A student reading this chapter will be able to:
1. Define the concepts of biosphere and climate.
2. List and explain the factors influencing climate.
3. Define the term “biome.” List the major global biomes and discuss their primary features.
4. Show the flow of energy through ecosystems.
5. List the various trophic levels.
6. Explain the various nutrient cycles including the carbon, nitrogen, and phosphorous cycles.
7. Define the term “succession,” explain the mechanisms of succession, and discuss the types of human intervention that interfere with succession.
We are on a living planet and are surrounded, immersed, and enveloped by life. It is both outside and inside of us. We breath it in, we swallow it, we walk on it, we touch it. Each footstep on a fertile lawn or forest floor will send tremors to trillions of bacteria; millions of algae, fungi, and protozoa; and hundreds of insects and worms. The skin on our bodies, when viewed microscopically, is a teaming matrix of tiny caverns filled with bacteria, viruses, and mites. So dense are the unseen life forms on our bodies that if our own tissues were to instantly disappear, we would still be recognizable by the remaining shell of microscopic life enveloping our body. Every breath draws in untold numbers of fungal spores, bacteria, viruses, and other microbes and plant spores. Life abounds most everywhere inhabited by humans. Life thrives on the nutrients in soil and water, the oxygen and carbon dioxide in the air, and the sunlight that ultimately powers most life. In those areas of earth where nutrients are depleted, oxygen is rare, sunlight is extinguished, or moisture is diminished, life becomes reduced or absent. This is true for most breathing creatures except birds. They exist from the coldest regions of Antarctica to Atacama, the hottest and driest deserts in the world. Conditions for most life are found in a layer about the globe that extends from approximately 8 kilometers in the atmosphere (where some microbial spores and insects may be found) to 8 kilometers below the ocean surface where some unusual life forms adapted to darkness and high pressure survive. This theoretical “layer of life” is called a biosphere because life is thought not to exist outside this area. Most life occurs in a much narrower layer extending from about a 182-meter depth in the ocean, where sunlight is able to penetrate, to the summer snow line of high mountain peaks, where a thin layer of soil supports plant life such as lichens and mosses. Within this biosphere, the forms and quantities of life vary dramatically. Surface or land-based life may be categorized into major regions known as biomes. Biomes are based on the dominant types of vegetation that are strongly correlated with regional climate patterns. We’ll explore the various types of biomes in short order, but first let’s look at the driving force of these regional differences—the climate.
Climate varies in latitudinal bands around the globe. Relatively constant warm and humid weather affects most equatorial countries, and as you travel north or south, the number of warm months diminishes and freezing months escalate. Climate can be viewed as average weather within a geographical area viewed over years, or even centuries. Climate, like weather, includes temperature, precipitation, humidity, wind velocity and direction, cloud cover, and associated solar radiation. Climate does change, but over centuries or millennia. Some of these climatic changes are dramatic. There have been many ice ages with the formation of glaciers resulting in major climatic changes globally. These climatic changes have occurred from different phenomena that may include (1) changes in ocean temperatures; (2) changes in the earth’s orbital geometry; (3) volcanic activity with increased atmospheric dust and reduced sunlight penetration; (4) variations in solar radiation; or (5) increases in atmospheric gases that absorb heat energy.1
Volcanic eruptions have been thought to be a major factor in climate change based on a range of studies that examine the changes in the environment. Volcanic eruptions can cause sudden and severe environmental changes. Some eruptions emit large volumes of sulfur and particulate matter that can change climate and produce depressed temperatures around the world. The impact of nine volcanic eruptions between 1883 and 1982 was analyzed and the study discovered that volcanic eruptions are associated with surface temperature anomalies that usually fall within the normal seasonal statistical variation and that volcanic eruptions may be related to temperature and circulation anomalies. However, questions are still unanswered as to the scale and patterns of the cooling.2
Many of these gases are produced by human activities such as the burning of fossil fuels releasing large amounts of heat-absorbing carbon dioxide.
