1. Global Warming and Urban Heat Islands

Question 1

Why might people try to deny climate change?

Answer 1

• Ignorance of facts
• Fear of detrimental impact on personal lifestyle
• Profit from environmentally damaging industries
• Personal comfort in denial - fear of reality
• Belief in ignorant leaders - (Donald Trump and Co)

Question 2

What are the sources of CO2?

Answer 2

• Burning fossil fuels
• Deforestation, especially “slash ‘n’ burn”

Question 3

How does CO2 contribute to global warming?

Answer 3

• Thought to be the main greenhouse gas
• Increased from 280 ppm in 1850 to 400ppm (global average)

Question 4

What are the sources of methane?

Answer 4

Methane is released by bacteria in:

• wet padi fields
• bogs
• waste landfill sites
• the guts of cattle and sheep

Question 5

How does methane contribute to global warming?

Answer 5

• 25 times more effective than CO2 as a greenhouse gas
• Increasing by up to 2% per p.a.

Not sure what p.a. means, but whatever. It’s in the textbook.

Question 6

What are the sources of CFCs?

Answer 6

Old aerosols and refridgerators

Note: No loger used in commercial products today

Question 7

How do CFCs contribute to global warming?

Answer 7

• Very efficient absorbers of long-wave radiation

Question 8

What are the sources of nitrous oxides?

Answer 8

• Nitrate fertiliser
• Burning fossil fuels
• Burning vegetation

Question 9

How do nitrous oxides contribute to global warming?

Answer 9

• Nearly 300 times as strong as CO2

Question 10

How do increasing temperatures provide evidence for global warming?

Answer 10

• Mean world temperatures have increased globally
• 9/10 warmest years on record have occurred since 2000.
• Upper ocean heat has increased significantly in the past 20 years as oceans store an estimated 63% of the heat caused by global warming.

Question 11

What other evidence besides increasing temperatures provide evidence for global warming?

Answer 11

• Areas of high evaporation such as the western Indian Ocean = saltier due to increased evaporation, seas such as the North Atlantic = less saline due to melting sea ice
• Artic sea ice has declined by roughly 2.4% per decade since 1980
• The acidity of oceans has increased by 26% due to absorption of CO2. (Oceans are still alkaline, just a bit less now…)
• Global sea levels rose by an average 3.1mm a year between 1992 and 2010, twice the rate of the last century.

Question 12

How is mitigation an effective response to climate change?

Answer 12

In principle, the only way to reduce our greenhouse gas emissions is to stop burning fossil fuels or relying on methane-producing agricultural industries to fund and support our lifestyles.

Though governments and corporations have the greatest say in reducing the world’s carbon footprint, changes in consumer lifestyles such as increasing the use of public transport, eating less meat and shopping locally can have a significant impact on reducing our emissions.

Other policies such as carbon capture and carbon offsetting also have the potential to reduce the rate of climate change.

Question 13

How might adaptation be an effective response to climate change?

Answer 13

Though not reducing the rate of climate change itself, adaptation seeks to reduce / manage its impacts.

This may include building higher sea walls to deal with rising sea levels, changing agriculture practices towards drought-resistant crops, and more efficiently managing water supply.

Question 14

What are the impacts of global warming?

Answer 14

• Increased ice melt decreases the albedo of the N and S poles, accelerating global warming further
• More frequent and violent storms due to greater moisture in air from evaporation
• Warmer temperatures in places with high pressure - USA, South Africa, Mediterranean - will cause more severe droughts
• Increased heatwaves - 30,000 people in Europe died in the hot summer of 2013
• Mass quantities of methane released if permafrost melts - tipping point?

Question 15

Why might individual action be able to reduce the impacts of climate change?

Answer 15

• Individual action creates a message that influences others to act.
• Giving up flying makes other people within their social connections more likely to give up flying as well.
• Small changes over a large population can have a huge difference.

Question 16

Give two examples which demonstrate the importance of individual action against climate change.

Answer 16

• By reducing your average meat intake by half, you can decrease your personal carbon footprint by 40%.
• In the UK, 15% of the population takes 70% of flights.

Question 17

Why might companies be responsible for climate change?

Answer 17

• Just 100 companies are responsible for 71% of global emissions.
• More than half of these emissions are produced by the top 25.

Question 18

Why is it in the best interest of businesses / governments to avoid investing in fossil fuels?

Answer 18

Fossil fuel companies risk wasting $2tn USD on fossil fuel investments which are projected to decrease in value in the face of international action on climate change, as well as more cost-effective investment into renewables.

Question 19

Which 5 companies produce the greatest shares of the world greenhouse gas emissions?

Answer 19

• China (Coal) - 14.32 %
• Saudi Arabian Oil Company (Aramco) - 4.50%
• Gazprom OAO - 3.91%
• National Iranian Oil Co - 2.28%
• ExxonMobil Corp. - 1.98 %

Question 20

Why might governments be responsible for climate change?

Answer 20

• Governments have a responsibility to implement climate measures on the behalf of individuals, who are often greatly restricted by income and have little capability to make a significant difference.
• 1/5 of global greenhouse emissions are backed by public investment (governments).

Question 21

Why is it important to pressure governments instead of individuals to make changes to reduce greenhouse gas emissions?

Answer 21

• Blame on individuals takes pressure off those who have the greatest emissions, as well as the greatest ability to act.
• Legislation can make changes where lifestyle can not - improved public transport to enable and incentivise reduction in car usage.

