Change in the Weather

Polar and Ferrel cells

Hadley Ferrel Polar

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...

Electromagnetic radiation

Electromagnetic radiation is one of the fundamental forms of energy. It is associated with oscillating electric and magnetic fields hence the name at right angles to each other and to the direction in which the radiation is traveling. It can be regarded as pure energy traveling either in waves or as a stream of particles, called photons. Although the two descriptions sound contradictory, in fact they are not. All types of electromagnetic radiation travel at the same speed, whether it is...

Heat islands and urban domes

Lysocline Layer

Air escaping from heated buildings, atmospheric particles absorbing infrared radiation at night, the reduction in wind speed, and the heat from thousands of engines combine to make the city into an island of warmth surrounded by a cool, rural sea. It is a heat island. During the day the temperature rises rapidly. On a sunny day in summer it may rise by as much as 31 F 17 C between dawn and the middle of the afternoon. It falls again at night, but in the early part of the night the city center...

Incoming radiation and the ozone layer

Incoming Radiation

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...

Latent heat and adiabatic cooling and warming

Latent Heat Condensation Water

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...

Tree rings and isotopes

We know now that the Maunder Minimum is real. Maunder's data were reliable and a period when there were very few sunspots did indeed coincide with a period of very cold weather. We know he was right because there is other evidence to support him, evidence that was not available in his own day. The supporting evidence comes from studies of tree rings and ice cores see Climates of the Past on pages 37-43 . Tree rings are made from the cells surrounding the trunk that are produced as new growth...

Thermohaline circulation and North Atlantic Deep Water

North Atlantic Deep Circulation

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...

The Great Conveyor

The NADW crosses the equator and continues down through the South Atlantic until it joins the West Wind Drift. This carries it toward the east. The NADW rises at intervals and mixes with the colder water of the West Wind Drift. These upwellings warm the air significantly between latitudes 60 S and 75 S. Dense, very salt water also sinks near the edges of the ice shelves in the Ross and Weddell Seas. It forms the Antarctic Bottom Water (AABW), which merges with the NADW. Part of the bottom water...

Sunspots and cloud formation

Even so, it seems unlikely that so small a change, never amounting to as much as 1 percent, could produce such a big effect. The answer is that the climatic effect is not due to direct heating. Solar astronomers believe that sunspots are magnetic disturbances. They occur in pairs, with magnetic field lines emerging from one sunspot Solar constant. The Sun subtends an angle of 0.5' at the Earth's surface. Solar radiation is emitted in all directions, but the Earth is exposed to only a tiny...

Ocean currents

Ocean Currents Normal And Nino

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...

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...

Glacials interglacials and geologic time

Glacials And Interglacials

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...

Trade winds and Hadley cells

Southern Hemisphere Trade Winds

Air over the equator is heated strongly by contact with the warm surface. The warm air rises all the way to the tropopause. There, trapped beneath the tropopause, it moves away from the equator. Cooler air flows toward the equator at low level, to take its place. Moving air tends to turn in a circle. This is called vorticity and it is why the water usually forms a spiral, or vortex, when it flows out of a bathtub. As the cool air moves toward the equator its vorticity swings it to the right in...

Cold winters in the lowlands

Away from the mountains, most winters were very cold. Olive trees in the south of France were killed by frost during the latter part of the 16th century and there were seven winters when the River Rh ne froze solid. Further north, in Flanders (now Belgium), the bitterly cold winters of the middle 16th century stimulated the introduction of a new style in landscape painting. Pieter Brueghel the Elder (c. 1525-69) painted Hunters in the snow in February 1565, depicting the first winter in which...

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...

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...

Snowball Earth

Once ice sheets start to grow they can advance rapidly. The white surface of the snow reflects sunlight and, more importantly, heat from the Sun (see the section How bright is the Earth on pages 113-120). This prevents the land from warming. The next winter, more snow falls and extends the ice-covered area, and low summer temperatures prevent it from melting. What matters is the cool summer, when the temperature does not rise sufficiently to melt the ice. It makes no difference how cold the...

