How the World Is Changing

The earth's climate is dynamic and always changing through a natural cycle. What the world is more worried about is that the changes that are occurring today have been speeded up because of man's activities. These changes are being studied by scientists all over the world who are finding evidence from tree rings, pollen samples, ice cores, and sea sediments. The causes of climate change can be divided into two categories - those that are due to natural causes and those that are created by man.

Human Causes

The Industrial Revolution in the 19th century saw the large-scale use of fossil fuels for industrial activities. These industries created jobs and over the years, people moved from rural areas to the cities. This trend is continuing even today. More and more land that was covered with vegetation has been cleared to make way for houses. Natural resources are being used extensively for construction, industries, transport, and consumption. Consumerism (our increasing want for material things) has increased by leaps and bounds, creating mountains of waste. Also, our population has increased to an incredible extent.

All this has contributed to a rise in greenhouse gases in the atmosphere. Fossil fuels such as oil, coal and natural gas supply most of the energy needed to run vehicles, generate electricity for industries, households, etc. The energy sector is responsible for about ¾ of the carbon dioxide emissions, 1/5 of the methane emissions and a large quantity of nitrous oxide.

Greenhouse gases and their sources

Carbon dioxide is undoubtedly, the most important greenhouse gas in the atmosphere. Changes in land use pattern, deforestation, land clearing, agriculture, and other activities have all led to a rise in the emission of carbon dioxide.

Methane is another important greenhouse gas in the atmosphere. About ¼ of all methane emissions are said to come from domesticated animals such as dairy cows, goats, pigs, buffaloes, camels, horses, and sheep. These animals produce methane during the cud-chewing process. Methane is also released from rice or paddy fields that are flooded during the sowing and maturing periods. Nearly 90% of the paddy-growing area in the world is found in Asia, as rice is the staple food there.

Methane is also emitted from landfills and other waste dumps. If the waste is put into an incinerator or burnt in the open, carbon dioxide is emitted. Methane is also emitted during the process of oil drilling, coal mining and also from leaking gas pipelines.

A large amount of nitrous oxide emission has been attributed to fertilizer application.

Natural Causes

There are a number of natural factors responsible for climate change. Some of the more prominent ones are continental drift, volcanoes, ocean currents, the earth's tilt, and comets and meteorites.

Continental drift

The continents that we are familiar with today were formed when the landmass began gradually drifting apart, millions of years back. This drift also had an impact on the climate because it changed the physical features of the landmass, their position and the position of water bodies. The separation of the landmasses changed the flow of ocean currents and winds, which affected the climate. This drift of the continents continues even today;

Volcanoes

When a volcano erupts it throws out large volumes of sulphur dioxide (SO₂), water vapour, dust, and ash into the atmosphere. Although the volcanic activity may last only a few days, the large volumes of gases and ash can influence climatic patterns for years. Millions of tons of sulphur dioxide gas can reach the upper levels of the atmosphere after a major eruption. The gases and dust particles partially block the incoming rays of the sun, leading to cooling. Sulphur dioxide combines with water to form tiny droplets of sulphuric acid. These droplets are so small that many of them can stay aloft for several years. They are efficient reflectors of sunlight, and screen the ground from some of the energy that it would ordinarily receive from the sun.

The earth's tilt

The earth makes one full orbit around the sun each year. It is tilted at an angle of 23.5° to the perpendicular plane of its orbital path. For one half of the year when it is summer, the northern hemisphere tilts towards the sun. In the other half when it is winter, the earth is tilted away from the sun. If there was no tilt we would not have experienced seasons. Changes in the tilt of the earth can affect the severity of the seasons - more tilt means warmer summers and colder winters; less tilt means cooler summers and milder winters.

The Earth's orbit is somewhat elliptical, which means that the distance between the earth and the Sun varies over the course of a year. We usually think of the earth's axis as being fixed, after all, it always seems to point toward Polaris (also known as the Pole Star and the North Star). Actually, it is not quite constant: the axis does move, at the rate of a little more than a half-degree each century.

So Polaris has not always been, and will not always be, the star pointing to the North. When the pyramids were built, around 2500 BC, the pole was near the star Thuban (Alpha Draconis).

Other natural factors that influence temperature and precipitation are elevation, latitude, winds, topography, and ocean currents.

Elevation is the distance above sea level. As you go higher up a mountain, the air pressure decreases and the gas molecules spread farther and farther apart. Less dense air holds less heat than dense air, so the farther above sea level you are, the lower the temperature will be.

