3.7.2 Global Warming

Global Warming

Global Warming

Changes in the global climate

• The global climate conditions of the Earth range over time leading to colder and warmer periods

• The last 2.6 million years are the Quaternary period when there have been 60 cold periods and warmer interglacial periods

• The last ice age ended approximately 25,000 years ago

• The evidence for these changes comes from:

  • Ice cores which trap ash, air bubbles and microbes

  • Preserved pollen

  • Historical sources such as diaries and art

  • Tree rings

Causes of Natural Climate Change

The greenhouse effect

• The greenhouse effect is essential to the survival of life on Earth:

  • Greenhouse gases in the atmosphere allow short-wave radiation from the sun through to the Earth's surface

  • The greenhouse gases absorb some of the long-wave radiation (heat) and stop it radiating out into space

  • This maintains the Earth's average temperature

  • Without the greenhouse effect the average temperature would be -18^oC

Greenhouse gases from natural sources  

• Water vapour - evaporation from the oceans/seas and plants

• Carbon dioxide - volcanic eruptions, wildfires and respiration

• Methane - emitted from oceans and soils as part of decomposition, termites also emit methane

• Nitrous oxide - soils and oceans

The enhanced greenhouse effect

• Human activity is increasing the number of greenhouse gases in the atmosphere:

  • Carbon dioxide (CO₂) levels in the atmosphere have increased by more than 100 parts per million (ppm) to 420ppm in 2020

• Increased amounts of greenhouse gases have led to the enhanced greenhouse effect:

  • Less long-wave radiation (heat) can escape the atmosphere

  • Average global temperatures have increased over 1^oC since pre-industrial times

Average Global Temperatures

Human Sources of Greenhouse Gases

Impacts of the enhanced greenhouse effect

Health

• Increased temperatures and lack of precipitation may lead to the spread of diseases:

  • Italy has experienced cases of malaria since 2017 when it was previously a malaria free area

  • An additional 280 million people may be affected by malaria

  • Water-borne diseases are more likely to spread

• Heat waves may become more frequent

• Heat stroke, dehydration and sunburn increase during heat waves

• Stagnant air during heat waves increases air pollution levels:

  • Respiratory diseases increase and those suffering from respiratory illnesses such as asthma may be more affected 

• Increased temperatures negatively affect people with cardiopulmonary diseases

• Diets may be restricted by food shortages leading to malnutrition and famine

Homes and settlements

• Increased flooding due to sea level rise and increased frequency and severity of storms will lead to displacement of large numbers of people

• Settlements in low-lying areas may have to be abandoned or need additional defences against sea level rise:

  • Moving settlements or improving flood defences will be costly

Agriculture

• Farmers may need to change the crop they grow if climate conditions become unsuitable

• Coastal flooding may lead to salt intrusion

• Reduced availability of water will mean that irrigation is limited or impossible

• Food shortages will lead to malnutrition and famine

Employment

• Job opportunities may change or decrease because:

  • Tourism may decline in some areas for example ski resorts may close due to the lack of reliable snow

  • Coastal resorts may be at risk of flooding leading to the closure

  • Farmers may have to change the crop they grow or livestock they raise or leave farming

  • In some areas agriculture may decline due to rising temperatures or changing rainfall patterns

Sea level rise

• Warmer temperatures cause the water in seas and oceans to expand, increasing the sea level

• Melting ice is adding to the increasing volume of water:

  • Average sea levels have risen 23cm since 1880

  • Sea levels are forecast to increase a further 30cm by 2050

• Low-lying coastal areas and islands are at higher risk of flooding:

  • The Maldives may be uninhabitable by 2050 

• Beach erosion will increase leading to greater coastal erosion 

• Coastal ecosystems including coral reefs and mangrove swamps will be affected

• Saltwater is contaminating freshwater supplies and affecting coastal agriculture

Ecosystem change

• The location of biomes may shift to the north (Northern Hemisphere) and south (Southern Hemisphere) as they rely on specific climate conditions:

  • Polar and tundra biomes are at risk of becoming extinct as they cannot shift any further north/south

• Increasing sea temperatures and ocean acidification have resulted in coral bleaching

• Migration and behaviour patterns of animals affected by changing temperatures:

  • Fish species are moving north and south of their usual habitats to seek cooler water

  • Reduced hibernation due to warmer winters

• Melting of ice caps/glaciers leading changing ocean currents

• Mangrove swamps and coral reefs are threatened by rising sea levels

• Loss of habitats through flooding, drought and wildfires

• Food webs breaking as species numbers are reduced and food sources are decreased

• Loss of plants and vegetation

Natural hazards

• Changes in climate patterns are likely to increase the frequency and severity of storms:

  • The 2020 Atlantic hurricane seas were the first most active on record and 2021 was the third most active

• The frequency and length of droughts are increasing

• Dry conditions lead to the increased risk of wildfires:

  • In 2021 Australia, Greece, South Africa, Brazil and USA were just some of the places to experience severe wildfires

  • In September 2021 the USA National Fire Centre reported 44.647 wildfires which had burned 5.6 million acres

• Rising sea levels together with increased storms lead to increased flooding risk

Responses to climate change

• Global warming and climate change require an international response because it affects the entire globe

• Responses can involve either adaptation or mitigation

• In 1988 the Intergovernmental Panel on Climate Change (IPCC) was set up to assess the 'risks of human-induced climate change

• This was followed by several international agreements

Earth Summit, Rio 1992

• Set out aims to stabilise greenhouse gas levels 

Kyoto Protocol 1997

• Delegates from 150 countries agreed to reduce greenhouse gas emissions

• It stated that industrialised countries would reduce emissions to below the levels in 1990

• Developing countries including China and India were exempt from the agreement

• The USA did not sign up for the treaty

• Canada withdrew in 2011 stating that without China and USA the treaty would not work

Paris Agreement 2015

• Global agreement to limit global warming to 2^oC (preferably 1.5^oC) above pre-industrial levels

• Agreement also includes reducing CO₂ emissions by at least 60% by 2050

• Signed by 196 countries including the USA and China (the USA withdrew in 2020 and rejoined in 2021) 

Conference of the Parties (COP)

• The United Nations (UN) holds an annual (every year) meeting to discuss climate change.

• COP26 was held in Glasgow in 2021 

• All nations agreed to take actions to further reduce greenhouse gas emissions

Reducing emissions 

• Emissions can be reduced in a number of ways including;

  • Reducing deforestation 

  • Increasing afforestation

  • Improving energy efficiency in industry and domestic appliances

  • Reducing emissions from industry

  • Improving public transport

  • Electric vehicles

  • Use of renewable energy and nuclear power