Greenhouse gas emissions combined with the El Nino phenomenon made 1998 the warmest year on average on Earth since the end of the 19th century, followed in descending order by 2002, 2003 and 2004, scientists said on Thursday. of NASA.
"We have observed a very clear trend in warming over the past 30 years mainly due to the increase in greenhouse gas emissions into the atmosphere," said James Hansen, climatologist at the Goddard Institute at Nasa for space studies.
In 2004, the average global temperature of the Earth was 14 degrees Celsius (57 degrees Fahrenheit), which is 0,48 ° C (0,86 ° F) higher on average than during the period from 1951 to 1980 , according to Mr. Hansen, cited on the NASA website.
The regions of the globe with the highest temperature increase were Alaska, the Caspian Sea region and Antarctica.
The solar energy retained in the atmosphere by the accumulation of greenhouse gases - in particular carbon monoxide coming from industries and cars - combined with the current of the Pacific El Nino could make 2005 an even warmer year than 1998, said NASA.
According to the agency, warming is now such that it affects the seasons by making them warmer permanently.
To determine whether the Earth is warming or cooling, scientists are raising temperatures at several points on the ground (by weather stations) and at the ocean surface (by satellite).
They then calculate the median temperature to establish an average temperature over the entire surface of the Earth.