Aerosols and Their Impact on Indian Monsoon

Whenever we hear about Climate Change we usually relate it with increasing levels of greenhouse gases, trapping heat and thereby causing global warming. But this need not to be always the correct predictions, there is growing concern that human activity might also be altering the climate in unpredictable ways. This he does by releasing a large amount of soot and other pollutants into the atmosphere in the form of tiny particles known as aerosols.

Aerosols

It is a tiny particle formed both naturally and anthropogenically; naturally formed aerosols are dust whipped by wind, sea salt, sulphate compounds arise by natural processes and plants release organic materials into the air and aerosols formed by anthropogenic activities are soot, sulphates from the burning of fossil fuel, fly ash from thermal plants & nitrates from vehicular emissions which forms the bulk of the haze.

Aerosols in the atmosphere by natural means are not invariably a bad thing in fact they act like a substrate around which water vapour could condense into droplets and helps to form  clouds. But those released by anthropogenic activities in form of pollutes may alter the climate adversely.

Aerosols are short-lived, unlike greenhouse gases that persist and thereby accumulate in the atmosphere for longer period, these fine particles stays aloft in the atmosphere only for one to three weeks.

They are not evenly distributed around the globe, probably they concentrated near places where they are generated and can also be transported by winds across continents. The quantity and the type of aerosols found in the atmosphere changes from time to time as per seasonal variations.

Experiments on Aerosols & its effects

When aerosols extended its effect on climate change, it was the Indian Ocean Experiment (INDOEX) conducted jointly by scientists and institutions from the Europe, United States, and India in the late 1990s. This experiment highlighted the extents of the problem posed by human pollutants on the climate and found that a thick haze over the Indian subcontinent and the surrounding oceans formed by the mixture of natural and anthropogenic aerosols is affecting climate change over south Asian countries and also affecting monsoon pattern in India.

Aerosols influence on Climate

• Aerosols influence the climate in a number of ways; these fine particles scatter sunlight and stop some of it from reaching the earth’s surface.
• The water-absorbing aerosols, such as sea salt and natural sulphates forms more cloud forming droplet that reflects more sunlight back into space and permits lesser light towards ground.
• Due to increased anthropogenic activities the soot particles are released in atmosphere in larger scale that blocks and absorb the sunlight and result into heating of the lower atmosphere and burning off the possibility of formation of clouds.
• This has also dimmed sunlight over South Asia and the northern Indian Ocean by as much as seven per cent between 1930 and 2000.
• It has enhanced the solar heating of the lower atmosphere by about 30 per cent to 50 per cent.
• Bonding of soot with dust might triple the dimming of sunlight and perhaps double the cloud burn-off than if dust and soot had remained separate.

Aerosols and India

• The Indo-Gangetic plain is one of the most polluted regions with the soot concentration in the world.
• In an experiment conducted by IIT Kanpur revealed that the soot concentration at a height of two km was higher than that at ground level in many European industrial areas this was also true with Hydeabad.
• India and China is the two major soot producers due to their population and rapid economic growth.
• Most of the soot above South Asian air comes from the burning of fossil fuel, whereas in India it comes from burning of wood, animal dung, agriculture waste and other forms of biomass.
• There is seasonal variation in the soot level, soot concentrations over the Indian subcontinent and the surrounding oceans are high principally from November to February.
• Natural aerosols account for nearly three fourth of all aerosols present globally.

As natural aerosols were important in determining the current climate it is the manmade aerosols that are more responsible for climate change in India.

Aerosol and impact on Indian Monsoon

• When scientist introduced the effect of aerosols on climate, the record collected showed that the India’s monsoon rainfall was decreasing over the last 50 years due to aerosols.
• The scientist has warned that the frequency of droughts in India could increase in the coming decades if pollution continued unabated.
• Aerosols have dimmed sunlight over the Arabian Sea and have consequently cooled that part of the ocean as compared to the southern Indian Ocean as we know that the rain system gravitate towards warmer side and this has reduced temperature gradient between those two parts of the ocean has slowed monsoon circulation and thereby decreased rainfall.
• The greenhouse gases pushing in one direction and is warming the ocean that results more rain whereas on the other side the aerosols are pushing in another direction for cooler oceans and results lesser rain.
• It is said that in coming years the aerosols might win and in other years the greenhouse effect might prevail. This altercation between the two could produce greater year-to-year variability in monsoon rainfall over South Asia.
• The role of natural aerosols (Dust) must be considered while looking at climate change as they dominant over South Asia and the neighbouring oceans during the pre-monsoon period.
• Incorporation of dust aerosols into a climate model by the U.K. Met Office in its research has made more accurate simulation of the African monsoon systems, this factor must also be considered while studying Indian monsoon system.
• On the ground of the effects of carbon dioxide on climate change is studied, we must adopt the same approach when looking at how aerosols will influence the climate.
• We need to develop a system to understand the role of aerosols in determining climate and the changes in aerosol levels on the complex Indian monsoon.
• It had taken over a century to evolve a consensus on greenhouse gases and global warming; hopefully it won’t take that long to find definitive answers to the impact of aerosols.

The solution on reducing aerosol effect on climate can be done simply by cutting pollution, but bringing about such reduction in countries such as India where the large population still depend on conventional fuel and also the their need to meet the energy for the vibrant economy. Thus the country like India has to find alternative non polluting source of energy to meet its need.