Proponents of the existence of a consensus about human responsibility in global warming based on the position of several scientific institutions and the number of climate scientists involved in the analysis of the IPCC. This consensus has sometimes been questioned by politicians, particularly the United States. But according to a study published in the journal Science by a historian of science, Naomi Oreske, analysis of 928 abstracts of scientific articles selected from a database using the keywords “climate change” and published between 1993 and 2003 shows that none of them challenged the consensus established by the IPCC. In 2005, a British anthropologist Benny Peiser challenged those results in an against-study. He said finding a number of articles denying the consensus. Peiser’s work has been subjected himself to criticism, such as not being limited to articles reviewed by committees of reading or to have improperly classified a number of articles among those rejecting the consensus. In 2006, Peiser admitted that the vast majority of climatologists is agreed with the argument that global warming is caused by human action but that was far from unanimous.

In addition, the United States, a petition was signed by more than 31,000 graduates from all scientific disciplines (more than 500 in atmospheric science and climatology and 9,000 doctors in all disciplines, calling into question the argument that the emission of greenhouse gases would cause a “catastrophic warming. The former president of the National Academy of Sciences, Frederick Seitz has supported this petition. Critics of the petition a point considered misleading which give the impression to potential signatories of an official publication of the National Academy of Science. The specialist in atmospheric chemistry Raymond Pierrehumbert also denounces the fact that the petition was accompanied by an article full of half truths presented as a takeover of an article published in a scientific journal. Finally, some are questioning the number of signatures stressing the impossibility of verification and a few oddities in the list.

In 2008 a report was published NIPCC of (Nongovernmental International Panel on Climate Change), written by Professor Fred Singer, with the collaboration of 24 scientists at the highest level. This report, including a French translation was published, says that this is the kind that changes the climate, not humans, and makes a severe criticism of the IPCC and its methods.

Character exceptional warming

The climate variations knows fair and a number of observers and scientists noted that the current warming is part of these variations.

Thus, a recent warming, the medieval climate optimum, took place in the Middle Ages, followed by a cooling period, the little ice age, leading to major changes in the extent of glaciers. It is believed that they were shorter in 1200 BC today, before rising raw ice between the fourteenth and the end of the nineteenth. Some walkways of ancient Rome are still covered by glaciers.

At the optimum medieval culture of the vine has grown in England. In addition, the Vikings have settled in the same period in Greenland, the name of this country, meaning “green countries in Danish.

In contrast, the arguments for not overestimate global warming based on the fact that on the one hand, the vines grow still in Britain, other than the name of Greenland has been chosen by explorer Erik the Red in order to attract settlers in 5000 and that their settlements were limited to the south of the island. The Histoire_du_Groenland shows that the Vikings were very poorly adapted to their environment unlike Inuit who replaced. The Vikings lived mainly on agriculture and livestock.

Criticism of the hypothesis of an increase in greenhouse

• The impact of human activity on global warming is illustrated by a comparison between the temperatures of weekdays and weekends in 2003, a U.S. study conducted by Forster on 30 years and more than 1,000 stations shows that the temperature of the weekend, 0.5 ° C on average, are stronger than other days of the week. This difference between weekdays and weekends is correlated with the weekly cycle of human activity (high and low this week on the weekend).

• Another argument made by scientists who doubt that human activity is responsible for the warming of the Earth is that the same phenomenon is also observed on Mars, and there is even up to four times faster , but there is no human activity on Mars, which may lead to believe that the cause is the cause of two observations. This hypothesis is however rejected by climatologists support the hypothesis that man, according to them, the causes of Mars are warming to this planet, and in no way linked to an external source, including solar, which would be shared with the Earth. Of warming would also measured 4 on other bodies in the solar system (Neptune, Jupiter, Triton, Pluto)

For Neptune, the explanation comes from its position on its orbit now ( “Summer” Neptunien) Explanation similar Triton. Jupiter is in a period where its giant storms merge, leading to an inability of the planet to more evenly distribute its temperature.Observations on the warming of Pluto are 2, separated by 14 years, and therefore does not draw any conclusion.

• Since 2002, the AQUA satellite of NASA makes accurate measurements of the cycle of atmospheric water vapor, the main greenhouse gas, clouds and precipitation in order to better understand the feedbacks in the evolution of atmospheric temperature. In June 2008, Dr. Roy Spencer (scientist), after analyzing data, concludes that, contrary to models used by various research centers, the atmospheric water makes a strong negative feedback to the greenhouse effect and that the assessment of global warming should be strongly reduced.

• Beginning in 2008, Ferenc Miskolczi, Hungarian physicist, publishes an article in a scientific journal of Hungary, which presents a new model of the “greenhouse effect confined in an atmosphere over semi-transparent.” His study concludes that the influence of greenhouse gases on global warming is overstated by the IPCC and to look for other causes global warming.

Assumption of fluctuations in solar activity