Variations in weather as well as climate have been a regular feature on Earth. Scientists have gathered various evidences of changes in climate and enumerated numerous theories of their causes as well.
Evidence in the form of plant and animal fossils, for instance, indicates marked changes in climate since the creation of the Earth during various periods of time. Recorded history indicates climatic fluctuations whose regularity is not certain. Lack of regularity in climatic fluctuations is apparent in, for instance, the annual cycle having seasons that are early or late and the reversal of the monsoon in southern and eastern Asia which is generally regarded as an annual phenomenon but occurs at widely differing rates.
In the last century or so, there has been an increased concern over the global climatic changes. The reason for this is the recognition that humans have been increasingly responsible for much of the change in climate being witnessed. Not only that, his many activities that show an utter disregard towards the environment have proved detrimental to nature as a whole.
One of the disastrous consequences of human activity has been global warming—a foremost challenge today. World temperatures have increased by around 0.7 °C since the industrial era began. This rise in temperature has been linked to increase in the concentration of greenhouse gases in the Earth’s atmosphere, a result of reckless industrial and technological advancement by man.
It is believed that beyond a threshold of a global temperature rise of 2 °C, there is a very huge risk of large-scale human development setbacks and irreversible ecological catastrophes. There is a need to do something urgently—from evolving policies to adapting to the climate challenges to actually reducing emissions and taking other steps so that the irreversible changes that are underway and threaten life on earth are not-amplified over the decades.
Different causes have been identified as active at different time scales. Most theories have highlighted the fundamental role of insolation in the energy processes that produce weather and climate. Increased solar radiation is a factor identified as responsible for warming of the atmosphere and melting of continental glaciers. Correlations between number of sunspot and weather have been established for specific regions only.
However, effects of sunspot activity are said to combine with solar phenomena including the rotation of the sun and the solar wind to bring about changes and precipitation patterns on the Earth. Paleoclimatologists have sought correlations between the magnetism of the Earth and climatic changes, like those related to ice ages and extinction of species.
Changes in the eccentricity of the Earth’s orbit, changes in the rate of the Earth’s rotation on its axis have been known to affect the diurnal heat budget and world climates. Explanations of climatic change have also relied on crustal movements on the Earth.
The drastic change in global climate has been attributed to radical variations in the amounts of atmospheric gases, especially those that absorb radiation in a selective manner. Carbon-dioxide and water vapour tend to create a greenhouse effect by transmitting short-wave radiation but subsequently absorbing some of the long-wave terrestrial radiation. An increase in carbon-dioxide, as is happening with increased industrial and other emissions, would produce higher surface temperatures.