Measurements*

by

J. Ernest "Sunny" Breeding, Jr., PhD Geophysics

Temperature Measurements

We have good measurements of temperature covering most of the world since about 1850. In parts of Europe we have measurements that extend back another 100 years.

Temperature Anomalies

Global average annual anomalies of global land-surface temperatures.

Fig. 3.1. Global average annual anomalies of global land-surface temperatures. (IPCC) See References for the sources of figures.

In Fig. 3.1 the global average annual surface temperatures are plotted from 1850 to 2005. The anomaly values plotted are relative to the 1961 to 1990 mean temperature. The black curve is a smooth curve of the decadal variations. The other smooth curves are the results of other investigators, and are presented for comparison. Note that the temperature scale is in tenths of a degree Centigrade (0.18 degrees Fahrenheit), a small variation. In the early years the temperature anomaly is close to - 0.3 degrees Centigrade (-0.5 degrees Fahrenheit). In the 1900s it is seen that there is a rapid increase in the global average annual surface temperature, especially after about 1970.

Global average annual anomalies of temperatures by region.

Fig. 3.2. Global average annual anomalies of temperatures by region. (IPCC)

It is very instructive to compare the global average annual anomaly temperature variations at high latitudes with those in the tropics. The values plotted in Fig. 3.2 from 1850 to 2005 are relative to the 1961 to 1990 mean temperature. The smooth blue curves show decadal variations. The middle plot for the tropics includes both land and sea surface temperatures, whereas the polar plots include only land temperatures. Sea surface temperatures are sparse and unreliable in sea ice zones. Note the difference in the temperature scales for the polar regions compared to the tropical region. By an inspection of the plots it is seen that the variation of temperature over time is quite a bit greater in the polar regions compared to the tropics. It follows that the polar regions are much more sensitive to global warming than the lower latitudes.

Sea Level Rise due to Thermal Expansion

Global sea level change due to thermal expansion.

Fig. 3.3. Global sea level change due to thermal expansion. (IPCC)

Fig. 3.3 shows the increase in the global sea level due to thermal expansion in the oceans. Because the Earth is warming the sea level has risen by about 0.9 inches (2.3 centimeters) from 1955 to 2005.

Measurement of Carbon Dioxide

Atmospheric carbon dioxide concentrations, Mauna Loa Observatory.

Fig. 3.4. Atmospheric carbon dioxide concentrations in parts per million (ppm), Mauna Loa Observatory. (SCRIPPS, NOAA)

A very important set of measurements of atmospheric carbon dioxide was started by Charles Keeling of the Scripps Institution of Oceanography in 1958. The carbon dioxide monitoring program is now run by the son of Charles Keeling, also of the Scripps Institution of Oceanography (Kahn, March 2014). Measurements are made at the Mauna Loa Observatory in Hawaii (Big Island), which is on a mountain at an elevation of 11,141 feet. The curve tracking the rise in carbon dioxide is known as the Keeling curve. The results from 1958 until recently are shown in Fig. 3.4. The level of carbon dioxide in the Atmosphere is variable throughout the year (Thompson, June 2014) because it is absorbed by plants when they are in bloom. Since most land masses are in the Northern Hemisphere compared to the Southern Hemisphere, the Northern Hemisphere controls the yearly variation. The concentration of carbon dioxide rises throughout the winter months because the plants are dormant then. A peak is reached in May. When the plants start blooming and through full bloom they pull carbon dioxide out of the air causing the concentration of carbon dioxide to decrease. The plants use the carbon dioxide for photosynthesis. However, plants cannot pull all of the carbon dioxide out of the atmosphere, so there is always some left over. The smooth black-line curve in Fig. 3.4 shows the trend. The dramatic increase in the concentration of carbon dioxide was completely unexpected. The measured value of carbon dioxide for March 2016, which is the montly average vaule, was 404.83 parts per million (ppm). The trend value in March 2016 was about 403.2 ppm. Measurements of carbon dioxide in the atmosphere at the Mauna Loa Observatory are recorded by NOAA. Go to the NOAA webpage for the latest observed value of carbon dioxide.

It is common to express very low concentrations in parts per million (ppm) where 1 ppm equals 0.0001 percent. So as a percentage the present value of the concentration of carbon dioxide in the atmosphere is about 0.04%. The reason it is so low is that there is an enormous amount of other gases in the atmosphere, especially nitrogen and oxygen. Carbon dioxide is a greenhouse gas, and is known to contribute to the warming of the Earth. We will discuss this more on Page 5, Causes of Climate Change. The fact that the trend in the concentration of carbon dioxide is increasing is not a good thing, and raises the question of what the concentration of carbon dioxide was at times prior to the measurements of Keeling. We will take a look at that.

Climates of the Past

We need climate data for time periods before direct measurements were possible. So we study things like glacial debris, ocean sediments, sea shells, stalagmites, ice cores, corals, fossils, and tree rings. These things contain properties that define the climate at the time they were formed.

Sediment Piston Corer

Piston Corer.

   

Sediment Core.