Scientists from the U.S. and Australia are reporting that during the last 100 million years there may have been a sudden release of greenhouse gases from the ocean floor. It is believed that gradual warming caused a change in ocean currents, which caused warm water from the surface to plunge deeper into the ocean. The solid methane that was trapped in the ocean sediments became gaseous. The methane would then explode from the sediments that resulted in mudslides. These mudslides allowed the methane to escape into water and then into the atmosphere. The methane reacted with the oxygen and formed CO2
, causing heat to be trapped in the atmosphere. The end result was an increase in ocean temperature by −15° to −12°C. This warming was so severe that it wiped out many species of marine life. Even though these conditions happened without humans around, it may be possible that we are creating the same conditions that caused this climate change. Today, a huge amount of heat-trapping greenhouse gases is being released into the atmosphere at a relatively fast rate. Based on work by the National Academy of Sciences, they conclude that the earth’s surface temperature has risen by about .555°C in the past century, with accelerated warming during the past two decades. They also report that there is new and stronger evidence that most of the warming over the last 50 years is attributable to human activities.3
The United States Environmental Protection Agency (USEPA) reports that human activities have altered the chemical composition of the atmosphere through the buildup of greenhouse gases—primarily carbon dioxide, methane, and nitrous oxide.3
The main greenhouse gas that caused this was CO2
. Since the Industrial Revolution, CO2
has been released, causing the atmospheric content to rise by 30 percent since the eighteenth century.4
These climate-changing gases will be discussed in more detail in Chapter 10
. Do you want to learn more about climate change and policies? Point your browser to (https://people.umass.edu/~envhl565/weblinks.html
) and click on any of the Chapter 1
Web links associated with climate change including:
• The Climate Diagnostics Center
• Climate Prediction Center
• Northeast Regional Climate Center
• United Nations Framework Convention on Climate Change, UNFCCC
Climate is most affected by temperature. By the end of the next century, some scientists predict that atmospheric CO2
levels will be double those of the pre-industrial era. They also suggest that this increase could have been much greater if not for a continuous
evolution of energy sources away from carbon producers such as wood and coal to more efficient sources like natural gas and burgeoning hydrogen. Regardless of our decreasing rate of CO2
-to-energy ratio, population explosions and economy increases have started a continuous rise in CO2
production. As a result, we can expect extreme changes in the world’s climate, weather, and lifestyle.5
The power that modifies, influences, and controls climate originates with the sun. The amount of sunlight striking a particular area of the globe determines the level of warmth and ultimately the movement of air and the amount of precipitation. Because the earth is a globe, which rotates about an axis that is tilted, the amount of sunlight striking the earth varies by region and time. The intensity or energy from the sun diminishes with the distance from the sun. More specifically, the intensity declines inversely with the square of the distance from the sun. Consequently, our distance of 149.6 million kilometers from the sun means we receive a very small fraction of the sun’s intensity (about one 2 billionth of the sun’s energy output pointed in this direction).6
Earth’s distance from the sun has little to do with the seasons. The seasons are caused by the tilt of the earth on its axis as it revolves around the sun. The earth is tilted at a 23.5-degree angle from a vertical axis drawn perpendicular to the plane of the earth’s orbit around the sun. This tilt causes some parts of the earth to get more slanting rays of sunlight some of the year and more vertical rays of sunlight at other times. When a hemisphere of the earth is tilted toward the sun, it is summer in that hemisphere. Moreover, because the earth is tilted, seasonal differences will occur as the earth rotates about the sun. As seen in Figure 1.1
, the equator receives vertical rays of the sun so that the largest amount of solar energy is absorbed in a band circumventing the globe at the equator. Further, the angle at the equator doesn’t vary much as the earth rotates about the sun so that there are no significant seasonal changes, and temperatures remain fairly warm and constant throughout. As an example, New England is tilted more towards the sun in the summer months and receives vertical rays but receives slanted rays in the winter because of the earth’s tilted axis (Figure 1.1
). Conversely, Australia, which is in the southern hemisphere, experiences just the opposite seasons. The sun impacts the earth in bands of decreasing energy extending north and south from the equator. Warmer
air can hold more moisture, and therefore may deposit that moisture as precipitation. Therefore, as you move further from the equator, the seasons develop and months of colder and drier air increase, producing major climatic regions following approximate latitudinal bands around the earth (Figure 1.2
). Sir George Hadley provided the first written explanation of global air circulation in 1735.1
Although modified in recent years, the basic concept still holds. The sun warms air at the equator. As the molecules of air absorb heat energy, they spread apart, causing the gases to expand and become less dense. This expanded air rises, traveling away from the equator. The warm air loses its heat by radioactive and convective cooling and subsides back to the earth where it flows towards the equator and completes...