Notes

Climate is the average weather conditions of a region over a long time. Every region has a typical climate. For example, Chicago usually experiences below-freezing temperatures in winter and warm temperatures in summer. The city of San Francisco, which is near the Pacific Ocean, has mild weather and moderate temperature changes throughout the year.

In recent years, however, there is evidence that the climate is changing globally. Earth’s average temperature is increasing. This increase in temperature is a matter of concern for people, especially scientists. After a lot of research, scientists have concluded that the increasing carbon dioxide (CO2) level in Earth’s atmosphere is the main cause of this climate change.

CO2 levels are rising for a number of reasons, but the primary reason is human activities.
To address rising levels of CO2, we first need to review how high levels can negatively affect the atmosphere.

Earth’s atmosphere behaves like a giant greenhouse. Greenhouse gases, such as CO2 and water vapor, cover Earth like the glass in a greenhouse. The Sun’s energy (ray 1) passes through the atmosphere to Earth’s surface. The planet warms and gives off heat energy that radiates toward space (ray 2). The envelope of greenhouse gases doesn’t let all of this outgoing radiation leave the atmosphere. As a result, some heat rays reflect back toward Earth (ray 3). This trapped heat keeps the planet warm. In general, that’s a good thing. Without this heat, Earth could not support life.

But right now, the level of greenhouse gases is too much of a good thing. The level is rising, which is causing the average temperatures on Earth to go up. The consequences of this increase in temperatures are hard to predict, but scientists are worried that if greenhouse gases are not controlled, sea levels will rise, climates will shift, and plant and animal diversity will change worldwide.

To control climate change, the first step is to control emissions of greenhouse gases. Many human activities emit CO2 into the atmosphere. Any activity that requires burning fossil fuel—turning on a light, driving a car, powering a factory—releases CO2 into the atmosphere.

Now, we probably can’t avoid all of these activities. But there are steps we can take to keep carbon emissions to a minimum. In the next activity, you’ll watch a video that shows how one region in Europe is reducing its CO2 emissions.


Controlling CO2 in the Ocean
Increasing CO2 levels cause changes in the oceans. CO2 in the atmosphere dissolves in ocean water, making it acidic. We measure the acidic and basic nature of a substance using the pH scale. The strongest acid has a pH of 1, and the strongest base has a pH of 14. The pH of pure water is 7—right in the middle. Water is neither acidic nor basic. As the level of CO2 increases in water, the pH decreases, making the water more acidic. An increase in the acid level in oceans is known as ocean acidification.

The image shows the pH scale and how ocean acidification affects marine life. Acids in the ocean can corrode shells and skeletons of organisms. Over time, more acid can lead to a decrease in their populations. That means less food for humans and other organisms living in and around the oceans. Of course, more CO2 in the ocean means that more CO2 also cycles back into the atmosphere.

Rising CO2 levels in oceans is a concern. The first step toward solving the problem is to monitor the acidity of ocean water. The National Oceanic and Atmospheric Administration (NOAA) has identified areas of acidification. It has set up stations to monitor the areas. One method to slow down ocean acidification is to reduce pollution in oceans. Some pollutants can increase the amount of CO2 dissolved in ocean waters.

Lowering pollution levels is one way to control ocean acidification. Another is growing more plants that consume CO2. Scientists have noticed that ocean waters are rich in iron where marine plants such as phytoplankton grow in abundance. So, they came up with the idea to add iron dust to the ocean to increase the growth of marine plants. This method is called ocean fertilization.

This technique is relatively new and also controversial. Just the right amount of iron must be used. According to some scientists, the growth of too much phytoplankton may result in an increase in greenhouse gases in air and in water. There is also the threat of toxins entering ocean water if the iron isn’t pure.

Depositing iron in the water involves a ship making a 12-hour zigzag cruise. It’s hard to know the effectiveness of this method since iron deposits are hard to trace after they’re spread. Ocean fertilization seems to be more effective in some areas than others. It works best in the warm waters near the equator.

We know that greenhouse gases such as CO2 cause climate change. So, our first step to combat climate change is to control the level of CO2 in the atmosphere. There are a few basic approaches to controlling CO2 levels:

Use up the CO2 that’s already in the atmosphere.
Change our habits to lower CO2 production.
Prevent CO2 from reaching the atmosphere.