Latitude measures how far you are north or south of the equator. Latitude determines the amount of solar energy received by that region. Regions close to the equator receive direct rays of the sun and therefore receive more radiant energy and are warmer. At the areas closer to the poles, the suns rays are at an angle so these areas receive less radiant energy and are cooler.

The world's four oceans are the Atlantic Ocean, Pacific Ocean, Indian Ocean, and Arctic Ocean. Water, like air, moves around the earth as warm or cold winds and currents. It moves in a cycle from ocean, to air, to land, and back to oceans. Ocean currents move vast amounts of heat across the planet - roughly the same amount as the atmosphere does.

Water in the ocean travels in paths called currents. Currents can either be warm or cold. The temperature of the water affects the temperature of the air above it. If the water is cold, it cools the air above it. If it is warm, it heats up the air above it. Ocean currents traveling away from the equator are warm, warming the air, which moves onto the land near these areas. Currents flowing toward the equator are colder, so the air masses, moving over these currents, are cooled. These cooled air masses then flow over the regions in their path.

Much of the heat that escapes from the oceans is in the form of water vapor, the most abundant greenhouse gas on Earth. Water vapor contributes to the formation of clouds, which shade the surface and have a net cooling effect.

It is important to us that the oceans stay healthy. 

• They drive our climate and weather
• They provide a livelihood for many millions of people worldwide through fishing, the exploitation of energy and mineral resources, shipping, and leisure activities
• The oceans pose threats through floods, tsunamis, storms, sea level change and coastal erosion. More than half the world’s population lives near the sea.

Unfortunately, oceans are used for waste disposal. Most waste eventually ends up in the oceans, with the result that marine pollution is a global problem - every part of every ocean is now affected. But the most critical threats are to shallow seas and shorelines near highly-populated areas.

The topography, or features of the land also influences the climate. The amount of precipitation in a region is affected by mountain ranges in that area. Mountains cause air to rise. Rising air becomes less dense allowing the condensation of water. Precipitation occurs. Air moving down the other side of the mountain becomes denser. Sinking air does not produce precipitation. The leeward side, or side facing away from the wind, receives much less precipitation.

Winds can greatly affect the amount of precipitation an area receives depending on the amount of moisture they are carrying. These winds can move air masses from the ocean onto a continent bringing moisture onto the continent. Or winds may move air masses from continent to the ocean, moving drier air from the continent. These winds affect the climate of an area.

Ways People Affect Climate

All of us in our daily lives contribute our bit to changes in the climate.

Electricity is the main source of power in urban areas. All our gadgets run on electricity generated mainly from thermal power plants. These thermal power plants are run on fossil fuels (mostly coal) and are responsible for the emission of huge amounts of greenhouse gases and other pollutants.

Cars, buses, and trucks are the principal ways by which goods and people are transported in most of our cities. These are run mainly on petrol or diesel, both fossil fuels.

We generate large quantities of waste in the form of plastics that remain in the environment for many years and cause damage.  

We use a huge quantity of paper in our daily life from paper towels, to writing paper, to gift wrap, to newspapers and magazines.

Timber is used in large quantities for construction of houses, which means that large areas of forest have to be cut down.

A growing population has meant more and more mouths to feed. Because the land area available for agriculture is limited, high-yielding varieties of crop are being grown to increase the agricultural output from a given area of land. However, such high-yielding varieties of crops require large quantities of fertilizers; and more fertilizer means more emissions of nitrous oxide, both from the field into which it is put and the fertilizer industry that makes it. Pollution also results from the run-off of fertilizer into water bodies.

 

The following is a list of 20th century climate-related changes observed in the Northern Hemisphere.
INDICATOR	OBSERVED CHANGE
Global mean sea level	Increased at an average annual rate of 1-2 mm.
Duration of ice cover of lakes and rivers	Decreased by 2 weeks in mid and high latitudes.
Arctic sea-ice extent and thickness	Thinned by 40% in recent decades in late summer to early autumn, decreased in extent by 10-15% since the 1950s in spring and summer.
Non-polar glaciers	Widespread retreat.
Snow cover	Decreased in area by 10% since global observations became available in 1960s.
Permafrost	Degraded in polar, sub-polar, mountainous regions.
Plant and animal ranges	Shifted north in elevation for plants, insects, birds and fish.
Breeding, flowering and migration	Earlier plant flowering, earlier bird arrival, earlier breeding season, and earlier emergence of insects.
Growing season	Lengthened by 1- 4 days per decade in last 40 years, especially at higher latitudes.
El Niño events	Increased frequency and intensity in the last 20-30 years compared to previous 100 years.

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