At the end of the Roman Empire in the year 550, there were only about 250 million people living on Earth. Now there are more people than that just in the United States. As of 2009, the world population was more than 6.7 billion.
In the past, famine or disease killed people at an early age. Many children died young. The death rate was high, and the birthrate was low. With today’s advances in health care, agriculture, and sanitation, human life spans have increased. The death rate has decreased, while birth rates have increased. The result has been an enormous increase in population.
Many people have become concerned about the human impact on ecosystems. Humans depend on the environment to supply everything they need to stay alive. Unfortunately, people have not always recognized this dependence. Today, there is a greater need for food, water, land, and resources than ever before. These increased needs have put a serious strain on our environment. People must learn what they can do to protect the planet and its resources, the materials that people use, for the future.
Limited Natural Resources
Natural resources are those things in the environment that we use to survive. The air we breathe, the water we drink, and the food we eat are natural resources. The products we use to build our homes, stay warm, and make all the things we use every day are also natural resources. All these resources are in limited supply and must be used by everyone on Earth. Many scientists fear that because of our rapidly growing population and wasteful habits, we are using Earth’s resources too quickly.
Scientists divide resources into two categories. Renewable resources are those that can be replaced within an average lifetime. Trees, animals, and crops are renewable resources.
Nonrenewable resources cannot be replaced easily. Topsoil and fuels, such as coal and oil, are nonrenewable resources. It took millions of years for fuels like coal and oil to form. When they are gone, they are gone forever.
Conservation is a method of using nonrenewable resources in ways that do not waste them. Forests, water, soil, and any other resources can be conserved by recycling, reusing, or reducing our use of products containing these resources.
Human activities not only use up our natural resources, they also pollute, or contaminate, the environment. Pollution, man-made waste that contaminates the environment, takes many forms. Solutions can be as simple as picking up litter or as complex as reducing the output of pollutants from industrial plants.
Solid waste is all the garbage that comes from homes, businesses, mines, farms, and even schools and hospitals. The chart below shows that the amount of trash we produce has greatly increased. In the 1960s, we produced trash at the rate of about 2.5 pounds of trash per person each day. Now we produce about 4.6 pounds of waste per person per day. Most of that waste ends up in landfills. Some waste is burned. But helpfully, more waste than ever before is recycled into other products.
Hazardous wastes come from the hundreds of chemicals that we produce and use in the United States. These chemicals include house paints and automotive oils and fluids, as well as many poisons used by farmers. Safely disposing of these wastes is an enormous problem. More and more states are trying to control how these hazardous wastes are handled.
Some air pollution is invisible. Compounds called chlorofluorocarbons (CFCs) cannot be seen, but they have caused a lot of damage. CFCs are now banned, but they once were released from aerosol spray cans. They damaged the ozone layer in’ the upper atmosphere. Ozone protects Earth from harmful radiation from the Sun.
Smog is a visible form of air pollution. It forms when water droplets in the air mix with compounds of nitrogen and sulfur, both of which are released when fossil fuels are burned.
Today, the US government tries to limit air pollution. Laws set air-quality standards for cars, factories, and power plants.
Earth’s water collects in ponds, lakes, rivers, and oceans. Water also collects between soil particles and cracks in rocks underground, where it is called groundwater. Any of these supplies of water can become polluted. Moreover, because water flows from place to place, pollutants can spread many miles from their original source.
Water pollution can come from mines, factories, and power plants. It can come from sewage that is improperly treated. Fertilizers from farms and lawns can also pollute the water. When fertilizers wash into a lake, they help algae and other plants grow too quickly. This can begin a process that kills fish and slowly drains the lake.
Pollutants can also travel from the air into the water. Gases from burning coal can mix with water droplets in the air. The droplets fall to Earth’s surface as acid rain. Acid rain can kill plants when it mixes into the soil. It kills fish when it mixes into lakes and rivers.
Uses of Land and Water
Like all other living things, humans need food, water, air, and a place to live. As the human population grows, so does its need for these resources. Three hundred years ago, for example, North America was home to only a tiny fraction of its human population today. Vast forests and open grasslands covered much of the land. Today, most of these tracts of forest and grasslands have been replaced by cities, suburbs, farms, and ranches. Water has been channeled out of lakes and rivers for human use.
Changes like these help humans live and grow. But they have unwanted effects, too. Sometimes these effects take many years to observe. Cutting down trees from a hillside makes room for new houses, but the soil may eventually wash away and carry the houses with it.
In the United States, many laws affect how people use land and water. Often these laws and policies are controversial. Should a farmer be allowed to sell his land for a new housing development? Where can one build new factories or power plants? The opinions and interests of businesses, landowners, and community members can all be different.
In the mid-1800s, about sixty million bison lived on the grasslands of North America. By the year 1900, there were fewer than one thousand. Hunters with rifles were the cause. The bison were over-hunted, meaning they were killed much faster than their numbers could increase. Over-hunting is one way that a species can become endangered. Many species are endangered because their habitats, or natural homes, are being destroyed. An endangered species has very few individuals left alive, and the species could die out completely. Species with no members still alive are described as extinct.
The current list of endangered species is very long. It includes animals of all shapes and sizes, from tiny snails to large elephants, tigers, and gorillas. Some of these species live only in zoos. Others are on the verge of extinction, meaning they could be lost forever.
Yet the American bison has recovered, as has the bald eagle and other species that were once endangered. They have been helped by nature preserves, conservation programs, and the work of scientists and citizens.
Global Climate Change
According to many scientists, the most significant environmental issue is global climate change. This issue is sometimes called global warming because it involves rising temperatures across Earth.
Climate is the average weather conditions from year to year. In a stable climate, the weather changes in a predictable way every year. Living things depend on these changes. The weather often determines the growing season for plants and the breeding season for animals.
Yet in recent years, scientists have been observing evidence of warming temperatures and climate change. In places across Earth, record high temperatures are being recorded more frequently. Traditional winter weather is lasting a shorter time and is not as cold.
The most dramatic changes are occurring near the North and South Poles. Glaciers are melting and ice sheets are thinning. Yet important changes are happening everywhere. In the western United States, wildfires resulting from dry summer weather are more common. In the southern Atlantic Ocean, hurricanes are more numerous than in the past.
What is causing climate change? Some scientists argue that the cause is the burning of coal, oil, and other fossil fuels. These fuels release a gas called carbon dioxide. Carbon dioxide is a natural part of Earth’s atmosphere. It helps trap heat in the atmosphere. Carbon dioxide levels appear to be rising, causing Earth’s temperatures to rise as well.