What would be the most likely result of an increase in the amount of greenhouse gases in the atmosphere?

Answer 1

Increasing the level of greenhouse gas in the atmosphere initially results in a reduction in the rate at which the earth radiates energy to space. Since the amount of incoming energy remains fairly constant this results in a build up of energy (in the form of heat) in the land/atmosphere/ocean system - almost all of it in the oceans.

The heat that affects us most immediately is the heat that is released into the atmosphere. Warmer air can hold more water vapour than colder air. That means that warmer dry air is much more desiccating than colder dry air and warmer humid air can result in much heavier precipitation than cooler humid air. As a result both floods and droughts become much more destructive.

The rate at which heat is released into the atmosphere is very dependent on conditions in the oceans, particularly the El Nino Southern Oscilation (ENSO). During the El Niño phase of ENSO the Easterly Trade winds weaken or even reverse and the tropical Pacific Ocean is flooded with warm water. The result is large amounts of heat are released into the atmosphere and global surface temperatures rise. A classical example is 1998 when the average global temperature soared. During a La Niña event the trade winds strengthen, the warm water is pushed to the Western side of the Pacific where it accumulates in a deep pond, cool bottom water wells up in the Eastern Pacific, much less heat is released into the atmosphere and global surface temperatures cool. Nonetheless because of the overall warming trend the temperatures during La Niñas during the last decade have been higher than the temperatures during El Niños for most of the previous century.

The warming atmosphere also means that heat waves are hotter and last longer and are more deadly to both people and crops.

As the ocean heats it expands and sea levels rise slowly. Most of the sea level rise during the 20th century was due to this expansion. However a more serious effect which has only recently had a marked effect is the way that warm water speeds up the rate at which glaciers in both Greenland and Antarctica discharge into the ocean. This process has resulted in an acceleration in the rate of sea level rise during the last decades of the 20th century and the beginning of the 21st. This acceleration is expected to continue and might well get much worse. As a result mean sea levels are expected to rise by about a metre by the end of the century.

Because our civilisation has developed during a time of very stable sea levels much of our population and infrastructure is at or near sea level. Places that will be particularly affected will include low lying Pacific islands which may find themselves completely inundated by the end of the century, intensely settled river deltas such as Bangladesh and low lying coastal settlements such as The Florida Keys, and indeed much of Florida.

Answer 2

An increase in greenhouse gases would likely lead to a stronger greenhouse effect, trapping more heat in the Earth's atmosphere. This can result in global warming, leading to changes in climate patterns, rising sea levels, and more extreme weather events.