition to effects of climate change on the hydrological cycle, water and food resources, a change in environmental conditions will affect ecosystems and increase the risk of loss of biodiversity. Occurrence of more extreme weather events and sea level rise could have devastating effects on low lying coastal communities. These impacts (e.g. reduction in crop yields, decrease in safe water supply, flooding and loss of ecosystems) can in turn affect human health and well-being.

Impact on ecosystems and biodiversity

As a consequence of climate change, ecosystems are under threat from:

• Increase in temperature and change in precipitation patterns.

• Increase risk of flooding.

• Drought conditions.

• Increase risk of wild fires.

• Increase spread of pests.

• Ocean acidification.

Changes expected include range shift and migration patterns of organisms.

Range shifts

• With a change in climatic conditions of temperature and rainfall, there is likely to be a general shift of biomes with animals and plants moving towards the poles and upwards in elevation.

• The geographical range for some species will expand which may threaten local species. E.g. Boreal forest expansion into tundra threatens tundra ecosystem and species such as snowy owl and caribou.

• Less adaptive species or those already near the top of their thermal tolerance range will decrease in number with a potential risk of becoming extinct.

• If change is rapid, species may not be able to move quickly enough and therefore die out.

Figure 1. Caribou in tundra ecosystem within Alaska.

International-mindedness

The shift in range may involve species crossing national borders. This may require neighboring countries to work together to effectively manage habitat and species conservation.

Migration patterns

• Migratory species usually move in response to seasonal changes. Climate change could alter the timing of migration and mating e.g. warmer temperatures could result in some birds nesting and having offspring earlier.

• This earlier production of chicks may not be matched by availability of food sources resulting in high mortality rates.

Overall there is expected to be a loss of some habitats and significant reduction in biodiversity. Some ecosystems are particularly vulnerable e.g.:

• Coral reefs are at risk from coral bleaching, ocean acidification and damage by extreme storm conditions.

• Mediterranean type ecosystems where higher temperature will lead to further drying increasing risk of wild fires and desertification.

• Sea ice ecosystems are threatened by higher temperatures reducing their duration and extent.

Figure 2. Sea ice under threat from climate change provide a habitat for polar bears.

Reduction in habitats and species can result in a loss of ecosystem services. Ecosystems provide a diverse range of services that include:

• Provisional services e.g. food (such as fruit or fish), freshwater and timber.

• Regulation and supporting services e.g.:

  • Many ecosystems act as carbon sinks, absorbing carbon dioxide from the atmosphere and storing it within the biota. Hence deforestation reduces carbon dioxide uptake and carbon stores.

  • Mangroves ecosystems provide coastal defences, protect against coastal erosion and provide important nursery grounds for fisheries.

  • Nutrient recycling.

• Cultural services e.g. aesthetic and spiritual.

Hence, damage to ecosystem can have a major impact on human livelihoods and well-being.

The following video gives some specific examples of migration and species loss ‘Animal Migration - climate change impact' by DW:

Don't forget that migration happens in the sea as well!

Impact on coastal systems and low lying areas

Over 40% of the world’s population live in coastal areas. As a result of climate change, coastal regions are at risk from increased storm intensity and rising sea level.

Storm intensity

Storms, including tropical cyclone out at sea can generate high energy waves that hit the coast with the potential to cause coastal erosion, inundation, damage to settlements and even loss of life. Changing weather patterns are increasing coastal exposure to extreme storm events.

Figure 3. Hurricane over the Atlantic.

Rising sea levels

The rise in sea level increases risk of flooding of low lying coastal regions which could lead to:

• Salinization of agricultural land reducing its capacity to grow many types of crops.

• Degradation of coastal ecosystems e.g. wetlands, estuaries, mangroves and beaches.

• Damage to inland ecosystems threatening wildlife.

• Contamination of freshwater resources with salt water including saline intrusion of groundwater resources.

• Damage to infrastructure, homes and industry leading to loss of livelihoods.

• Risk to human life (e.g. death from drowning).

Low lying coastal areas such as the Netherlands, Bangladesh and The Maldives are especially at risk.

Impact on human health

Climate change may affect health through:

• Insufficient water and food resources.

• Degraded ecosystems reducing goods and services.

• Extreme weather such as heatwaves, storms and floods.

Heatwaves

• Heatwave episodes can result in cardiovascular and respiratory problems especially within the elderly and urban poor.

• The European heatwave in 2003 was the hottest summer in 500 years and contributed to about 35,000 deaths across Europe. The extreme conditions also exacerbated the effects of air pollution.

• Heatwave conditions can increase occupational health risk. Working in hot environments can lead to heatstroke and death.

Storms and intense rainfall

• Storms and floods could lead to injury or death by drowning.

• In the aftermath of an extreme event, lack of safe drinking water and poor sanitation could favour diseases e.g. cholera and typhoid.

• Flood waters could be contaminated with toxic chemicals or pathogens causing health problems e.g. from flooded chemical stores or with sewage effluent.

• Some communities may lose their homes and become refugees.

• Loss of harvest from extreme weather conditions could increase malnutrition.

Disease

A rise in temperature could result in a rise in the number of cases of disease as a result of:

• Increase geographical range of disease vectors e.g. malaria or dengue carrying mosquito.

Figure 4. Change in geographical distribution of malaria by 2050.

• Increase reproduction and survival rates of disease vectors e.g. Improved survival rates of midges that transmit Bluetongue virus to livestock, has allowed the disease to spread northwards in Europe.

• Increase geographical range and season of allergenic pollen.

