Climate change

• Global warming

  The warming of earth’s overall temperature.
• Climate change

  the long-term effects of global warming on environments and ecosystems
•  Methods used to reconstruct past climate:

  sea floor sediments

  Lake sediments

  Ice cores

  Tree rings

  Fossils
• Marine/sea floor sediments:

  >Foraminifera (tiny sea creatures) accumulate in seafloor sediments

  > Chemical composition of the shells indicates ocean temperatures at the time they were formed.

  -) process of abstracting sediments require releasing additional co2/pollution

  -) disturbs aquatic life

  -) inaccuracy: chemical composition may be disturbed due to oceans increased acidity from increased co2 levels in atmosphere
• Lake sediments

  • Pollen grains and spores can identify past vegetation and paleoclimatic conditions.
  • Diatoms (single celled algae) record the climate in their shells
  • Varved sediments – reflect seasons in previous climates:
  • light layers - coarse sediment from high energy meltwater run-off in summer
  • dark layers - fine sediment deposited in winter

  -)process of abstracting sediment may disturb nearby wildlife

  -)challenging to collect
• Ice cores:

  • Ice forms air bubbles which are trapped – stores gaseous composition of the atmosphere.
  • Drilling through layers of ice allows us to look back at past climates.
  • Colder climates have lower frequencies of hydrogen and o2.

  -) process of drilling and investigation disrupts environment

  -) considered environmentally unethical
• Tree rings:

  • Dendrochronology – dating of past climates through tree ring (annule growth)
  • Annules vary in width each year depending on moisture availability and temperature
  • compare with rock strata it is in

  -) tree rings may be drastically changed due to other factors more recently

  -) deforestation has removed majority of older existing trees

  -) process of cutting down trees - environmentally unethical
• Fossils

  • Plants and animals require specific env conditions.
  • Where they exist in fossil record can be used as proxies for past climate

  -) fossils may be read and interpreted incorrectly on timeline

  -) may not be aware of other creatures that could survive in those temperatures

  -) fossilisation/ sedimentation may impact preservability
• Past climates of earth

  100 million years ago: Mid-cretaceous era

  35 million years ago: Oligocene era (Glaciation of Antarctica )

  Quaternary glaciation

  Present interglacial : Holocene
• Earth's alternating periods

  • Greenhouse earth - atmospheric CO2 conc, global temp and sea levels high
  • Icehouse earth - low co2, low temperatures and large parts of continental surface is submerged by ice.
• People’s influence on global climate is so dominant we have entered new geological period – the Anthropocene
• Natural drivers of climate change

  Volcanic eruptions

  Plate tectonics and continental drift

  Ocean circulation

  Milankovitch cycles

  Solar output

  Natural Greenhouse Gases
• Volcanic eruptions:

  • Pump large amounts of volcanic ash and sulphur dioxide into stratosphere.
  • Has potential to change global climate short term:
  • Ash is quickly removed; sulphur dioxide is more persistent and has cooling effect:
  • Sulphur dioxide in atmosphere is converted to sulphuric acid forming sulphate aerosols - reflect solar radiation, lower temps in troposphere.

  NE: Mount Pinatubo, Philippines, 1991

  • eruption injected 20 million tonnes of sulphur dioxide into stratosphere.
  • Following 3 years, earth’s climate was reduced by approximately 1.C
• Plate tectonics and continental drift:

  • Driven by plate tectonics and seafloor spreading.
  • Uplift released carbon into atmosphere at mid-ocean ridges
  • Global configuration of continents changed dramatically over 250 million years.
  • Pangaea was split
  • -explains periodic extreme shifts of earth’s climate between greenhouse and icehouse conditions
  • -as larger continental areas occupy higher latitudes, land with permanent ice cover expands, increasing global albedo and positive feedback, causing global cooling
• Ocean circulation:

  Continental drift modifies circulation and energy transfer:

  • formation of isthmus of Panama closed gateway between pacific and Atlantic oceans.
  • Intensified Gulf stream, conveying warm surface water from Caribbean to North Atlantic
  • Evaporation increased, prevailing winds deposited more precipitation, diluting salinity of North Atlantic and Artic oceans - weakened downwelling of water
  • Less saline surface water and reduction in heat transferred by Gulf Stream, led to expansion in sea ice in North Arctic
  • Amplified by positive feedback - albedo
• Solar output:

  Variations in sun’s output contributes to earth’s climate change.