Ocean gyres and boundary currents

Global Maps Gyres

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...

City air is drier but rainfall is higher

This is the first and most obvious difference between the urban and rural environments. It means that rain does not soak into the ground, but is removed by storm drains. When the rain ceases the streets dry very quickly. Rainwater is removed too quickly for much of it to evaporate and there are fewer areas of standing water ponds and lakes than there are outside the city. Consequently, there is less evaporation in the city than there is in the countryside....

Outgoing radiation

Terrestrial 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...

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...

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,...

Diurnal and seasonal changes

Seasonal Changes Weather

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....

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...

Warm weather everywhere

The benign conditions were not confined to Greenland and Iceland, of course. During the early Middle Ages the climate was warmer over most of the Northern Hemisphere. A prolonged period of weather that is warmer than the weather before or after it is known as a climatic optimum. This period is the medieval optimum. For about 200 years, beginning around 880, farmers were growing wheat around Trondheim, Norway, and they grew barley as far north as about 69.5 N. This is north of Narvik and well...

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...

Milankovitch on Mars

The cycles that Milankovitch proposed are much more clearly evident on Mars than on Earth. This is because Mars is closer to the outer giant planets and has no large moon. Consequently, its orbital eccentricity varies from 0.00 circular orbit to 0.13 more than twice that of Earth over the course of 95,000-99,000 years. Obliquity changes even more dramatically, from about 13 to 47 , over 120,000 years. The Martian equinoxes also pre-cess, returning to an initial position over a period of about...

Will there be more ice ages

Snowball Earth, if it existed, ended many millions of years ago. No one suggests that the world could freeze over again to that extent, but most scientists agree that there will be more ice ages. When Louis Agassiz proposed it, the Great Ice Age was believed to have been a single event that ended once and for all it was confined to the Pleistocene epoch, and we now live under quite different conditions, in the Holocene. Then, as geologists unraveled more of the Earth's recent history, it became...

Adhemar and Croll

Milankovitch was not the first person to wonder whether the onset and ending of ice ages might be linked to astronomical cycles. In Les Revolutions de la Mer (1842) the French mathematician Alphonse Joseph Adhemar (1797-1862) observed that because of the eccentricity of the Earth's orbit and the obliquity of its axis, Antarctica received about 170 fewer hours of solar radiation each year than the Arctic. That, he proposed, is why it is the colder pole (he was wrong see the sidebar Why the...

The Medieval Optimum

Cahokia is an archaeological site covering 2,200 acres (890 hectares). It is located in southern Illinois, about eight miles (13 km) to the northeast of St. Louis, Missouri. One of its principal features is Monks Mound, a four-sided pyramid rising in four terraces to a height of 100 feet (30.5 m) and covering 12 acres (5 hectares). A temple once stood at the top. Monks Mound is the largest prehistoric earthwork anywhere in the Americas, and it is just one of about 120 mounds at Cahokia. In...

Jean Baptiste 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...

Potential temperature

There is an apparent paradox, however. When a fluid cools, its molecules move closer together, increasing its density. If a rising fluid, such as air, grows colder it must become denser, and it cannot rise above fluid that is less dense. Yet temperature decreases with height throughout the troposphere see the section Composition and structure of the atmosphere, on page 1 . It seems to follow that air at the top of the troposphere must be Cold air is denser than warm air, because its molecules...

The year sunspot cycle

As he worked away patiently with his examination of sunspots, Maunder found a pattern emerging. In 1843 the German astronomer Samuel Heinrich Schwabe (1789-1875) had discovered that the number of sunspots increases and decreases over a regular 11-year cycle. Maunder found that the solar latitudes in which sunspots emerge change in a regular way over the course of the sunspot cycle. The first ones appear some distance from the solar equator and later ones move gradually closer to the equator...

Preface Of Greenhouse Effect

Several years have passed since the publication of the first edition of the Dangerous Weather series of books. Much has happened during that time and my friends at Facts On File and I felt it would be appropriate to revise all of the books in the series in order to bring them up to date. As we began to prepare the new editions, it occurred to us that none of the books so much as mentioned climate change, yet in the minds of many people this is the single most important environmental issue of...

