Natural vs Human causes

• The natural greenhouse effect

  • The radiation emitted by the sun has a high energy short wavelength and can pass through greenhouse gases
  • This short wave radiation heats up the ground, causing it to emit long wave radiation
  • Some of this radiation escapes into space
  • The rest of the long wave radiation is absorbed by greenhouse gases and reemitted back down to the earth's surface.
  • This warms the atmosphere and is the natural greenhouse effect
  • Without it, global temperature would be -18 degrees
• The enhanced greenhouse effect


  • When the concentration of greenhouse gases increase, there are 2 changes
  • 1: Less long wave radiation escapes into space
  • 2: More long wave radiation is absorbed and reemitted > higher temperatures
• Tectonic activity reduces atmospheric CO2

  • Tectonic uplift occurred when the Indian plate collided with the Eurasian plate, causing the Himalayas to form
  • As air rises, condenses and forms clouds, this creates precipitation > typically in the form of relief rainfall in mountainous regions like the Himalayas
  • CO2 is dissolved into these water droplets, forming carbonic acid
  • This transfers carbon from the atmosphere store into the hydrosphere store
• Climate conditions 100 mya

  CONDITIONS:

  • Average global temperature 6-8 ° higher than today - present: 15 ° global average
  • No polar ice caps do it being a warm phase > low albedo > more absorption of solar radiation > higher temperatures

  WHY:

  • Atmospheric CO2 levels 5x higher than today > greenhouse effect > temperature increases
  • The continents configuration was very different which affected ocean circulation and the earths energy budget
• Climate conditions 55 mya

  CONDITIONS

  • Spike in global temperatures during the Eocene epoch, where the average temperature peaked 23 ° (the thermal maximum) at the time when Pangea was splitting into different continents - lasted c. 200,000 years

  WHY

  • Huge amounts of carbon were released into the atmosphere and oceans in the form of CO2 and Methane > enhanced green house effect
  • Globe warmed by 5-9 ° over a long period of time > ecosystems adapted
• Climate conditions 33 mya

  CONDITIONS

  • Rapid transitions to colder conditions and this continued until present day > Oligostene period
  • CO2 levels decreased rapidly from c. 1000 ppm to 600 ppm
  • Glaciation of Antartica as it rapidly descended into a permanent icehouse state

  WHY

  • A major reduction in atmospheric greenhouse gases, especially CO2, as well as changes in tectonic processes
  • Permanent icehouse state > higher albedo > more insolation was reflected > lower temperatures > increased diagenesis > increased accumulation > higher albedo > ice albedo positive feedback loop
• Climate conditions during Quaternary glaciation

  CONDITIONS

  • Cyclic changes of climate between long and cold glacial periods, and shorter and warmer interglacial periods

  WHY

  • Glacial periods = temperatures were well below zero, lasting around 100,000 years
  • Interglacial periods = warmer temperatures lasting around 10,000-15,000 years
• Climate conditions in the last 450,000 years

  CONDITIONS

  • 1/3 of surface continent covered in snow and ice
  • Ice sheets 1 km deep in Scotland
  • Most recent glacial = Devensian period

  WHY

  • Four major glacial and interglacials periods
• Climate conditions in the Holocene - last 11,700 years

  CONDITIONS

  • Began at the end of the last glacial
  • Temperatures warmed up
  • Ice sheets and glaciers shrunk
  • Sea levels risen by 100 m
  • Only remaining continental sheets: Antarctica and Greenland

  WHY

  • Human activity: burning fossil fuels, non-renewable energy, deforestation led to increased atmospheric CO2> enhanced greenhouse effect
• Natural causes of climate change

  • Milankovitch Cycles
  • Volcanic eruptions
  • Tectonic eruptions
  • Solar output
• Natural Cause: Milankovitch Cycles

  • Orbital Eccentricity
  • Obliquity - tilt
  • Precession - wobble
• Orbital Eccentricity


  • It is a 100,000 year old cycle
  • It refers to the shape of the earth’s orbit around the sun as it drifts away from a perfect circle and reaches maximum eccentricity at certain points
  • When the earth is at its furthest point from the sun- aphelion -temperatures decrease > accumulation of snow and ice
  • This means that the surfaces have a high albedo > reflect a large amount of incoming radiation > contributes to the earth's cooling
• Obliquity - tilt


  • Revolves around the tilt of the earth’s axis with it currently being at 23.5 °
  • Over a c. 40,000 year cycle, the earth’s tilt varies between 22 and 24.5 degrees
  • During periods of maximum tilt the earth’s winters become colder as snow and ice accumulates
  • The ice has a high albedo > reflects sunlight > inhibits melting > potentially leads to the growth of ice sheets and glaciers > contributes to glacial periods
• Precession - wobble


  • Occurs every c. 23,000 years
  • Involves the earth’s ‘wobble’ on its axis which impacts the timing and intensity of seasonal variations in different hemispheres
  • This cycle can emphasise seasonal differences as it affects the distribution of ice and climate patterns
• • When all three Milankovitch cycles occur simultaneously they amplify each other’s effects which leads to cold glacial periods
  • These cycles take place over long geological timescales
  • Play a crucial role in shaping the earth’s climate through creating future climate shifts
• Natural Cause: Volcanic eruptions


