Climate Change and Definition*
J. Ernest "Sunny" Breeding, Jr., PhD Geophysics
Global warming is an important topic that is more and more in the news. Unfortunately, there is much confusion in the media, and therefore the public, about global warming. Some groups maintain that our planet is in imminent danger whereas others say there is no problem at all. So what should someone believe? The purpose in these pages is to give the view of the vast majority of climate scientists. A great deal has been learned in the last few decades through the use of new technology to make measurements and the analysis of these data. As a result, we have a much better idea about what is happening to our planet. This is a complicated research effort, and crosses many disciplines including, geology, geophysics, geochemistry, biology, oceanography, and meteorology.
In these pages I will give a definition of climate change, which is often misunderstood; present evidence that our planet is warming, and at a rapid rate; explain why climate scientists think that man is responsible for the present warming; show what we think should be happening based on the most recent ice ages; look at what global warming could mean for the future; and discuss what we can do about global warming. My focus will be on the science and not issues such as "Cap and Trade," which are decisions made by politicians, and do not change the science.
I was fortunate to earn my PhD in geophysics at Columbia University and to study at the Lamont-Doherty Earth Observatory, an institute of the university. This is one of the leading centers for studies of the earth, including climate change. Because of this background I will from time to time highlight some of the great research being done at Columbia University. A video of the Lamont-Doherty Earth Observatory Programs is narrated by Tom Brokaw, and showcases the wide range of research being performed there.
Definition of Climate Change
There is a lot of confusion in the media and public about the terms climate and weather. They are not the same thing. Weather describes the conditions at a given time. An example would be the temperature in New York City at a specific date and time. Climate is weather averaged over a time interval. An example would be the average daily temperature in London for a given year.
In considering the temperature of the earth we are mainly interested in the global view rather than what happens at a specific location. Although day-to-day and year-to-year fluctuations can be interesting, our main interest is determining if there is any long-term trend occurring over many years. It is easier to deal with the change in temperature at each location rather than the actual temperatures. To determine the global average surface temperature the earth is first divided into elemental areas such as boxes that span 5 degrees of latitude and longitude. The change in temperature over a period of time such as a number of years is found for each elemental area. Then the global average is found of all of the elemental area temperature changes, usually for ten or many more years. As an example see the change in temperatures for elemental areas shown in Figure 1.1 for the years 1976 to 2000.
Fig. 1.1. Temperature trends by region. Red circles are positive values and indicate warming while blue circles are negative values and show cooling. No color represents no change. The size of the circles depicts the amount of increase or decrease with amounts from the smallest to the largest of .2, .4, .6, .8., and 1.0 degrees centigrade per decade, where 1 degree Centigrade equals 1.8 degrees Fahrenheit. (3rd IPCC) See References for the sources of figures.
In an inspection of Figure 1.1 for the years 1976 to 2000 the most striking feature is that most of the elemental areas are red. The climate change for the vast majority of the elemental areas spread over the earth is warming. Because of regional effects a few of the regions are experiencing cooling. This is not unusual. But it should be obvious to everyone that the average of all of the values in Fig. 1.1 will be a positive number. It should be clear that our planet is experiencing global warming. When an analysis is made of data over a recent period of 100 years it is found that the global average surface temperature of the earth has increased by 0.8 degrees Centigrade (1.4 degrees Fahrenheit). That may not seem like much, but consider that the current global average surface temperature of the Earth is about 15 degrees Centigrade (59 degrees Fahrenheit.) During the last ice age this value was about 9 degrees Centigrade (48 degrees Fahrenheit.) The difference in the global average surface temperature between the last ice age and now is only about 6 degrees Centigrade (10.8 degrees Fahrenheit.) This small change in temperature for such drastically different climates is why climate scientists worry about an increase in the global average surface temperature of 2 or 3 degrees. Such an increase will cause much damage to the earth and the creatures that live on it. Another big worry is that of the increase in the global average surface temperature over the last century, as much as three-quarters of it occurred in the last 30 years (Hansen, 2009.) The rate of warming is increasing, and that is not good news. The global distribution in elemental area surface temperature changes from 1901 to 2012 is shown in Fig. 1.2. Note that some parts of the Earth have warmed a lot more than other parts.
Fig. 1.2. Global average surface warming in degrees Centigrade during the past century. Note that 1 degree Centigrade equals 1.8 degrees Fahrenheit. (5th IPCC)
Understanding the Global Average Surface Temperature
Our usual experience in temperature changes is to consider what happens at a given location. It is not unusual at some locations and times of the year for the temperature to vary by as much or more than 25 degrees Centigrade (45 degrees Fahrenheit) in a 24-hour period. There can also be equally large differences when comparing temperatures at a given time between high latitude and tropical locations during the winter months. The variation in the global average surface temperature over time is much smaller, and it is important to remember this. A very small change in the global average surface temperature can cause major damage to the Earth, as we will see in Page 2.
It has been noted that climate scientists are more interested in the long term trends rather than year-to-year variations in the global average surface temperature. This is not a new concept. For example, the same is true for investors in the stock market. Investors know that there will be both losses and gains from year-to-year in specific stocks and bonds. The important thing for a retirement fund is that over a 30- or 40-year period the trend is positive with an overall nice gain.
It is important to remember that the global average temperature is defined in terms of measurements at the surface of the Earth. This is a practical definition since the Earth's surface is where measurements are easily made, and we have years of global measurements of temperature that were made there. The definition has given us a good indication of the changing health of the Earth. But it should be realized that the warming of our planet also takes place in the lower atmosphere and at depths within the Earth, especially the oceans. In fact, a large percentage of the heating of the Earth takes place in the oceans. So we should not be surprised if the surface definition does not always give us a complete picture of the warming of the Earth. We will examine all of these concepts and more in the following pages.
There is an enormous amount of evidence that shows that the Earth is warming. We consider that next.
Page 1: Climate Change and Definition
Page 2: Evidence of Global Warming
Page 3: Measurements
Page 4: Ice Ages
Page 5: Causes of Climate Change
Page 6: Predicting the Future
Page 7: How Can We Fix Our Climate?
Page 8: References
*A slide show version of these pages on climate change is available for presentations to groups. See References for more details.
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