The Sporer Minimum Dalton Minimum and Maunder Minimum
Then, in 1889, Maunder read an article by another German astronomer, Friedrich Wilhelm Gustav Sporer 1822-95 . Sporer was also studying sunspots and he had discovered something very interesting. Astronomers had been observing and recording sunspot activity for centuries, but Sporer found that very few had been observed between approximately 1400 and 1520. This period came to be known as the Sporer Minimum. It was a time of very cold weather. People called it a Little Ice Age. The Baltic Sea...
The Mongol Empire
In the 13 th century the Mongolians eventually established what may have been the biggest empire the world has ever seen. The story began during a prolonged period when the climate was moist. Traces of earlier shorelines show that sea level in the Caspian Sea was much higher then than it is now, and that it was rising. The steppe pastures grew dense and rich under the increased rainfall and warmer weather associated with it. The people flourished and the population increased, but around 1200...
Specific heat capacity
When any substance absorbs heat, its temperature rises. The amount of heat that must be absorbed to produce a one-degree rise in temperature varies from one substance to another. It is known as the specific heat capac- ity of the substance, usually denoted by the symbol c, and is measured as the units of heat that must be absorbed for a one-degree increase in temperature. The scientific units are joules per gram per kelvin and are written as J g-1 K-1. Alternatively, the units can be given as...
Out of the steppes of Central Asia
Central Asia is a vast region of grasslands called steppe. Traditionally, its inhabitants were nomadic pastoralists, driving their herds and flocks from one seasonal pasture to another. Many Mongolians still live a seminomadic life. Drought is a common occurrence in the dry climate. It makes farming unreliable, but only occasionally does it seriously injure the nomads. Droughts in Central and Western Asia around 300 c.e. forced people known as the Hunni, or Huns, out of their homelands. They...
Oxygen isotopes and heavy water
Water molecules from ice cores and shells taken from sediments have another story to tell. They contain oxygen of two different types and two different types of hydrogen. Most chemical elements exist as two or more isotopes. Different isotopes of an element are identical chemically, but they have different atomic masses. Oxygen has three isotopes, two of which are important 16O and 18O. Seawater contains 99.76 percent H216O and 0.2 percent H218O. It also contains 0.03 percent HDO the remainder...
Reading stalagmites
Victor Polyak and Yemane Asmerom, scientists at the University of New Mexico, used uranium-thorium dating to determine the age of the bands in stalagmites taken from caves in the Carlsbad Caverns National Park and Hidden Cave in the Guadalupe Mountains National Park, both in southwestern New Mexico. What they found was a clear link between changes in the local climate and the way of life of the people living there at the time. They found evidence of climate changes that had changed the course...
Siting the thermometer
No matter how accurate it may be, a thermometer will give very inaccurate readings if it is incorrectly sited. If a glass thermometer is placed in direct sunlight, for example, the mercury or alcohol in the bulb will absorb solar radiation and its temperature will rise for that reason. The thermometer will then display the temperature inside the bulb, but this will be quite different from the temperature of the surrounding air. This is why the air temperature must always be taken in the shade....
Hipparchus and the precession of the equinoxes
The axial wobble was another effect Milankovitch studied, but he was not the first person to notice it. That person was the Greek astronomer and mathematician Hipparchus c. 190 b.c.e.-c. 120 b.c.e. . Hipparchus was the greatest of all Greek astronomers, and some of the discoveries he made and the deductions he made from them are still important today the axial wobble is one of them. He also calculated the length of the year as 365.25 days, diminishing by 0.003 day each year, and the lunar...
Ocean gyres and boundary currents
Ocean currents are like rivers that flow through the water around them. They are quite distinct. Kuroshio means black water and the Kuroshio Current is clearly visible as a stream less than 50 miles 80 km wide moving at up to 7 MPH 11 km h . When an ocean current moves toward or away from the equator, the Coriolis effect influences its direction. Currents start to turn as they approach continents. The Coriolis effect intensifies as currents move farther from the equator. This makes them turn...
Glacials interglacials and geologic time
As well as classifying rocks, geologists were also dividing the history of the Earth into episodes they called eras, periods, and epochs. The table Geologic Time Scale below lists the present divisions of geologic time the history of the Earth with the approximate dates when they began. The Great Ice Age occurred recently, so the period of time that encompassed it was called the most new epoch, but using the Greek words pleistos most and kainos new to make the word Pleistocene. The Great Ice...
