"We had an El Nino episode in the early part of the year that's now faded, but that has contributed to the warmth not only in equatorial Pacific but also contributed to anomalously warm global temperatures as well," Jay Lawrimore, the chief of climate analysis at the NOAA, said.

Severe droughts

There are fears that a prolonged global heatwave will cause severe droughts and harm crop yields.

In Russia, a state of emergency has been declared in 19 regions as temperatures in the capital, Moscow reached a record 37 degrees.

Russia's grain lobby said the country is facing the worst drought in 130 years. Almost 25 million acres of crops in central and European areas of Russia have already been destroyed by drought, according to authorities.

The heatwave in Russia is part of a larger system across much of Europe that is causing crops to wither, forest fires to ignite and road surfaces to melt.

From Russia's Urals mountains to western Germany, a week of temperatures in the mid-30s has baked northern parts of Europe, which are usually spared the heat of warmer Mediterranean regions - and forecasters are warning of more to come over the next week.

This year has been the driest in Britain since 1929 and the use of hosepipes has been banned in the northwest of England.

Authorities in Berlin have reportedly issued a ban on long swimming trunks, claiming they soak up too much water, as throngs of Germans headed to outdoor swimming pools to escape 38 degree temperatures. 

Elsewhere, northern Thailand is struggling with the worst drought in 20 years, while Israel is in the midst of its longest and most severe drought since the 1920s.

'Pretty warm'

In the US, farmers in the Midwest agricultural belt worry that hot temperatures and dry weather could hurt corn and soybean crops.

"It's going to be pretty warm across eastern Nebraska, Iowa, western portions of Missouri, mid to upper 90s [Farenheit]," Donald Keeney, the senior agriculture meteorologist with Cropcast Ag Services, said.

In June, sea ice in the Arctic melted to its thinnest-ever state. The Jakobshaven Isbrae glacier, one of the largest in Greenland, recently lost a three sq km chunk in one of the largest single losses of glacier ice ever recorded. 

But Lawrimore said that it remained to be seen if 2010 would overtake 2005 as the warmest complete year on record.

"This year the fact that the El Nino episode has ended and is likely to transition into La Nina, which has a cooling influence on the global average temperature, it's possible that we will not end up with the warmest year as a whole," he said.