In the first approach, we neutralize the amount of CO2 emitted into the atmosphere by using it up.

Conservation
Trees remove CO2 from the air for photosynthesis. As the level of CO2 in the air drops, the air becomes purified. We should maintain the current number of trees and plant new trees and vegetation to control CO2 levels.

Reforestation
Reforestation involves planting new trees in areas where they have been cut down or destroyed by fire. Usually, nature takes care of the reproduction of trees. But this process takes longer than we would like. So, scientists have started growing trees in large numbers using modern methods. They use high-quality seeds and select the right kinds of trees for the region. They can also sow seeds faster using special machinery.

The second approach is to change our habits to lower the amount of CO2 that enters the atmosphere.

Reduce CO2 Emissions
Power stations, factories, and vehicles burn fossil fuels and emit large amounts of CO2 into the atmosphere. We can make small changes in our daily lives to help reduce CO2 emissions. For example, we can reduce the use of private vehicles whenever possible. Instead, we might use public transportation, walk, or bike. Carpooling is an excellent option.

Another lifestyle change we can make is to limit the amount of electricity we use. We should use energy-efficient bulbs and unplug devices we aren’t using.



A third approach to lowering CO2 levels is to keep CO2 from reaching the atmosphere in the first place. Carbon dioxide removal (CDR) techniques physically remove CO2 from emission sources. Let’s look at a few CDR methods.

Carbon Dioxide Scrubber
CO2 scrubbers clean factory gases before they are emitted into the atmosphere. The scrubbers are used in power-generating stations that use fossil fuels. The image shows a simple diagram of a scrubber. Air containing CO2 passes through a scrubber that captures the gas. After the scrubber absorbs the CO2, clean air flows out.

Carbon Capture and Storage
CO2 emitted from burning fossil fuels can be captured and stored in places where the gases will not leak into the atmosphere. The storage locations are usually underground. The image shows how CO2 emitted by a cement factory passes through pipes to reach several kinds of underground storage, such as coal and salt beds.

So, what happens to all of this stored CO2? Let’s find out.

The CO2 that is captured can be used in a number of different ways. Here are a few of them:

Enhanced oil recovery. At times, it can be difficult to pull all of the oil from an underground basin. The image shows how CO2 is used to flush out those last drops of oil.
Paper production. CO2 is used to control pH levels in paper production.
Metal fabrication. Building metal structures by cutting, bending, and assembling metal parts is metal fabrication. While building these structures, the metal parts have to be joined or welded together by heating them. CO2 is sprayed as a shielding gas before welding. The spray protects the metal from reacting with oxygen and water vapor in the atmosphere.
Food and beverage production. CO2 is used in the production of bubbly sodas and soft drinks.

Fossil Fuel Alternatives
It’s clear that we should make an effort to bring down the levels of CO2 to slow the effects of climate change. One of the primary ways we can reduce CO2 levels is by finding clean sources of energy.

Clean sources of energy are natural resources that are renewable, such as solar energy and energy from wind and water.

Let’s see how each of these energy sources is useful.
Solar Energy
Energy that we get from the Sun is solar energy. We use solar energy directly as heat or convert it into electrical energy. You may have used watches and calculators that run on solar cells. These cells convert solar energy to electric energy. As shown in the pictures, solar cells can also power streetlights and even houses. Huge solar panels are used to produce the large amounts of energy used in houses. Many regions in the United States are harnessing solar energy by putting up solar panels in open areas to supply even greater amounts of energy.

When solar energy is converted to electric energy, there are no CO2 emissions. Solar energy is a renewable form of energy since the Sun continues to shine each day. A disadvantage of using solar energy is the high cost of panels. Also, solar energy is not available at night, and solar panels absorb less energy on cloudy days. But scientists are developing improved panels that work efficiently in all sorts of weather.

Water is a renewable form of energy. In a hydroelectric power plant, water controlled by dams releases large amounts of kinetic energy as it flows. This energy can be used to generate electricity and is a low-carbon source of energy.

The main concern is that hydroelectric power plants can’t be built everywhere. To build dams, there must be a natural flow of water. When building dams, we must also respect the habitats of local plants and animals.

Like flowing water, wind has a lot of kinetic energy. Energy harnessed from the wind is called wind energy. Wind turbines are devices used to generate electricity. Wind is a clean source of energy because there are no CO2 emissions in this process.

