Global Warming

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To look at the issues involved in global warming

Recent Climate Change

The global temperature of the Earth has increased over the last century.

Current temperatures are 1.02 °C over the 1950-1980 average

Global-Annual Temp-2020.png

In fact global temperatures are now the highest in the last couple of thousands of years

Common Era Temperature.svg

Current Temperatures

2020 and 2016 were tied for the hottest year on record.

The six hottest years were: 2020 = 2016, 2019, 2017, 2015, 2018

Map of temperature anomaly in March, 2017. Red color indicates the greatest temperature anomaly.

Natural Greenhouse Effect

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The above picture shows the natural greenhouse effect in red. All objects emit heat in the form of infrared (IR) radiation. Gases in the atmosphere absorb the IR radiation from the Earth and reradiate it back to the surface. This regulates the temperature.

The natural greenhouse effect allows life to survive on Earth.

But problems occur when humans cause additional greenhouse effects.

Greenhouse Gases

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Greenhouse Gases (GHG) Gases which absorb infrared radiation causing the greenhouse effect

Now we can define global warming:

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Global Warming Warming of the Earth due to increases in the amount of human generated greenhouse gases in the atmosphere

Major human-generated greenhouse gases [1]:

  • Carbon dioxide 76% of all greenhouse gas emissions
  • Methane 16%
  • Nitrous Oxide 8%
  • F-gases 1%

Black carbon also contributes to global warming.

Carbon Dioxide

Carbon dioxide is by far the most important of the greenhouse gases, causing most of the global warming. Atmospheric concentration is about 400 ppm.

Largest sources of carbon dioxide:

  • Burning of carbon-based fuels
  • Deforestation and burning grasslands for crop production

Mauna Loa CO2 monthly mean concentration.svg


Methane is at lower concentrations, but has a stronger greenhouse effect. Concentration is about 1.5 ppm, greenhouse effect is 29 times that of carbon dioxide.

Largest sources of methane:

  • Agriculture (60%)
  • Cattle and other ruminants
  • Manure
  • Rice farming
  • Disturbance of peatlands
  • Natural wetlands and permafrost
  • Leakage from natural gas pipelines, tanks, etc.
  • Landfills and wastewater treatment plants

Nitrous Oxide

Nitrous Oxide (N20) is at low concentrations and has a strong greenhouse effect. Concentration is about 0.3 ppm, greenhouse effect is 298 times that of carbon dioxide.

Largest sources (60% natural, 40% anthropogenic):

  • Natural denitrification in soils
  • Breakdown of fertilizers

Fluorinated Gases

Fluorinated gases (F-gases) which contribute to climate change include:

  • Hydrofluorocarbons (HFC's) - used as substitutes for CFC's and HCFC's (HFC's do not destroy the ozone) - these are to be phased out by 2047
  • Perfluorocarbons (PFC's) - used in electronics and other industries
  • Sulfur Hexaflouride (SF6) - used in high-voltage switches

Black carbon

Soot or Black Carbon are very fine particle of pure carbon.

Formed from incomplete combustion of carbon-based fuels (both fossil fuels and biomass).

Black carbon's effect on global warming is that, unlike most particles which reflect light, black carbon absorbs sunlight, heating it up and contributing to global warming.


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Key points
Increasing of greenhouse gases (especially carbon dioxide) can cause an increase in the greenhouse effect, which increases the temperature of the Earth's atmosphere

Impacts of Global Warming

Changing of the weather

Global warming will cause shift in climate

An animation of how the Earth's climate would change can be found here

  • Generally, more hot days and fewer cool days.
  • Tropics will get less precipitation.
  • Polar regions will get more precipitation.
  • Temperate regions will shift north.

Extreme weather events

Extreme weather events will increase. These include:

  • Heat waves
  • Droughts
  • Typhoons, hurricanes, and tropical cyclones
  • Severe storms, tornados, etc.
  • Floods
  • Wildfires

Food security

Changing of the climate, along with extreme weather, will reduce crop yields and decrease food security.

Melting of sea ice

Sea ice is the frozen sea. Most of the Arctic Ocean, especially around the North pole is sea ice.

One of the biggest effects of global warming has been melting of sea ice, ice sheets, and glaciers due to rising temperatures.

