Download Weather, Climate, and Atmosphere Reading Activity

Weather, Climate, and Atmosphere Reading Activity
Article 1
Ocean Circulations
Much like the earth’s atmosphere, which circulates warm and cold air across the earth, the
ocean also circulates warm and cold water across the world.
Why do I care? Ocean circulations have a big impact on weather patterns and atmospheric
circulations that affect our weather in the Southeast.
I should already be familiar with: Density, Temperature
Ocean circulations are very complex and can travel in different directions depending on how
deep you look in the ocean, but the main source that drives all ocean circulations is the energy
from the sun. Two important by-products of the sun’s energy that affect circulation are wind and
ocean density.
How does wind affect ocean circulation?
Surface ocean currents are primarily affected by wind patterns. Trade winds can push water
along the top of the ocean and aid in the formation of surface currents. One example of a winddriven circulation affecting an ocean current is the Gulf Stream. The Gulf Stream takes very
warm water from the Gulf of Mexico and parts of the Caribbean Sea and transports it northward.
During the winter, the Gulf Stream can have a great effect on storm systems along the East Coast
of the United States. For example, nor’easters can strengthen and grow over the Gulf Stream and
bring heavy snow or rain, strong winds, and damaging beach erosion to the East Coast. It used
to be thought that the flow of the Gulf Stream alone helped keep Europe warm in winter, but it
has been recently shown that the temperate climate of Great Britain comes from warm air
moving along with the Gulf Stream over the Atlantic Ocean. This keeps temperatures along the
western coast of Europe milder than continental areas farther east away from the coast.
How does ocean density affect ocean circulation?
Deep ocean currents are primarily driven by ocean density. In order to understand how density
can affect ocean circulation, we need to understand what density is. Density for salt water
depends on two things: temperature and salinity (how salty the water is). A more common name
for this kind of circulation is known as a thermohaline circulation. In Greek, “thermos” stands
for heat, while “haline” means salinity (the amount of salt in water). Although warmer ocean
water near the surface of the ocean is less dense and contains less salt than colder, deeper ocean
water, warm water actually is capable of holding more salt than cold water.
So why is the deeper, colder water saltier than the warmer, surface-based seawater? One answer:
It is due to freshwater runoff. At the ocean’s surface, fresh water from rivers or precipitation
falling from the sky mixes with the ocean water and dilutes it. As a result, the water at the ocean
surface is less salty than the water below it. Another answer: formation of ice at high
latitudes. In the northern Atlantic and Pacific Oceans, when the air gets cold enough for ice to
form on the surface of the ocean, the dissolved salt is excluded from the ice that forms, leading to
cold and extra salty water forming at these latitudes as the fresh water becomes ice. This very
dense water sinks to deep levels in the ocean and spreads out from there. The bottom topography
of the ocean and the arrangement of the continents helps steer this deep salty water around the
globe.
From this, we can get underwater currents that can be thousands of feet below the surface of the
ocean. In a way, the thermohaline circulation can work together with wind-driven circulations
and create a conveyer belt that circulates all around the world. Thus, the combined thermohaline
circulation and wind-driven circulation has also been dubbed the ‘Great Ocean Conveyor Belt'.
How does this relate to public health?
Increasing carbon dioxide levels in waters and warmer water temperatures impact global ocean
circulations, which are one of the primary drivers of weather, temperature, precipitation, and
seasons, and therefore affect a variety of aspects of health.1,2
1
Climate Institute. Oceans and sea level rise: Consequences of climate change on the oceans,
thermohaline circulation. <http://www.climate.org/topics/sea-level/index.html#thermohaline>
Accessed December 6, 2012.
2
National Oceanic and Atmospheric Association, PMEL Carbon Program. Ocean carbon uptake.
<http://www.pmel.noaa.gov/co2/story/Ocean+Carbon+Uptake> Accessed November 23, 2012.
Review
1. How have warm ocean currents been thought to affect climate in Britian?
2. Deep ocean currents are caused by differences in ocean density. What two factors most
affect ocean density?
3. Highlight the definition of “haline”.
4. As we get further north (and farther from the equator) the temperature of the ocean
decreases. How might the time of year influence the temperature of the ocean?
5. How might increasing ocean temperatures be a health risk?
Article 2
How does the atmosphere resemble a greenhouse?
Farmers use greenhouses to extend the growing season. A greenhouse traps heat. Days that are
too cool for a growing plant can be made to be just right. Similar to a greenhouse, greenhouse
gases in the atmosphere keep Earth warm.
The Greenhouse Effect
When sunlight heats Earth’s surface, some of the heat radiates back into the atmosphere. Some
of this heat is absorbed by gases in the atmosphere. This is the greenhouse effect, and it helps to
keep Earth warm. The greenhouse effect allows Earth to have temperatures that can support life.
Gases that absorb heat in the atmosphere are called greenhouse gases. They include carbon
dioxide and water vapor. Human actions have increased the levels of greenhouse gases in the
atmosphere (Figure below). The added gases have caused a greater greenhouse effect. How do
you think this affects Earth’s temperature?
Human actions have increased the natural greenhouse effect.
Like a blanket on a sleeping person, greenhouse gases act as insulation for the planet. The
warming of the atmosphere is because of insulation by greenhouse gases. Greenhouse gases are
the component of the atmosphere that moderate Earth’s temperatures.
Greenhouse Gases
Greenhouse gases include CO2, H2O, methane, O3 (Ozone), nitrous oxides (NO and NO2), and
chlorofluorocarbons (CFCs). All are a normal part of the atmosphere except CFCs. The table
below shows how each greenhouse gas naturally enters the atmosphere (Table below).
Greenhouse Gas
Source
Carbon dioxide
Respiration, volcanic eruptions, decomposition of plant material; burning
of fossil fuels
Methane
Decomposition of plant material under some conditions, biochemical
reactions in stomachs
Nitrous oxide
Produced by bacteria
Ozone
Atmospheric processes; Absorbs ultraviolet radiation
Chlorofluorocarbons Not naturally occurring; made by humans
Different greenhouse gases have different abilities to trap heat. For example, one methane
molecule traps 23 times as much heat as one CO2 molecule. One CFC-12 molecule (a type of
CFC) traps 10,600 times as much heat as one CO2. Still, CO2 is a very important greenhouse gas,
because it is much more abundant in the atmosphere.
Summary
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Greenhouse gases include CO2, H2O, methane, O3, nitrous oxides (NO and NO2), and
chlorofluorocarbons (CFCs).
Greenhouse gases trap heat in the troposphere. Some greenhouse gases can trap more
heat than others.
Levels of greenhouse gases in the atmosphere are increasing due to human activities.
Review
1. What mode of thermal energy transfer does the Sun use to heat our atmosphere?
2. What is insulation? What effect does insulation have on global temperature?
3. What is the greenhouse effect?
4. How does Earth's atmosphere resemble a greenhouse?
5. What type of radiation does ozone absorb?