Like solar energy and water, wind is freely available. But building wind turbines has a high initial cost. Also, not all areas are suitable for turbines. So we can’t fully depend on wind energy to produce electricity. The map shows locations of wind turbine farms across the United States in 2011.
Other natural forms of energy can replace fossil fuels and help reduce CO2 emissions.

Nuclear Energy
An atom is made of protons and neutrons in the nucleus, or center, with electrons revolving around the nucleus. Within the nucleus, enormous amounts of energy bind neutrons and protons together. When a nucleus splits, this energy is released. The released energy is called nuclear energy. Nuclear plants use nuclear energy to generate electricity. Among the many elements available, uranium atoms are used in nuclear plants because they can be split more easily. Uranium is not a renewable source of energy, but large amounts are available across the globe. Just one ton of uranium can replace 16,000 tons of fossil fuel.

Here’s how a nuclear plant works:
The main part is the nuclear reactor. In the reactor, fuel rods full of uranium pellets, or bullets, are placed in water.
Inside the fuel rods, uranium atoms split, releasing energy.
This energy heats the passing water, creating steam.
The steam moves through a turbine—much like the turbine in a hydroelectric dam or a wind turbine—which turns a generator to create electricity.
The steam cools and turns back into water, which can then be used over again. At some nuclear power plants, extra heat is released from a cooling tower.
There are some disadvantages to using nuclear energy. Building and maintaining nuclear reactors is expensive. Also, disposing of radioactive waste from power plants must be done carefully to prevent damage to land and water. Radioactivity lessens over time. Waste can be stored until it no longer poses an environmental threat.

If you could insert a thermometer straight into Earth, you would notice the temperature getting warmer as the thermometer went deeper. That’s because beneath its surface, Earth is full of heat. This heat is geothermal energy.

Because of this heat, groundwater sometimes heats up and changes to steam deep inside Earth. When this steam is brought to the surface, it can be used to spin a turbine in a generator to make electricity. Cold water is then returned to Earth for reheating. Hot springs and geysers are places where we can find steaming water below the surface.

The image shows how geothermal energy is used to make electricity at a geothermal power plant:

Hot water is pumped from deep underground through a well under high pressure.
When the water reaches the surface, the pressure drops, which causes the water to turn into steam.
The steam spins a turbine, which is connected to a generator that produces electricity.
The steam cools off in a cooling tower and condenses back to water.
The cooled water is pumped back into Earth to begin the process again.
Using geothermal energy generates little pollution, and the hot water is renewable if sources are properly managed. But sources of geothermal energy can’t be moved—power plants must be built right above the hot water basins. Finally, the initial cost to build a geothermal power plant is quite high.

Biomass is material from plants and animals. Biomass contains stored energy. Plants absorb energy from the Sun during photosynthesis. So, when we burn biomass, this stored energy is released as heat. For example, wood is biomass that produces energy when burned. Fuel that we get from biomass is known as biofuel. The biofuel made from corn is corn ethanol, which is used as fuel in vehicles. This fuel emits CO2, but it emits much less than burning fossil fuel does.

In some power plants, biomass is used to heat water and create steam to generate electricity. The image shows a power plant where wood scraps are used as fuel. Power plants in the United States use biomass to produce electricity that services 1.3 million homes.

Biomass is found in abundance and is renewable. Using biomass also helps manage waste. But the fuel we get from biomass is not as efficient as fossil fuel.

Garbage. No one likes to think much about it, and no one likes the smell of it. But it’s a part of our day-to-day lives. An area where waste is buried in the ground is known as a landfill. Humans dispose of a lot of garbage every day. Getting rid of garbage the right way is a challenge for everyone.

The image shows how the methane from landfills can be used to make electricity:

Trash decomposes in a landfill or a dump and releases methane gas.
As methane rises, it is captured in wells.
The methane is burned in the power plant to produce heat and electricity.
Methane is a greenhouse gas. If the emissions aren’t controlled or reused, it can eventually reach the atmosphere, adding to the warming of Earth.

We can help the planet by reducing the amount of garbage we throw away. One way is reusing or recycling goods instead of buying new goods. Another way is using food waste to make compost, which can be used as fertilizer.

Watch the video on the next screen to see how composting makes something good out of garbage.