  Volcanic eruptions release Sulphur Dioxide (SO2) into the atmosphere > form sulphate aerosols > often take several years to fully disperse > aerosols have a high albedo > reflect a large amount of incoming solar radiation > temperatures decrease > contribute to short term climate fluctuations
• Natural cause: Tectonic activity


  2 contributing factors

  • Tectonic Uplift
  • Position of continents
• Tectonic uplift


  • Tectonic uplift is the process of when two continental plates collide eg. Indian plate collided with the Eurasian plate > formed the Himalayas
  • As air rises, condenses > forms clouds > creates precipitation > relief rainfall in mountainous regions like the Himalayas
  • Water droplets absorb Carbon Dioxide > forms carbonic acid
  • Transfers carbon from the atmosphere to the hydrosphere > leads to chemical weathering
  • The carbon is eventually transferred into rivers and oceans > contributes to the acidification of ocean waters
• Position of continents


  • Pangea shift occurred 250 million years ago
  • It refers to the movement of the Earth’s continents from a single land mass, Pangea, to their current positions through tectonic processes like uplift
  • Tectonic uplift causes carbon to be transferred out of the atmosphere > reduces the natural greenhouse effect> temperature decreases > shapes long term climate change patterns
• Solar output


  • Sunspot activity can be used as a proxy for solar output
  • Solar output follows an 11 year cycle
  • It refers to the amount of energy emitted by the Sun over a certain period of time
  • Sunspot activity is not enough to impact global climate significantly
  • Near the end of the 17th century, sunspot activity declined to almost zero for several decades
• Carbon emissions


  1800: 280 ppm

  present: 420 ppm
• Humans have influenced the climate system leading to a new epoch, the Anthropocene
• Evidence the world has warmed since the late 19th century

  • Increases in global temperatures - surface, atmospheric and oceanic
  • Shrinking of valley glaciers and ice sheets
  • Rising sea level
  • Increasing atmospheric water vapour
  • Decreasing snow cover and sea ice
• Increased global temperatures


  • Average global temperature increased by 1.1 degree since 1800
• Shrinking valley glaciers and ice sheets

  • Thickness of valley glaciers has decreased by 12 m/ year
  • This adds 1 mm/year to sea levels
• Rising sea levels

  • Sea levels have risen by 20 cm since 1800
  • Due to two factors including thermal expansion and melting of valley glaciers
• Increasing atmospheric water vapour

  • For every 1 degree increase in temperature caused by enhanced CO2 levels, rising levels of water vapour will double
  • Increased atmospheric water vapour > enhances greenhouse effect > positive feedback loop
• Decreasing snow cover and sea ice

  • Decline in snow cover of 2 % per decade since 1966
  • Antarctica's snow cover and sea ice decreases by 1 % per decade
• Greenhouse gases and changes in emissions

  • Greenhouse gases are gases in the atmosphere such as CO2, methane, nitrous oxide and water vapour
  • They absorb long wave terrestrial radiation
  • Methane is the most potent - absorbs and emits more heat than CO2 > 25 x more potent
• Why was there a surge in GHG emissions in the past two centuries?

  • High surge in demand for energy
  • Increase in global population
  • Change in land use
• High surge in demand for energy

  
  

  • This is due to industrialisation and technological advancements, particularly in transport and manufacturing
  • Energy supply accounts for 26 % of GHG emissions
  • 2/3 of emissions come from fossil fuels
• Change in land use

  
  

  • This is due to deforestation and the draining of wetlands for food production and urban development
  • 1/3 of emissions come from deforestation
  • Forestry and agriculture combined accounts for 31 %
• Changes in GHG emissions around the world

  • 1850-1960: Most GHG emissions from Europe and N.America
  • 1960-present: Europe responsible for 50 % of emissions, USA responsible for 35 %
  • 1960-present: Asia's emissions increased significantly, driven by China and India's economic growth
  • 2011: Asia responsible for 53 % of global emissions
  • Overall: HUGE 254 % increase in total emissions from 9,000 to 32,000 with every country emitting more
• Contribution to anthropogenic GHG emissions over time


  AC example: UK

  EDC example: China
• UK trends in Carbon emissions

  • UK's main energy source was coal for much for the 20th century
  • This peaked in 1916 at 137 million tonnes
  • Until 1970, the reliance on coal in an expanding economy meant that carbon emissions increased each year
  • 1980s: decline due to economic recession
  • 2009: Global financial crisis > sudden reduction in CO2 from fossil fuels
• Reasons for the fall in UK CO2 emissions

  • Shift from coal as a primary fossil fuel for electricity generation to gas
  • Development of nuclear power stations in the 70/80s and renewable energy in the 90s
  • Improved energy conservation through energy efficient homes, offices and factories
  • International obligations/ legally binding laws in reductions of CO2 emissions
• Recent changes in UK's energy mix

  MAJOR reductions in fossil fuels

  • 2014: 87 % from fossil fuels
  • Present: 13 % from fossil fuels, 57 % renewable energy
• How has China's carbon emissions changed historically?

  • Until 1970s : economy mainly rural and largely dependent on biofuels
  • Industrialisation led to urbanisation > rural-urban migration
  • Average incomes increases > GDP increased from $300 to $13000
  • Industrialisation was made possible by huge energy consumption, mainly from coal > increased carbon emissions
• China vs UK's energy mix

  China: mostly coal - 65%

  UK: mostly natural gases - 35%
• Recent changes to China's energy mix

  Mostly coal: 65%

  China pledges to become carbon neutral before 2060