Urban heat

Earth's energy budget

View the video for an overview of the Earth's energy budget before reading the summary text below.

The global heat budget is the balance between the energy the Earth receives from the Sun and the energy it gives back into space. When sunlight reaches Earth, some of it is reflected by clouds, ice, and bright surfaces, but most is absorbed by the land, oceans, and atmosphere, warming the planet. 

Albedo is a measure of how much sunlight a surface reflects compared to how much it absorbs. Investigations into albedo will be conducted during fieldwork.

Once absorbed, heat is transferred from the tropics towards the poles by wind and ocean currents.

Solar energy that is absorbed at the surface is transferred into the atmosphere by evaporation, conduction/ convection, and the release of thermal infrared radiation (heat). 

• Evaporation moves heat as water changes from liquid to gas

• Convection/conduction carries heat upwards through the movement of warm air

To keep Earth's temperature stable, the incoming energy must balance the outgoing energy. If more energy is absorbed than released, the planet warms. If more energy escapes than is absorbed, it cools. Factors like greenhouse gases, cloud cover, and ocean currents all help control this delicate balance.

Activity 1 - Earth's energy budget

Analyse the Earth's energy budget images.

1. Draw a flowchart showing the journey of solar energy.

• Step 1 - use arrows to identify and sketch solar energy flows

• Step 2 - use the following words to annotate your flowchart -  absorption, albedo, conduction, convection, evaporation, heat, reflection, solar energy, thermal radiation.

• Step 3 - use colours to highlight heating and cooling processes.

2. Observe the image 'Sydney city sunrise'. Predict what may occur with these processes in urban areas.

Urban heat

Urban heat and more specifically the urban heat island effect is where urban areas experience warmer temperatures, 1 °C to 3 °C higher, than the surrounding suburban, rural and bushland areas. This occurs primarily as there is less green cover and more hard surfaces which absorb, store and radiate heat. 

Urban heat and climate change

In NSW, the climate has been gradually warming since the 1960s. Australia's average temperature has warmed by 1.4°C since 1910 when national records began. Temperatures are predicted to increase about 1.0°C in the near future (by 2030) and by about 2.6°C in the far future (by 2070). In addition, the number of hot days over 35°C will increase and the number of cold nights will decrease. 

In urban areas these changes will increase urban heat and amplify the urban heat island effect.  Heat-related impacts will increase, making increased temperatures and extreme hot weather events more severe, and more difficult to manage.

Research on urban heat in NSW was conducted and published by the NSW Government in 2015. It found climate change is expected to impact urban heat in areas such as Sydney and is predicted to impact people’s health and wellbeing,  economic productivity, urban wildlife and ecosystems, and urban infrastructure and services.

Urban heat significantly affects liveability. Reports have concluded that increased exposure to higher temperatures negatively affects health and wellbeing, sleep, crime, income and productivity. Older people, children and people with existing medical conditions are more vulnerable to these impacts.

Heatwaves, a period of 3 or more consecutive days of high temperatures worsen the impacts. Research conducted by Western Sydney Regional Organisation of Councils (WSROC) found that between 1987 and 2016 in Australia, more than 500 people lost their lives as a result of heatwaves and a further 2,800 were injured. Heatwaves are more deadly than other natural disasters including storms, fires and floods.

Professor Mattheos Santamouris from UNSW Sydney High Performance Architecture explains energy poverty and the extreme impacts on human health from warming cities. 

Activity 4

1. View the YouTube video and use a see-saw strategy to discuss the the concept of heat vulnerability.

2. Learn more about the impacts of urban heat at the Western Sydney Regional Organisation of Councils - Project Turn Down The Heat