Extreme heat grips Northern Hemisphere on summer solstice

SINGAPORE (Reuters) - Extreme heat across large tracts of the Northern Hemisphere raised fears for crops in China, fuelled forest fires in Portugal and Russia's Far East, forced flight cancellations in the Southwest U.S., and melted tarmac on roads in Britain.

As Wednesday marked the summer solstice - the longest day of the year - forecasters said temperatures in Paris were expected to hit 37 Celsius (100 Fahrenheit), Madrid could see 38C, and London was set for 34C with warnings of thunderstorms.

Children play at a water fountain on a hot day in Singapore June 21, 2017.

Rounding up the record temperatures set in the past two months, the World Meteorological Organization (WMO) said the Earth was experiencing "another exceptionally warm year" and the heatwaves were unusually early.

"Parts of Europe, the Middle East, North Africa and the United States of America have seen extremely high May and June temperatures, with a number of records broken," the WMO said late on Tuesday.

The trend seen during the past two months has put average monthly global temperatures among the highest ever recorded since data began to be collated in 1880.

Even before this month, U.S. National Oceanic and Atmospheric Administration (NOAA) data showed Europe, the United States and Northeast Asia - including eastern China, Japan and South Korea - had experienced unusually warm weather between March and May.

In China, the world’s top grain producer, hot and dry conditions in the main corn belt have delayed plantings and stunted crop development, especially in the province of Liaoning where soil moisture levels are at their lowest in at least five years.

Thomson Reuters Eikon data shows that precipitation in Liaoning for the past month has been between 40 and 60 percent below the seasonal norm.