Layers of the atmosphere

Height Layers 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...

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...

Seasons and Tropics

What Causes Seasons Change

If the Earth were upright, so its north-south axis of rotation intersected the plane of the ecliptic at a right angle, the plane of the ecliptic would divide the Earth exactly at the equator. The person wishing to stand directly beneath the Sun could choose any point on the equator to do so. In fact, though, the Earth's rotational axis is tilted from the vertical by 23.5 . Consequently, as the Earth travels around its orbit, the Sun appears to move north and south, and it is directly overhead...

The carbon reservoirs

The carbon is engaged in a cycle, but although photosynthesis and respiration make up the biggest part of that cycle, they are not the whole of it. Quantities in the carbon cycle are always given as the amount of carbon, not carbon dioxide, because it is carbon, not oxygen, which moves through the cycle. The diagram illustrates the carbon cycle in a simplified form. The Earth contains about 1,100 million billion tons (1017 tonnes) of carbon. Almost all of it is contained in carbonate...

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...

Cloud condensation nuclei

Water vapor will not condense very readily unless there are small particles onto which it can form droplets. These particles were first identified by John Aitken see the sidebar and they are known as Aitken nuclei or cloud condensation nuclei. The air contains large quantities of them, especially over land. Cloud condensation nuclei are of a particular size and the air contains particles of many other sizes. Some are solid and some liquid. The bigger ones are visible to the naked eye. You can...

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...

Sea levels and higher rainfall

The rise in temperatures was accompanied by a rise in sea level due partly to the expansion of the seas as the water temperature rose and partly to the melting of mountain glaciers. Measuring changes in sea level is complicated by the fact that the level of the land also changes. It can be lowered by coastal erosion and in places it is still rising as a result of removing the weight of the ice sheets of the most recent ice age (see Is the sea rising on pages 158-163). In this case, however,...

Exotic diseases

Among the species that may find new territories to colonize, some are insects that transmit diseases. Fears have been expressed that tropical diseases may spread into countries of the temperate regions. Malaria is the most dreaded of these. Such fears are greatly exaggerated. Indeed, the risk may be nonexistent. Malaria was once common in parts of Britain. Known as ague, it occurred in marshy areas in the east of the country, along parts of the Thames Estuary, and in the low-lying marshes of...

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...

The enhanced greenhouse effect and global warming potentials

The change that Arrhenius studied is additional to the greenhouse effect that had regulated the global climate throughout the history of the planet. It is an enhanced greenhouse effect that is caused by a number of greenhouse gases in addition to carbon dioxide. Water vapor is the most powerful of all greenhouse gases, but it is never included in the list of greenhouse gases because its concentration varies greatly from place to place and hour to hour and is considered to be outside our...

Most warming in high latitudes

The climate models suggest that warming will be most marked in the Arctic. Already there is less sea ice and the strongest warming signal of all comes from northwestern North America, including Alaska, and northeastern Siberia. Winters in these places are milder than they were. This is the expected response to increased carbon dioxide. It occurs because during the Arctic winter the surface radiates its absorbed heat, and the temperature plummets. Cold, dense, subsiding air produces large...

Radiation From The Sun And From The Earth

There are three ways for heat to travel from one place to another. The most immediate is conduction. When you hold a warm object in your hand, heat passes from the object to your hand, making its surface temperature rise. This is conduction. It requires that two bodies at different temperatures be placed in direct contact with each other. Convection works by gravity, and heat can be transferred by this means only through fluids. Contact with a warm surface raises the temperature at the base of...

Louis Agassiz and the Great Ice

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...

Edward Walter Maunder And The Unreliable

In 1873 a young man called Edward Walter Maunder (1851-1928) left his job at a London bank and started work at the Royal Observatory, Greenwich, to the east of London. He had no formal qualification as an astronomer, but his new post was as a photographic and spectroscopic assistant. The Royal Observatory was a state institution, and its staff belonged to the civil service, admission to which was by public examination. Maunder passed the examination, so he was accepted into the service and...

