Measuring Global Warming

GOES Weather Satellite
Broadcasters use data from meteorological satellites to predict weather and to broadcast storm warnings when necessary. Satellites such as the Geostationary Operational Environmental Satellite (GOES) collect meteorological and infrared information about the atmosphere and the ocean. A camera on the GOES is continuously pointed at Earth, broadcasting satellite images of cloud patterns both day and night. Here, the GOES-C satellite is being encapsulated inside its payload fairing aboard a Delta rocket.

As early as 1896 scientists suggested that burning fossil fuels might change the composition of the atmosphere and that an increase in global average temperature might result. The first part of this hypothesis was confirmed in 1957, when researchers working in the global research program called the International Geophysical Year sampled the atmosphere from the top of the Hawaiian volcano Mauna Loa. Their instruments indicated that carbon dioxide concentration was indeed rising. Since then, the composition of the atmosphere has been carefully tracked. The data collected show undeniably that the concentrations of greenhouse gases in the atmosphere are increasing.

Scientists have long suspected that the global climate, the long-term average pattern of temperature, was also growing warmer, but they were unable to provide conclusive proof. Temperatures vary widely all the time and from place to place. It takes many years of climate observations to establish a trend. Records going back to the late 1800s did seem to show a warming trend, but these statistics were spotty and untrustworthy. Early weather stations often were located near cities, where temperature measurements were affected by the heat emitted from buildings and vehicles and stored by building materials and pavements. Since 1957, however, data have been gathered from more reliable weather stations, located far away from cities, and from satellites. These data have provided new, more accurate measurements, especially for the 70 percent of the planetary surface that is ocean water. These more accurate records indicate that a surface warming trend exists and that, moreover, it has become more pronounced. Looking back from the end of the 20th century, records show that the ten warmest years of the century all occurred after 1980, and the three hottest years occurred after 1990, with 1998 being the warmest year of all.

Greenhouse gas concentrations are increasing. Temperatures are rising. But does the gas increase necessarily cause the warming, and will these two phenomena continue to occur together? In 1988 the United Nations Environment Program and the World Meteorological Organization established a panel of 200 leading scientists to consider the evidence. In its Third Assessment Report, released in 2001, this Intergovernmental Panel on Climate Change (IPCC) concluded that global air temperature had increased 0.6 Celsius degree (1 Fahrenheit degree) since 1861. The panel agreed that the warming was caused primarily by human activities that add greenhouse gases to the atmosphere. The IPCC predicted in 2001 that the average global temperature would rise by another 1.4 to 5.8 Celsius degrees (2.5 to 10.4 Fahrenheit degrees) by the year 2100.

The IPCC panel cautioned that even if greenhouse gas concentrations in the atmosphere ceased growing by the year 2100, the climate would continue to warm for a period after that as a result of past emissions. Carbon dioxide remains in the atmosphere for a century or more before nature can dispose of it. If greenhouse gas emissions continue to increase, experts predict that carbon dioxide concentrations in the atmosphere could rise to more than three times preindustrial levels early in the 22nd century, resulting in dramatic climate changes. Large climate changes of the type predicted are not unprecedented; indeed, they have occurred many times in the history of Earth. However, human beings would face this latest climate swing with a huge population at risk.