Polar and Ferrel cells
Extremely cold, dense air also subsides over the North and South Poles. It produces the two polar high-pressure regions. Air flows out from them and is deflected to become the polar easterly winds. Any object moving toward or away from the equator and not firmly attached to the surface does not travel in a straight line. As the diagram illustrates. It is deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. Moving air and water tend to follow a clockwise...
Transferor he Latent heat and the Bowen ratio
The absorption and release of latent heat see the sidebar Latent heat and dew point on page 32 also transfer energy from one part of the Earth to another through the movement of clouds. When water evaporates over the ocean, absorbing latent heat, and condenses when it crosses the coast, releasing latent heat, energy has been transported from the ocean to the land. This is an important component of the overall movement of heat. Latent heat does not affect the temperature the heat is hidden,...
Cold weather during the Dark Ages
The abandonment of Cahokia marked the end of a period when the climate was relatively warm and moist over all of the Northern Hemisphere. That warm period followed a period of cold weather lasting from the second half of the third century until the ninth century c.e. There was heavy snow over much of Europe in the winter of 763-64, and the intense cold killed many olive and fig trees. The winter of 859-60 was so cold that the ice was thick enough to bear the weight of horse-drawn wagons on the...
Carbonate lysocline and carbonate compensation depth
The fate of dissolved carbon depends on the temperature and pressure under which it is held. Carbon dioxide is more soluble at low temperatures and high pressures. The fizz in a can of soda is produced by carbon dioxide that is held in solution under pressure and usually chilled. Opening the can releases the pressure, and the carbon dioxide escapes into the air as a mass of tiny bubbles. Warm the can before opening it and the escaping carbon dioxide will eject a froth of liquid. When carbon...
Changing land use alters the albedo
Other changes do alter the surface albedo, however. Felling a broad-leaved, deciduous forest to provide farmland increases albedo, and converting a coniferous forest to meadow has an even larger effect. As albedo increases, more solar radiation is reflected and the surface temperature decreases. Changing forest to farmland has a cooling effect. Planting forests, on the other hand, may have a warming effect, because it reduces albedo, although the warming this caused would not be sufficient to...
Layers of the atmosphere
There is no clearly defined top to our atmosphere. About 90 percent of it lies between the surface and a height of about 10 miles 16 km . Above COMPOSITION OF THE PRESENT ATMOSPHERE ammonia nitrogen dioxide sulfur dioxide hydrogen sulfide 365 p.p.m.v. 18 p.p.m.v. 5 p.p.m.v. 2 p.p.m.v. 1 p.p.m.v. 0.5 p.p.m.v. 0.3 p.p.m.v. 0.05-0.2 p.p.m.v. 0.08 p.p.m.v. variable 4 p.p.b.v. 1 p.p.b.v. 1 p.p.b.v. 0.05 p.p.b.v. p.p.m.v. means parts per million by volume 1 p.p.m. 0.0001 percent. p.p.b.v. means parts...
Radiometric dating
All radiometric dating methods work in the same way as radiocarbon dating, by measuring the proportions of a radioactive element and the stable element into which it decays. One of the two isotopes of rubidium 87Rb decays to an isotope of strontium 87Sr with a half-life of 48 billion years 10 times the age of the solar system . Radioactive potassium 40K decays to argon 40Ar with a half-life of 1.277 billion years. The most widely used dating methods, however, are based on the decay of uranium U...
Weather balloons and satellites
Weather balloons are free from such types of interference. They use standard instruments, calibrated to recognized standards, and they measure temperature and pressure in air that is well clear of the surface. The measurements are very reliable, but their global coverage is poor and there have been changes in the instruments used and the way their data is processed that have left gaps in the record. Balloons are released from land-based stations and there are far more in North America and...
Indus Valley civilization
Climate change can bring an end to civilizations, as well as triggering their birth. The most spectacular example of this is found in the Indus Valley, in Pakistan. From about 2500 b.c.e. until about 1700 b.c.e. a civilization flourished there. People grew wheat, barley, peas, sesame, dates, melons, and possibly cotton. Traces of cotton that were found there by archaeologists are the earliest known from anywhere in the world. There were elephants, rhinoceroses, cattle, and water buffalo. The...
