Humans in the Biosphere Global Warming and the Ozone Layer 2/12/10

Global Warming All life on Earth depends on climate conditions like temperature and rainfall. Our planet is getting warmer—the 2000s were the warmest decade ever recorded. The term used to describe this increase in the average temperature of the Earth is global warming.

Global Warming

Global Warming Scientists are trying to determine if this is a natural cycle of climate change or if it is caused by human activity. The most widely accepted hypothesis is that global warming is at least partially due to human activities that add carbon dioxide and other greenhouse gases to the atmosphere. What do you think?

Global Warming According to this hypothesis, the burning of fossil fuels combined with cutting and burning of forests worldwide is adding carbon dioxide to the atmosphere faster than it can be removed in the carbon cycle. This causes heat from the sun to be trapped in the air instead of being bounced back into space, which makes the planet warmer.

Global Warming What can happen if the Earth continues to warm? The polar ice caps could melt, raising sea levels and flooding coastal areas of the world. Ocean currents that carry weather to different parts of the world could shift, leading to flooding in some areas and droughts in others, cold weather in some areas and hot weather in others.

Ozone Layer The ozone layer is a part of the atmosphere 6 – 10 miles above the Earth’s surface that has a high concentration of a gas called ozone (O3).

Ozone Layer The ozone layer serves a very important function in our atmosphere: it absorbs harmful ultraviolet radiation from the sun which can cause sunburns, skin cancer, and eye damage in animals and tissue damage in plant leaves.

Ozone Layer Beginning in the 1970s, scientists noticed the ozone layer was thinning when they saw a hole first over Antarctica then over the Arctic Circle as well. They found that the holes were causes by gases called chlorofluorocarbons, or CFCs.  CFCs drift high up into the atmosphere and when they reach the ultraviolet radiation from the sun, they break apart into free radicals. These free radicals then combine with the ozone molecules and break them apart. In this way they deplete the protective ozone in our atmosphere.

Ozone Layer CFCs were once used as propellants in aerosol cans, as coolant in refrigerators and air conditioners, and in producing plastic. Because of scientific research about the damage CFCs caused, they were banned in the US and many other nations in 1987. These molecules can last in the atmosphere for as long as 100 years, but we are already seeing a decrease of them in our atmosphere. This shows that the ban is working to help our ozone layer become healthy again.

Humans in the Biosphere PESTICIDES AND BIOLOGICAL MAGNIFICATION 2/15/10

Pesticide Use & Biological Magnification Americans use billions of liters of fresh water each day for everything from drinking and washing to watering crops and making steel and plastics.

Pesticide Use & Biological Magnification Pollution from human activities threatens water supplies in several ways. Chemicals that are not disposed of properly can enter streams and rivers. Wastes discarded on land can seep through soil and enter underground water supplies that we tap with wells. Sewage, from our sinks and toilets, contains nitrogen and phosphorous compounds that encourage the growth of algae and bacteria which can damage ponds and lakes.

Pesticide Use & Biological Magnification DDT was one of the first chemical pesticides used. It is inexpensive, remains active for a long time, and kills many different insects such as disease-carrying mosquitoes. DDT can also poison other animals that it is not intended for, like frogs, birds, and mammals. It causes nervous system problems and makes birds’ egg shells thinner.

Pesticide Use & Biological Magnification When DDT was sprayed, it drained into rivers and streams at low concentrations that seemed harmless. However, DDT is nonbiodegradable—this means it is not broken down by metabolic processes in bacteria, plants, or animals. Also, when DDT is picked up by organisms, they cannot eliminate it from their bodies. Instead they store the chemical in their tissues

Pesticide Use & Biological Magnification Why is this a problem? Aquatic plants pick up DDT from the water. A herbivore eats many plants during its life, so the DDT can become concentrated to levels ten times higher than levels found in the plants. Then, when a carnivore eats herbivores, the toxic chemical is concentrated even further.

Pesticide Use & Biological Magnification In this process, called biological magnification (also bioaccumulation), concentrations of a harmful substance increase in organisms at higher trophic levels in a food chain or food web. 10,000 ppm 1,000 ppm 100 ppm 10 ppm