Earth’s climate and its components

Climate is a measure of the average pattern of variation in temperature, humidity, atmospheric pressure, wind, precipitation, atmospheric particle count and other meteorological variables in a given region over long periods of time.  Climate is different from weather, in that weather only describes the short-term conditions of these variables in a given region.

Earth’s climate is a complex system with a number of key components, all of which play important roles:

1.     The atmosphere (including its various layers)

2.     The hydrosphere (oceans, lakes and rivers)

3.     The cryosphere (snow and ice)

4.     The lithosphere (soils and rocks) and

5.     The biosphere (living things)

These components are constantly interacting and adjusting to both internal and external factors. It is the continuous alterations to these components that produce the environmental conditions that we experience. Living things act as sources and sinks for carbon. Snow and ice are of paramount importance in controlling the planet's albedo - the amount of sunlight that may be reflected straight back into space. They are in turn sensitive to both air and water temperatures. The oceans act as sinks and sources for both carbon and heat energy and are sensitive to atmospheric conditions overhead, and so on.

The Atmosphere

The earth’s atmosphere, which is a mixture of many different gases, surrounds the earth and extends upwards for more than a hundred kilometers. The atmosphere consists mainly of Oxygen (78%), Oxygen (21%) and Argon, Carbon Dioxide, and traces of Helium, Hydrogen (1%).  Ozone Beyond this height atmospheric gases are present in very low concentrations.  The proportion of gases changes at different levels in the atmosphere.

The atmosphere reflects some of the Sun’s energy, absorbs and radiates some  energy, and transmits some of it to the Earth’s surface.  Once the energy of the Sun reaches Earth’s surface, the atmosphere traps much of it, warming the Earth.

The atmosphere also transfers heat energy and moisture across the Earth. Incoming solar radiation (insolation) is redistributed from areas in which there is a surplus of heat (the equator) to areas where there is a heat deficit (the North and South Pole). This is achieved through a series of atmospheric convection cells.  These operate in a similar way to, and indeed interact with, the ocean conveyor. For example, as the oceans at low latitudes are heated, water evaporates and is transported poleward as water vapour. This warm air eventually cools and subsides. Changes in temperature and CO2 concentrations can lead to: changes in the size of atmospheric cells; warming in the troposphere; and disproportionately strong warming in Arctic regions. The strong interactions between ocean and atmospheric dynamics, and the significant feedback mechanisms between them, mean that climate researchers must consider these Earth components as interlinked systems. The necessity to assess ocean-atmospheric changes at the global scale has implications for the way in which research is conducted. It is only by integrating palaeo evidence of past changes, with present day monitoring, and projected models, that we can begin to understand such a complex system.

Some components of the Sun’s energy are sometimes dangerous to humans and animals.  Ozone (O3) in the atmosphere prevents most of the harmful energy from reaching us.  There is more naturally occurring ozone gas in the stratosphere than any other part in the atmosphere.  In the Stratosphere, ozone absorbs high-energy UV radiation from the Sun, preventing it from reaching Earth’s surface.  The decrease in the ozone in the Stratosphere is mainly caused by compounds called chlorofluorocarbons (CFCs) which are used for refrigeration in air-conditioners and refrigerators.  CFCs belong to a family of chemical compounds called halocarbons.  They are molecules made up of carbon atoms linked by chemical bonds to fluorine, chlorine, bromine, or iodine. In this case, chlorine and fluorine are linked to the carbon atoms.

In the stratosphere the chlorine atoms from the CFCs react with ozone molecules, destroying the protective ozone layer. Each CFC molecule can destroy hundreds or thousands of ozone molecules.

In contrast to stratospheric ozone, the ozone in the troposphere has a toxic and corrosive effect.  UV radiation from the Sun which escapes the stratospheric ozone layer and makes it to the earth’s surface combines with the exhaust from cars to produce toxic chemicals and ozone gas at ground level, this is called photochemical smog.  Photochemical smog is harmful to human health, damages buildings, and affects plants and animals.  The ozone gas created this way does not move up into the stratosphere and offers no sign of UV protection.

