What is the greenhouse effect?

In order to understand what the greenhouse effect really is, we have to begin by answering the question: how have we arrived at the present temperatures on earth?

The graph below explains.

The heat on earth comes from the sun (1). That heat is partly absorbed by the earth itself (2), but a substantial part is reradiated also, into space (3). The heat absorbed is reradiated by the earth as infra-red radiation (4). The greenhouse gases: water vapour, carbon dioxide, methane, nitrous oxide... absorb this infra-red radiation and in turn reradiate it in the form of heat (5).   These gases thus ensure that a considerable part of the heat from the sun remains within the atmosphere after all.

To some extent it works in the same way as a greenhouse: the heat of the sun can come in, while the gases ensure that the stored heat remains inside. Hence the name: greenhouse gases. If we were to lose all that reradiated heat, the average temperature on earth would be eighteen degrees below zero. It is not, however: in fact it is some fifteen degrees above zero.

Together the greenhouse gases do not even amount to one per cent of the earth's atmosphere. Nevertheless minor fluctuations in the amount of greenhouse gases can have major consequences. On the other hand, you cannot just ban the greenhouse gases, for that would cause the temperature on earth to drop. Too much is just as bad as too little, or in other words: tamper with the quantities of those gases, and you are in for trouble. Today one thing is crystal-clear: the amount of greenhouse gases in the atmosphere is increasing. This has been scientifically established (see table 1 for the figures).

Since the end of the 19th century the average temperature on earth has also risen by 0.3 to 0.6°C. Hence the strong suspicion that there is a connection between the greenhouse effect and the temperature increase. However, until several years ago it could not be said with certainty whether global warming was caused by humankind. Indeed, it could also be a purely climatic phenomenon: a kind of natural evolution in the long term. Recent research enables us to state with almost 100% certainty that it is human interference which is changing the global climate. Owing to the emission of greenhouse gases, man is contributing actively to global warming.

This leads to a number of findings.

The first and most obvious finding is: if we want to prevent further warming, we shall have to make sure that the quantities of greenhouse gases do not increase any further.

Second finding: even now there are too many greenhouse gases in the atmosphere, so it is not enough to maintain the status quo: we have to bring about a decrease. This is less evident than it seems, though, considering that most greenhouse gases are granted a long life.

It is quite possible, then, that we are still inhaling the carbon dioxide that was produced when Napoleon's soldiers lit a fire on their march to Russia.

Or: in the year 2190 the carbon dioxide which is coming out of the chimney of your central heating at this moment will still be in the air.

Third finding: if we want to reduce the amounts of greenhouse gases in the atmosphere, we shall first have to find out where those gases are produced, by whom and in what way. Then follows the question how we can avoid that production, or at least reduce it. 

What are the consequences of the greenhouse effect?

As we have seen before, the greenhouse mechanism is an absolute necessity for the survival of the earth. It only started being a problem when an excess of greenhouse gases was generated. In the last one hundred years, this has caused two important phenomena: the average global temperature has risen by 0.3 to 0.6°C, while in the same period the sea level has risen by 10 to 25 cm. The second phenomenon automatically follows from the first one: due to heating, the water in the oceans expands, thus taking up more space, and furthermore the ice of glaciers and the polar ice caps melts.

That rise in temperature and sea level may not appear to be very dramatic, but let us see what the future has in store for us if we simply go on like this.

The short and medium-term effects in Belgium (2000-2020)

A good indicator for the situation in Belgium are the emissions of carbon dioxide (CO₂): indeed, in 1994 that gas accounted for approx. 82% of greenhouse gas emissions. Between 1990 and 1994 CO₂ emissions increased by approx. 6.3%. If no measures were taken, the emission of CO₂ would continue to rise, as is indicated in the table below.

The long-term global effects (2100)

The IPCC (Intergovernmental Panel on Climate Change) - a worldwide forum of some 2,500 scientists and experts organised by the United Nations - has calculated the figures for all greenhouse gases and made a forecast for the year 2100. They have worked out six different scenarios. Each of these scenarios is based on different assumptions about the growth of the world population, the development of the economy, the evolution of technology and so on.

The table below shows the most and the least favourable forecasts of the IPCC:

 Even in the most favourable scenario, there will be an impact on the temperature and on the sea level in 2100, as is shown by the following table:

Thus, the earth will warm up more in one hundred years than it has done in the past 10,000 years. As for the sea level, there is an additional problem: oceans warm up slowly. After the year 2100 this process will probably continue for some time, so that the effect will make itself felt far beyond 2100. That is why the sea level is expected to rise more eventually than the 50 cm mentioned.

The consequences of climate change

In themselves the facts are fairly abstract: an 'average' rise of the temperature by 2°C, a rise of the sea level by 50 cm, but what do these figures mean in actual practice? How will these changes affect our daily lives?

