GREEN HOUSE EFFECT

            The greenhouse effect likewise amplifes the effect of the Sun’s radiation. Greenhouse gases—carbondioxide (CO₂), methane, and water vapor are examples—trap sunlight in the atmosphere. Without any greenhouse gases, sunlight would pass through the atmosphere and strike Earth, which would absorb a portion of the sunlight. (Land absorbs less sunlight than water.) The rest would rebound from Earth as infrared radiation, passing out of the atmosphere and into space. Greenhouse gases do not, however, permit infrared radiation to pass into space, but rather absorb it as heat, in turn heating the atmosphere. Of the greenhouse gases, methane breaks down in the atmosphere after a few decades. CO₂, however, may linger centuries in the atmosphere.

Earth produces CO₂ through volcanic eruptions, spewing large quantities of it into the atmosphere. Since the Industrial Revolution, humans have increased the concentration of CO

2 by burning fossil fuels. Humans are adding CO₂ to the atmosphere faster than natural processes can reduce its concentration. As the concentration of CO₂ in the atmosphere increases, so does temperature.

Counterbalancing the effect of volcanoes in increasing CO₂ in the atmosphere, three factors reduce CO₂ and so cool Earth. First, CO₂ dissolves in rainwater to form carbonic acid, taking a portion of the gas out of the atmosphere. Second, the ocean absorbs CO₂. Microorganisms in the ocean convert CO₂ into carbonates, taking the gas out of circulation. Third, photosynthetic algae and plants consume CO₂ during photosynthesis, converting it into sugars. Plants also affect the climate through transpiration, a process that adds water vapor to

the atmosphere.

Water vapor traps more heat than either methane or CO₂. Like methane, water vapor does not persist in the atmosphere, but rather falls to the ground as rain. Te clouds that carry water vapor reflect sunlight back into space without letting it penetrate to Earth. Water vapor, therefore, has a complex effect on the climate. Water vapor is a greenhouse gas that warms Earth, but the clouds that carry water vapor cool the planet by blocking out sunlight. Clouds cover half the planet, reflecting 30 percent of sunlight, thereby cooling Earth.

Rain affects climate in several ways. It is abundant at the equator and at 30 degrees latitude, where it drenches Earth in monsoons. Rain is also plentiful at the windward side of mountains. As they rise to cross a mountain, clouds cool and release water vapor as rain. On the leeward side of mountains, clouds have little water vapor left to discharge as rain, and so the climate is arid. The climate is likewise arid between 15 and 30 degrees latitude, where air at low pressure prevents clouds from rising, cooling, and releasing their water vapor as rain. Rain sustains the growth of plants. Rapidly growing rainforests consume large amounts of CO₂, though humans are chopping them down at an unsustainable rate.

Heat from Earth’s core augments the heat supplied by the sun. Radioactive elements in the core decay over time, converting mass into energy, just as the sun and nuclear reactors do. This energy is in the form of heat and pressure. Pressure forces heat, in the form of molten rock, toward Earth’s surface. Volcanic eruptions, in addition to spewing huge amounts of CO₂ into the atmosphere, transfer molten rock from inside Earth to the surface, where molten rock liberates its heat.

Despite the fact that volcanoes liberate heat and release CO₂, their effect on the climate is not always in the direction of higher temperatures. Volcanoes also spew debris, dust, and ash into the atmosphere. These particles block out the Sun and so may cool Earth. The eruption of Mount Tambora, in 1815, ejected huge clouds of debris into the atmosphere. Feeling the full effects of the eruption, 1816 was so cold that it is remembered as the year that had no summer.

Wind affects climate by carrying warm or cool air across the land. Warm air originates at the equator and follows ocean currents to higher latitudes. Cool air, originating at the poles, blows to lower latitudes. When warm and cool air meet, warm air rises and cool air sinks. As warm air rises, it cools, and sheds its water vapor as rain. The areas along contrasting weather fronts are, therefore, places of abundant rainfall.

In their restlessness, the continents affect climate. Earth is not a static entity as was once believed. Rather, the continents wander across Earth, changing their position and their orientation toward one another. When continents have moved toward the poles, their climates have cooled. Only when Antarctica, for example, moved to the South Pole did it acquire glaciers. In contrast, when continents gather near the equator, as Pangea did, the climate becomes balmy. Plants grew in abundance and herbivores became large, setting the conditions for the evolution of the dinosaurs.

Nor is Earth’s orbit constant. In the 17th century, German astronomer Johannes Kepler demonstrated that Earth’s orbit, as is true of the orbits of all the planets, is an ellipse. At one extreme, the ellipse is pronounced, and Earth is nearest the Sun at the closest approach of the ellipse and furthest from the sun at the greatest distance of the ellipse. The climate in these instances alternates between warmth when Earth is near the sun, and cold when Earth is far from the Sun. At the other extreme, Earth’s orbit, though still an ellipse, is nearly circular. Earth, being roughly the same distance from the Sun at every point in its orbit, receives roughly the same amount of sunlight year round, and so has a uniformly warm climate.

A cold climate reinforces itself through the accumulation of snow and ice, both of which reflect sunlight back into space. By this mechanism, Earth, covered with snow and ice, cools because it reflects, rather than absorbs, heat in the form of sunlight. At the culmination of this feedback loop is an ice age, with Earth covered in glaciers. However, a warm climate can also reinforce it self through the accumulation of CO₂ in the atmosphere. At the culmination of this feedback loop CO2 accumulates until all snow and ice have melted. The succession of climates, with varying temperatures, makes clear that climate is not static, but changes over time. The current climate is a warm interlude at the end of the Pleistocene ice age. Whether the climate will stay warm or descend into another ice age remains open to question.

 Source: Encyclopedia of Global Warming and Climate Change (Click Here)