Greenhouse gas emissions combined with the El Nino phenomenon made 1998 the hottest year on average on Earth since the end of the 19th century, followed in descending order by 2002, 2003 and 2004, scientists said Thursday. from NASA.
"We have observed a very clear warming trend over the past 30 years mainly due to the increase in greenhouse gas emissions in 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, quoted on the Nasa website.
The regions of the globe with the greatest temperature increase were Alaska, the Caspian Sea region and Antarctica.
Solar energy retained in the atmosphere by the accumulation of greenhouse gases - especially carbon monoxide from industries and automobiles - combined with the El Nino Pacific Current could make 2005 an even hotter year than 1998, NASA said.
According to the agency, the warming is now such that it affects the seasons by making them permanently warmer.
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 so as to establish an average temperature over the entire surface of the Earth.