The consequences of the rise of the sea level

It is unpredictable where the effect of the rise of the sea level will be the most tangible, as there are too many unknown elements. Generally speaking, however, there is a big chance that low-lying islands such as the Maldive Islands or atolls in the Pacific will disappear from the map. Elsewhere, harbours, cultural and historical sites by the sea and tourist beaches are in great danger. It is evident also that as the sea level rises, infrastructural works such as dikes, storm surge barriers, etc., will have to be modified.

Swamps and estuaries often play an important part in preventing floods. In addition, they are often characterised by a rich fauna and flora. If due to the rise of the sea level they remain flooded permanently, they will no longer be able to perform that drainage function and the survival of the entire biotope would be jeopardised.

River deltas for many countries are the places where the indispensable food is produced, and they stand a chance of disappearing. The most vulnerable among them are the Amazon, the Ganges, the Indus, the Mekong, the Mississippi, the Niger, the Nile, the Po and the Yangtze.

Finally, floods, storms and tropical cyclones will worsen and thus cause more damage than they do today.

The consequences for agriculture

There can be no doubt that climate change will affect agriculture. The rise of the sea level already has one direct effect: low-lying coastal areas will be flooded and will no longer be useful for agricultural purposes.

Moreover, due to the rise of the sea level the groundwater in coastal areas will become more saline. This means that apart from the risk of flooding, the agriculture in these areas must also fear damage to crops as a result of excess salt.

Besides, it is expected that extreme weather conditions will occur more frequently, involving heavy storms or very dry and hot periods. Also, the present climat zones will move towards the poles: for temperate climates a shift by 200 to 300 kilometres can be expected for every extra degree Celsius. This poses problems for the cultivation of certain crops: indeed, 200 kilometres farther away the soil may not be equally suitable. The terrain can be barren, which may mean that the same crops cannot be grown there. Besides, due to global warming the moisture of the soil will decrease; this in turn has a negative effect on the germination of crops.

Warming also means that summers will have more periods of drought. To get some idea of their impact, we can take the drought of 1988 in the United States as an example. Crop yields dropped by no less than 40%.

The consequences for nature

As has been described in the previous item, the greenhouse effect will cause a shift of climat zones towards the poles.

Even if this shift will not lead to spectacular changes like desertification or flooding everywhere, yet its influence on natural systems will probably be considerable.

Many existing natural ecosystems will no longer be able to adjust quickly enough to changing circumstances and will thus be thoroughly disturbed or may even disappear. There is a real chance that the natural environment (the habitat) of many plant and animal species will move faster than those species can, so that their chances of survival are seriously threatened. Consequently there are great risks that climate change will lead to a reduction of biological diversity.

The impact on the drinking-water supply

Not even considering climate change, we shall inevitably face an increasing drinking-water problem over the next few decades. Not only does the world population grow, but it also consumes more and more fresh water per person. Add to this that the drinking water is ever more highly polluted with industrial waste and manure. All of this results in a decreasing amount of drinking water being available for an increasing number of people. That in itself may cause conflicts, not to mention the fact that the supplies of drinking water are often managed by different countries simultaneously. Plus global warming to cap it all. Higher temperatures lead to more evaporation of the available water, which means less water.

Another additional effect will be felt in coastal areas in particular. Due to the phreatic decline the level will be supplemented with salt seawater. This makes it unsuited for agricultural purposes or household use. Coastal cities or agricultural communities will therefore have to start looking for other sources of fresh water, which are scarce enough as it is.

The social impact

People often tend to talk exclusively about the measurable and visible consequences of the greenhouse effect. However, the political and social consequences will be equally far-reaching.

Firstly, it is a problem which cannot be solved by one country or one government. Climate change is a global phenomenon, which is all the more complex because its effects are different for each and every country. It is almost certain that specific countries will benefit from a climate change, while numerous others will only lose by it. The first group will be far less inclined to tackle the problem than the second. Differences are bound to occur among the losers, too: some will dispose of the money or the means to minimise the impact if not avoid it altogether, others will not...

Secondly, climate change, together with other environmental issues and the phenomenon of the overpopulation, will most probably cause poverty and hunger to increase globally. That will result in an ever stronger tendency of entire populations to migrate to places where there is no hunger and poverty.

Thirdly, there is the present conflict between Northern and Southern nations, which will be accentuated. For now the problem is compounded by the question who has the right to dispose of how much of the fresh water and of the agricultural land.

However, even within one single society on its own climate change will cause problems and material for conflicts. Thus, the health care system will have to adapt to different environmental factors, as will agriculture. Industry and households, too, will need to learn to use water differently - something that cannot be achieved if we do not change our attitude. The risk of floods becomes bigger, as well as the chance of long periods of drought, so that major infrastructural works will need to be carried out. Such works usually entail huge price tags. In some way or other we shall have to think of a solution for all those problems.

Information provided by: http://www.environment.fgov.be