Global warming is the major cause of the recent extreme weather in the Northern Hemisphere, according to Sun Chenghu, a researcher with the National Climate Center (NCC).

Extreme weather has plagued America and European countries during late June and early July. In the US, a rare persistent heat wave has killed at least 30 people with temperature hitting 40 C in some places. Since July, the UK, Russia, and Germany have been struggling against severe flooding which has claimed at least 140 lives.

The NCC found temperatures in the Northern Hemisphere have been generally higher than normal since July, especially in North America. There has been a 2 degree higher-than-normal temperature observed on America's Eastern Seaboard. And in parts of the south, temperatures 6 degrees above normal temperature have been witnessed.

Rainfall has also been unevenly distributed. North America saw less than normal rain while it increased by 30 percent in Europe. The rainfall in Russia has doubled normal levels since July 7, according to the NCC.

Sun said the hot weather and rainstorms, a reflection of abnormally atmospheric circulation, should be understood against the backdrop of global warming.

Global warming rates differ in high and mid-and-low latitudes, leading to different depths of atmosphere. This slows the west wind and weather system in North America and mid-and-low latitudes, providing conditions for extreme weather.

For the case in America, when a high pressure ridge dominates weather system, it will be hot and this will usually last one week. However, this time, it is rare to see the high pressure ridge controlling the weather system for such a long time and across large regions, said Sun.

At the same time, the low pressure system has controlled the weather system over Europe, leading to severe rainstorms. This comes as a result of abnormal distribution of surface temperatures in the North Atlantic Ocean.

Source: By Zhang Yong and Sun Nan of China Meteorological News