The axial wobble
There is a third, more subtle cycle that takes place over about 25,800 years. It concerns the way the Earth's rotational axis wobbles. This is not the same thing as the way its obliquity changes the two motions are at right angles to each other. Earth behaves like a spinning top, and a spinning top has certain properties. As long as it maintains a high enough angular velocity, or rotational speed, and it experiences no outside force, the top is stable. It will remain upright, spinning on its...
The faint Sun paradox and the Gaia hypothesis
This is because of the faint Sun paradox. Stars slowly grow hotter as they age. This means that in the distant past the Sun was cooler than it is today. Svante August Arrhenius 1859-1927 , a Swedish physical chemist, was the first scientist to calculate the influence of atmospheric carbon dioxide on the air temperature. He published the results in 1896, in a paper, On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground Philosophical Magazine, vol. 41, pp. 237-71 ....
Latent heat and adiabatic cooling and warming
Water also absorbs heat when it evaporates. This heat supplies the energy needed to break the hydrogen bonds that hold molecules together. Because it is used to break the hydrogen bonds between individual molecules, this heat does not raise the temperature of the liquid water. It is known as latent heat, because it appears to be hidden see the sidebar Latent heat and dew point below . Heat energy that is absorbed when water evaporates is released when the hydrogen bonds form once again and the...
When the cycles coincide
Each of these three cycles of eccentricity, axial tilt, and axial wobble or precession of the equinoxes has a very small effect by itself. The diagram illustrates all three. What would happen, however, if all three cycles were to coincide Suppose that when the precession of the equinoxes places Earth farthest from the Sun during the Northern Hemisphere winter, the Earth's orbit is also at its greatest obliquity, so that the distance between Earth and the Sun is at a maximum. The two effects...
Mesosphere and mesopause
The stratopause is a region where temperature remains constant with height. The atmospheric layer above it is the mesosphere, extending to a height of about 50 miles 80 km . At the top of the mesosphere the air pressure is about 0.00015 lb. in.-2 1 Pa 0.01 mb one-millionth of the pressure at sea level. Temperature remains constant with height at the stratopause, but then decreases. The temperature at the upper boundary, the mesopause, varies widely. In winter it can be as low as -148 F -100 C ,...
Erik the Red and settlements in Greenland
Around 980 or 982, Erik Thorvaldsson, nicknamed Erik the Red because of the color of his hair, discovered the eastern coast of Greenland. Erik lived in Iceland, but he had quarreled with his neighbors and the quarrel had deteriorated into a fight in which two men were killed. Erik was convicted of manslaughter and exiled for three years on pain of death. Having little choice, he set sail, heading west toward where his friend Gunnbjorn Ulfsson claimed to have sighted land. He settled near the...
Breaking the bond evaporation
A molecule in a mass of liquid water is pulled by the molecules around it, but it is pulled equally strongly from every direction. If it is at the surface of a body of liquid, however, it is pulled from the sides and from below, but not from above, so it is not quite so securely held. If it can acquire a little more energy, the molecule will move faster and faster until the hydrogen bonds linking it to its neighbors break and the molecule is free to enter the air. It then enters the layer of...
JeanBaptiste Fourier John Tyndall and the greenhouse effect
The absorption of outgoing radiation that warms the Earth is usually likened to the effect of a greenhouse rather than a blanket. It is called the greenhouse effect, a name it acquired in 1822, when Jean-Baptiste Joseph Fourier 1768-1830 first used that metaphor. Fourier was a French mathematician and physicist who made many important contributions to science and had an interesting and exciting life. A supporter of the French Revolution, he was later arrested and narrowly escaped the...
Louis Agassiz and the Great Ice Age
The debate was at its height when one of the most talented scientists of his generation turned his attention to it. Louis Agassiz see the sidebar Louis Agassiz and the Great Ice Age on page 62 had already made a reputation based on his studies of fossil fish. In Recherches sur lespoissons fossiles Studies of fossil fishes he classified more than 1,700 species. Agassiz was born in Switzerland of French parents and was very familiar with Swiss glaciers. He was also in search of attractive places...
Thermohaline circulation and North Atlantic Deep Water
At the edge of the Arctic Circle, where water freezes at the ocean surface, it is the process of freezing that drives the Great Conveyor. Ice is less dense than liquid water that is why ice floats. Water becomes denser as its temperature decreases and it reaches its maximum density at a little above freezing. Freshwater is densest at 39.2 F 4 C and seawater is densest at 35.6 F 2 C . The sea loses heat into the very cold air. This chills the sea surface and increases the density of the...
