the instrumental record

introduction

According to the Global Warming Theory the world is getting warmer and warmer. This is happening, the theory says, because of human activity, especially the adding carbon of dioxide to the atmosphere by burning fossil fuels such as coal and gas. According to the theory, if we continue to heat the atmosphere, we will almost certainly do serious damage to our environment.

part 1: the instrumental record

There is no simple way of taking the Earth’s temperature. We can find out a sick person’s temperature just by putting a thermometer into their mouth, but it isn’t possible to take the temperature of the whole world by putting one thermometer in one place. The only way to do it is by recording the temperature at many different places and then using the results to calculate the “mean temperature” of the whole Earth.

Scientists have been keeping temperature records for many years. Recently, because of concern about global warming, these records have become extremely important. Some of them are very old. In Berlin, in Germany, they go back to 1701, and in England some go back to 1659. Now, in 2008, there are almost 7300 “stations” spread around the world keeping records and reporting them to several large databases. The data gathered in this way is called “the instrumental record.”

In modern times at least, scientific temperature readings have been taken in a careful, consistent manner. Along with other meteorological instruments, the thermometers are kept inside "Stevenson screens." A Stevenson screen is a box set on top of a wood or metal post. It approximately 750mm high, 600mm wide, and 500mm deep. Its sides are made of pieces of wood or metal set at an angle. This prevents any direct sunlight from entering the box but permits air to move freely in and out. The boxes are painted white and repainted every two years. They are kept away from trees or buildings. In the northern hemisphere, the door is on the northern side of the screen and in the southern hemisphere it is on the southern side.

More than seventy percent of the Earth’s surface is covered by water so, to get an accurate record, it is necessary to take the temperature at sea as well as on land. Most of this work is done by ships as they pass back and forth across the ocean. Some ships are equipped with a Stevenson screen hung from a ceiling. Usually, however, the ocean data comes from measuring the temperature of water in buckets lowered over a ship’s side or water from the ship’s engine intake.

part two: what the instrumental record shows

The Intergovernmental Panel on Climate Change—or the “IPCC”—is a part of the United Nations. It was established in 1988. Its purpose is to provide reliable information on climate change. The staff of the IPCC do not do any research themselves. Their job is only to gather information from climate scientists, to examine that information, and to make reports. Since its beginning, the IPCC has published four reports. Before these reports are published, they go through a very strict review. Business people and government advisers participate in these reviews along with scientific experts.

The most recent IPCC report appeared in 2007. According to that report, the instrumental record shows that over the preceding one hundred years, the Global Mean Surface Temperature rose by approximately 0.74°C. The temperature did not rise at an even rate over all those years. There were two periods of continuous warming, from 1910 until 1945 and from 1976 until the time of the report. From 1906 to 1915 and from 1945 and 1976, the mean temperature fluctuated, but it did not show any definite trend, either up or down. The mean temperature has risen in almost all parts of the world, but in some places the increase has been much larger than in others. At Point Barrow, in Alaska, for example, it has risen by 2.5°C in thirty years, and on the Antarctic peninsula, winter temperatures are up by 5°C.

The IPCC report also points out that eleven of the twelve hottest years since the instrumental record began were between 1995 and 2006. It also says that it is "very likely" that over the fifty years before 2006 there was a trend toward fewer cold days and cold nights. And it says it is “likely” that during the same period there was a trend to more “heat waves”—periods of extremely hot weather—in most parts of the world. The IPCC’s use of “likely” and “very likely” is important. It shows how cautious the report’s authors are. They avoid exaggeration. They make it clear that no one can be a hundred percent certain about the amount of global warming there has been up to now, or how much there will be in the future. (The report explains that the phrase “very likely” indicates a probability of 90-99% and “likely” indicates a probability of 66-90%.)

The IPCC goes beyond reporting the current temperature of the Earth’s atmosphere. It also makes predictions about the future temperature. The report predicts that over the next twenty years, the global mean temperature will increase at about 0.2°C per decade. This means that by 2028 the Earth’s temperature will have risen to about 1.14°C above its 1908 level. The IPCC also says that it cannot make predictions that go farther into the future because, after 2028, everything will depend on what human beings have done, or not done, to slow down the temperature increase. The report also says, however, that if human beings do everything possible to stop the increase, by around 2050 the world will start to cool slightly. The report also makes it clear though that if we continue living as we are now, by the year 2100, the global temperature will likely have risen to around 5.4°C above what it was in 1908. If that happened, there would likely be serious damage to the environment and to our water and food supplies,

part three:global warming sceptics and the instrumental record

One reason the authors of the IPCC report are cautious is that they know whatever they say, they will be criticized by “climate change sceptics.” Since concern about human-caused climate change first became widespread in the late 1980s, there have been quite a few sceptics—some of them scientists themselves—who have refused to believe it is a real problem. Some sceptics admit that the Earth’s mean temperature has been rising for a long time but deny that human activity is the cause. Others are even more sceptical. They deny that there really is a long-term trend of rising temperatures. In other words, they say the instrumental record doesn’t give an accurate picture of the world’s temperature.

One argument the sceptics use is to claim that the instrumental record is inaccurate because it ignores the effect of "urban heat islands." They point out that a lot of temperature data is collected in cities and that cities tend to be warmer than rural areas. They say that if all the data were properly collected, the instrumental record wouldn’t show a trend toward global warming.

Several climate scientists have done research to find out whether or not there is any truth in this sceptical criticism of the global warming theory. Their results seem to show that urban heat islands have no significant effect on the instrumental record. Cities are slightly warmer than their surroundings, espcially at night because the air is surrounded by tall buildings and therefore less open to the cool night sky than the air in rural areas. The lack of vegetation in cities and the ability of concrete buildings to absorb and hold heat also contribute. Despite all this, however, climate scientists have been able to find only a very slight difference between the temperature data collected in cities and the data collected in surrounding rural areas. (One reason for this is that the Stevenson screens in cities have often been set up in cooler park areas.) According to the Fourth Assessment Report of the IPCC, the effect of urban heat islands on the instrumental record is no more than .0006°C per decade.

Even more important than the fact that there is only a small difference between city and rural temperatures, is the fact that this difference seems to have no significant effect on the data that show a trend toward higher temperatures. And of course from the point of view of the global warming theory, it is the trend that is important. In other words, it is not the fact that the Earth has a particular temperature that is important but the fact that the temperature has been going up. During the time that the temperature has apparently been rising the Earth’s population has risen greatly and a much higher percentage of the population has been living in cities. So it would not have been surprising to have found that, because of all this growth, although there seemed to be an upward trend in temperatures, there was not one in fact.

The research however, seems to indicate that sceptics are wrong to “blame” the apparent trend toward higher temperatures on the urban heat island effect. The IPCC confirms this conclusion in its Fourth Assessment Report by saying that the effect on the instrumental record cannot be more than .0006°C per decade. And the IPCC also points out that the data is no longer collected from the few urban stations where urban heat really was exaggerating the trend.

summary and conclusion

Long term temperature records show that the Earth is getting warmer. Climate scientists say that, if we continue to live as we are living now, the warming trend will continue and, within a hundred years, this will cause serious damage to human life. Climate change sceptics disagree with this and say that because of the urban heat island effect, the temperature records are inaccurate. Climate scientists reply that their research shows urban heat islands do not have an important effect on their measurements.

fl, 2008