We can make environmentally friendly choices every day. Our choices can be as simple as drinking from a reusable bottle instead of a disposable bottle and recycling a can instead of throwing it in the trash. It can be passing on an old computer to be reused instead of dumping it in the trash. Everyone can help to reduce CO2 and methane emissions. These actions will really help our planet. Take a minute to reflect on how you are doing your part to control your carbon footprint.

Scientists and engineers from many different fields are working together to fight climate change through new technologies. One of these fields is ecology. Ecologists study the effects of climate change, specifically its effects on species other than humans.

Ecologists deal with the relationships between groups of living things and their environment. They study how human behavior affects plants and animals. Here are a few actions they take to keep an eye on the effects of climate change:

Track changes to the makeup of species.
Determine why marine life is moving to cooler ocean waters.
Monitor the risk of disease and survival rates of plants and animals.
Study shifts in the migration and breeding behaviors of plants and animals.

Ecologists have an important role to play in confronting climate change. They might keep a record of an individual species and its population trends. Ecologists also determine which species are at risk of extinction.

They work with environmental engineers and conservation scientists to protect species at risk and their habitats. They even work with politicians on policies that will protect natural habitats and species, such as limiting the hunting of endangered animals.

The scientists frequently search for evidence of life on other planets. They will tell you that liquid water is a must-have component. However water is a far more complex compound.

Water is the only compound found naturally in three distinct physical states of matter; solid (ice, snow, hail, sleet, and frost); liquid (liquid water, dew, rainwater); and gas (water vapor, steam, moisture in the air).

You may have looked at the oceans, snow-capped mountains, or the clouds in the sky. You may consider that these three physical states are static. Water, although, is constantly in motion, transitioning between these three states of matter in different ways.

The transition of water between one state to another can be classified into six different categories. In each category, the molecular structure of the water is impacted by energy in the form of heat to change its physical state.

1. Solid to liquid: Melting

When heat is applied to solid water (ice), the water molecules begin to vibrate faster and move further apart. This allows the solid to become liquid. This process of melting (also known as fusion) will increase the water’s temperature to its melting point. Here the entire solid has transitioned into liquid form.

2. Liquid to solid: Freezing

When the temperature of a liquid is lowered, the opposite process occurs. Particle motion slows down, and the particles start to align in specific patterns to form crystalline solids. You can observe this in ice crystals. Most substances that are able to transition into a liquid form contract as they start to crystallize. Water is unusual in that it expands as it freezes, with larger crystals that allow ice to float on the liquid water below.

3. Liquid to vapor: Evaporation

When water transitions from a liquid state to a vaporous state, the conversion process is referred to as vaporization. With the addition of heat energy, the surface molecules of the water break away. They then become free gas particles. This process of evaporation continues until all of the liquid has transitioned to vapor. If the heat energy is strong enough, bubbles can form in the liquid. The water is then said to be boiling. For water, this occurs when the temperature of the liquid reaches it boiling point of 100°Celsius (212°Fahrenheit).

4. Vapor to liquid: Condensation

As water in its vaporous state cools, an initial cluster of particles will form droplets that further cool the gas. This leads to the process of condensation. You can see multiple examples of this process; the formation of droplets of water on the outside of a glass containing a cold beverage or on your glasses as they steam up when you move from a cold room to the outside on a hot and humid day.

5. Vapor to solid: Deposition

When water vapor transforms directly into solid form without going through the liquid phase first, it is called deposition. You can see different examples of this; in the frost outlines blades of grass and twigs on a cold morning; in the patterns of frost on a window pane; and in the ice crystals of snow fall.

6. Solid to vapor: Sublimation

Perhaps the least well-known transition process for water is where ice transforms into vapor without going through the intermediate liquid stage. Technically, the ice is melting, but there is no liquid or corresponding change in temperature. This process is critical to water’s role in balancing Earth’s climate. Suppose ice couldn’t sublimate in the cold Arctic and Antarctic regions. The water would then remain stored in the ice packs indefinitely and would significantly reduce the replenishment of the water on land through the water cycle.

Properties of Water
The molecular simplicity of water (H20) often disguises what an unusual compound it is compared with others. For example, it is the only compound that can be found on the earth in all three physical states.