Stratosphere and stratopause
The layer above the tropopause is called the stratosphere because L on-Philippe Teisserenc de Bort 1855-1913 , the French meteorologist who discovered and named it, thought that at this height the atmospheric gases separated into layers, or strata, according to their masses. This was incorrect, but the name stuck. Temperature remains constant with height through the lower stratosphere, but it begins to increase with height above about 12 miles 19 km and the rate of increase accelerates above 20...
Milutin Milankovitch And His Astronomical Cycles
Milutin Milankovitch was born on May 28, 1879, in the village of Dalj, on the Croatian side of the border between Croatia and Serbia, near the Croatian town of Osijek. At that time Serbia was an independent nation and Croatia was part of Austria-Hungary. He studied at the Vienna Institute of Technology and in 1904 he was awarded a doctorate in technical science. Dr. Milankovitch worked for a time as the chief engineer for a construction company, but in 1909 he accepted an offer to teach applied...
The complete electromagnetic spectrum
Blackbody radiation is not confined to a particular wavelength or even waveband a range of wavelengths. The amount of energy a blackbody radiates is proportional to its temperature, and its temperature determines the wavelength at which it radiates most intensely, but to either side of this peak the radiation tails off toward longer and shorter wavelengths. Visible light forms only a part of the electromagnetic spectrum, but it is the region at which the Sun radiates most intensely, in the...
The water molecule and the hydrogen bond
Movement requires energy and it is the Sun that supplies the energy for the movement of water from the ocean to the land the hydrologic cycle. Once the water is moving, particular physical properties of air and water interact to produce our weather. A water molecule comprises one atom of oxygen and two of hydrogen H2O . The three atoms share electrons. That is what binds them together, but it does so in such a way that lines drawn from the two hydrogen atoms to the center of the oxygen atom...
Diurnal and seasonal changes
The budget is complicated still further by the Earth's rotation and by its tilted axis. Obviously, the surface absorbs no solar energy at night, when it is dark. There is a very large variation in energy gain and loss over the 24hour cycle. In the tropics this can amount to a net gain of about 1,000 W m-2 at noon and a net loss of about 70 W m-2 at midnight. As the illustration shows, the Earth's axial tilt produces the seasons by turning first one hemisphere and then the other to face the Sun....
Troposphere and tropopause
The lowest layer, extending to about 10 miles 16 km over the equator, seven miles 11 km over middle latitudes, and five miles 8 km over the poles, is the troposphere. This is the region where the air is constantly being mixed and where all the world's weather happens. It is also the layer in which the temperature decreases with height. Its upper boundary, known as the tropopause, is the height at which the temperature ceases to decrease as you climb higher. This means that air that is rising...
Ocean currents
Like the atmosphere, ocean currents transport heat. Instead of transporting it by means of vertical cells, in which air rises, moves horizontally, and subsides again, the oceans transport it by a system of surface and deep currents. Ocean currents have names, many of which are familiar. Most people have heard of the Gulf Stream, for example, and perhaps of the California and Labrador Currents. There are also the Kuroshio and Oyashio Currents which affect the weather in Japan, and the Peru...
The Radiation Balance
Earth receives energy from the Sun in the form of solar radiation. It then radiates the energy it has received back into space in the form of terrestrial radiation see Radiation from the Sun and from the Earth on pages 128-134 . The two are in balance the amount of outgoing energy from the Earth is equal to the amount of incoming energy from the Sun. If this were not so, the Earth would grow steadily hotter or colder. The global climate does change over time, of course, and at present many...
Outgoing radiation
The Earth then radiates away the energy it has absorbed. The diagram summarizes the global energy budget. The numbers in the drawing refer to the percentages of the total energy budget. Those with a plus sign represent incoming solar energy and those with a minus sign represent outgoing terrestrial radiation. Other numbers indicate the movement of energy between the Earth and atmosphere. The table shows the budget in more detail. The surface of land and sea receive 51 percent of the solar...
Incoming radiation and the ozone layer
Solar radiation enters the atmosphere. About 18 percent of the incoming shortwave radiation is absorbed by ozone near the top of the stratosphere and in the troposphere by clouds, water vapor, and aerosols. Absorption by oxygen O2 and ozone O3 produces the ozone layer by the reactions 03 photon O2 O O3 O 2O2 M is a molecule of any substance, but usually nitrogen. This sequence of reactions absorbs ultraviolet radiation and when governments acted to halt and reverse the depletion of the ozone...