As the world is facing serious challenges caused by the continuously increasing levels of greenhouse gases in the atmosphere, we are required to understand and become aware of our possibilities of trying to reduce the atmospheric concentration of greenhouse gases and especially carbon dioxide (CO2). It has been estimated that the increasing levels of greenhouse gas emissions will drastically speed up global warming, which clearly influences the climate, the biodiversity, and the ecosystems of our planet. Global warming has already been causing, for example, sea level rise and extreme weather conditions in different parts of the world. 

This activity aims at raising pupils' awareness on the process of carbon fixation in forests. However, before starting, pupils should be introduced to the process of photosynthesis and the importance of forests in the process of reducing the atmospheric concentration of CO2. In this activity, pupils will learn about the impact of climate change and global warming on the carbon cycle of forests, what is meant by the term carbon footprint, and how the carbon footprint can be reduced.

The activity consists of four parts of which all include detailed research questions and instructions. However, the activity can be modified according to the pupils' background knowledge and skills. The specific instructions can be left out in order for pupils to design and construct their own research questions.

• In the first part, Activity 1., pupils use the Carbon Tree simulation (http://www.carbontree.fi/) to study how carbon dioxide (CO2) is fixed in trees (and vegetation) through the process of photosynthesis and how the time of the year and the different weather conditions influence the rate at which CO2 is fixed. 

• In the second part of the activity, Activity 2., pupils are asked to calculate the energy required to charge their cell phone battery and the carbon dioxide emissions caused by the charging of the battery. An example of the calculations is provided. 

• In the third part of the activity, Activity 3., pupils will present their results of the calculations of Activity 2. Pupils are also asked to calculate the total carbon dioxide emissions caused by charging the cell phones of each pupil in the classroom. The term carbon footprint can be introduced and discussed. 

• The fourth part of the activity, Activity 4., involves working in groups and in collaboration with pupils' families: First, pupils are asked to investigate the use of electronic devices at home for one week. Pupils' families can also be asked to collaborate and collect data on their use of electronic devices. At school, pupils will work with the collected data and calculate the estimated amount of energy consumed by using electronic devices for one week (or one year). The energy consumption is then converted into an estimation of the amount CO2 produced per one week (or one year) per family. The result is then used to draw conclusions on how the carbon footprint can be reduced by changing the daily habits of using electronic devices. Finally, the project can be presented to the families and the other pupils of the school. The activity can be further expanded for example by interviewing the audience (pupils and teachers of the school) about their use of electronic devices and their estimations of their own carbon footprint.

Resources needed 

• Computer and internet access

• The application used in this activity is available on the Carbon Tree website: http://www.carbontree.fi/. The website is available in English, Finnish, Swedish, and Chinese.

Activity 1.

Carbon dioxide is one of the most crucial greenhouse gases in the atmosphere, which is mainly caused by the human lifestyle, e.g. the increased use of fossil fuels. Forests are able to slow down the increasing of the carbon dioxide levels in the atmosphere by carbon fixation. However, the changing climate and the increasing levels of carbon dioxide, on the other hand, also have an influence on the rate of carbon fixation and thus also the carbon cycle of the forests. In this activity, pupils will complete five assignments by using the Carbon Tree simulation.

Before starting the activity, pupils should be introduced to photosynthesis, which is a process during which plants and trees absorb carbon dioxide from the air and release the oxygen that we breathe. In addition to the photosynthesis, trees do also release carbon dioxide. The white dots of the Carbon Tree simulation illustrate the carbon dioxide molecules whereas the exchange of the carbon dioxide is expressed as a moving stream of these white dots. 

A positive number at the bottom of the page (carbon flow) indicates the absorption of carbon dioxide from the atmosphere and the negative number implies that the tree is releasing carbon dioxide into the atmosphere. More information on how to use the Carbon Tree simulation is available on the website. 

In Assignment 1., pupils are asked to observe how the different seasons affect the rate of carbon fixation and the movement of carbon dioxide molecules in the atmosphere. This is done by changing the observation time from Christmas Eve to Midsummer and finally to the pupil's own birthday. Pupils will record how much the carbon flow was on each day at 12 o'clock and based on their observations and recordings, they are asked to draw conclusions on how the time of the year affects the carbon flow and at what time of the year the carbon flow is at its highest. 

