By David Okul
We think that a basic understanding of the atmosphere is instrumental in explaining climate change.
Without our atmosphere, there would be no life on earth. Two gases make up the bulk of the earth’s atmosphere: nitrogen (78%), and oxygen (21%). Argon, carbon dioxide and various other trace gases make up the remainder.
Scientists divided the atmosphere into four layers according to temperature: troposphere, stratosphere, mesosphere, and thermosphere. The temperature drops as we go up through the troposphere, but it rises as we move through the next layer, the stratosphere. The further away from earth, the thinner the atmosphere gets. The figure below shows the different layers
TROPOSPHERE
This is the layer of the atmosphere closest to the Earth’s surface, extending up to about 10-15 km above the Earth’s surface. It contains 75% of the atmosphere’s mass. Temperature and pressure drops as you go higher up the troposphere.
The Tropopause: At the very top of the troposphere is the tropopause where the temperature reaches a (stable) minimum. Some scientists call the tropopause a “thermal layer” or “cold trap” because this is a point where rising water vapour cannot go higher because it changes into ice and is trapped. If there is no cold trap, Earth would loose all its water!
Most of what we call weather occurs in the troposphere. The uneven heating of the regions of the troposphere by the Sun causes convection currents and winds. Warm air from Earth’s surface rises and cold air above it rushes in to replace it. When warm air reaches the tropopause, it cannot go higher as the air above it (in the stratosphere) is warmer and lighter … preventing much air convection beyond the tropopause. The tropopause acts like an invisible barrier and is the reason why most clouds form and weather phenomena occur within the troposphere.
The Greenhouse Effect: Heat from the Sun warms the Earth’s surface but most of it is radiated and sent back into space. Water vapour and carbon dioxide in the troposphere trap some of this heat, preventing it from escaping thus keep the Earth warm. This trapping of heat is called the “greenhouse effect”.
However, if there is too much carbon dioxide in the troposphere then it will trap too much heat. Scientists are afraid that the increasing amounts of carbon dioxide would raise the Earth’s surface temperature, bringing significant changes to worldwide weather patterns … shifting in climatic zones and the melting of the polar ice caps, which could raise the level of the world’s oceans. We will discuss more of the greenhouse effect, for now know that it occurs in the troposphere.
STRATOSPHERE
This layer lies directly above the troposphere and is about 35 km deep. It extends from about 15 to 50 km above the earths surface.
The stratosphere is warmer at the top than the bottom. The lower portion has a nearly constant temperature with height but in the upper portion the temperature increases with altitude because of absorption of sunlight by ozone. This temperature increase with altitude is the opposite of the situation in the troposphere.
The Ozone Layer: The stratosphere contains a thin layer of ozone molecules (with three oxygen atoms) which forms a protective layer shielding life on Earth from the Sun’s harmful ultraviolet radiation. But this ozone layer is being depleted, and is getting thinner over Europe, Asia, North American and Antarctica. “Holes” are appearing in the ozone layer.
While green house effect occurs in the troposphere, ozone layer depletion occurs in the stratosphere.
MESOSPHERE
Directly above the stratosphere, extending from 50 to 80 km above the Earth’s surface, the mesosphere is a cold layer where the temperature generally decreases with increasing altitude. Here in the mesosphere, the atmosphere is very rarefied nevertheless thick enough to slow down meteors hurtling into the atmosphere, where they burn up, leaving fiery trails in the night sky.
THERMOSPHERE
The thermosphere extends from 80 km above the Earth’s surface to outer space. The temperature is hot and may be as high as thousands of degrees as the few molecules that are present in the thermosphere receive extraordinary large amounts of energy from the Sun. However, the thermosphere would actually feel very cold to us because of the probability that these few molecules will hit our skin and transfer enough energy to cause appreciable heat is extremely low.
Green House Effect
There are two common meanings of the term “greenhouse effect”: There is a “natural” greenhouse effect that keeps the Earth’s climate warm and habitable. There is also the “man-made” greenhouse effect, which is the increase of Earth’s natural greenhouse effect by the addition of greenhouse gases from the burning of fossil fuels (mainly petroleum, coal, and natural gas). Carbon dioxide amount in the stratosphere has increased. Compared to a pre-industrial atmospheric concentration of around 270 parts per million (ppm), the average concentration has increased to close to 400 ppm in 2012. This causes the man-made portion of the greenhouse effect.
You can think of greenhouse gases as sort of a “blanket” for infrared radiation — they keep the Earth’s surface and lower layers of the atmosphere warmer, and the upper layers colder, than if the greenhouse gases were not there. About 80-90% of the Earth’s natural greenhouse effect is due to water vapor and clouds. Most of the rest is due to carbon dioxide, methane, and a few other minor gases. While the remaining gases in the atmosphere (e.g. nitrogen, oxygen) also absorb and emit a small amount of infrared radiation, their radiative effect on temperature is so weak that they can be neglected. While methane is a much more potent greenhouse gas than carbon dioxide, there is far less of it in the atmosphere. It is the carbon dioxide concentration that is increasing, due to the burning of fossil fuels (as well as from clearing rainforest), and it is believed by many scientists to be responsible for the global warming of the last 50 years or more.
Also, the concentration of methane, although extremely small (measured in parts per billion), has also increased in recent decades contributing somewhat to the strengthening of the greenhouse effect. The reasons for this increase, though, remain uncertain.
Global warming
Global warming is the process where the earth’s temperatures are actually getting warmer because of human activities that increase greenhouse gases. The greenhouses gases (GHG) include carbon dioxide (the major one) and methane. Other minor green house gases are nitrous oxide and water vapor. The gases make the temperature of the earth to become warmer. Carbon dioxide occurs from burning fossil fuels e.g. from vehicles and industries. Fossil fuels include petrol products, diesel etc.
Scientists believe that greater amounts of carbon dioxide in the atmosphere, and hotter temperatures on Earth, will significantly change the climate across the whole planet. This climate change is already beginning to happen in parts of the world. If you live in a very cold place like Alaska or Greenland, you might think a bit of global warming sounds like a great idea. But climate change doesn’t necessarily mean things will get hotter. Some places will be hotter some of the time, but most places will simply see more erratic and extreme weather. That could mean heavier rainfall on occasions, more snow in some places, longer periods of drought, more storms and hurricanes, and more frequent heat waves. All these can be disastrous!!!
Reducing global warming
- Reduce, Reuse, Recycle
Do your part to reduce waste by choosing reusable products instead of disposables. Buying products with minimal packaging (including the economy size when that makes sense for you) will help to reduce waste. And whenever you can, recycle paper, plastic, newspaper, glass and aluminum cans
- Plant trees
If you have the means to plant a tree, start digging. During photosynthesis, trees and other plants absorb carbon dioxide and give off oxygen. They are an integral part of the natural atmospheric exchange cycle here on Earth, but there are too few of them to fully counter the increases in carbon dioxide caused by vehicles, manufacturing and other human activities. A single tree will absorb approximately one ton of carbon dioxide during its lifetime.
- Encourage Others to Conserve
Share information about recycling and energy conservation with your friends, neighbors and co-workers, and take opportunities to encourage public officials to establish programs and policies that are good for the environment.
Remember anything that reduces the amount of carbon dioxide will reduce global warming and the greenhouse effect.
