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GLOBAL WARMING or climate change

If it were only a few degrees that would be serious, but we could adapt to it. But the danger is the warming process might be unstable and run away. We could end up like Venus, covered in clouds and with a surface temperature of 400°C.
Stephen Hawking, physicist

I'm more worried about global warming than I am about any major military conflict.
Hans Blix, Head of UN Nuclear Inspections in Iraq.

The greenhouse effect

The greenhouse effect is a natural phenomenon without which the average temperature of the earth’s surface would be about -18°C instead of the more hospitable 15°C; the greenhouse effect could be likened to a huge duvet that helps the earth protect us from extreme cold.

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Humans are causing the earth’s temperature to rise

Climate change is due to an increase in the concentration of greenhouse gases in the atmosphere that began with the industrial era.

Since about 1850, humans have been releasing increasing amounts of greenhouse gas into the atmosphere largely through the burning of fossil fuels (coal, petrol and gas), an activity that lies at the heart of the industrial development that is the cornerstone of our modern existence. This augmenté in greenhouse gas concentrations in the atmosphere has also enhanced the greenhouse effect; our duvet has thickened, and instead of protecting us from the cold it is beginning to make us too hot.

Since 1850 the average global temperature has risen by 0.6°C and in France by 1°C. The process is accelerating: the 7 hottest years ever recorded occurred in the last 10 years.

 Changes in average temperatures in Metropolitan France since 1901 (Source Météo France – ONERC)

The curve shows changes in yearly average temperature represented by variations in relation to the mean in Metropolitan France 1971-2000.

The rise in average temperature is clear, 2003 being the hottest year.

The curve showing changes in the average global surface temperature - not just in France - looks roughly the same.

How severe is 0.6°C?

Because we are used to temperatures ranging from -5° in winter to 25° in summer a rise in temperature of 0.6° might not seem so severe.

It is probably easier to appreciate if we consider our own body temperature: at 37°C we feel normal, at 39°c we feel distinctly less normal, at 42°C we are quite simply… dead!!

0.6°C might still not seem very severe, and yet it is a sign that greater changes are taking place, changes the consequences of which might be more severe for the planet than we think.

Scientists have only relatively recently begun observing the effects of climatic disturbance.

What is the situation in France today? 

French climate scientists are currently studying the effects of global warming on temperature: summers are becoming hotter and there is less frost in winter; there are more droughts in summer, and rainy periods last longer, all of which in turn affects natural areas, the flora and the fauna.  

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What is the outlook for the future?

Scientists have developed computer models that enable them to project the climate of the future. According to predictions based on these models by 2100 the earth’s temperature will have risen by somewhere between 1.4 and 5.8 °C.

The inaccuracy of these estimates are 50% due to human activity (the higher/lower our CO2 emissions the greater/lesser the increase in the greenhouse effect and the rise in the earth’s temperature), and population growth, and 50% due to the imprecision of climatic projections.

Prediction of average summer temperatures in France until 2100

This simulation corresponds to an average prediction by climate forecasters (denominated A2).

Source : Institut Pierre-Simon Laplace, 2001

On notera en particulier que l’été 2003 correspond à un été moyen en 2075…

It is particularly worth noting that the temperature for the summer of 2003 corresponds to the average predicted temperature of a summer in 2075…

An increase of between 1.4 and 5.8 °C might not seem so drastic either. A comparison with the past might prove helpful here. Incredible though it may seem, during the last ice-age the earth’s average temperature was only 5°C

Similarly, computer models projecting what France’s climate might be like by the end of the 21st century developed by the French Met Office (Météo France) predict a markedly hotter and drier climate:

  • Temperatures typical of Brittany and the Atlantic coast will be experienced countrywide in winter
  • In summer temperatures typical of the Côte d’Azur will apply to most of the country, except in the Côte d’Azur itself which will feel more like North Africa . 
  • Precipitation levels in Brittany and the Atlantic coast will resemble current precipitation levels in Barcelona .

The idea of Lille becoming more like Nice might seem desirable to some. However, olive groves replacing sugar beet and wheat fields in the space of less than 100 years is unlikely to be the only disruption to our way of life, and the accompanying effects promise to be far less desirable than an all year round holiday on the Côte d’Azur!!

More reasons for reducing CO2 emissions 

Another major disadvantage of greenhouse gases is how long they stay in the atmosphere: the average lifespan of carbon dioxide (CO2) is 125 years; of nitrous oxide (N2O) - which warms the climate 10 times more than CO2 - 150 years, and of fluoride gases - which warm the climate 16.000 times more than CO2 - about 120 years. In other words when we drive for 30 minutes to go to work or take a two hour flight to Morocco on holiday we are emitting CO2 that will be warming the climate for 125 years!

What can we do to reduce our emissions?

Greenhouse gases

The main greenhouse gases and the human activity responsible for their emission:

  • Carbon dioxide (CO2) is produced by the combustion of fossil energy (coal, petrol, gas) and the cement industry
  •  Methane (CH4) derives largely from livestock farming, paddy fields, landfill sites and oil and gas fields. 
  •  Nitrous oxide (N2O) is produced by nitrogenous fertilizers and other chemical techniques.
  •  Fluoride gases (HFC, PFC) are the propellants used in aerosol cans, air-conditioning systems, the manufacture of foam rubber, computer components, and in aluminium smelting.
  •  Sulphur hexafluoride (SF6) is used in electrical applications such as high voltage transformers, and between the panes of glass used in double-glazing.

 Unlike CO2, CH4 and N2O, which are also by-products of the natural cycle of water, air, animal and plant life, SF6 and the fluoride gases are entirely by-products of industrial activity.

