Name at least three human activities or human-induced effects, which can be observed from space and have the potential to impact the environment.
For thousands of years, human activities have resulted in noticeable impacts on local environments, including the effects of building villages and cities, clearing forests, excavating minerals, and using the atmosphere and oceans for waste disposal. Fortunately, satellite sensors are now available to reveal and monitor these activities, and the data gathered by satellite remote sensing can contribute to policy decisions that should help reverse ongoing detrimental changes to the environment.
Listed below are some of the more obvious activities that have been observed using remote sensing technology.
POPULATION AND URBANIZATION
Population patterns can be determined from nighttime visible satellite imagery because many of the world'd most heavily populated areas are illuminated by the bright lights of cities and towns. The invention of electric lighting combined with escalating human population have altered how the Earth looks at night from above. One hundred years ago, nighttime images from space would have probably not revealed any presence of human activity. There is a maxim that says the world's population is increasing, but the sum of the intelligence on the planet is a constant. This can be debated, but it's almost certain that as global population increases, the vulnerability of humans to various changes, climatic or otherwise, increases as well. In many countries, coastal areas are expected to experience rapid growth, and if predictions of climate warming prove correct, this means that the rise in sea level, associated with the warmer temperatures, will imperil a proportionately larger number of inhabitants. Because of continuing population pressures, few societies have the option to simply move to a relatively pristine place to avoid the damage they have inflicted on other areas. Today, almost one half of the people in the world live in cities, but by the year 2025, nearly 2/3 of the world's population will be urban. People in rural areas, especially in the developing countries, will continue to stream into the cities in an effort to look for better ways to live. In the next century, the world as viewed from nighttime visible satellite imagery, may appear to be spattered with blobs of light that shows where the bulk of the human population lives.
FIRES
One of the most desructive wildfires in the history of Alaska has been raging in the south central part of the state for the past week. This fire, which may have been ignited by fireworks, has been fueled by dry brush and timber, after a winter and spring of unusually light amounts of rain and snow south of the Mt. Mckinley area. I'm not sure if it has been determined whether or not this is a natural fire or a result of human influence, but the fires and the devastation produced by them are often observed from satellites. Satellite data taken in the visible wavelenghts can detect smoke patterns and thus, gives an approximate location of forest fires. But this data may not show the exact location of the fire itself, which can be obscured by the smoke. Satellites having infrared channels, however, are capable of detecting hotspots, like fires. While the fire is the principal agent of destruction, the associated smoke can travel thousands of miles and can also impact the environment. The smoke, being composed of minute ash and carbon particles, is effective in blocking out some of the incoming solar radiation (remember the blue moon answer). If the fires are massive enough, temporary cooling from the smoke is possible. This happened in the Persian Gulf as a result of the oil well fires set in Kuwait in 1991.
OIL SPILLS
Ever since large quantities of oil were first transported by ship, concerns have been raised over potential environmental damage in the event of a major oil spill. These fears have been realized all too often. A big problem has been the leaky tankers that are moving all the oil around and leaving a lot of it behind to pollute the oceans. Someone once said that since spills are becoming such an eveyday occurrence and are so hard to clean up, perhaps it would be easier to fill all the oceans with oil and then use the tankers to transport clean water back and forth. Oil spills, such as the Exxon Valdez spill in Alaska in 1989, for example, can be observed using a combination of satellite data taken in the visible, near-infrared and middle-infrared wavelenghts. For clean-up purposes, satellite data needs to be available at a high resolution on a daily basis. Unfortunately, the sensors having the best resolution (those that can see objects on the ground smaller than the size of a football field) are not capable of viewing the same place on the Earth's surface, everyday at the same time.
CONTRAILS
When a jet aircraft passes overhead, a white condensation trail, (contrail) often marks the path of the jet. Contrails result from the condensation of water vapor produced by the combustion of fuel within the jet engine. Hot, moisture-laden air from the engines mixes with much colder air outside the jet. The exhaust air condenses as it cools, producing a man-amde linear cloud. While easy to see from the ground, because of their small width, contrails cannot always be observed from satellites looking back towards Earth. However, satellites operating in the visible wavelenghts can frequently detect these features. If lower clouds are present, it may be difficult to distinguish these clouds from the higher contrails. When this happens, infrared satellite data generally gives better results, since the higher contrails, being colder, show up differently (brighter) on the infrared images. With the increase in the number of commercial jets flying overhead, contrails have become increasingly visible across our skies, and on a small scale they may play a role in altering the local energy budget. Their effect is similar to that of cirrus clouds, allowing shortwave (visible light) energy to pass through with relatively little absorption, but absorbing a higher percentage of the longwave (invisible infrared) energy emitted by the Earth.
VANASHING LAKES
Several of the world's seas and lakes are shrinking due to human activities. The largest body of water in this category is the Aral Sea in the former Soviet Union. The rivers which once fed this inland sea no longer do, as their water has been diverted for irrigating crops such as cotton. Just thirty years ago, the Aral Sea was the fourth largest inland water body. It's currently sixth on the list and has lost much of its water in a timespan not much longer than a single generation. Over 40% of its area has disappeared between 1960 and 1990. So much of the Aral Sea has dried up that Muynak, a former fishing center, is now thirty miles from the shore. In the case of the Aral Sea, considerable damage had occurred before space observations were available for monitoring. Now that the monitoring of large lakes or seas from space is so straightfoward, in the future, no large-scale shrinkage of any water body should occur without being apparent through satellite observations at an early stage.