Why Study the Earth?


Human Impacts

In the past 100 years, human actions have altered fundamental elements of the biogeochemical cycles of the Earth. Since 1850, atmospheric carbon dioxide has increased by about 30 percent, atmospheric methane by more than 100 percent. It also appears that the capacity of the troposphere to oxidize trace constituents has decreased during the same period, which could lead to more rapid accumulation of certain gases.

Changes in land use management, water pollution, and industrial inputs to the atmosphere have affected cycles of essential elements within ecosystems. These human impacts have influenced interactions between terrestrial and marine ecosystems, the atmosphere, and the hydrosphere. Precipitation has become acidic over widespread areas, agriculture and forestry practices have increased rates of soil erosion, and land use and industrial development continue to alter the chemical composition of surface water, ground water and coastal seawater.

"Humans have had a tremendous impact on our planet. We have left our mark in many wayspolluting our rivers, damaging our ecosystems, spreading pesticides, and dumping toxic waste in our oceans and landfills to name a few. The damage can be reversed, but it will take years of cooperation by every individual and every nation." *

* Pathways of Understanding: The Interactions of Humanity and Global Environmental Change," May 1992, CIESIN, p40.


Ninety percent of the population increase in the developing world is in urban areas, which will triple in population by 2025.

In the image at the left, you can see the island of Manhattan in the center of New York City, the population of which has been growing since its founding more than three centuries ago. This image was taken by the MODIS Airborne Simulator (MAS) on July 18, 1993.

According to Census Bureau data, as of 1990 the population of New York City was 7.3 million people.

"The number of people who inhabit the Earth has grown from perhaps 10 million, at the close of the last great Ice Age-10,000 years ago-to an estimated 5 billion today: a phenomenon, in terms of global consequence, that overshadows almost anything that has ever happened to the planet.

"With population growth comes a greater need for housing, energy, food, water, etc., which places huge demand on our natural resources. This could threaten the well-being of the Earth that has served us so well." *

* Human Dimensions Quarterly, Vol.1, No. 1, Winter 1994

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