In Assignment 2., pupils are asked to find out what parts of the tree are used in the process of respiration. The information can be found from the articles available on the website.

In Assignment 3., pupils are asked to explain which factors influence the rate of carbon fixation of trees and how the change of these factors influences the photosynthesis. Pupils are able to change the weather conditions to observe changes in the rate of the carbon fixation.

In Assignment 4., pupils will try to explain what factors influence how much trees release carbon dioxide. To draw conclusions, pupils will observe how different weather conditions influence the carbon dioxide release by changing the weather conditions of the simulation ("Set Weather"). Based on their observations, pupils should be able to explain the phenomenon.

In Assignment 5., pupils will conclude and describe the circumstances of when the net exchange rate of the carbon dioxide of a tree is at its highest. Pupils can change the numeric values for temperature, light, humidity of the ground, humidity of the air, and the amount of carbon dioxide in the air to observe the influence of different factors.

Activity 2.

Further research: Charging a mobile phone

Electricity can be produced in a variety of ways and all methods produce different amounts of carbon dioxide, i.e. they have a different carbon footprint. The electricity generation in Finland generates on average 220 grams of carbon dioxide per kilowatt hour of produced energy. 

The carbon dioxide emissions of charging a cell phone can be calculated based on the information on the battery of the cell phone. Most of the batteries include the information on the capacity of the battery in watt-hours (Wh). The amount of watt-hours on the cell phone battery expresses the required amount of energy needed per charging time.  

Instructions for Activity 2:

Pupils are asked to investigate the carbon footprint of charging their own cell phone by answering the following questions:

Look at the battery of your cell phone:

1. Find battery capacity in watts. How much is it?
2. If your cell phone is charged every night from scratch to full (0% - 100%), how much energy does it require during a year?
3. How large is the carbon footprint caused by the use of electricity to charge the cell phone in a) a year? b) in one charging?
4. How long does it take for "the carbon tree" to absorb the carbon emissions of a single charge of a cell phone?
a) in the spring? b) in the summer? c) in the winter?

Example: 
The capacity of the battery in the example cell phone is 8.09 Wh. If your cell phone is charged at least once a day, it will use about 3-kilowatt hours of energy in one year:

365 days * 8.09 Wh = 2953 Wh or about 3-kilowatt hours of energy/1 year

The average of CO2 emissions per one kilowatt-hour is approximately 220 g.

3 kWh produces therefore 660 g of CO2. If this amount is distributed over the time period of 365 days, a one-day charge of the cell phone will produce approximately 1.8 g of CO2.

To answer question 4. pupils are asked to use the Carbon Tree simulation.

Activity 3.

In the third part of the activity, pupils are asked to prepare a presentation and share the results of the calculations of Activity 2. The presentation should include the estimated energy usage of charging their own cell phone after which the total carbon dioxide emissions caused by charging the cell phones of each pupil in the classroom can then be calculated. Pupils will also discuss the meaning of the term carbon footprint and how they can take action to reduce their own carbon footprint.

Activity 4.

The fourth part of the activity involves working in groups and in collaboration with pupils' families.

First, pupils are asked to investigate the use of electronic devices at home for the time period of one week. Pupils' families are also asked to collaborate and collect data. At school, pupils will work with the collected data and calculate the estimated energy usage of using the electronic devices for one week or for a year. The energy consumption is then converted into an estimation of the amount CO2 produced per one week/a year per family (see the cell phone example).

The results of the calculations are used to draw conclusions on how the carbon footprint can be reduced by changing the daily habits.

Finally, the project can be presented to the families and the school. The activity can be further expanded for example by interviewing the audience (pupils and teachers of the school) about their use of electronic devices and about their estimations on their own carbon footprint.

• Examples for calculating the energy usage for one year can be found here: http://ed.fnal.gov/ntep/f98/projects/nrel_energy_2/measurement.html.
• More ideas and resources for teaching about energy and energy consumption can be found on the website of the NEED Project (The National Energy Education Development Project): http://www.need.org/