  -Solar output follows an 11-year cycle.

  - Higher solar output = warmer climates /seasons

  -Positive correlation between number of sunspots and solar energy output

  -‘Maunder minimum’ – number of sunspots decline to almost 0 correspond to the winters in the ‘Little ice age’, Europe
•  Natural Greenhouse Gases:

  • Plate tectonic movements created extensive fold mountain ranges.
  • Uplift increased rainfall erosion and chemical weathering by carbonic acid in rainwater.
  • So large volumes of co2 removed from atmosphere and stored in carbonate sediments in oceans.
  • Phytoplankton blooms extracted co2 from oceans + atmosphere and stored as marine sediments.
• Milankovitch cycles - changes in earths orbit around the sun
• Milankovitch cycles

  Obliquity (tilt of earth’s axis)

  Eccentricity of Earth’s orbit

  Precession of the equinoxes
• 1.        Obliquity (tilt of earth’s axis)

  • Alternating Periods of 40,000 years, earth’s axis tilt varies from 22.C to 24.5.C.
  • When tilt is close to 22.C, seasonal temperature differences are reduced.
  • Snow/ice accumulated in winter doesn’t melt in summer, allowing glaciers and ice sheets to expand.
  • Has positive feedback effect, increasing reflection of incoming solar radiation, lowering temperatures further.
• 2. Eccentricity of Earth’s orbit

  • Follows an elliptical path around the sun.
  • solar radiation occurs between perihelion and aphelion.
  • Aphelion is the point of the Earth's orbit that is farthest away from the Sun.
  • Perihelion is the point of the earth’s orbit that is closest to the sun.
  • Ice ages respond to periods of maximum orbital eccentricity:the Northern Hemisphere is tilted away from the sun in the winter.
  • As rocks heat up quicker than water.
  • most of the landmass on Earth is in the Northern Hemisphere, and most of the Southern Hemisphere is ocean.
• • Aphelion is the point of the Earth's orbit that is farthest away from the Sun.
  • Perihelion is the point of the earth’s orbit that is closest to the sun.
• 3. Precession of the equinoxes

  • Shift which occurs with a periodically around 22,000 years due to gravitational influence of the moon and Jupiter affecting intensity of the seasons
  • If perihelion occurs during northern hemisphere’s winter winters become warmer and summers cooler

  -  Snow and ice accumulating in winter wont melt in summer

  -  So ice and snow expand, triggering glacial periods
• Industrialisation increases consumption of fossil fuels

  • burned for industrial uses
  • contributing to co2 concentrations in atmosphere
  • exacerbating warming within atmospheric envelope
  • increasing earth’s temperature.
• Anthropogenic climate change – theory explaining present days long-term increase in average temperatures of earth’s atmosphere as an effect of human industry and agriculture.
• Evidence of warming since the late 19th century

  1. increase in global temperatures
  2. Shrinking valley glaciers and ice sheets
  3. rising sea levels
  4. increased atmospheric water vapour
  5. decrease in snow cover and sea ice
• Increase in global temperatures: evidence

  Steep rise in temp of surface and ocean temperatures: 1.6.C and 0.8.C above average in 21st century

  Every following year since 1980 has recorded above average June temperatures
• Shrinking valley glaciers and ice sheets: evidence

  • In past century valley glaciers have retreated and disappeared
  • Alps valley glaciers may shrink by 80-95% by end of century
  • However, melting SHOULD take centuries for polar ice sheets
  • Losses of ice due to:Warming of atmosphere
  • Meltwater penetrates ice, increasing velocity of glacier flow to warmer altitudes, causing ocean warming
• Rising sea levels : evidence

  • Since 1900s average Sea level rise of 1 mm/year
  • Processes that account for rise:

  Thermal expansion of oceans as world’s climate warms

  melting of land-based ice sheets and glaciers, expanding volume of water, increasing sea levels
• Increased atmospheric water vapour : evidence

  • Water vapour (GHG) traps huge amounts of heat radiated from earth’s surface creating a natural greenhouse effect.