Map of arctic ice for September 16, 2012. The orange line is the median extent from 1979-2000. This was the lowest sea ice extent on record. The most recent version of this image is available here
Graph showing loss of ice in September (usually the annual minimum) from 1979 to 2014

Ice sheets

  • Unlike sea ice, ice sheets and glaciers are formed on land
  • Ice sheets (>50,000 sq. km) are found in only two places: Greenland and Antarctica

The ice sheet in greenland is of the most concern. Greenland's ice sheet is 1.7 million square kilometers in area and averages 2.3 kilometers deep. It holds 7% of the world's freshwater.

Greenland has been losing ice at a rate of 286 billion tons of ice per year since about 2000.

Graph of land ice loss in greenland since 2002


  • Glaciers are found on all continents except Australia
  • Glaciers are important as sources of freshwater, many major rivers are feed by glaciers
  • Many glaciers are disappearing due to melting from global warming. Some areas may lose all of their glaciers.

Sea level rise

The melting of the ice sheets and glaciers causes the amount of seawater to increase. Also heating water causes it to expand.

Model estimates now say that sea levels will rise 0.9 m.

10 percent of world's population lives less than 10 m above sea level.

Freshwater and coastal systems

  • Changing precipitation and melting snow and ice affect water quantity and quality
  • Sea level rise, along with extreme weather, will cause submerging, coastal flooding, and coastal erosion
  • Many small island countries are especially vulnerable. Some islands may be submerged


Global warming can also affect wildlife, including:

  • Shifting geographical ranges
  • Changes in seasonal activities
  • Changing migration patterns
  • Changing species interactions
  • Increased extinction rates

Social impacts

Golbal warming also has impacts on social issues:

  • Increased health problems (heat-related problems, infectious diseases, etc.)
example: Malaria-carrying mosquitoes cannot live in cold climates. Already we have see malaria further north than previously
  • Displacement of people
  • Risk of violent conflict
  • Inequalities in development may be increased

Permafrost melting

Permafrost is soil which remains frozen all year.

Melting of permafrost is a feedback mechanism. It releases methane, which increases global warming, which in turn causes more permafrost melting creating a loop.

Ocean Acidification

This effect is due to the carbon dioxide directly and not temperature change.

Carbon dioxide dissolves in the ocean to create acid conditions.

This in turn has an effect on marine organisms.

Acidic conditions increase the solubility of calcium carbonate in shells of shellfish, coral, etc.


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Mitigition - Reducing the amount of greenhouse gases. Therefore, reducing the amount of global warming


  • Previously, most international agreements were based on keeping warming to 2 °C above preindustrial levels
  • Under the Paris Agreement, that was changed to 1.5 °C
  • Warming reached 1 °C in 2017

Methods of mitigation

  • The most important methods were discussed under the Sustainable Energy section under Energy.
  • Of these the most important is phasing out of fossil fuels. The Intergovernmental Panel on Climate Change (IPCC) has stated that complete phase out must be done by the year 2100 (with 80% renewable energy by 2050)[ref 1].

Other Methods:

  • carbon tax - taxing companies for each ton of carbon dioxide they produce
  • carbon markets (controversial) - trading carbon emissions on an open market (like a stock market)

Carbon removal:

  • Afforestation and reforestation.
  • Bioenergy with carbon capture
- Carbon capture (or sequestering) is capturing CO2 and then pumping it underground
  • Soil sequestering
  • Direct Air Capture
Important to note these methods are unproven

Agricultural practices

  • Reduction in amount of nitrogen fertilizers used
  • Conservation agriculture (no till, agroforestry, etc.)
  • Livestock management
  • Changing diets (especially in amount of meat consumed)

Land-use changes

  • Ecosystem restoration
  • Wetland management
  • Prevention of destruction (especially drainage and fires) of peatlands

Very Controversial (and probably not achievable) methods - Geoengineering ???

Geoengineering - mega projects to reduce effects of global warming
  • examples: setting huge mirrors in outer space, adding huge quantities of iron filings to the ocean, injecting aerosols of sulfur dioxide into the stratosphere
  • problems: hugely expensive, most are not technically feasible with today's technology, may have undetermined consequences, and questions about governance
  • note most of these do not address ocean acidification


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Measures to reduce the effects of global warming


  • Building sea walls
  • Changing crop types
  • Generating a fund to help low income countries (the most talked about adaptation measure)


  1. Note that CFC's are often given, but due to the Montreal Protocol they now account for less than 0.1% of all emissions


  1. Fossil fuels should be phased out by 2100 says IPCC