The worldwide drought of 1988, accompanied by tremendous forest fires, floods, and a super hurricane, caught people’s attention. It was in the midst of that hot summer that James Hansen, a reputable NASA scientist, testified before Congress that he was “99% confident” the globe was heating up.Later, Hansen said the warming was probably due to an increased greenhouse effect, brought about by the production of huge amounts of carbon dioxide gas from burning fossil fuels in cars and power plants around the world.
Hansen’s 1988 statement contains three points that are part of our understanding of the phrase global warming as it is used today:
The second and third points are the roots controversy that we will explore in Chapter 7. In this chapter, we focus especially on point 1, which, although it's not disputed by many people now in the 21st century, there are still those, mostly non-scientists, who contend that the average global temperature had not been increasing in the 20th century and does not continue increasing into the 21st century.
When scientists make statements, they back up what they say with evidence that can be questioned, checked and reproduced by other scientists. In coming to his conclusion that Earth is warming, Hansen used data collected since 1866—when systematic temperature measurements began at a large number of sites around the world. A graph of the data he presented is shown below. Each point on the graph represents the yearly average of the temperature taken at hundreds of sites around the world in that year.
The average global temperature varies a lot from year to year but, overall, it is warmer today than it was 130 years ago. The single graph shown above was the result of many years
of work by the Goddard team and more than a 100 years of effort by
meteorologists all over the globe.
Hansen’s team at Goddard did not simply average results non-critically. For example, they knew that sometimes a new thermometer might be installed at an observing station, or that the location of the thermometer might be moved. In some cases, cities might grow up around a weather observing station, and the decrease in the local foliage would cause warming near the thermometer. (This is called the urban heat island effect.) To avoid these problems, observers graphed results for each station over the entire length of the record, and these were compared with temperature measurements within a few hundred miles. “Jumps” in the data, or other “unreasonable” measurements could then be adjusted or eliminated before calculating overall averages.
Hansen, using mathematical/statistical tools determined that he was 99% confident that the changes were not due to random fluctuations in the data—and so not due to chance occurrence.
Other scientists have looked critically at Hanson's data and results to see what might be wrong with it. For example, Patrick Michaels, a University of Virginia climatologist, found that a thermometer on St. Helena Island in the South Atlantic had been moved down a mountain slope in the 1970s. The change in location gave a false impression of rapid warming, said Michaels. Hansen investigated the claim, found it to be true, and made a correction. Because of such findings, the work of improving and updating the Goddard data continues to this day.
After the publication of Hansen’s report another group of scientists, working independently, made a new survey of world temperatures since 1850. Philip Jones and Tom Wigley—climatologists at the University of East Anglia in Norwich, England—used different techniques to average the temperature measurements, and included many more measurements from the oceans.
As an example of the kinds of corrections that Jones and Wigley needed to make when adding the marine measurements, they noted that before about 1940, ocean temperatures were measured by hauling up a sample of water in a canvas bucket and inserting a thermometer in the water. After 1940, thermometers were inserted in engine water-intake pipes. They found evaporation from the canvas bucket lowered the temperature, so they had to add 0.8°C to measurements made by the old method in order for both types of measurements to be comparable. A graph of their data is shown below.
Average Global Temperature Measurements
Source: British Meteorological Office and University of East Anglia (http://www.cru.uea.ac.uk)
It is not until many scientists have confirmed a particular finding does the scientific community come to consensus about a new hypothesis or research findings. The Wigley and Jones study strengthened the conclusions of Dr. Hansen by show the same general trend in global temperature over time. In the next investigation you will see additional evidence of this process taking place within the scientific community concerning global warming.
Climatologists—scientists who study long-term changes in weather patterns—are concerned about the prospect of global warming. Their predictions include rising sea levels, which would submerge coastal areas; increased droughts and forest fires; and floods. While some countries with cold climates would benefit from a warmer world, most countries would suffer serious disruption.
An increase of 1°C may not seem like much since we usually think in terms of weather—the day-to-day change in local conditions. However, the United Nations panel predicts a change in the global climate, which is the temperature of our entire planet averaged over 30 years. The report goes on to predict that a change in Earth’s climate is likely to seriously affect the lives of people, plants, and animals.
In summary, scientists have examined millions of temperature measurements taken around the world over the past century. Although there have been disagreements about the data, the great majority of scientists who study climate agree that the surface of our planet is warming.
Research into the nature of global warming, its mechanisms, causes and effects, continue. Government agencies such as National Aeronautics and Space Administration (NASA) and National Oceanic and Atmospheric Administration (NOAA) are especially engaged in Earth observations monitoring global warming and climate change.
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