  - Air holds 7% more water vapour with a 1.C increase in temperature.

  • amount of water vapour is directly proportional to temperature and rates of evaporation
  • Vapour amplifies global warming by positive feedback
• Decrease in snow cover and sea ice : evidence

  • Diminishing snow cover increases absorption of solar radiation
  • Sun’s energy warms ground
  • Temperature increases creating positive feedback effect:
  • As Volume of sea ice decreases
  • more solar energy is absorbed by open sea surfaces, raising air temperatures, causing rapid melting
• Reasons why anthropogenic emissions have increased since the pre-industrial era.

   

  • Globalisation and technological demands in manufacturing industries
  • transport  
  • Huge population growth (reaching 8 billion in 2024 compared to 1 billion in 1800s)
  • Increased living standards: consumerism / waste / air travel / car ownership
  • Land-use changes: (1/3 of GHG)deforestation/ draining of wetlands for agriculture, cultivating soils and urban development - meet demands of population for resources and space
  • Fossil fuels: (2/3 of GHG) burning of fuels for energy
• The balance of anthropogenic emissions around the world and how this has changed in history

  >Co2 and GHG emissions in period 1850 -1950 originated from industrialised economies of North America and Europe

  >Since 1960s, shifts in emissions of GHG: Fossil fuels (CO2)

  • Declined in Europe, North America – shifted to natural gas – produces 2x less co2.
  • Increased in Asia, namely China and India reliant upon coal as main fuel source.
  • expansion of the world economy between 1990 and 2012 stimulated by globalisation and growth of EDCs increased consumption of fossil fuels and 50% in CO2 emissions.
• The balance of anthropogenic emissions around the world and how this has changed in history.

  Methane emissions from land-use changes:

  • Highest in China / USA
  • Followed by Brazil and Indonesia due to effects of large-scale deforestation in Amazon and Indo-Malaysia
  • Transfers carbon from biosphere to atmosphere
  • 40% of planet’s land surface is used for agriculture in comparison to 7% in 1700s.
• Highest emitters / year

  Russia – 5% of global emissions

  USA – 15% of global emissions

  Europe – 5% in 2019 from 15% in 1990

  China – in 2020 (30% global emissions)
• Natural green house effect:

  • Absorb sun’s long-wave radiation, reflects short-wave preventing earth’s surface heating providing stability for ecosystems
  • Insulate the earth during the night to envelope earth’s surface with infra-red radiation, prevent freezing.

  -E.g. carbon monoxide, nitrogenous oxide, methane, co2, water vapour
• Increase in CO2 by 1/3 since 1900s enhances natural effect:

  > Driven by Deforestation in Amazon and permafrost melting in arctic> Increases evaporation rates and water vapour concentration and > increases release of carbon and methane from biosphere to atmosphere

  > Enhanced effect increases absorption of long-wave radiation in atmosphere,

  > increasing insulation,

  > raising global temperatures, melting ice sheets/snow.
• global mean energy balance maintained by

  • Energy exported from surface to atmosphere by convection currents.
  • Thermals and latent heat released when water vapour cools/ condenses.
  • GHG absorb heat radiation to regulate global temperatures.
• How humans impact global mean energy balance:

  1. Increased concentration of GHG absorbs larger proportion of terrestrial radiation, which is returned to surface, raising global temperatures.
  2. increases evaporation and transfers more latent heat to atmosphere, increasing concentration of water vapour and other emissions reduces albedo and reflection of incoming solar radiation (increasing energy in atmosphere)
  3. melts snow, glaciers, sea ice (E.G. Greenland)
  4. Changes in global oceanic circulation and release of CO2 from soils, permafrost, rainforests, and undersea stores as methane
• Why is there a debate?

  IPCC supported by scientists who favoured global warming:

  • supported by satellite imagery and climate models revealing human activity and increased release of GHG is a forcing agent of climate change.

  Dissenters argue that:

  • Warmer global temperatures will be equally met by global cooling and an imminent new glacial period.
  • rising temperatures in first half of 20th century was due to increased solar output and volcanic activity.
  • Undermined by continued rise in temp since 1950s despite reductions in solar and volcanic activity.