Climate is the weather averaged out over a long period of time. This includes temperature, wind speed and direction, precipitation (rain, snow etc) and humidity. During the year, any given location will experience weather that follows a particular pattern. Every year will be slightly different, but if you take an average of those recorded weather patterns for many years or decades you get climate.
What is Climate Change?
Climate change has come to replace term global warming in the media recently. Global warming was a term used to describe the increase in average temperature of the planet during recent decades, due to man's emissions of greenhouse gasses. It is now realised that the effect of greenhouse gasses is not only to increase the global average temperature, but also to change the climate generally including rainfall and the frequency of severe weather events. Climate change is, therefore, a more accurate description of what is going on.
Climate change as a term is most commonly used to describe the man-made effect on the Earth's long term weather patterns, particularly since the 1900's. However, it is also used to describe changes made by natural events such as volcanic eruptions, the weathering of rocks and photosynthesis.
What is a Greenhouse Gas and what is the Greenhouse Effect?
Greenhouse gasses are those gasses that contribute to the greenhouse effect. The 'greenhouse effect' is a term used to describe how our planet stays warm. The glass in a greenhouse allows light to pass through but prevents the heat from escaping, making the air inside the greenhouse much warmer than the air outside. Greenhouse gasses have the same effect on our planet, letting sunlight in to warm the atmosphere but preventing some of the heat from escaping. The greater the quantity of greenhouse gasses that are in the atmosphere, the warmer the earth becomes.
Greenhouse gasses include carbon dioxide, methane, nitrous oxide and water vapour. You may have noticed that clear, starry nights are often a lot colder than nights with cloud cover. This is because the water vapour in the cloud acts like a blanket to prevent the heat escaping. During the day, the reverse happens as the clouds act like giant mirrors, blocking sunlight and reflecting it back into space before it has had chance to warm the air underneath. Other greenhouse gasses such as carbon dioxide do not condense into droplets to form clouds in the way that water vapour does, so these gasses do not become opaque enough to reflect sunlight during the day. This makes them particularly effective at warming the planet.
If there were no greenhouse effect at all, our planet would about 30°C cooler than it is now. We need a certain amount of greenhouse gasses in the atmosphere to keep our planet's temperature 'just right'. Even a change of only 1°C is enough to drastically change the climate and sea levels. Too much greenhouse gas, however, could heat our planet to such an extent that life as we know it would be impossible. A good example of this is the planet Venus. Although it is further away from the sun than the planet Mercury, the temperature on Venus is hundreds of degrees hotter than Mercury due to its own greenhouse effect (its atmosphere is about 97% carbon dioxide).
99% of the Earth's atmosphere is made up of a mixture of Nitrogen (78%) and Oxygen (21%). The other 1% is made up of other gasses, including greenhouse gasses. 1% doesn't sound like much, but it is this 1% that influences our climate. Argon, Carbon Dioxide, Methane, Water Vapour, Nitrous Oxide, Ozone and Halocarbons are the main constituents of this 1%.
Carbon dioxide is the most talked about greenhouse gas. All other greenhouse gasses are compared to carbon dioxide, using the gas as a base unit to measure the warming strength of other gasses. If you were to look at records of the Earth's temperature going back millions of years and compare it to the record of the amounts of Carbon Dioxide in the atmosphere, you will see that there is a very close correlation between the two. Of the 1% of trace gasses in the Earth's atmosphere, Carbon Dioxide accounts for a larger proportion than any other gas. Carbon Dioxide is therefore thought to be the most important gas in influencing the average global temperature, being responsible for as much as 60% of man-made global warming.
Carbon Dioxide has existed on Earth for the past 4 Billion years. The Earth itself is only 4.6 Billion years old, so the gas has been around for most of the planet's life. At one time, it accounted for up to 80% of the Earth's atmosphere, compared to 0.04% today, and much of the original amount has been removed from the air by plant life. Much of this carbon has been fossilised since then in the forms of coal, oil and natural gas. By burning these materials we are releasing 4 billion years worth of carbon, which had been absorbed by photosynthetic life, back into the Earth's atmosphere in one go.
Carbon Dioxide is released into the atmosphere by a number of natural and man-made processes. Whenever you exhale, you are breathing out carbon dioxide. If a volcano erupts, carbon dioxide is emitted. When a plant dies and breaks down, carbon dioxide is released. Fortunately, the amount of carbon dioxide produced by decaying plants, cellular respiration and volcanic eruptions is almost perfectly balanced by the amount absorbed by plants during photosynthesis (the process of absorbing carbon dioxide from the air, bonding it with hydrogen that has been split from water by sunlight, to make new cells for the plant's growth) and by the surface of the ocean (which absorbs carbon dioxide by dissolving it in the water).