The Hydrosphere

The Earth’s hydrosphere is made up of all the water on the planet that can be stored in the oceans, rivers, streams, groundwater, or water vapor (excludes glaciers and ice-sheets). It is in constant movement, transferring water and heat throughout the atmosphere in the form of water vapor and precipitation. The oceans, which cover more than 70% of the earth’s surface, play a fundamental and complex role in regulating climate. The oceans are able to absorb twice as much solar energy as the atmosphere and land combined. Ocean currents transport this heat from the equator toward the Poles. In the past, long-term, natural oscillations in the oceans’ capacity to store and transport heat have led to global temperature changes. Future climate changes—whether natural or human-induced—will also be strongly influenced by the powerful dynamics of the seas.

As part of a vast planetary cycle of evaporation and rainfall, the oceans are also fundamental to the movement of water around the globe. Measuring changes in precipitation patterns, and understanding how they may lead to droughts in some regions and flooding in others, is a major part of predicting the potential effects of global climate change on human activities and natural ecosystems.

Thermohaline circulation (a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes), or what is known as the conveyor belt, transports the absorbed heat from the equator to the poles to regulate and moderate Earth’s climate. When the conveyor belt changed speeds in the past, it affected the global climate and temperature. It is extremely important to understand how the hydrosphere interacts with the other spheres and how this affects global climate change.

Energy is absorbed when water evaporates from the oceans and lakes, this process has the effect of cooling its surroundings.  Energy is given off when water vapour condenses into clouds in the atmosphere, this process warms the surroundings.  Large bodies of water have an effect on the climate of nearby regions.  Water absorbs and stores more thermal energy than land, it also heats up and cools down more slowly than land.  Regions near an ocean or large lake tend to be cooler in the summer than inland locations (the water takes a long time to warm up as it absorbs thermal energy), they also tend to be warmer in the fall (as the water slowly emits stored thermal energy).  Regions that are downward from a large body of water have more snowfall in the winter.

There are many pressing climatic issues directly linked with the hydrosphere which should be examined. These include rising sea-levels, decrease in Arctic sea ice, change in precipitation events, melting permafrost, and human impact on the hydrosphere.

The Cryosphere

About 2% of all Earth’s water is frozen in the form of snow and ice, sea ice, lake and river ice, snow cover, glaciers, ice caps and sheets, and frozen ground.  Although most of this ice is located at the two poles, snow and ice can be found on all seven continents. Sea ice or pack ice, only a few meters thick, formed from frozen sea water, floats in the ocean near the North and South Poles.  Ice sheets are enormous areas of permanent ice several kilometres thick, stretching over land areas of the Antarctic and Greenland.  Surfaces covered in ice and snow reflect more radiant energy than surfaces covered in soil, rock, or vegetation.  Most of the Earth’s polar regions are covered in ice, these regions reflect back a great deal of the Sun’s energy, which is why the polar regions are so cold.

In many parts of the world the cryosphere is a seasonal visitor. For most of the world’s population, the cryosphere is a lifeline. With nearly 70% of Earth's fresh water stored in glaciers and ice caps, more than a billion people around the world rely on the cryosphere as a source of drinking water. In Arctic regions, sea ice provides a home for animals like seals and polar bears, feeding and breeding areas for a variety of migrating species, and hunting grounds for local communities. 

Acting like a highly reflective blanket, the cryosphere protects Earth from getting too warm. Snow and ice reflect more sunlight than open water or bare ground. The presence or absence of snow and ice affects heating and cooling over the Earth's surface, influencing the entire planet's energy balance. Changes in snow and ice cover affect air temperatures, sea levels, ocean currents, and storm patterns all over the world.

Just as changes in the cryosphere can influence climate, changes in climate can also dramatically alter the Earth's snow- and ice-covered areas. Unlike other substances found on the Earth, snow and ice exist relatively close to their melting point and can easily change back and forth between solid and liquid. With just slight variations in Earth's temperature, thousands of square miles of snow and ice can accumulate or melt, making the cryosphere one of the most powerful indicators of climate and climate change.

