Weather and Climate Change

Introduction

The Earth’s atmosphere is composed of 21% oxygen (O2), 78% Nitrogen (N2), and ~1% other gases

(including water vapor, argon, carbon dioxide, hydrogen, and helium). Oxygen is essential for life and is used

by most organisms for cellular respiration while carbon dioxide is used by plants and certain bacteria for pho-

tosynthesis.

Our atmosphere is composed of five layers:

1. Troposphere – nearest to the Earth’s surface; layer in which weather occurs (rising and falling air);

comprises one half of total atmosphere; air pressure is decreased to 10% of that at sea level.

Concepts to Explore

 Atmosphere

 Weather

 The Water Cycle

 Climate

Figure 1: Clouds are visible accumulation of water droplets that accumulate in the Earth’s lowest

layer of the atmosphere, the troposphere.

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Weather and Climate Change 2. Stratosphere – contains the ozone layer (important for UV ray absorption).

3. Mesosphere – layer which meteors burn up in upon entering the Earth’s atmosphere.

4. Ionosphere/Thermosphere – locations of auroras (e.g., aurora borealis); layer in which the space shut-

tle orbits.

5. Exosphere – upper limit of the Earth’s atmosphere; layer where Earth’s atmosphere merges with outer

space.

Weather is the state of the atmosphere at a given time and place and includes temperature, pressure, the

type and amount of precipitation, wind, clouds, etc. Weather conditions can change hour to hour, day to day,

and season to season. Our weather is caused by uneven heating of the Earth from the sun. The resulting

temperature differentials generate wind that forces warm air to flow to regions of cooler air. This flow can oc-

cur both horizontally across the surface of the Earth (e.g., from tropical to polar regions) and vertically, caus-

ing clouds, rain, and storms to develop as warm, moist air cools and condenses as it rises. In addition to driv-

ing our weather, the sun’s energy also is responsible for regulating how water moves on, above, and below

the Earth’s surface through the water cycle.

The water cycle describes how the amount of water on Earth remains constant over time. Water exists in

three different states (in solid form as ice, as liquid water, and in a gas as water vapor) and cycles continu-

ously through these states. The temperature and pressure determine what state water is in. The water cycle

consists of the following processes:

 Evaporation of liquid water to a gas (water vapor)

Figure 2: The water cycle – can you name the steps? Refer to Lab 2 for help!

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Weather and Climate Change

 Condensation of water vapor to liquid water

 Sublimation of solid water (ice) to water vapor (think dry ice)

 Precipitation occurs when water vapor condenses to clouds/rain

 Transpiration occurs when liquid water moves through plants from roots to leaves, changes to water

vapor and is released to the atmosphere through holes (stoma) in the leaves

 Surface run-off occurs when water moves from high to low ground

 Infiltration occurs when water fills porous spaces in the soil

 Percolation occurs when ground water moves in a saturated zone below Earth’s surface

Clouds form at many different altitudes in the troposphere when water vapor in warm air rises and cools. The

water vapor condenses on microscopic dust particles in the atmosphere and transforms into either a liquid or

solid and is visible as clouds. Warm air can hold more water vapor than cool air. Thus, clouds often form over

the tops of mountains and over large bodies of water, since the air over these formations is typically cooler

than the surrounding air.

Figure 3: Clouds.

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Weather and Climate Change

Climate is defined as the long-term average pattern of weather in a given region. Our climate is influenced by

five components: the atmosphere, the hydrosphere (mass of liquid water), the cryosphere (mass of solid wa-

ter; ice), the land surface, and the biosphere (life on Earth). Climate change refers to the observed accelerat-

ed increase in the Earth’s temperature over the past 100 years and its predicted continued increase. The

Earth’s average temperature has increased approximately 1 – 1.5 degrees F since 1900 (see figure below)

and is projected to rise an additional approximately 3 – 10 degrees F over the next 100 years.

Changes in the Earth’s atmosphere have contributed to global warming. Global warming is due to the accu-

mulation of “greenhouse gases”: carbon dioxide (CO2) from burning fossil fuels (oil, gas, and coal); methane

(CH4) from agriculture, landfills, mining operations and gas pipelines; chlorofluorocarbons (CFCs) from refrig-

erants and aerosols; and nitrous oxide from fertilizers and other chemicals. Increased temperature results in

increased evaporation, accelerated polar ice melting, increased number of extreme temperature days, heavi-

er rains/floods, and more intense storms. These changes will have important implications across public

health, infrastructure, energy, economic, and political arenas.

Figure 4: Global Temperature Anomalies. Source: www.nasa.gov