Human presence across the face of the Earth is substantial and growing. Increasingly, from the perspective of outer space we can see the "fingerprints" of human presence on our landscapes. From the herringbone patterns of tropical deforestation, to the large square patches of agricultural fields, to the concrete splotches of urban sprawl, humans have attained the magnitude of a geological force as we reshape our environments. Scientists estimate that between one-third and one-half of our planet's land surface has been transformed by human enterprises. Yet, scientists cannot say what, if any, long-term impacts these changes will have on global climate systems.

Figure 1: The graph above shows average carbon dioxide (CO2) concentration in parts per million by volume (ppmv), observed continuously at the Mauna Loa Observatory in Hawaii. Atmospheric CO2, a major greenhouse gas, has increased approximately 40 ppmv since 1958, largely because of human activities. Superimposed on the long-term increase is the annual cycle due to photosynthetic activity (data archived at Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory).

Since the industrial revolution, scientists have observed a continued and accelerating rise in the levels of greenhouse gases in the atmosphere (Figure 1). Of particular concern is the increase in the buildup of carbon dioxide, which is a direct result of urban consumption of fossil fuels as well as the widespread use of fires in the tropics for deforestation. Over the last century, scientists have measured a 0.5-degree rise in average global temperatures that is due, at least in part, to increased levels of greenhouse gases. How will land plants respond to these changes in temperature and carbon dioxide levels? Will they delay or accelerate the global warming trend? Will plant biomes (e.g., forests, tundra, and grasslands) move in response to climate change? Will the world's ice sheets and glaciers retreat as warmer climates move to higher latitudes? Scientists cannot answer these questions now. But with the launches of NASA's Landsat-7 and Terra satellites, unprecedented new data becomes available to scientists around the world that will help them better understand and predict how Earth's changing land surfaces affected climate, as well as how climate changes will further cause land surfaces to change.

next: The Carbon Cycle

by Steve Graham
May 13, 1999

Changing Global Land Surface

Introduction

The Carbon Cycle

Greenhouse Warming

Plants, Snow & Ice

Terra & Landsat Observations