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The greenhouse effect

The earth receives all its energy from the sun. Some of this solar energy is radiated off the earth’s surface back into space, and some of this radiated heat is trapped by the greenhouse gases in the earth’s atmosphere. Ninety-five per cent of this natural greenhouse effect is caused by water vapour and carbon dioxide (CO2), and 5% by other gases also naturally present in the earth’s atmosphere, by methane (CH4), nitrous oxide (N2O) and ozone (O3). The phenomenon has been in existence for millions of years, and without it Earth would not enjoy the hospitable temperatures to which we are accustomed.

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Greenhouse gases on the increase

Atmospheric concentrations of CO2 have increased by 30%, methane concentrations have more than doubled, nitrous oxide concentrations have risen by about 30%, and hitherto non-existent industrial greenhouse gases have been introduced into the atmosphere.

Increase in atmospheric concentrations of greenhouse gases since 1000 AD (IPCC, 2001).

Results come from analysing air bubbles measured in the ice (Blunier et al., 1993; Etherigde et al., 1996; post 1958 results from direct measurements.)

During 400,000 years the average temperature of the earth’s surface and atmospheric concentrations of CO2 evolved at a very similar rate :

Changes in CO2 concentrations (top graph) and atmospheric temperatures (bottom graph) over the last 400,000 years.

This data comes from studies of Antarctic ice in Vostok. The concentrations are expressed in parts per million. (Source : J.R. Petit, J. Jouzel, et al. Nature n°369, 3 June 1999 )


In the first of the curves shown in the three graphs, CO2 concentrations have reached about 360 ppm, or 30% higher than at any time during the last 400,000 years!!

If this rate of increase continues CO2 concentrations will have reached 780 ppm by 2100.

Thus we are releasing much higher levels of CO2 into the earth’s atmosphere than ever before and creating an imbalance we may be unable to redress.

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Climatic disturbances:

Over the course of the 20th Century climate scientists have observed the following changes (IPCC report, 2001):

  • A 0.6°C increase in the earth’s surface temperature.
  • A 5 to 10% increase in rainfall in the northern hemisphere.
  • A 3% decrease in rainfall in northern and western Africa .
  • A 10% decrease in snow cover since the late 60’s, and receding glaciers.
  • Ice-melt on lakes and water courses in the high and mid latitude areas of the northern hemisphere 2 weeks earlier.
  • In the last few decades a 40% decrease in the Arctic ice mass between late summer and early fall.
  • A rise in sea level of 10-20 cm.

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In France : the French scientific community made the following observations :


  • Since 1900 average temperatures in France have risen by 0.6°C - 1.1°C depending on the area (map supplied by Météo-France, Direction de la Climatologie). 


  • All Alpine glaciers studied have decreased in volume since 1900.

    Variations in average thickness of 4 Alpine glaciers (in metres of water)

    The triangles represent measurements, and the solid-line curves the results of the numerical model.

    (Source : Adapted from Vincent, Journal of Geophysical research 2002, documents by the Laboratoire de glaciologie et géophysique de l’environnement – CNRS)

  • Since 1600 the Bosson glacier in the Alps has receded about 800 metres, and the Argentière and the Mer de Glace by about 1,200 metres.

    Variation in length of 4 Alpine glaciers since 1600

    (Source : Laboratoire de glaciologie et géophysique de l’environnement – CNRS)

Vines and fruit trees

  • At Châteauneuf-du-Pape and Tavel the grapes crop nearly a month earlier than they did fifty years ago.

  • Varieties such as the Grenache or the Syrah grapes that were well adapted to local climate conditions in the Avignon region up until 1985 are now almost unsuited to it.

    Changes in climate type in the Avignon region
    The graph shows changes in the Huglin index of the Avignon vineyards since 1965. This index illustrates adaptations of grape varieties to particular local climates.

    After about 1985 a clear change appears, and Avignon changes from a ‘temperate-hot’ climate to a ‘hot’ climate. The year 2003 is particularly noteworthy.

    Changes in the Huglin index mean that grape varieties such as the Grenache or the Syrah grapes that up were well adapted to the local climate conditions in the Avignon region until 1985 are now almost unsuited to it.

    The same phenomenon has been recorded in the Dijon region which has changed from a ‘cool climate’ to a ‘warm climate’

    (Source : CNRS) 

Fruit and vegetables

  • Fruit trees in the Rhone Valley now crop 1-3 weeks earlier than they did 30 years ago.
  • Williams’ pear trees now crop 2-3 weeks earlier than they did 40 years ago

    Changes in cropping of Williams’ pears trees in 3 different areas: Bergerac, Angers, Saint-Epain (Tours).

    Sources : J.M. Bore, INRA Angers ; C. Lavoisier, la Morinière ; M. Peschescot, domaine de Castang.

    Earlier cropping can be disadvantageous to trees as it places them to out of sync with other natural cycles, and can endanger their health.

  • Des espèces comme l’abricotier ont montré, dans le sud de la France, des symptômes de dérèglement physiologique liés au manque de froid (Liennard 2003).


  • In the south of France species such as the apricot tree have shown signs of physiological stress relating to lack of cold (Liennard 2003).

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What France’s climate might be like by the end of the 21st century:

Maps showing simulated computer projections of France’s climate now and in 2100
They correspond to the average scenario envisaged by climate forecasters (scenario A2
(Source : Météo France - Michel Déqué)

Average temperature in winter (°c) 

Present climate (left) and climate in 2100 (scenario A2)

Average temperature in summer (°c)

Present climate (left) and climate in 2100 (scenario A2)

Average rainfall in summer (°c)

Present climate (left) and climate in 2100 (scenario A2)

Probability of summer temperatures exceeding 35°C  

Period 1961-1990 (left) and period 2071-2100 (right)

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