San Francisco Frontiers - A roundup of the extreme heat hitting the globe

Here is a roundup of the prolonged spell of extreme heat scorching millions around the globe.

- Wildfires, closures in Greece -

Greece said Thursday that archaeological sites, including the Acropolis, will be closed during the hottest hours of the day due to a new heatwave.

The nation is preparing for further high temperatures until Sunday, with peaks of 43 degrees Celsius (109 degrees Fahrenheit) expected in the centre of the country on Thursday.

As Greece announced the restrictions, firefighters were still battling wildfires west of Athens, which have so far burned thousands of hectares (acres).

- Spain's 'hellish' heat easing -

In Spain, the heat peak has passed, but temperatures remained high overall on Thursday, with readings above 25C recorded at 120 of the 900 stations in the official meteorological network.

The mercury did not fall below 30C in southern city of Malaga during a night described as "hellish" by the meteorological services -- heat exceeded 39.5C by Thursday morning.

Temperatures in excess of 35C were forecast across the southern half of the country, leading authorities to warn of "very high to extreme" risk of fire.

Lloret de Mar, a popular tourist resort, is seeking ways to conserve its increasingly-sparse water supplies by switching off beachfront showers.

"It's a shame because it was nice to shower off," said Jonas Johanson, a 28-year-old tourist from Denmark.

- Hot nights, fire fears in France -

The heatwave left southeastern France facing increased risk of wildfire, but the situation could improve somewhat on Friday.

During the day, parts of southern France were experiencing temperatures often in excess of 35C -- and up to 40C in some areas.

Authorities have raised a fire alert for Thursday and Friday for several parts of the southern coast, where the persistence of heat even after sundown heightened the risk to health.

- High risk for US homeless -

Phoenix, like much of the US southwest, is surrounded by desert, and its 1.6 million residents are accustomed to brutal summer temperatures.

But this year's heat wave is unprecedented in its length: it has already helped the city break its previous record of 18 straight days at or above 110 degrees Fahrenheit (43 degrees Celsius), with similar highs forecast into next week.

With its population growth among the highest in the United States, coupled with a lack of affordable housing, Arizona has seen the number of homeless people go up 23 percent in recent years.

The World Health Organization said this week that the extreme heat in the northern hemisphere is putting an increasing strain on healthcare systems, hitting those least able to cope -- including the homeless.

- North Africa blazes -

A border crossing with Algeria had to close temporarily, according to Tunisian officials who confirmed 470 hectares (1,100 acres) of forest were burned, and that firefighters and an army helicopter were battling flames.

The Mediterranean region was ranked as a climate-change "hot spot" by scientists, with the United Nations' Intergovernmental Panel on Climate Change warning of more heatwaves, crop failures, droughts, rising seas, and influxes of invasive species.

B.Turner--SFF