GREENHOUSE EFFECT – CAUSES, CONSEQUENCES AND CONCERNS FOR THE WORLD

WHAT IS GREENHOUSE EFFECT

Greenhouse effect is a natural process by which the Earth’s atmosphere retains some of the heat of Sun, thereby maintaining adequate warmth for survival of life.

The Sun sends electromagnetic radiation to Earth from an enormous distance of 93 million miles. In fact, all objects whose temperature is more than absolute Zero do emit thermal radiation. The Sun emits radiation of short wavelength (wavelengths of visible spectrum and near infrared spectrum). Whereas, the Earth emits long wavelength radiation (mid and far infrared wavelength spectrum).

The reason for this difference in wavelengths emitted by Sun and Earth is because of difference in their surface temperatures. Surface temperature of Sun is much higher (5500 degree C/9900 degree F). So, it gives off short wave radiation in comparison to Earth which being much cooler emits long wave radiation.

The lower zone of Earth’s atmosphere called troposphere which surrounds 5-9 miles above surface has certain gases like carbon dioxide , water vapor, methane which trap some amount of the electromagnetic radiation given off by Sun. So, while Earth re-emits electromagnetic radiation back to space, it also absorbs some of it. This accounts for retention of heat into our atmosphere.

This is important for us as the heat so trapped makes our planet warm and habitable.

But, in recent times, increase in greenhouse effect has been found to be associated with serious outcomes like global warming and climate change.

WHY IS IT CALLED SO

Greenhouse effect has been named so because it bears similarity with a ‘greenhouse‘ used for growing plants which is made of glass. When sunlight falls on the greenhouse, the glass traps some heat which keeps the greenhouse warm for plants to grow even in winter.

The Earth’s atmosphere has been compared to the glass of greenhouse trapping heat in a similar way.

Despite this analogy, the way they both work varies. A greenhouse preserves heat by blocking convection whereas Earth retains heat by slowing down radiative transfer.

WHY IS IT IMPORTANT

Some baseline greenhouse effect is required to keep Earth warm enough to support life. Imagine, if there was no greenhouse effect our planet would be as cold as -18 degree C / -0.4 degree F. It is because of greenhouse effect that we have a comfortable temperature(average of 15 degree C / 59 degree F).

WHAT ARE GREENHOUSE GASES

A gas is called as a greenhouse gas if it absorbs radiation of longwave. In simple words, greenhouse gases are those gases in Earth’s troposphere which trap some fraction of long wavelength outgoing Sun’s radiation from the Earth’s surface.

Following are examples of greenhouse gases:

• Carbon dioxide
• Water vapor
• Methane
• Nitrous oxide
• Ozone
• Hydrofluorocarbons
• Perfluorocarbons
• Sulfur hexafluoride
• Nitrogen trifluoride

Gases that contribute to maximum greenhouse effect in decreasing order are:

Water vapor > carbon dioxide > nitrous oxide > methane > ozone.

SOURCES OF EMISSION

CARBON DIOXIDE – burning fossil fuel, deforestation

METHANE – livestock, agriculture, landfills, natural gas system

WATER VAPOR – occurs naturally

NITROUS OXIDE – fertilizers, fossil fuel, industries

HYDROFLUOROCARBONS – refrigerant, aerosol

PERFLUOROCARBON – refrigerant, aluminium production

SULFUR HEXAFLUORIDE – electrical equipments

NITROGEN TRIFLUORIDE – solar panels, LED’s

OZONE – naturally occurring, nitrous oxide, volatile organic compounds

ENHANCED GREENHOUSE EFFECT

The augmentation of natural greenhouse effect as a result of increase in amount of greenhouse gases due to man-made causes like cutting forests, rapid industrialization and fossil fuel combustion resulting in climate change and rise in temperature is known as enhanced greenhouse effect.

MEASUREMENT

IN TERMS OF TEMPERATURE CHANGE – Greenhouse effect can be measured as a temperature change of 33 degree C / 59 degree F. [Since average temperature is 15 degree C with greenhouse effect and would be -18 degree C without it].

IN TERMS OF ENERGY FLOW CHANGE – Greenhouse effect is an energy flow change of 159 W/m² (watts per square meter). [Since the average rate at which longwave radiation leaves Earth’s surface is 398 W/m² but on the other hand only 239 W/m² of this reaches space].

CONSEQUENCES OF GREENHOUSE EFFECT

As we have already seen, enhanced greenhouse effect has resulted in global warming and climate change.

An increase in global temperature of about 1.2 degree C (2.2 degree F) has already occurred since the era of Industrial revolution. It has been noted that since 1981, the average global surface temperature is rising at the rate of 0.18 degree C / 0.32 degree F per decade.

Carbon dioxide concentration has shown elevation from 313 ppm in 1960 to 400 ppm in 2013.

Even though this change appears to be very small, this can be dangerous as even a little increase in average global temperature can have huge impact on our climate.

This is evident from the fact that glaciers are melting faster than normal. This is a great concern for us as the melted ice drains into oceans as a result of which sea levels rise. This could lead to flooding of surrounding regions.

According to IPCC, annual rise in global sea levels from 1961 – 1993 was about 1.8 mm (0.07 inches) per year. Whereas a considerable escalation in sea levels has occurred to 3.1 mm (0.12 inches) per year since 1993.

Global warming can alter precipitation pattern affecting rain.

Loss of glaciers due to melting can affect countries that depend on it for consumption, irrigation and hydroelectricity.

MEASURES TO REDUCE GREENHOUSE EFFECT

We must take steps to minimize emission of greenhouse gases to decrease global warming.

We can adopt following measures –

• Use of alternative power sources like solar power and biofuels to lessen fossil fuel burning.
• Planting trees.
• Forest conservation.
• Cutting down use of nitrogen based fertilizers.