Question 22

What is an urban heat island?

Answer 22

An urban heat island is a metropolitan area which is significantly warmer than its surrounding rural areas.

Question 23

How strong is the urban heat island in Vancouver?

Answer 23

Temperatures in the city centre / downtown are 7-9 °C warmer than in the surrounding rural areas

Question 24

How do levels of transpiration / evaporation cause an urban heat island?

Answer 24

Cities have less vegetation / surface water than surrounding rural areas. This means that cities are cooled less than rural areas by evaporation and transpiration, resulting in warmer temperatures in cities.

Question 25

How do differences in albedo levels lead to urban heat islands?

Answer 25

Urban areas have more dark surfaces which have a low albedo, increasing the amount of heat absorbed in cities during the day leading to higher temperatures in cities than in rural areas.

Question 26

How do different sizes of surface area lead to urban heat islands?

Answer 26

Tall buildings have a larger surface area on which they can receive thermal energy.

These buildings then release solar energy at night, developing an urban heat island with a more consistent temperature than rural areas.

Question 27

How does mechanical heat lead to urban heat islands?

Answer 27

Mechanical heat is waste heat released from mechanical operations e.g. AC units / Cars. As many more of these appliances are found in urban versus rural areas, they create an urban heat island in cities.

Question 28

How do different levels of specific heat capacity lead to urban heat islands?

Answer 28

Tarmac has a low specific heat capacity, which means that heat from solar energy is quickly emitted, raising temperatures in urban areas far more than in rural areas to create an urban heat island.

Different materials heat up more quickly / slowly depending oon their composition.

Question 29

How does the wall effect create urban heat islands?

Answer 29

Prevailing winds are reduced / redirected by tall buildings, reducing its cooling effect in urban areas (as heat is not distributed) to create urban heat islands.

Question 30

How does the canyon effect create urban heat islands?

Answer 30

In urban areas, air is able to circulate at roof level but air between tall buildings is unable to circulate - convection currents cannot form so heat is not dispersed leading to urban heat islands.

Question 31

When is an urban heat island at its largest?

Answer 31

• At night (before sunrise)
• In the summer (high pressure and lots of heating)
• When there is no wind (high pressure)
• When the sky is clear (high pressure)
• When the weather doesn’t change throughout the night (stable conditions)

Question 32

What are the consequences of urban heat islands?

Answer 32

• Growing season up to 15 days longer in a city
• Warmer climate in the winter
• Less snow and ice
• More rainfall
• Intensification of heatwaves and increased mortality rate from heatstroke.

Question 33

How do ‘cool pavements’ function in Los Angeles?

Answer 33

‘Cool pavements’ refers to using paving material that has a higher albedo than normal paving materials e.g. tarmac.

This reflects more solar energy so less heat is absorbed and transferred to the air above

Question 34

How does making pavements permeable decrease the strength of urban heat islands?

Answer 34

Pavements can be made permeable to let water infiltrate.

• these pavements have a 16% higher evaporation rate than impermeable pavements, increasing the cooling effect from evaporation)

Question 35

How does urban greening in Louisville, Kentucky, decrease the strength of urban heat islands?

Answer 35

Integrating vegetation into urban areas such as through green walls / rooves, planting trees and increased green space increases levels of transpiration in urban areas, releasing water which evaporates and cools the air

Question 36

How do White Rooves in Chicago decrease the strength of urban heat islands?

Answer 36

Similar to cool pavements, painting rooves white increases the albedo of the surface so more solar energy is reflected, so less heat is absorbed, leading to cooler cities.

Question 37

How does the Vancouver Heat Island influence fog?

Answer 37

Fog is frequent in the city, especially in the winter, because:

• Lower wind speeds and more frequent calm periods allow the fog to remain in contact with the ground and cool via conduction
• Greater number of condensation nuclei from air pollution (smoke, dust and sulphuric acid (H2SO4) particles around which condensation can occurr.

Question 38

Where are the highest temperatures of the Vancouver Heat Island?

Answer 38

Highest temperatures are in the most built-up areas e.g. downtown, suburbs and university campus as there are more dark surfaces with a higher albedo.

Question 39

How does the Vancouver Heat Island influence humidity?

Answer 39

• Absolute and relative humidity are lower during the day in the city due to less surface water and vegetation for evaporation and transpiration to occur. Rainfall runs off down gutters and drains.
• However, humidity rises over the harbour - Burrard Inlet and the Fraser river where evaporation is possible.
• At night, humidity is slightly higher over the city because in colder rural areas, more dew is deposited from the air making it less humid.

Question 40

What is the pattern of precipitation in Vancouver?

Answer 40

For every increase in height by 100m, precipitation increases by 100mm.

The mountain edge of Vancouver receives double the precipitation of the main city.

Question 41

How does Vancouver influence its own wind patterns?

Answer 41

Skyscrapers in the CBD can cause turbulence and vertical updrift, with eddies in the lee of buildings.

Canyon-like streets have the strongest gusts where winds are funnelled between tall buildings.

However, winds are generally less strong in the city centre because tall buildings obstruct and deflect airflow and increase friction.

Question 42

Why does Vancouver Heat island have reduced losses of heat from radiation?

Answer 42

Tall buildings turn streets into ‘canyons’ giving a reduced sky view and smaller angle of heat loss at night.

More built up areas have smaller radiational heat losses and therefore have the highest temperatures.