Aquelques days of the new intergovernmental (expert group) IPCC report on climate change, it is useful to take stock of the analyses and the deductions updated by the scientific community. Climatologists, oceanographers, biologists, physicists, biogéochimistes, glaciologists, ethnologists now converge to accuse the greenhouse effect to disrupt the planet. If it will take a few more years to rigorously prove the responsibility of the human, this convergence of observations and modelling throws the last doubts in the vast majority of researchers. Some indicators are attributable to global warming, others show strong coherence with the phenomenon, but their multiplication is a clear signal. Researchers do not hide their theories may underestimate complex phenomena. But a few feedbacks tested models will in the sense of an amplification of global warming. Uncertainties relate more to the State of the climate but on predictions for the future.
What role plays the effect
The greenhouse effect is essential on Earth: the atmosphere was composed of oxygen and nitrogen, without greenhouse gases, the temperature of the planet would be 18 C on average. The problem is that the concentration of greenhouse gas exploded: since 1750, the concentration of CO2 has increased by 30, that of methane has doubled. The current atmospheric carbon, 380 ppm content (i.e., 380 cm cubes per cubic metre of air), has not been reached since millions of years. Equivalent variation rate dates back to 20,000 years. One half of the CO2 in the atmosphere stays, the other is taken over by vegetation. These greenhouse gases block received reflection from the Earth to the space of the thermal energy of the Sun. Direct result, the Earth's temperature has increased by 0.6 C in a century. Such warming is not unprecedented: during the Cretaceous period 100 million years ago, was 6 C more than today ' today. But the interglacial transitions occurred over longer periods.
The atmosphere responds quickly, between a few days and a few years. The oceans, a contrario, operate on a few thousand years. The vegetation adapts to changes in a few tens, even hundreds of years.
How to react
Ocean level rises of 3 millimetres per year currently. This expansion of the seas comes their warming and the melting of the polar and mountainous glaciers. The effect is severe: the height of the seas has ranged from 10 to 20 centimetres over the past century against more than 100 meters the last million years. At the height of the last glaciation, the level of the oceans increased one metre every twenty years.
What is the impact
on the ice
About 90 of the glaciers are shrinking. They accuse of deficits for mass for fifty years, in the Alps for one hundred and fifty years (less snow in winter, warmer in the summer) and the extent of sea ice decreases: the pack ice of the Arctic loses 15 to 20 percent of its ice during the summer. The satellite "Grace", spilled into the Atlantic by the Greenland ice volume has almost doubled over the past five years. The direct link with the global warming is not established but becomes more and more convincing. It also notes that permafrost (soils and subsoils perennially frozen) begin to melt. The balance sheet is more blurred on the Antarctic, best protected by its temperatures below 30 C. Some of its coasts and its peninsula lose their ice. The East coast on the other hand have more precipitation. These data come from measures, modelling of glaciology are yet to their stages.
What are the reactions of the living world
Since 1990, malaria spread, a first case arrived in Corsica last year. Dengue is developed and has appeared in more than 1,500 metres above sea level. Bird migration patterns are disturbed and some populations are already in reduction as the Flycatcher black, missing 90 Netherlands in 20 years.
Seedlings, the grape harvest and harvest are increasingly early. The harvest of wheat in France was brought forward three weeks in a few decades. Corn was able to make its full cycle in the North of the France. The exhibit of winters causes delays flowering, or even flower necrosis on fruit trees.
Forest buds with ten days in advance in the spring from the 1950s. Foresters have measured trees of 30-40 productivity gain, due to the greenhouse effect, nitrogen rain can also explain it. New clues suggest parallel a Browning of the forests, sign of deterioration of their health. Some species such as FIR already suffer increases temperatures and drought.
In the North of the Canada Inuit, found that bears have become scarce. The melting of ice around their houses causes the development of fungi, source of toxic fumes in the housing.
What is the impact
Scientists argue a "likely increase" heavy rains in the mid and high latitudes of the northern hemisphere, a slight increase in heat waves and cold waves decrease. The rise in the frequency of drought beginning to be close to warming. Since 1995, Atlantic cyclonic activity increased clearly but debate remains however very open about its origin.
t it in France
The average temperature increased France of 0.9 C on the century. Its climate is moved from 200 kilometres to the North. At Rennes, it freezes on average 20 days less. And Besançon, there are seventeen additional days during which the temperature exceeds 25 C. Vegetative growth of plants to Nancy has increased by one month. The duration of the period of Montluçon pollen allergy has increased from ten to twenty days of 1989 to the present.
What is the human responsibility
The climatologists have shown that a warming similar to that of the 20th century has occurred in the prehistoric past, in the absence of the man. There is no evidence in the scientific sense of current liability but a beam of convincing evidence. To measure the part of the natural warming of the anthropogenic part, researchers have multiplied simulations of scenarios of climate drift in the 20th century. Even with plausible changes in sunlight, of the effect of aerosols, etc., models are the observed climate data that by integrating human releases. To the doubts scientists have sought other indices. Geochemists brought an inevitable argument: the carbon dioxide in the atmosphere from human activities has a special isotopic composition distinguishes the natural carbon. In its geological burial, he lost almost all its carbon-14. Several measurements showed that in the 20th century, the atmosphere has been more in addition to poor CO2 carbon 14. We have seen for example in the isotopic composition of tree rings.
Today, climatologists believe that natural variability and human impact are of equal importance, but they expect to see the anthropogenic signal appear increasingly more clearly. The responsibility for economic development is little dispute: a US citizen emits 5.5 tons of carbon per year, an Indian 300 kilos.