Liquid water exists all over the surface of the earth, even in the Arctic and Antarctic regions. In its purest form, it freezes at 0°C (32°F) and boils at 100°C (212°F). Start adding salt to create a brine; you can then lower that freezing temperature even further. Place the water under pressure, such as that found around deep sea thermal vents; you can then raise the boiling temperature as high as 650°F. No other liquid has such a broad range without transitioning into another physical state.

When a body of water freezes, a protective layer of ice forms at the surface. This layer prevents lower layers from freezing and permits aquatic life to persist. The frozen water has a lower density than the liquid water. This allows the ice to float on the surface. Let’s look at unique properties of water.



Heat Capacity
Water also has unique properties in terms of heat capacity. It can store and transport tremendous amounts of heat. This serves two important functions in the continued existence of life on Earth;

It protects aquatic life from sudden changes in air temperature above the surface of the water.
It allows ocean currents to transfer heat from warm tropical area to cooler temperate and arctic areas. This serves to moderate Earth’s climate and make temperate and arctic regions habitable.
You can expand this concept to a worldwide scale. You can see how the oceans and lakes help to balance the temperature ranges. This includes the temperature ranges experienced by coastal or lakefront residents compared with the residents of inland cities and towns. For this reason, a coastal state like Oregon will have milder summers and winters than a Midwest state such as Nebraska, even though Oregon lies at a higher latitude.


Heat of Fusion
Scientists identify the amount of heat needed to prompt a phase change (from liquid to solid, solid to liquid, or liquid to gas) as the heat of fusion. Melting an ice cube, for example, takes a large amount of heat. However if you measure the temperature during the process, you will see that it stays at 0°C (32°F). Similarly, the temperature of boiling water will not rise above the boiling point (100°C) as the water changes state to become vapor.

Heat of Vaporization
Water needs even more heat to break the hydrogen bonds so that the water molecules can fly off as gas. Scientists call this a high heat of vaporization. This characteristic is critical to the existence of life. This is because the liquid left behind after vaporization becomes cooler (evaporative cooling). For example, this allows the human body temperature to be regulated through sweating. On a larger scale, the evaporative cooling of ocean water in hot areas of the planet, such as the tropics, helps to regulate climate temperatures.

Stages of the Water Cycle
Earth’s surface is covered with 70 percent of water. This is the same percentage of water that’s been on Earth since the planet began. The recirculation of water through the hydrologic or water cycle means that the rain falling on us today contains the same water as the rain that fell on the dinosaurs.

There are large bodies of water such as lakes and oceans. Water is in constant motion through the water cycle. Water is evaporating from the earth’s surface into clouds (vapor); condensing into water droplets; and falling back through precipitation in either liquid (rain) or solid (snow) form.

Since the water cycle is in constant motion, it technically doesn’t have a starting point. However, hydrologists typically begin at the earth’s surface and trace the journey of the water back to that surface. Let’s learn about various stages of the water cycle.

Evaporation: The water cycle is powered by the sun. The sun heats water in the oceans, lakes, and rivers. This water evaporates as water vapor, which rising air currents take up into the atmosphere. This is a very energy intensive process. It requires around 600 calories of energy for each gram of water evaporated. The rate of evaporation can be impacted by many factors; such as air temperature, air pressure, and solar radiation. Water also evaporates from plants and soil through a process known as evapotranspiration.

Condensation: The cooler temperatures in the atmosphere cause the water vapor to transition into droplets. These can form dew, fog, or clouds. The same air currents that bring the water vapor into the atmosphere continue to move the clouds around until they grow and collide. Here the water droplets are released as precipitation. Condensation can also occur when the amount of vapor in the air reaches its saturation point. The vapor condenses back into liquid. All of the energy that was used to evaporate the liquid water at the planet’s surface is released back into the environment.

Precipitation: Depending on the local air temperature, the water droplets that condense in the atmosphere can fall in different forms; namely liquid form as rain; solid form as ice, hail, or snow. In colder climates, the falling snow or ice can accumulate as ice caps or glaciers. The frozen water can then be stored for thousands of years. In warmer climates, the fallen snow will melt with the arrival of spring and the liquid water will flow as snowmelt.

Infiltration: Slower moving water can soak into the ground in a process known as infiltration. Here the volume of water is sufficient to break through the boundary surface of the soil. It percolates through the different layers of soil and porous rock. It is driven by both gravity and capillary action pulling the water through the soil.

