Other Aspects of Climate Change

There are various other aspects and issues related to climate change. There are certain other factors also (discussed below) which affect the climate changes. But we have not understood them very clearly so far.

1. Role of Aerosols

Since the industrial revolution, the emission of aerosols to the atmosphere has also increased. Aerosols are particles having diameter less than 10 μm. They tend to remain in the atmosphere by collision with the air particles which overcome the gravitational attraction.

It has been observed by researches that aerosols emitted from coal (sulphates) may cause global cooling because they act as seeding for clouds. They provide surface for water to condense on. The resulting cloud formation reflects the incoming solar radiation. Similar cooling was observed after the 1991 eruption of Mount Pinatubo in the Philippines. About 20 million tonnes of sulphur dioxide was released which circles the globe for about 2 years cooling the earth’s atmosphere.

Such volcanic eruptions emitting ash and aerosols lower the temperature. The global warming was counterbalanced by the above cooling in 1991-92. By 1994, when the aerosols had settled, the global temperature returned to previous higher levels.

2. Nino and ENSO

Nino refers to the child, the Christ child because these events often begin at the coast of South America near Christmas time. They cause a disruption of the ocean-atmosphere system in the tropical Pacific. During Nino, the eastern equatorial Pacific Ocean becomes unusually waπn and the westward moving equatorial current reverses. The rise in temperature of sea surface waters off the South American coast has ecological consequences. Warm surface waters inhibit upwelling of nutrient-rich cold water which supports marine ecosystem and major fisheries.

Nino events occur at intervals of two to seven years and last for about 12 to 18 months. Upwelling releases CO₂ to the atmosphere. Nino events reduce the oceanic CO₂ outgassing and thus perturb the global CO₂ cycle.

The Nino of 1982-83 was very strong. These conditions developed in 1991­92 and also in 1993. Nino caused floods, droughts and killed thousands of people. It also damaged crops, buildings and other structures and caused heavy loss.

Nino events alternate with El Nina events in which ocean water get unusually cool and cause effects opposite to Nino events.

3. External Factors Affecting Climate Change

(i) Variation in Solar Output

There are changes in solar energy associated with 11-year sunspot cycles or 22-year solar magnetic cycles. Historical dates suggest that colder conditions in Europe coincide with periods of reduced or no sunspot activity.

(ii) Variation in Earth’s Orbit

The earth orbits around the Sun. The Yugoslav astronomer M. Milankovitch described variations in earth's orbit in 1920s. They result by three interacting effects which are as follows:

∙ Variation in the shape of the elliptical orbit (over 95,000 year cycle)

• Variation in the tilt of the Earth’s axis of rotation (over a 42,000 year cycle)

• Variation in the time of year when the Earth is closest to the Sun (over a 21,000 year cycle)

The analysis of ocean cores shows that these three cycles appear in the oxygen isotope and faunal records. It shows that they are associated with the timing of glacial and interglacial phases.

(iii) Continental Drift

The continents have redistributed over the surface of the Earth over millions of years. This has caused the creation of major oceans and mountain belts, which affect the climate.

Around 450 million years ago, the Sahara desert was located near the South Pole and it was glaciated. Similarly, Britain was located much further south in latitudes 20^o-30^o, where trade winds created desert conditions. Thus, over the time, there have been drastic changes over global climate both for continents and oceans.