1. What is Global Warming?




Solar Radiation - The Sun's Energy

The sun radiates energy.  The energy reaching Earth is either:
  • Reflected by clouds
  • Absorbed by the atmosphere
  • Or reaches the surface

Energy reaching Earth's surface is either:
  • Reflected
  • Absorbed

Albedo (α) measures how reflective a surface is, and has a value between 0 and 1.  

α=0  Total Absorption of Energy.  
α=1  Complete Reflection of Energy.


M1: Albedo of Ocean, Ice and Snow

Source: NSIDC​
​Rank the following surfaces in order of highest to lowest albedo. Use Figure M1 and Table M2 to help you.
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  1. Dense pine forest canopy
  2. Blanket bog cut for fuel (black)
  3. Thick Clouds
  4. Arctic ice
  5. Arctic snow polluted with soot
  6. Desert
  7. Open ocean
  8. Arctic sea ice covered in fresh snow
  9. Bare soil after three days of rain
  10. A field of wheat
​

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M2: Albedo of Various Surfaces

Source


Energy Balance

What happens to the energy absorbed by the land and ocean?  Depending on the surface's albedo, it increases the material's temperature. The lower the albedo, the more energy is absorbed, and the hotter it gets.  The material then emits thermal radiation.  
 
Solar energy that is absorbed by the land and oceans is radiated back towards space as thermal radiation.  This thermal radiation either:
  • Penetrates the atmosphere and returns to space
  • Is absorbed by the atmosphere
  • Is reflected by the atmosphere back towards the land and oceans.
 
In this way, the atmosphere acts like a blanket that traps the heat of your body as you sleep, keeping you warm.  Some thermal radiation escapes through the blanket, some gets trapped in the blanket, and some is reflected towards your body. 

This trapping of thermal radiation, known as the Greenhouse Effect, warms the planet (see Video M3).   Without it, the Earth's temperature would  be on average -18°C. 
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The amount of solar energy entering and leaving Earth is known as the Earth's Energy Budget .


M3: The Greenhouse Effect


How Humankind Affects Earth's Energy Balance

 A number of atmospheric gases contribute to the greenhouse effect, including carbon dioxide (CO2), nitrous oxide (N2O) and methane (NH4). Humankind adds greenhouse gases  (GHG) to the atmosphere through manufacture, agriculture, land use and other activities.  As a result, the atmosphere traps more heat.  How much a greenhouse gas pollutant forces heat to become trapped is called its radiative forcing, or climate forcing.

Concentrations of various greenhouse gas pollutants in the atmosphere have increased significantly since the industrial revolution, especially in the last 50 years.  For example, carbon dioxide has increased nearly 40%, and methane 150% (Source: NASA). However, Methane traps 28 times more heat than an equivalent weight of carbon dioxide, and stays in the atmosphere for around 12 years.  Nitrous oxide traps 265 times more heat than an equivalent weight of CO2, and has a residency time in the atmosphere of 114 years (Source: IPCC).  But the global economy emits many more gigatons (Gt) of carbon dioxide than it does other GHGs, and CO2 resides in the atmosphere for up to 200 years.  So which GHG contributes most to global warming?
1.  Graph M4 illustrates the emissions of each gas in terms of its equivalence to a ton of carbon dioxide.  Graph M5 illustrates each gas' relative radiative forcing after taking into account its residency time and total emissions. Use both graphs to rank the various greenhouses gases in terms of:

​i)   Gigatons (Gt), equivalent to CO2,  emitted annually 
​ii)  Greatest contribution to radiative forcing (climate forcing)

​Greenhouse Gases
A. Nitrous Oxide
B. Carbon Dioxide
C. Methane 
D. Chlorofluorocarbons (CFCs)


2.  Since the 1990s, the radiative forcing impact of CFCs  has levelled off. Why, when the radiative forcing of carbon dioxide, methane and nitrous oxide have increased?

Need a Clue?
  • Visit the Ozone Hole to discover whether CFCs have been used less since the 1990s?
  • What is the residency time of CFS (how long the gases linger in atmosphere)?
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M4: Global Greenhouse Gas Emissions by Gas.


Source​


M5: Radiative Forcing Caused by Major Long-Lived Greenhouse Gases, 1979-2014

Source
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The Ozone Hole


Warming in 2015

How do we measure if Earth is warming? Weather stations across the globe take temperature measurements.  These temperatures can be averaged, so a mean surface temperature for region over a period of time can be calculated.  By comparing the temperatures measurements, scientists can measure how many degrees a region has warmed during a period of time.

For example, compared to the thirty-year period (1956-1985), were the last thirty years (1986-2015), warmer or cooler? Does the answer depend on the region? Does it depend on the season?

Use the arrows to navigate Slide Show M6 to answer the above questions. Then answer the questions below:
​   
  1. Which regions experienced warming between the two periods during all four seasons? 
  2. Have you or your relatives experienced warmer or cooler, drier or wetter, seasons during your lifetime?
  3. During which season has the Arctic warmed most between the two periods? 
  4. How would temperature increases in the Arctic affect sea ice? 
  5. Could any recent famines be attributed to a warming climate?
  6. Could climate change increase the rates of malaria? Why?

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M6: Map of Regional Temperature Differences Between the Periods
1956-1985 and 1986-2015

Temperature Difference (°C)
You can make your own temperature maps at NASA.
You can compare time periods between 1800 - 2015. 
Using the drop-down menus on the the NASA map maker, set:
  • 'Map Type' to Anomalies.
  • 'Time Interval' to 2006-2015
  • 'Base Period' to 1906-1915.
  • 'Mean Period' to NH Winter.

During the last one hundred years, did any regions experience at least 2°C of warming?

The Rate of Global Warming

Is the rate of warming increasing or slowing down? According to the Intergovernmental Panel on Climate Change's (IPCC) Fifth Assessment Report, ​the rate of warming has slowed between 2000-2015. However, a recent study by Stanford scientists suggests that the 'climate change hiatus' never happened, and warming may have increased. Did warming slow? Read the article at Stanford News, or study the scientific paper, to decide for yourself.
How does Global Warming change climates around the world?

2. How Global Warming Affects Climate

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