Fig. 3.5. Piston Corer. (WHOI)

   

Fig. 3.6. Sediment Core. (Oregon State)

A sediment record from the sea floor can contain the record of past climates going back hundreds of thousands of years. Fig. 3.5 shows an example of a piston corer that can be lowered below a ship for more than a mile (1.6 kilometers). Corers are long hollow tubes that can weigh a ton or more. They are triggered when they hit the bottom, and the piston allows a long tube of soft sediments to be captured without being disturbed very much. Lengths can be up to 90 feet (27 meters). Maurice Ewing, the first director of the Lamont-Doherty Earth Observatory, was one of the early developers of the piston corer. He described them as cookie cutters. Fig. 3.6 displays a sediment core being prepared for study. Much can be learned by analyzing the sediments, shells, and other things that fell to the ocean floor. Things like the sea shells are called climate proxies, because information about the climate at the time the shells were formed can be determined by geochemical analyses. Also, some forms of life existed only during cold climates while others existed only during warm climates. When they are identified within cores they become climate markers. The lower you go into the tube the further back in time you go. The Lamont-Doherty Earth Observatory has the largest Library of Mud, which is described in a nice short video by National Public Radio (NPR), and illustrates the importance of sediment samples to research on climate change.

Ice Cores

Ice core drill.

   

Ice Core.

Fig. 3.7. Ice core drill. (Wikipedia)

   

Fig. 3.8. Ice Core. (Wikipedia)

Some of the longest records of our past climates are found in ice cores. Ice cores of long length have been recovered in Greenland and Antarctica. In Antarctica an ice core was obtained in 2004 that records changes in climate going back about one million years. The ice core is obtained by drilling though the ice with a hollow drill. See Fig. 3.7. This takes many months to obtain a long length of an ice core about 4 inches (10 centimeters) in diameter. An example is shown in Fig. 3.8. Note the rings which are annual layers. Within the ice are wonderful proxy data such as bubbles that were trapped in the snow as it fell. The bubbles can be analyzed to determine the concentration of gases that existed in the atmosphere at the time the bubbles were formed. Dust in the layers tells us about dry periods when it is blown from deserts by the wind and falls onto the ice.

Tree Rings

Tree rings.

   

Tree ring cutout.

Fig. 3.9. Tree rings. (Wikipedia)

   

Fig. 3.10. Tree ring cutout. (Yukon Beringia)

It is likely everyone knows that you can count tree rings to determine the age of a tree. The annual rings are created by seasonal changes. Fig. 3.9 shows an example of tree rings, and Fig. 3.10 illustrates how these rings tell us about past climatic conditions. In fact, tree rings provide a very accurate determination of when the years were wet versus years of drought. Wet years produce wide rings while dry years yield narrow rings. By comparing the tree rings of different trees it is possible to extend the climate history back about two thousand years. A tree ring core can be obtained from a tree using a hollow drill without doing damage to the tree. A very interesting video describes how Dr. Brendan M Buckley of the Lamont-Doherty Earth Observatory collected Tree Rings in Asia to study past climates; he was able to show that an Asian civilization failed years ago due to an extremely long drought.

Proxy Data

I have mentioned proxy data, which are very important for determining the characteristics of past climates. Proxies are things like sea shells, tree rings, and the bubbles in ice cores. From geochemical analyses of the proxies we can determine climate variables such as temperature, levels of carbon dioxide, and ratios of oxygen isotopes (discussed in Page 4, Recent Ice Ages). This is possible because the formation of these things depends upon temperature and other climate variables. It is also important to know the age of a proxy. This is determined by the dating of radioactive elements found within a core or the time record of the reversals of the Earth's magnetic field which shows up in bits of magnetized rocks in cores.

Records of Past Climates

Proxy Temperature Data

Temperature Variations in the Northern Hemisphere since 700 AD.

Fig. 3.11. Temperature Variations in the Northern Hemisphere since 700 AD. (IPCC)

Figure 3.11 shows proxy temperature data from 700 AD to near the present in the Northern Hemisphere. Numerous examples of different proxy data are presented to show consistency. The data are determined as an anomaly compared to the 1961 to 1990 mean value. The temperature anomalies determined by direct measurements are shown in (a), and date back to before 1750. In (b) proxy data are plotted along with the instrumental data (black curve), and the agreement is quite good and shows the rapid rise in temperature that started in the 1900s. Plot (c) is an overlap of reconstructed temperature anomalies on a multi-decadal time scale. The dark area illustrates where there is the most agreement between the different records. It is seen that this occurs at about the -0.3 degrees Centigrade (-0.5 degrees Fahrenheit) temperature anomaly. It seems quite clear that over the last 1,300 years the long term trend of the global average surface temperature in the Northern Hemisphere remained fairly constant until the dramatic rise in temperature that occurred in the 1900s. We conclude that the present global warming is a relatively recent phenomenon.

Proxy Greenhouse Gases Data

Atmospheric Concentrations of long-lived greenhouse gases for the last 2000 years.

Fig. 3.12. Atmospheric Concentrations of long-lived greenhouse gases for the last 2000 years. (IPCC)

Proxy data were used to determine the concentrations of greenhouse gases over the last 2,000 years. It is seen in Fig. 3.12 that they were fairly constant until about 1760 when they begin to increase; this coincides with the Industrial Revolution. In the mid 1900s the curves of the greenhouse gases show a rapid increase in atmospheric concentrations, and this is of great concern.

It is interesting to consider the recent ice ages, and to take a detailed look at the most recent ice age. We do that next.

Pages

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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