Man made atmospheric carbon dioxide is mostly produced by the burning of the fossil fuels: gas, coal, oil and their derivatives. Unlike natural processes that produce carbon, there is no counter-balancing system to absorb the carbon dioxide that we produce. This means that man-made carbon dioxide continues to build up in the atmosphere over time. Carbon dioxide can stay in the atmosphere for 100 years before it is re-absorbed by plant life, dissolved in the oceans or washed out of the air by rainfall, so man-made carbon dioxide is particularly persistent.
We have come to rely upon fossil fuels and our way of life is largely based upon it. Whenever you plug in an electrical appliance and switch it on, the chances are that the electricity you are using is coming from a coal-burning power station, unless you are signed up to a green energy tariff. When you switch your heating on at home, the chances are it is either gas or oil that is being burnt to heat the water in the pipes. This is, of course, unless your hot water and heating comes from solar panels, ground source heat pumps or geothermal sources as it does in geologically active countries such as Iceland.
Factories, businesses and transport are major users of fossil fuels, either directly or indirectly in the form of a fuel for electricity and heat generation. They are also responsibly for mass deforestation due to their demand for timber and paper, which is another large contributor to man-made greenhouse gas emissions.
Deforestation is a double-edged sword, because not only is carbon dioxide released when trees are cut down, but removing the trees also removes the very thing that absorbs carbon dioxide from the air. More carbon dioxide is produced and less is removed from the atmosphere as a result.
So far, carbon dioxide levels are 30% greater now than they were before the Industrial Revolution and most of this is in the Northern Hemisphere where the majority of fossil fuel burning has occurred. This is expected to rise to 100% sometime between 2045 and 2100.
Water vapour is the biggest contributor to the natural greenhouse effect. Nearly all the water vapour in the Earth's atmosphere is naturally occurring, mostly from the evaporation of seawater. On a cloudy night during winter, temperatures will often stay a few degrees higher than normal. On a clear winter's night, temperatures tend to drop by a few degrees and frost often results. This is a direct example of one form of water vapour in clouds raising the temperature of the air underneath.
The amount of water vapour in the Earth's atmosphere depends on the temperature. Warmer air can hold more moisture, whereas colder air can hold very little. If the planet were to get warmer due to extra greenhouse gas emissions, the air would be able to hold more water, resulting in more water vapour in the atmosphere, which in turn would result in even warmer temperatures. This is turn would further increase the amount of water the air could hold, resulting in even more water vapour in the atmosphere, resulting in even higher temperatures and so on, and so on....
Water vapour in the atmosphere can eventually condense on airborne particles such as dust and pollen into droplets of liquid water to form clouds. Clouds are not purely water vapour. Water vapour is a colourless gas; clouds are a collection of tiny droplets of liquid and frozen water mixed with water vapour and small particles that are light enough to float on air.
Because water vapour eventually condenses, producing clouds, it quickly becomes opaque (meaning it is no longer transparent). The tops of the clouds are able to reflect sunlight back into space, helping to keep the air underneath them cool. A process that cools the Earth by reflecting sunlight back into space is called an Albedo Effect. In the case of an albedo effect caused by cloud cover, it is more commonly known as Global Dimming. It is for this reason that cloudy days are usually cooler than sunny days.
At the moment, man-made water vapour is not contributing significant amounts to the global total, but that could change if Hydrogen Fuel Cells become widely used as they emit water vapour as an exhaust gas.
Methane is a very strong greenhouse gas. It is 21 times more effective than Carbon Dioxide at warming the atmosphere. Fortunately, it exists in much lower concentrations that Carbon Dioxide and it is thought to contribute to 20% of man-made global warming. It also stays in the atmosphere for about 1/10th of the time that Carbon Dioxide does.
Methane naturally occurs in the Earth's atmosphere as a result of the biodegrading of organic material by bacteria. Every time you pass wind, you may be emitting methane. In fact, livestock flatulence is thought to be a significant contributor to atmospheric methane levels. Other factors that contribute to the levels of methane in the atmosphere are agriculture (particularly Rice Paddies), Landfill, Coal Mining, Gas Production, Burning of Biomass, Termites and evaporation from oceans, freshwater and wetlands.
Frozen methane exists below the sea floor in shallow oceans, created by decaying organic matter. It can also be found in permafrost. These deposits are called "Methane Hydrates". During periods of cool temperatures and high pressure, these deposits remain stable, slowly allowing some of the methane to escape. During warmer periods, these deposits can become very unstable, emitting tonnes of methane into the oceans, which then bubbles up to the surface and into the atmosphere. This is what is thought to have caused a sudden 7°C increase in global temperatures, 55 million years ago, although it is believed that the release was due to tectonic plate movements (earthquakes). The warming effect of the Methane lasted about 100,000 years.
