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Rainforests: Nature's Carbon Bank

Science · Rainforests · ages 9-11

Name ______________________ Date ____________

Burning trees adds CO2 to the air. Why can this increase Earth's average temperature?
- Extra CO2 slows Earth's heat loss to space
- Extra CO2 speeds heat loss to space
- Extra CO2 makes the Sun send more heat
What do rainforest trees do with some of the carbon dioxide they take in as they grow?
- They keep it as CO2 gas inside the wood
- They store some of its carbon in new wood
- They change all its carbon into oxygen as they grow
True or false: rainforest trees release water vapor that helps rain clouds form.
Circle one: True False
In a made-up model, a forest takes in 9 units of carbon and releases 6 units during one year. What does this show?
- It is a carbon sink during that year
- It releases more carbon than it takes in
- It takes in no carbon during that year
A patch of growing trees is cut down. The wood is kept as furniture, and no trees replace those removed. Which carbon-cycle change still occurs?
- The furniture keeps taking in CO2
- All stored carbon becomes CO2 when trees are cut
- The removed trees no longer take in CO2
A large area of rainforest near farms is cleared. How could losing the trees affect rainfall?
- Rainfall must double as bare land supplies more vapor
- Rainfall may drop because leaves release less water vapor
- Rainfall must stay the same as trees supply no vapor
A forest is cleared. Ten years later, nearby farms report less rain. What can these observations tell us?
- Clearing is a possible cause; other causes must be checked
- Clearing is the only cause; no other change needs checking
- Clearing cannot be a cause; trees have no role in rainfall
Diego says, 'If we don't burn cut wood, its carbon can never return to the air.' What does Diego miss?
- All its carbon leaves at once when a tree is cut down
- Only living leaves store carbon; wood stores none at all
- Decay can return carbon from cut wood to the air

Answer key

For grown-ups. Fold this page away before handing over the rest.

Rainforests: Nature's Carbon Bank W1-mt_HJd-8EEC6N-s1

Extra CO2 slows Earth's heat loss to space · CO2 absorbs and sends out some of Earth's outgoing heat. Extra CO2 slows heat loss to space and increases greenhouse warming. This is separate from the fire's heat.
They store some of its carbon in new wood · During photosynthesis, trees use CO2 to make food. Some of its carbon becomes new wood in trunks, branches and roots.
True · Leaves release water vapor through transpiration. When moist air cools, that vapor can form cloud droplets.
It is a carbon sink during that year · The forest takes in more carbon than it releases during the same year: 9 units is more than 6. It is a carbon sink in this model year.
The removed trees no longer take in CO2 · Furniture can keep some carbon stored, but it does not continue the trees' photosynthesis. Removing the growing trees stops their CO2 uptake even if their wood is not burned.
Rainfall may drop because leaves release less water vapor · Fewer trees can mean less water vapor from transpiration. This can reduce moisture for rain, though winds and other weather changes also affect rainfall.
Clearing is a possible cause; other causes must be checked · Losing trees can reduce moisture from transpiration, so clearing is a possible cause. These observations alone do not rule out winds or other weather changes.
Decay can return carbon from cut wood to the air · Burning is not the only release pathway. As cut wood decays, carbon can return to the air as CO2. Some wood products keep carbon stored for years.