Ice cores drilled from ice sheets and glaciers provide annual records of temperature, precipitation, atmospheric composition, volcanic activity, and wind patterns going back more than 800,000 years. Today, scientists also use satellites to observe the cryosphere and monitor changes. Using these data, they are able to make predictions about what the cryosphere and Earth's climate might look like many years from now. 

The Lithosphere

The lithosphere is a part of the climate system that is made up of the solid rock, soil, and minerals of Earth’s crust.  Together with the hydrosphere, the exposed lithosphere absorbs higher-energy radiation from the Sun, coverts it into thermal energy, and then emits the energy back as lower-energy infrared radiation. 

Mountains and other land formations affect how air moves over an area.  As clouds are blown upward over mountains, they lose their moisture as rainfall on the windward side.  The leeward side of the mountain receives little rain.  This process is called the rain shadow effect.  At high altitudes atmospheric pressure is lower because there is less air above pushing down.  As the air from lower altitudes rises to high altitudes, it expands and cools down.  Therefore, at high altitudes the air is cooler than at low altitudes.  This creates the Alpine climate.  Alpine climate is the average weather (climate) for the regions above the tree line. This climate is also referred to as a mountain climate or highland climate.

The energy emitted and reflected by the lithosphere as infrared radiation is trapped in the troposphere by greenhouse gasses in the atmosphere. The amount reflected depends on the albedo at the surface, forests absorb a lot more than savannah, and ice reflects still more. The lithosphere determines what vegetation grows on the surface (due to topography and surface nutrients), so it plays a small part played in short term climatic effects on the earth.

Volcanic and hydrothermal vents in the lithosphere emit hot gasses into the oceans and the atmosphere.  One of the most important emissions is CO2 which drives global warming, but there are also aerosols such a sulfur compounds which reduce warming by a process called global dimming.  The overall influence on climate depends on the substance and quantity being released. Large volcanic eruptions have been observed to affect climate on short time scales of a few years due to the masses of these gasses erupted into the atmosphere, and extremely large events in prehistory such as the Deccan Traps probably had significant and long lasting influences on climate that led to mass extinctions.

On longer time scales, the lithosphere influences climate through the position of the continents via tectonic movement. Land masses at the poles mean glaciation is more likely to occur. Shallower oceans mean much warmer temperatures on land. So climate is also influenced by these factors but over very long periods.

The Biosphere

There are many different ways in which plants, animals and other life-forms on earth affect climate. Some produce greenhouses gases that trap heat and aid global warming through the greenhouse effect, while others reduce the amount of greenhouse gases. Here are some examples:

Plants: The greenhouse gas carbon dioxide is taken out of the atmosphere by plants as they make their food by photosynthesis. During the night, plants release some carbon dioxide into the atmosphere. They take much more carbon dioxide out of the atmosphere than they put in.

Farm animals: The greenhouse gas methane is made as farm animals, such as cattle and sheep, digest their food. 

Wetlands and rice patties: Microbes in natural wetlands and rice paddies produce methane gas.

Factories and power plants: carbon dioxide gas is releasing into the atmosphere when fossil fuels are burned to make the power needed for most factories and power plants.

Cars and trucks: Carbon dioxide gas is released when fossil fuels are burned to power cars and trucks.

Fertilizers: The greenhouse gas nitrous oxide is produced when human-produced fertilizers breakdown in the soil.

Wildfires: Carbon dioxide is released into the atmosphere as wildfires burn. However, if a forest of similar size grows again, about the same amount of carbon that was added to the atmosphere during the fire will be removed. So, fires affect greenhouse gases in the short term, but not on long timescales.

Human Population:  It is significant to note that humans control many of the examples listed above.  Today, far more greenhouse gases are being released into the atmosphere than taken out. This contributes to the greenhouse effect and global warming.  The major anthropogenic sources of atmospheric CH4 are rice cultivation, livestock farming, the burning of coal and natural gas, the combustion of biomass, and the decomposition of organic matter in landfills.

Notes & Handouts

The Himalayas

Kumaon Himalayas

Askot Basemetals

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