Doubts about economic growth

Critics also point out that the projections of economic growth, on which emissions of greenhouse gases are based, may be flawed. This is not a criticism of the climate science, but of the economic techniques the scientists have used in order to develop the scenarios. Projections of future global warming are based on the assumption that economic growth, especially in the countries that are still industrializing, will lead to increasing emissions of greenhouse gases. The rate of economic growth...

The cyclesources and sinks

There are two principal components of the natural carbon cycle, both of which are in balance over the year. Photosynthesis removes about 132 billion tons (120 billion tonnes) of carbon from the air each year, and respiration returns a similar amount. About 99 billion tons (90 billion tonnes) of carbon dissolves into the oceans each year and a similar amount comes out of solution and enters the air as carbon dioxide. In addition to these large exchanges of carbon, there are also smaller ones....

Perturbing the natural cycle

When the Industrial Revolution began, water was the principal source of power. Factories had to be sited close to a place where there was a sufficient fall of water to drive a water mill. When steam engines were introduced factories could be sited anywhere because they used coal as a fuel. With that change, from water power to steam, the process of industrialization began releasing carbon that had been stored below ground as coal. This perturbed the natural carbon cycle. At first the effect was...

How Earth acquired its three atmospheres

We know that our own climate can change, but we tend to assume that the atmosphere itself has always been the same as it is today, composed almost entirely of nitrogen (78 percent) and oxygen (21 percent). That is wrong. Our present atmosphere is the third atmosphere the Earth has possessed. The first atmosphere is the one that cloaked the planet while it was forming, around 4.5 billion years ago. At that time rocks were continually smashing into the surface, and each time this happened the...

Diseases favored by wet weather

People were often hungry, even if food shortages did not amount to famine, and the cool, wet conditions favored the development of fungi and bacteria that caused disease. In the course of the 14th century the average life expectancy in England fell from about 48 to 38 years. This was due only partly to hunger. There was also disease. Agriculture retreating from marginal land From time to time entire villages succumbed to ergotism, caused by the ergot fungus (Claviceps purpurea). Ergot grows on...

The expansion and contraction of ice sheets

There are several reasons why sea levels rise and fall. The biggest changes are associated with the growth and disappearance of ice sheets during an ice age. Ice sheets represent a vast quantity of water. Even today, when we are living in an interglacial episode between ice ages, the Greenland and Antarctic ice sheets contain between them about 6.85 million cubic miles (28.56 million km3) of ice. Add to this the smaller valley glaciers and ice caps, and the total amount of ice is approximately...

Radiation emission and absorption

Once the surface of the Earth becomes warmer than the interplanetary space surrounding it, its surface begins to emit radiation at a wavelength that is proportional to its temperature (see Radiation from the Sun and from the Earth on pages 128-134). Earth emits radiation in the infrared waveband, at wavelengths of approximately 3-30 pm (pm are micrometers, equal to millionths of a meter). Its radiation is most intense at about 10 pm. As the diagram on page 97 shows, water vapor absorbs...

Effect on radiation

The extent to which they affect radiation also depends on the time of day. As the diagram shows, when the Sun is high in the sky its radiation travels a shorter distance through the atmosphere than it does when it is low, and consequently it encounters and reacts with a smaller number of aerosol particles. Scientists still have much to learn about the way aerosols affect radiation and, through that, the climate. In its 2001 scientific report, the Intergovernmental Panel on Climate Change (IPCC)...

Models have limitations

Climate models are now very detailed, but they still have limitations. Some climate processes are not yet fully understood and so assumptions have to be made about the way they function. Models are also limited by computing power. This affects the size of the grid. At present, the best models of the atmosphere over land use a grid with a side that is about 155 miles (250 km) long. Above the boundary layer the lowest layer of air, extending to about 1,700 feet (519 m), in which the air is...

Sea levels and storms

Some of the most dramatic consequences that have been predicted to accompany climate change also turn out to be exaggerated. There have been warnings of a rapid rise in sea level, of more and fiercer hurricanes, more tornadoes, and even of more blizzards. Sea levels have risen, but the rise predicted by the models, of 4.3-30 inches (0.11-0.77 m), is modest (see Is the sea rising on pages 158-163). Coastal erosion is serious in some places, but it is not due to global warming. The frequency of...