Environmental refugees

Climate change can cause environmental disasters leading to loss of livelihood. People may migrate to other areas where they could be viewed as competing with locals for resources. This can lead to tensions and conflict developing. Hence, economic, social and political problems can arise.

An increase in extreme weather events and coastal inundation is expected to increase the number of environmental refugees. Norman Myers (Environmental Scientist) estimated that by 2050 there will be about 150 million environmental refugees.

International-mindedness

Environmental refugees may require international cooperation and collaboration to provide a solution to resettle people that have lost their homes and livelihoods.

Examiner Tip

Ensure you are able to discuss both the advantages and disadvantages of climate change.

Climate change debate

There are differing viewpoints on the causes of climate change and its predicted impacts. The overall scientific consensus is that climate change is occurring and is contributed to by human activity. Individuals such as Al Gore (former US Vice-President), more recently Pope Francis together with organizations such as the Intergovernmental Panel on Climate Change (IPCC) have helped to raise the issues of climate change on the political agenda.

Figure 1. Al Gore’s campaign to take action against climate change includes a book and documentary entitled ‘An inconvenient truth’.

There is concern that climate change will cause sudden changes which we will probably be unable to reverse and is referred to as the tipping point. We are still unsure when this may happen or under what conditions a tipping point would be triggered.

Also under scrutiny are the accuracy of models used to make predictions that inform the decisions and actions we take.

Tipping point

Definition

The IPCC define tipping point as: ‘A level of change in system properties beyond which a system reorganizes, often abruptly, and does not return to the initial state even if the drivers of the change are abated. For the climate system, it refers to a critical threshold when global or regional climate changes from one stable state to another stable state. The tipping point event may be irreversible.’

Examples of potential tipping points include:

• Increased temperatures in the high northern latitudes could lead to dieback of Boreal forest and their replacement with temperate forest or grasslands.

• An increase in greenhouse gases (GHGs) resulting in a rise in ocean temperature and ocean acidification is likely to lead to the death of corals. Scientists estimate that coral cover in the Great Barrier Reef in Australia could drop to less than 10% from the combined effects of ocean temperature rise of 1-2°C and pollution. This 10% coral cover is the estimated tipping point for reef growth, below which the coral reef may never recover.

• Impact of climate change such as prolonged drought together with deforestation could lead to a stage where the amazon forest becomes savanna or desert; habitats more adapted to drought and wildfire events.

Figure 2. Climate change could exacerbate desertification.

Models used in climate change

Models are used to predict future change in climate to prioritize and aid decision making. Models attempt to represent natural systems and are mathematical formulae based on existing data and knowledge as discussed in subtopic 1.2 Systems and models. A visual representation of the projections can also help understanding.

Climate change models are complex and levels of uncertainty arise from:

• Use of incomplete data sets.

• Use of data measured using different protocols and equipment.

• Incomplete understanding of positive and negative feedback systems e.g. effect of clouds.

• Incomplete understanding of effects of ocean circulation system.

• Unknown tipping points.

• Difficulty in predicting human behaviour and associated GHG emissions.

• Difficulty in predicting when major volcanic events will occur.

• Differences in interpretation of information from models leading to differing predictions.

The IPCC use models to make projections for different scenarios from business as usual to radical reductions in GHG emissions. The projections help to identify the areas at most risk. This can be used by policy makers and politicians to decide where to prioritise use of resources.

Examiner Tip

Ensure that using an example you are able to discuss the advantages and disadvantages of using models in Environmental Systems and Societies.

Viewpoints

Climate sceptic view

Groups which do not believe that climate change is occurring or is caused by humans are lobbying to make their views heard. For example, Martin Durkin, film producer made a documentary ‘The great global warming swindle’ arguing that the evidence for climate change was not accurate and fuelled by scientist keen to maintain funding for their research. Many climate sceptic groups are funded by businesses that could be adversely affected by mitigation action. The current Trump administration is keeping this debate alive!

Figure 3. Sarah Palin, former Governor of Alaska is famous for her anti-climate change views.

Climate sceptics’ dispute human activity is responsible for climate change. They argue:

• That human induced global warming is not proven, changes in climate have always occurred and warming has occurred before prior to humans changing GHG levels.

• Warming is a natural phenomenon and a result of natural cycles e.g. related to sunspot activity or Milanokovich cycles.

• Climate change models used are inaccurate and impacts are exaggerated.

• Data that is technologically verifiable has been collected for only relatively short time period.

• Scientists manipulate results to attract future funds for research.

Climate advocator view

In contrast to climate sceptics, climate advocators believe that climate change is predominantly human induced and major reforms are required to stop emissions. They argue:

• There is sufficient scientific data from a variety of sources as evidence of warming occurring (e.g. data from sediments and ice cores and direct measures).

• Levels of GHG emissions from human activity since the industrial revolution correlates with rise in average global temperature.

• Current rate of global temperature increase is unprecedented.

• There is scientific consensus that climate change is occurring.

• It is too late to avoid some problems of climate change and we also need to focus on how to adapt to changes.

Figure 4. The findings of these studies illustrate that most scientists agree that humans are responsible for climate change.

Some climate advocates also argue that climate change predictions are under estimates and that tipping points are not considered and abrupt changes are likely to occur over a short time e.g. melting of Antarctic ice.

International-mindedness

Due to the scale of climate change, international coordination is necessary to deal with the impacts.

Environmental Value Systems

Depending on EVS the approach taken to deal with impacts of climate change vary. Decisions made by people with ecocentric and anthropocentric values will be driven by their responsibility to safeguard the environment for future generations and for other species.