Groundwater: As the water percolates through the soil and rock, it passes through a zone of aeration. Here air is still present called vadose water. Once the soil is saturated, and no air is present, it is called groundwater. The boundary between the two is referred to as the water table. In some areas of the country, that water table can be so high as to directly impact construction. In Florida, for example, the water table is so high that basements are a rarity in home construction.

Groundwater recharge: This is also known as deep drainage or deep percolation. It is a hydrologic process by which the water moves down from surface water to groundwater. It then enters the aquifer, which is the underground layer of permeable rock or soil. If the water then finds openings in the land surface, it can return through groundwater discharge. It would emerge as a freshwater spring.



Runoff: Depending on the rate and volume of rainfall, the water that falls back onto land will be absorbed into the soil or flow over the ground as surface runoff. The water that infiltrates into the soil will join the general flow as subsurface runoff. The water that percolates down into the aquifer will join the flow as groundwater runoff. When each of these components enters a stream or river, the flow is called total runoff.

Storage: The water cycle is always in constant motion with no real start or end point. However, there are three places in which water is stored; in the atmosphere as water vapor and clouds; on the surface of the earth as a liquid; as solid in oceans, rivers, lakes, and glaciers; and stored beneath the ground as a liquid in the soil and aquifers, and as a solid in the permafrost layer. Atmospheric water can move around the planet very quickly, driven by wind currents. The movement of groundwater is determined by geological formations related to the soil and rock structures.

Stormwater runoff: Extended periods of rainfall in a thunderstorm, a heavy rainstorm, or a large snowmelt can produce more water than the soil can absorb. Suppose there is no other way to direct the movement of water away from the surface. At this point, the storm runoff can cause flooding and soil erosion. The volume of fast-moving water can damage natural habitats. Water in urban areas can also collect trash and pollutants such as oil, grease, chemicals, and pesticides.

Prompted by changes in the Water Quality Act of 1987, developers are now required to install stormwater management systems. This would handle the movement of polluted water from roads and other paved surfaces in both commercial and residential areas. In built-up residential or commercial areas, this water is usually diverted into stormwater runoff systems. This either stores it in retention ponds or direct the water flow back to rivers and streams to avoid flooding.

Water Resources
Water covers 70 percent of the earth’s surface. It is easy to assume that water is an abundant resource for everyone on the planet. The reality is very different: 97 percent of that water is seawater, with only 3 percent being drinkable fresh water. Most of that fresh water is frozen solid in glaciers and ice caps. This leaves the human race dependent on a limited number of fragile water resources. Let’s look at some of those resources.

Surface water:
The water falls to the ground through precipitation. This can be intercepted before it infiltrates into the soil by a process known as catchment. It can be directed into a holding area called a reservoir for future use. Depending on the local geographic topology, this catchment and storage can be built around natural streams, rivers, and rock catchment areas. A more man-made approach can be taken to deliberately divert river flow or stop it altogether through the use of dams. The added bonus of dam construction is the ability to generate hydroelectric energy.

Smaller residential solutions include rainwater tanks that divert rainfall from the roof, using gutters, into storage tanks.

Groundwater, Rivers, and Lakes:
Rivers and lakes provide the most easily accessible water resource. However the water levels can vary depending on the water source; such as snowmelt, groundwater discharge from a freshwater spring, or smaller streams. High local temperatures can also create problems with rapid evaporation.

Subsurface runoff and groundwater resources can be accessed through the construction of wells. This can pump the water to the surface. Alternatively, groundwater can be accessed through bores that reach low-lying water. This can be high enough pressure to gush out of the hole without the need of a pump.

Oceans and Glaciers:
Large chunks break off the glacier ice shelf into the ocean water as icebergs. These floating stores of fresh water could technically be towed around the world and be used as a water resource. However, the loss of volume due to melting plus the transportation costs of delivery would make the project inefficient.

The ability to remove salt from sea water using reverse osmosis in large desalination plants has been around for centuries. However, the cost of up to $5 per thousand gallons versus $2 per thousand gallons for conventional freshwater makes these projects expensive.