Frozen methane hydrates could be used for cheap hydrogen production. The chemical formula for methane is CH4. The C stands for carbon and the H stands for hydrogen. The number 4 means that there are 4 hydrogen atoms (there is only 1 carbon atom) in each molecule of methane. The carbon can be bonded to another chemical, freeing up the hydrogen, which can then be used as a clean fuel. The problem is that, as yet, no process has been developed to safely extract the methane from the frozen deposits in large quantities without making them unstable. At the moment, the best treatment appears to be releasing methane from the permafrost and burning it as it emerges, producing carbon dioxide and water vapour (which are both weaker greenhouse gasses).
Methane is eventually cleared from the atmosphere in 10-12 years. It reacts with a compound of oxygen and hydrogen, called OH radicals. The end product is Carbon Dioxide and Water, both of which are greenhouse gasses. However, only a limited amount of OH radicals exist in the atmosphere and, when these are all used up, methane could remain in the atmosphere for hundreds or even thousands of years.
The quantities of methane in the atmosphere are currently 2.5 times the amount of pre-industrial levels. It may even be cheaper and easier in the short term to concentrate on reducing methane emissions than reducing carbon dioxide emissions.
Nitrous oxide has the greatest potential warming effect of all the greenhouse gases, being 200-300 times more effective at trapping heat than carbon dioxide. There is nearly a thousand times more carbon dioxide in the Earth's atmosphere than Nitrous Oxide so, whilst it has an extreme warming effect, it is not very abundant. It can remain in the atmosphere for 150 years.
Nitrous oxide is produced by the activity of microorganisms, which remove nitrogen from the soil and put it in the atmosphere. It is also released into water by the plant life that lives in the oceans and flooded forests. The Nitrous Oxide gradually makes its way to the surface and on into the atmosphere. Plants absorb nitrous oxide from the air and fix it in the soil as ammonia. This cycle keeps the balance of nitrous oxide constant.
The main man-made source of Nitrous Oxide is through the use of nitrogen-based fertilisers. However, burning biomass and fossil fuels also produces Nitrous Oxide, as do sewage works and water treatment centres.
Since pre-industrial times, the levels of Nitrous Oxide in the Earth's atmosphere have increase by 16%.
Whilst it is known that Ozone is a greenhouse gas, it is not known precisely how effective it is at trapping heat. Ozone is created from oxygen by high-energy ultraviolet (UV) light from the sun. It is instantly destroyed by low-energy UV sunlight and the chlorofluorocarbons (CFCs) contained within aerosols and cooling systems. The Ozone Layer is a thin veil of ozone that exists in the upper reaches of the atmosphere.
Ozone can be created by pollution from the burning of fossil fuels reacting with sunlight. It can be very poisonous at ground level, especially to people with respiratory diseases.
Ozone also plays an important role in protecting us from the sun's harmful ultraviolet rays, due to the way it interacts with them. The ozone layer does exactly this and is too far from the surface of the earth to cause health problems.
Halocarbons are used in cooling and heat exchange systems. The most infamous of these is Chlorofluorocarbons (CFCs), which were banned in 1987 in many countries due to their role in the depletion of the ozone layer. Other types of Halocarbons include Hydrochlorofluorocarbons (HCFCs) and Hydrofluorocarbons (HFCs). The quantity of Halocarbons in the atmosphere is miniscule compared to other greenhouse gasses, but they are 3000 to 13,000 times more powerful than Carbon Dioxide and can remain in the atmosphere for hundreds to thousands of years.
These gasses do not occur naturally on Earth; they are all man-made. HFCs were designed to replace CFCs. They are not as damaging to the ozone layer, but they are just as effective at trapping heat.
Due to the amount of time they linger in the Earth's atmosphere, CFCs will continue to warm the Earth for centuries to come, despite the fact that they are no longer being produced. There are no restrictions on HFCs and their concentrations are rising all the time.
How Much Will the Climate Change?
There is much debate and speculation as to how the climate will change over the next 100 years. Computer models offer the best means of prediction and the BBC is currently running the largest climate change prediction experiment in the world.
In 2001, the Intergovernmental Panel on Climate Change (IPCC) stated that:
"...most of the warming observed over the last 50 years is likely to be attributable to human activities."
They predicted a rise in global temperature of between 1.4°C as a best-case scenario and 5.8°C as a worst-case scenario by the year 2100. However, new research groups are creating new models with more powerful computers all the time. Since then, predictions of a rise in temperature of as much as 12°C have been predicted by the year 2100.
There could be 30% less rainfall and as much as 50% of the world's surface could be covered by uninhabitable desert. Sea levels are expected to rise with the melting of polar ice caps. It is notable that 25% of the world's untapped oil lies in the Arctic Ocean. At present, it would be very difficult to mine this oil, but if the Arctic Ice Cap melts, oil companies will be able to build oil rigs and cash in. The countries around the Arctic Ocean (USA, Canada, Norway, Russia and Denmark) are already fighting over who owns the seabed and, therefore, the drilling rights.
Predicting how the climate will change is vital so we can plan for the future and take appropriate measures to reduce the amount of change.