Causes of Climate Change (HL IB ESS OLD COURSE - IGNORE)

Anthropogenic Influence on Climate

• Human activities have significantly increased atmospheric concentrations of greenhouse gases since the Industrial Revolution

  • Particularly carbon dioxide emissions from burning fossil fuels

• This has led to:

  • Global warming: average global temperatures have risen due to enhanced greenhouse effect

  • Climate change: altered weather patterns, sea level rise and impacts on ecosystems and human societies

Global rate of emissions

• Since 1950, the rate of anthropogenic carbon dioxide emissions has significantly accelerated

  • This acceleration is due to several factors, including:

• Industrial Revolution:

  • It began in the late 18th century in Europe

  • Marked a turning point with the widespread use of fossil fuels such as coal and later oil

• Technological advancements:

  • The 20th century saw rapid industrialisation, transportation development and urbanisation

  • These all contributed to increased emissions

• Population growth:

  • The global population has increased exponentially

  • This has increased demand for energy and resources, further accelerating emissions

Analysis of ice cores, tree rings and sediments

• Ice cores, tree rings and sediment deposits provide important data for understanding:

  • Historical climate patterns

  • The relationship between carbon dioxide levels and global temperatures

• Ice cores:

  • Layers of ice in glaciers trap air bubbles containing the gases from ancient atmospheres

  • Analysis of these bubbles shows historical carbon dioxide levels

    • Ice is deposited as water freezes over time, so the deeper into the ice you go, the older it is

• Tree rings:

  • Trees form annual rings with varying widths based on climate conditions

    • Thicker rings indicate favourable (warmer) conditions, potentially linked to higher carbon dioxide levels

  • Analysis of the width of tree rings can provide a measure of climate during each year of growth

  • Taking cores from the trunks of older trees can provide samples that go back over hundreds of years

• Sediments:

  • Deposits in lakes and oceans contain remains of organisms sensitive to environmental changes

    • This provides indirect evidence of past climates

Positive correlation between carbon dioxide and global temperatures

• Research using data from these sources shows a clear positive correlation between atmospheric carbon dioxide concentrations and global temperatures

  • Carbon dioxide levels: as industrial activities have increased, so have atmospheric carbon dioxide levels

  • Temperature records: proxy data from ice cores, tree rings and other sources indicates that periods with higher carbon dioxide concentrations correspond to warmer global temperatures

  • Modern instrumental records: direct measurements since the mid-20th century confirm a sharp rise in temperatures, aligning with increased emissions

• Since the Industrial Revolution, atmospheric carbon dioxide levels have risen to their highest in Earth's history

  • Before, the highest atmospheric carbon dioxide concentration was around 300 parts per million (ppm)

  • It is currently above 400 ppm

• Data show a correlation between changing atmospheric carbon dioxide levels and temperature over thousands of years

  • Correlation does not equal causation

  • However, this is convincing evidence supporting the hypothesis that carbon dioxide emissions from human activity are driving up global temperatures

Average global temperatures

• Thermometers can be used to measure air temperature

• Records from the mid-1800s show an overall trend of increasing average global temperatures

  • There are some short time periods within this window during which temperatures have declined, but the overall trend is upward

• The time period since the mid-1800s corresponds with the time during which humans have been burning fossil fuels

• 90% of global carbon dioxide emissions come from industry and burning fossil fuels

  • As carbon dioxide, methane and water vapour are released, they act as greenhouse gases and trap heat within the Earth’s atmosphere

  • Human activities are responsible for almost all of the increase in greenhouse gases in the atmosphere over the last 150 years

The Enhanced Greenhouse Effect

• The enhanced greenhouse effect is different from the natural greenhouse effect

  • It is the result of human activities that release excessive greenhouse gases into the atmosphere

  • This leads to an intensified trapping of heat and results in global warming

• The natural greenhouse effect is a necessary process

  • It helps regulate the Earth's temperature by trapping some heat to maintain a habitable climate

• The enhanced greenhouse effect disrupts this balance as a result of greenhouse gas concentrations being artificially increased beyond natural levels

Modelling Climate Change

Systems diagrams and models

• Representing cause and effect:

  • Systems diagrams and models are tools that can be used to visualise how different factors interact and cause climate change

  • They help us understand cause-and-effect relationships and how changes in one part of the system affect others

Feedback loops

• Feedback loops are processes that can either amplify or dampen the effects of climate change

  • Positive feedback loops amplify changes

  • Negative feedback loops reduce or counteract changes

• Global energy balance:

  • The global energy balance is the balance between the energy Earth receives from the Sun and the energy it radiates back into space

  • Changes in this balance can significantly impact the climate

Changes in solar radiation and terrestrial albedo

• Solar radiation is the primary source of energy for Earth's climate system

• Variations in solar radiation can lead to changes in climate

  • For example, the Maunder Minimum (1645–1715), a period with very few sunspots, was associated with cooler global temperatures

• Changes in solar radiation can initiate feedback loops

  • Decrease in solar radiation: can cause cooling, leading to an increase in snow and ice cover

    • This increases the Earth's albedo, causing further cooling (negative feedback loop)

    • For example, during the Maunder Minimum, reduced solar radiation contributed to the Little Ice Age

  • Increase in solar radiation: can cause warming, reducing snow and ice cover

    • This decreases the Earth's albedo, causing further warming (positive feedback loop)

Carbon dioxide and methane release

• Carbon dioxide and methane are greenhouse gases

• Carbon dioxide and methane get trapped in permafrost as organic matter freezes before it can fully decompose

• Positive feedback loop:

  • When the permafrost thaws due to warming temperatures, these trapped gases are released into the atmosphere

  • These greenhouse gases then contribute to further global warming and climate change

Crossing the planetary boundary for climate change

• Climate change is one of the nine planetary boundaries outlined by the planetary boundaries model

  • Planetary boundaries are thresholds that lead to significant environmental changes if they are crossed

• Evidence suggests Earth has already crossed the boundary for climate change

  • The Intergovernmental Panel on Climate Change (IPCC) is a leading authority on climate science

  • IPCC reports provide comprehensive assessments of climate change, based on the latest scientific research

  • These reports show:

    • Significant increases in global temperatures:

      • Over the past century, the average global temperature has risen by approximately 1.1 °C

      • The most rapid warming has occurred in recent decades

    • Rising greenhouse gas concentrations:

      • Levels of carbon dioxide and methane in the atmosphere have increased dramatically

      • Due to human activities like burning fossil fuels, deforestation and agriculture,

    • Current impacts:

      • These changes contribute to more frequent and intense extreme weather events, such as heatwaves, storms and flooding

      • As well as long-term effects like rising sea levels and shifting ecosystems