Cities are less windy except along urban canyons

Cities are less windy than the surrounding countryside. The average wind speed is up to 30 percent lower inside the city than it is outside and there are 5 percent to 20 percent more calm days. This is due to the friction caused by buildings. Wind blowing in from outside is deflected this way and that, so there are many eddies and the wind inside the city is gusty, but each of the structures it blows against absorbs some of its energy. The buildings slow the wind. There are exceptions, however....

The spectrum and the rainbow

Light is a form of electromagnetic radiation, and when white light passes through a prism it separates into a range of colors violet, indigo, blue, green, yellow, orange, and red. These are the colors of a rainbow and they are made in the same way, because raindrops act as prisms. When light crosses from one medium, such as air, to another, such as water, its speed and direction change. The light bends. This is called refraction. Light striking a raindrop is refracted as it enters the drop,...

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 ,...

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...

Albedo and temperature

Light that is not reflected is absorbed. We make use of this fact. In cold weather we often wear dark clothes, hoping they will absorb such heat as the Sun delivers, and in hot weather we wear light-colored clothes to reflect heat. Winter clothes are also thicker, of course, and we wear more layers of them, and summer clothes are thinner and we wear fewer layers. That is really why winter clothes are warm and summer clothes keep us cool, but the albedo of the clothes contributes to the effect....

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...

Heat islands and global warming

A weather station located in a large urban area will consistently show higher temperatures than a weather station located in the open countryside. If the temperature record is being used to detect signs of climate change, this is not necessarily important, because both sets of readings will change together. They will be in step, so that any warming or cooling trend should appear in both. There is a problem, however, where a city spreads to engulf a weather station in a formerly rural area. The...

Slow recovery and the origin of the traditional Christmas scene

The world began to recover during the 18th century, but the recovery was hesitant. The winter of 1708-9 was mild in Ireland and Scotland, but the sea froze along the Flemish coast and people crossed the Baltic on foot. In 1716 the Thames froze so solidly that the tide raised the ice by 13 feet (4 m) without disturbing the fair being held on it. The 1720s and 1730s, on the other hand, brought some of the mildest winters of the century, although the summer of 1725 was the coolest ever recorded....

How glaciers begin and move

Glaciers are sometimes described as rivers of ice. This is misleading, because the glaciers associated with ice ages and with the Greenland and Antarctic ice caps are not like rivers, although they flow. A glacier begins as a fall of winter snow that fails to melt the following summer. This snow is called firn and its edge, beyond which the winter snow does melt in summer, is the firn line. More snow falls the following winter, to become a new layer of firn, and its weight compresses the snow...

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....

Revealing the past

Climates are changing constantly, but slowly. Even the present global warming, which many people fear may eventually amount to a significant shift in climate, is measured by the extent to which temperatures might rise over the course of a century. The timescales are longer than a human lifetime. This makes them difficult to comprehend, because the weather we experience today is little different from the weather our grandparents knew, so it is hard to detect any change at all. If we are to...

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...

Isostasy and glacial rebound

Ice is very heavy and the present Greenland ice sheet is an average 10,000 feet (3,000 m) thick and the Antarctic ice sheet 6,900 feet (2,100 m). During an ice age, ice sheets of this thickness cover a much greater area. The immense weight of ice depresses the crust beneath it. The Earth's crust is made from solid rocks that lie above the hot, slightly plastic rocks of the mantle. The mantle behaves like a liquid with respect to the solid rocks of the crust, so...

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...

How oxygen accumulated

At that time the Sun was young and weak. The thermonuclear reaction in its core had made it start to shine, but it was about 25 percent to 30 percent dim mer and cooler than it is today. Nevertheless, this was enough to warm the surface layers of water and to provide light for the first cells to begin manufacturing sugars by photosynthesis. Those cells were cyanobacteria and they lived in microbial mats the fossil remains of those mats are called stromatolites. Oxygen is a by-product of...

