Without the natural Greenhouse effect the Earth would be too cold for life. Scientists estimate that the Earth would be some 18⁰C colder without this natural warming effect. The small amount of carbon dioxide and other greenhouse gases such as methane and water vapour in the atmosphere act like a blanket and trap enough of the sun's heat to keep the temperature on our planet within a stable range capable of maintaining life.

The swings in the Earth's temperature and weather which we often complain and moan about so often are very small and mild when compared to the climates on other planets. Our weather and temperature in our atmosphere are both controlled by the presence of certain greenhouse gases. If we increase the amounts of these gases then more of the sun's heat will be trapped in the atmosphere and temperatures on Earth will start to rise. This warming of the Earth can lead to climate change which can have a huge affect on all life on our planet.

Over the last 150 years the amount of the greenhouse gas carbon dioxide in the atmosphere has more than doubled. This is mainly due to:

• The burning of fossil fuels such as coal to generate electricity as well as the burning of natural gas to heat homes and industry.
• The burning of petrol and diesel as a fuel for transport in motor vehicles, trains etc.

• Wide spread deforestation also releases large amounts of CO₂ into the atmosphere and also prevents the removal of CO₂ by photosynthesis. The clearing of forests to make way for farming also has a large impact on the amount of CO₂ released as farming is an energy intensive activity. Large areas of forest are being cleared in countries like Brazil to make way for cattle and to produce large amounts of timber to sell which boasts their economies and provides jobs.

• Cows release either by burping or farting up to 500 litres of the greenhouse gas methane per day and there are approximately 987 million cows on Earth. Scientists have estimated that cows alone release just over 3 gigatonnes (3 billion tonnes) of methane into the atmosphere every year and this amount is growing year upon year. Methane is up to 28 times as effective at trapping the Sun's heat in the atmosphere as carbon dioxide gas. The increase in the food requirements of a growing world population means more farming which ultimately means fewer forests and more cows. This cycle leads to an increase in both methane and carbon dioxide concentrations in the atmosphere.
• In Asia rice is a major part of people's diet. The growing of rice in paddy fields also releases large amounts of methane gas into the atmosphere. The paddy field used to grow rice contain lots of slow moving water with low oxygen levels, this water contain bacteria which produce large quantities of methane gas.

The carbon dioxide and other gases such as methane are able to trap more of the sun's heat in the atmosphere; this has seen average global temperatures rise. Many scientists believe that this increase in temperature is one of the main drivers for climate change and could cause:

• Melting of the ice-caps and cause widespread flooding
• The planet's climate to change. In Britain we could see more stormy wet winters and dry summers, with droughts and other extreme weather patterns becoming more common.
• Many plants and animal species may die out and become extinct simply because they will be unable to adapt to their new environment e.g. Beech trees are tall trees with fairly shallow roots and this shallow root system means they cannot tolerate prolonged hot dry conditions such as those which are likely to be present in a world experiencing global warming.
• Some scientists believe that global warming may alter or change hot water ocean currents that bring hot water from the tropics to the cooler parts of the northern and southern hemispheres. If these hot water currents stop or retreated further south then global warming could actually put large areas of the Earth in an ice-age. e.g. There is a warm water ocean current called the Gulfstream which brings hot water from the Gulf of Mexico to warm the northern hemisphere, including Britain. There is evidence that the amount of hot water carried by the Gulfstream is reducing and it may even stop altogether.
• As carbon dioxide levels rise more of it will dissolve in the ocean. This will acidify the oceans and seas which will have a lower pH. This will harm many aquatic plants and other organisms living in marine environments. Rising sea temperatures can also have dramatic affects on many marine organisms e.g. rising sea temperatures can put enormous stresses on corals, living in coral reefs. The rising temperature stresses the coral and this causes them to expel their algae. This results in coral bleaching where the coral loses their colour. This leaves the coral open to disease and may result in the coral dying. However as the seas and oceans warm their ability to dissolve carbon dioxide decreases; this will ultimately lead to an increase in CO₂ levels in the atmosphere and an increase in the rate of global warming.

How does the Greenhouse effect work?

The Sun emits short wave infrared radiation which provides the warm needed for life to thrive on Earth. This short wave infrared emitted by the Sun is able to pass through the atmosphere and warm the land and oceans. When the hot land and sea cool back down you might expect the infrared (heat) radiation they give off to escape back into space, however they emit infrared radiation of a longer wavelength which certain gases such as carbon dioxide, methane and water vapour trap and stop it from being emitted into space. The end result is that the heat is trapped in the atmosphere - The Earth warms up; this is the Greenhouse effect.

Time to act?

Since the industrial revolution over 180 years ago the average global temperature has risen by about 1.1⁰C. This might not sound like much but many scientists are worried that if the temperature rises by 1.5⁰C then many of the ecosystems on Earth could become permanently damaged; there could be widespread climate change with severe flooding and droughts with more severe and frequent storms/hurricanes/typhoons and the possibility of wide spread impacts on food production and the ability of millions of people to access clean drinking water. Many plants and animals will not be able to adapt or change their behaviour to deal with this new climate and will ultimately through loss of habitat and food become extinct.

Many countries have agreed to cut their emissions of carbon dioxide gas in order to try and prevent further warming. However not all countries have signed up to this pledge, indeed some of the largest producers of greenhouse gases are refusing to cut their emissions in case it damages their economies. At the COP 26 in Glasgow some countries want to delay cutting their emissions until later in this century. With the havoc caused by the Covid-19 pandemic it remains unclear as to how many governments will react in order to revive the economies of their countries. Some campaigners are hoping that a new "world" might emerge following Covid where there could be a green revolution and the accelerated introduction of new greener and less polluting technologies in an attempt to reduce the effects of climate change.

It is important to realise that not everyone agrees that the Greenhouse effect is actually real; there is a small group of scientists and others who argue that the Earth has gone through natural periods in the past where average temperatures have risen and fallen over time. They would say that it is difficult for scientists to model such complex systems as the Earth's weather and climate. This leads to simplified models, opinions and data which not everyone agrees with. As a scientist you should consider all the facts available and not be swayed by the media or accepted opinion, other people and organizations may have their own agenda which they wish to push, which could result in them twisting or distorting the facts. You need to consider all the information from all available sources before making up your own mind!

Key Points

• Human activity such as the burning of fossil fuels, agriculture, food production and many industrial processes are increasing the amounts of greenhouse gases into the atmosphere. Greenhouse gases are gases which trap the infrared radiation (heat) from the sun and prevent it from escaping back into space. Carbon dioxide, methane and water vapour are all good greenhouse gases.
• Rising temperatures due to the Greenhouse effect or global warming can affect the weather and climate of planet Earth.
• Rising temperatures can result in:
• Ice-caps at the poles melting, this will result in sea levels rising and cause widespread global flooding.
• As the planet warms this will lead to weather patterns changing. Some areas will get more rain while others will become drier. There is likely to be more storms, droughts, floods and heat waves. Plant and animal species may become extinct due to the fact they are unable to survive in fast changing habitats.
• Some scientists believe that global warming may even trigger an ice-age.

Check your understanding - Questions on Greenhouse effect and climate change

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