Water supplies can only be replenished with rainfall; the precipitation step in the water cycle. Suppose areas have an arid climate and very low average annual rainfall. Here water must either be: drawn from surface or groundwater sources such as springs, wells, and bores; or transported long distances using aqueducts or complex pipe infrastructures. Sometimes there are multiple users competing for those resources. Here residential and agricultural requirements, extended periods of low rainfall, called a drought, can put a huge strain on the water supply. The State of California, for example, entered a fourth straight year of drought in 2015. This prompted the Governor to introduce aggressive emergency conservation regulations to achieve a 25 percent reduction in water use.


Protecting a Fragile Water Supply
You can take steps to reduce water consumption; such as installing low-flow showers and toilets; and using waste water for irrigation. The greater risk to our fragile water supply comes from contamination. This may leave what little water you do have unsafe to drink.

It is very easy for hazardous pollutants and pathogens to enter our water supply. Chemical waste from factories are pumped directly into rivers or allowed to leach into the soil. This takes it directly into the aquifer. Pesticides from farmland or household landscaping can also leak directly into surface water or groundwater. Underground gasoline storage tanks at gas stations can also develop leaks over time. This would allow the chemicals to go directly into groundwater supplies. Proactive steps such as less use of chemicals and more frequent inspection of gasoline storage tanks, can be taken to control the risk of contamination.



Think about how our bodies sweat during physical activities such as running, working out at the gym, or playing a quick game of touch football. These activities make us constantly reach for our water bottles. We drink water to replace the water that our bodies lose.

Our bodies require water to function. These functions include respiration, as well as removing excess water as sweat and waste. This water can eventually rise into the atmosphere through evaporation. Moist air rises because it’s lighter than dry air. High in the atmosphere, this vapor condenses into water droplets that fall back to Earth as rain. It sounds odd, but the water we drink today has been circulating on Earth for billions of years.

We often label our water bottles so we can tell whose is whose. But the water inside them doesn’t really belong to us. We are only borrowing it from Earth for a short time.

Imagine coming home from a walk on a hot day. You’re sweaty and thirsty. You grab a glass, fill it with ice, and pour cold water in it. After a while, the outside of the glass appears to be nearly as sweaty as you are! Soon, you’ll see water streaking down the outer surface of the glass.

What causes the water droplets to form on the outside of the glass? Let’s look closer at the cause of this phenomenon.


Water condensing on a glass demonstrates the water cycle. Likewise, an invention that can change humidity from the air into liquid water also employs the water cycle.

Humidity is the amount of water vapor in the air. On some days, you may feel like the air is heavy and your skin is sticky. The reason is high humidity. Humidity slows down the evaporation rate of sweat from your skin and makes your skin feel clammy.

When the water vapor from the air encounters cooler temperatures, such as the surface of a glass, it condenses back into liquid water. The condensation appears as water droplets.

Water and Earth’s Spheres
The water cycle is defined by water’s ability to change form with a change in temperature. The water cycle goes through Earth’s four spheres.

When rain falls, some of it seeps into the soil and some makes puddles. The rest of the water reaches streams, oceans, rivers, and lakes. Soon, the ground dries and the puddles disappear. Drying occurs because the Sun heats the water on the ground. Heating causes the water to evaporate. Evaporation also occurs at the surfaces of oceans, lakes, and other bodies of water. In a long, hot dry spell, the rate of evaporation can be greater than the amount of rain received at that location. Weather forecasters might then warn people of low water levels in rivers, lakes, and other bodies of water.

All living organisms contribute to the amount of water vapor in the air. Plants excrete excess water in the form of water vapor. The air that humans and animals breathe out also contains water vapor.

Clouds and Precipitation
Different processes add water vapor to the atmosphere, and that water vapor rises. Similar to a glass of ice water, the air surrounding mountaintops can be quite cold. When water vapor rises to these cool places, it condenses into water, forming clouds. Clouds may look like large puffs of cotton, but they actually consist of tiny droplets of water.

If the temperature in a cloud drops low enough, the water droplets turn into ice. The process of water vapor turning to liquid droplets or solid ice is called precipitation. When the clouds become heavy with precipitation, Earth’s gravity pulls the precipitation to its surface as rain or snowfall.

Rain and snow fall on mountains, on the ground, and on bodies of water such as oceans and lakes. When gravity pulls the water down a mountainside, it’s called surface runoff. Runoff may collect in ponds or reach other bodies of water such as rivers and seas. From these bodies of water, the water evaporates once again and returns to the atmosphere.