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...

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...

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 ....

Glaciers begin advancing

After 1550, the climate grew markedly colder. Glaciers began advancing and in late May or early June 1595 (there is some uncertainty about the precise date), the Gi troz Glacier in Switzerland entered the River Danse, damming it and causing a flood when the dam broke that submerged the town of Bagnes, killing 70 people. As recently as 1926 there was a house in Bagnes that still had a beam bearing the inscription Maurice Olliet had this house built in 1595, the year Bagnes was flooded by the Gi...

Transport Of Heat By The Oceans

Edmonton, Alberta, and Dublin, Ireland are in almost the same latitude 53.58 N and 53.37 N respectively . July is the warmest month in Edmonton, with an average daytime temperature of 74 F 23 C , and January is the coldest month. The average nighttime coldest temperature in January is -4 F -20 C . July is also the warmest month in Dublin, with an average daytime temperature of 67 F 20 C , and January is the coldest month, with nighttime temperatures of 34 F 1 C . Edmonton is warmer than Dublin...

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...

The domestication of animals and plants

Around 12,000 years ago the most recent ice age was drawing to a close (see the section Ice ages of the past and future on pages 61-69). The global climate was growing warmer and the great ice sheets and mountain glaciers were retreating. In the Zagros Mountains, where modern Iran, Iraq, Syria, and Turkey meet, people had lived until then in caves and hunted wild game, mainly sheep and goats. At about that time sheep became the more important source of their food and there is archaeological...

Eccentricity

A circle may be big or small, but it is always a circle. Ellipses, on the other hand, vary in shape as well as size they are more elliptical or less so. When the ellipse represents the path of an orbiting body, the extent to which the ellipse is stretched is known as the eccentricity of the orbit. Eccentricity can be measured. The two foci and the center of an ellipse all lie along the major axis the longest straight line that will fit inside the ellipse. Suppose, in the drawing, that the body...

The significance of precession

Our ordinary, everyday calendar is based on a year that is measured from equinox to equinox and solstice to solstice. This is called the tropical year and it contains an average of 365.242 solar days. A solar day is the time the Earth takes to complete one rotation. Its average length is 86,400 seconds ( 24 hours). Measure the year from one perihelion to the next, however, and the length is slightly different 365.259 mean solar days. This is about 25.13 minutes longer. It means that the...

Respiration

Carbohydrate foods fats, sugars, and starches are used to supply the energy needed to power the processes that allow living things to function. Even when we are lying down quite still, our bodies require energy. The minimum amount they need is known as the basal metabolic rate (BMR), and it is measured in a person who has slept for at least eight hours and is lying motionless and who has not eaten for at least 12 hours because digestion uses energy. The BMR for an adult person is 1,200-1,800...

Some clouds are more reflective than others

These differences are real and significant. A deep layer of dense cloud is much more reflective than a thin layer of more diffuse cloud. Dense cloud forms at a lower level than diffuse cloud, so cloud albedo also changes according to the height of the cloud. The table shows just how large the difference is. The surface of undulating cloud tops that covers most of the sky usually altostratus is more than twice as reflective as the thin, wispy, cirriform clouds. Heaped up cauliflower clouds...

Measuring Climate Change

Measuring the temperature is surprisingly difficult. We are used to having thermometers around the house and these are good enough for most purposes, but they have their limitations. There is a joke among physicists The person who has a thermometer knows the temperature the person who has two thermometers is never quite sure. Galileo (1564-1642) invented the first thermometer called a thermo-scope in 1593. It is shown in the illustration. It was a gas thermometer and its principle is very...

Cities are less sunny

One reason people find the countryside attractive may be that they believe it to be sunnier. They are quite right. On average, city dwellers experience 5 percent to 15 percent fewer hours of sunshine over the year, 15 percent to 20 percent less solar radiation in total, and 5 percent less ultraviolet radiation in summer and 30 percent in winter. The drawing shows why this is so. Buildings shade the ground and the taller the buildings are, the deeper the shade that they cast. The extent of the...