Climate Change

• 1. Methods used to reconstruct the Earth's past climate:

  • Sea-floor sediments - The fossil shells of tiny sea creatures called foraminifera, which accumulate in sea-floor sediments, can be used to reconstruct past climates. The chemical composition of foraminifera shells indicates the ocean temperatures in which they formed.
  • Ice Cores - Ice cores from the polar regions contain tiny bubbles of air - records of the gaseous composition of the atmosphere in the past. The colder the climate, the lower the frequency of oxygen and hydrogen atoms.
• 3. Methods used to reconstruct the Earth's past climate:

  • Tree rings - Tree rings (annules) vary in width each year depending on temperature conditions and moisture availability.
  • Fossils - Plants and animals require specific environmental conditions to thrive. Some, such as coral reefs, are highly sensitive in temperature, water depth and sunlight.
• 2. Methods used to reconstruct the Earth's past climate:

  • Lake sediments - Past climates can be reconstructed from pollen grains, diatoms and varves in lake sediments. Pollen analysis identifies past vegetation types. Diatoms are single-celled algae found in lakes with cell walls made of silica. They record evidence of past climates in their shells. Varves are tiny layers of lake sediment comprising alternating light and dark bands.
• The current geological period is known as the Holocene. It began at the end of the last glacial, 11,700 years ago. The Holocene is, therefore an inter-glacial period: a brief interlude separating glaciers which have dominated 90% of the Quaternary. During the Holocene ice sheets and glaciers have shrunk and the sea level has risen by over 100m, and with the exception of Antarctica and Greenland, ice sheets have disappeared from the continental surface.
• The Quaternary period spans the last 2.6 million years. The main feature of the Quaternary has been cyclic changes of climate, with long cold periods or glacials interrupted by shorter, warmer inter-glacials.
• Natural forcings, which induce change in the climate system, may be external or internal. External forcings include astronomical shifts in the Earth's orbit and axial tilt, equinoxes and fluctuations in solar output. These forcings control the incidence and distribution of solar radiation on the planet's surface. However, among internal forcings there are volcanic eruptions, continental drift, changes in ocean circulation and fluctuations in CO2.
• External forcing mechanisms hypothesised by Milankovitch:

  1. Obliquity (Tilt of the Earth's axis) - Over a period of around 44,000 years, the Earth's axial tilt varies from 22 degrees to 24.5 degrees. (Current tilt is 23.4 degrees). When the tilt is close to 22 degrees, seasonal temperature differences are reduced. As a result, snow and ice, accumulated during winter, do not melt during the summer, allowing glaciers and ice sheets to expand. This has a positive feedback effect, increasing the reflection of incoming solar radiation and lowering temperatures further.
• External forcing mechanisms hypothesised by Milankovitch:

  2. Eccentricity of the Earth's orbit - The Earth's orbit around the Sun follows an elliptical path. The eccentricity of the orbit varies from near-circular to markedly elliptical over periodicities of 96,000 and 413,000 years. With maximum eccentricity, differences in solar radiation receipt of around 30% occur between perihelion (When the Earth is closest to the Sun) and aphelion (When the Earth is furthest from the Sun). Ice ages correspond to periods of maximum orbital eccentricity.
• External forcing mechanisms hypothesised by Milankovitch:

  3. Precession of the equinoxes - The Earth gyrates on its axis like an enormous spinning top, so that the point in the Earth's orbit when the planet is closest to the sun (perihelion) changes over time. This shift or precession which occurs with a periodicity of around 22,000 years is due to the gravitational influence of the moon and Jupiter and affects the intensity of the seasons. If perihelion occurs during the northern hemisphere's winter, winters will be warmer and summers cooler. Snow and ice accumulating may not melt completely
• Natural Forcings:

  1. Volcanic eruptions - Change the climate in the short term through sulfur dioxide having a cooling effect by reflecting solar radiation.
  2. Plate Tectonics - As a larger continental area occupies higher latitudes, the land area with permanent ice cover expands.
  3. Ocean Circulation - Oceans can absorb large amounts of current so when ocean currents and downwelling patterns change, this may change atmospheric carbon.
  4. Solar Output - The Sun's output is not constant but varies over time.
• In recent decades, humankind, due to population growth and technological advances, has become the dominant influence forcing environmental change. This change, which is both deliberate and inadvertent, marks the end of the Holocene period: today the Earth has entered a new geological epoch known as the Anthropocene.
• Evidence that the world has warmed since the late 19th Century:

