Grade 7: Weather and Climate
Revision Guide
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What is our climate system?
The atmosphere covers the Earth.
It is a thin layer of mixed gases
which make up the air we breathe.
Atmosphere
This thin layer also helps the
Earth from becoming too hot or
too cold.
Oceans
Oceans cover about 70 percent of
Earth's surface. Their large size
and thermal properties allow them
to store a lot of heat.
Land
Land covers 27 percent of Earth's
surface and land topography
influences weather patterns.
Ice
Ice is the world's largest supply of
freshwater. It covers the
remaining 3 percent of Earth's
surface including most of
Antarctica and Greenland. Ice
plays an important role in
regulating climate, because it is
highly reflective.
Biosphere
The biosphere is the part of
Earth's atmosphere, land, and
oceans that supports any living
plant, animal, or organism. It is the
place where plants and animals,
including humans, live.
Key Terms
Weather = describes the day-to-day
conditions of the atmosphere. Weather
can change quickly - one day it can be dry
and sunny and the next day it may rain.
Climate = Describes average weather
conditions over longer periods and larger
areas.
What causes weather?
Because the Earth is round and not flat,
the Sun's rays don't fall evenly on the land
and oceans. The Sun shines more directly
near the equator bringing these areas more
warmth. However, the polar regions are at
such an angle to the Sun that they get
little or no sunlight during the winter,
causing colder temperatures. These
differences in temperature create a
restless movement of air and water in great
swirling currents to distribute heat energy
from the Sun across the planet. When air in
one region is warmer than the surrounding
air, it becomes less dense and begins to
rise, drawing more air in underneath.
Elsewhere, cooler denser air sinks, pushing
air outward to flow along the surface and
complete the cycle.
What is the Water Cycle?
Earth has a limited amount of water. So,
that water keeps going around. We call it
the water cycle. The water cycle begins
with evaporation. Evaporation is when the
sun heats up water in rivers, lakes or the
ocean. Then turns it into water vapour or
steam. The water vapour or steam leaves
the body of water and goes into the air.
Transpiration is the process by which
plants lose water out of their leaves.
Condensation is when water vapor in the air
gets cold and changes back into water to
form clouds. Think of it this way, when you
open a cold soda on a hot summer day, your
soda will start to sweat as water droplets
form on the outside of the can.
Precipitation occurs when so much water
has condensed that the air can't hold it
anymore. This is how we get rain or snow.
Collection happens when the precipitation
falls and is collected back in the oceans,
lakes and rivers. When it falls to the
ground, it will soak into the earth and
become ground water. This is the water
cycle and it just keeps repeating.
The Bare Bones:
What causes weather – a summary
1. The sun heats Earth – but unevenly.
2. Earth in turn warms the air, which rises.
3. Rising air leads to wind, because air from a colder
place flows in to replace.
4. The Sun’s heat also causes water to evaporate, giving
water vapour.
5. When the air rises it cools. So the water vapour
condenses, giving clouds of water droplets. Droplets
join to make larger drops, which fall as rain.