  • Increases in global temperatures (2023 broke records).
  • Shrinking valley glaciers and ice sheets. (Russell Glacier, Greenland shrinking)
  • Rising Sea Levels. (Around 3mm a year)
  • Decreasing snow and sea ice.
• Before 1800, CO2 parts per million (ppm) was at 280 ppm but this increased to 426 ppm as of 2024.
• CH4 has 25 times the global warming potential than CO2.
• Reasons for rising emissions since the pre-industrial era:

  • The huge surge in demand for energy.
  • Global population increase with rising living standards.
  • Land-use change. E.g. Deforestation and the drainage of wetlands.
• In 1988, the International Panel on Climate Change (IPCC) was set up.
• 97% of climate scientists support the view that global warming is taking place.
• Once global temperatures increase above the 2 degree threshold, it is widely held that abrupt and irreversible climate change will begin to occur.
• In 1992, 41 countries joined an international treaty, the UN Framework Convention on Climate Change (UNFCCC), to consider what action should be taken to limit global warming.
• Efforts from the UNFCCC brought around the Kyoto Protocol of 1997.
• What year was the Kyoto Protocol?

  1997
• The Kyoto Protocol, for the first time set legally binding targets on countries to reduce their greenhouse gas emissions. 192 countries were parties to the Kyoto Protocol, though several major emitters, including the USA and China never ratified the treaty.
• The Kyoto Protocol was split into two sections:

  • The first section outlined a target of decreasing GHG emissions by 5% below 1990 levels by 2012.
  • The second section outlined a target of decreasing GHG emissions by 18% below 1990 levels by between 2012 and 2020.
• The Climate Change Act (2008) commits the government to reduce emissions by at least 80% by 2050.
• In an attempt to provide a balanced discussion and accommodate dissenting views, some media organisations, including the BBC, have been accused of false balance. By giving disproportionate coverage to sceptics, they suggest that climate change is more controversial than experts believe.
• Current global temperature predictions would result in a 2 - 4 degrees increase.
• Current sea level increase projections are at around 1 metre.
• Climate Change will affect:

  • Marine ecosystems (Marine ecosystems, fish stocks) (Affect tourism and food supplies)
  • Terrestrial ecosystems (Wetlands may expand which would attract birds but habitats may also be destroyed by sea level rise and desertification.)
  • Human health (Rise in heat stroke)
  • Extreme weather (Dangerous to humans and habitats)
• Coastal communities and habitats may be some of the most vulnerable.
• Mitigation strategies to cut global emissions of GHG:

  • Energy efficiency and conservation.
  • Fuel shifts and low-carbon energy sources.
  • Carbon capture and storage.
  • Geoengineering. (Use of technology to modify the environment.)
  • Reforestation and forest conservation.
• Adaptation strategies to reduce the vulnerability of human populations at risk:

  • Retreat strategies. (Managed realignment)
  • Accommodation strategies. (New crop strains)
  • Protection strategies. (Hard engineering)
• The IPCC published its 6th report in 2021.
• The EU Emissions Trading System (EUETS) is the world's largest GHG trading scheme. Introduced in 2003, it includes more than 11,000 power stations and industrial plants from across the EU.
• Denmark has its own ambitious targets to reduce its GHG emissions: an interim 40% reduction by 2020 and by 2050, all energy consumption is expected to be from renewables.
• Demand for fossil fuels in Denmark will be reduced by carbon taxes and tax exemptions on hydrogen fuel cell and electric cars.
• Copenhagen, the capital and largest city in Denmark, developed its own adaptation strategy in 2011. The aim is to create 'climate-proof neighbourhoods'. Detailed plans have been drawn in the event of heavy rain overwhelming the city's drainage systems.
• California's policies are far more radical and far-reaching than those of the US government.
• In California, legislation passed in 2006 - The Global Warming Solutions Act - set absolute state wide limits on GHG emissions and committed the state to decarbonisation and a clean energy economy,
• The target set by California is to reduce GHG emissions by 80% below 1990 levels by 2050.
• What is this graph called?

  The Keeling Curve