Parts of Europe, Asia and North America were preparing for record heat with health warnings and evacuations.

Across Europe, Asia and North America governments were preparing for record heat with health warnings and evacuations.

Europe could record its hottest-ever temperature this week on Italy’s islands of Sicily and Sardinia where a high of 48 degrees Celsius (118 degrees Fahrenheit) is predicted, the European Space Agency (ESA) said.

Here is what you need to know:

What is a heatwave?

A heatwave is an extended period of higher-than-normal temperatures relative to what is expected at that time of the year.

What is the effect of heatwaves on humans?

Heatwaves can lead to several illnesses, including exhaustion, heatstrokes and even death.

Increased intensity of heatwaves has been linked to cardiovascular and respiratory diseases. Those who remain most vulnerable to scorching temperatures are outdoor workers, the elderly, and children.

What is the reason behind the heatwaves?

Environmentalist Anjal Prakash says global warming – as a result of the burning of fossil fuels – played a major role in the extremely high temperatures witnessed globally.

“As we put more and more carbon in the world’s atmosphere, the Earth’s temperature has warmed by about 1.16 degrees since the pre-industrial age,” Prakash, who has previously worked with the United Nations Intergovernmental Panel on Climate Change (IPCC), told Al Jazeera.

“The carbon dioxide that builds up in the atmosphere … traps heat, leading to what is also known as the greenhouse gas effect – the Earth acts like a greenhouse where heat gets entrapped inside,” he added.

This phenomenon, Prakash said, was “disrupting” many interconnected systems in Earth’s environment, leading to many catastrophic consequences for human beings.

July 4 was recorded as the hottest day ever globally, according to data from the US National Centers for Environmental Prediction.

The average global temperature reached 17.01C (62.62F), surpassing the August 2016 record of 16.92C (62.46F) as heatwaves sizzled around the world.

Which countries are affected by extreme temperatures?

In Europe, countries such as Italy and Greece are witnessing scorching temperatures, with authorities sending out warnings to the public to take caution when outside.

Sicily and Sardinia could wilt under temperatures as high as 48C (118F), the ESA warned, and “potentially the hottest temperatures ever recorded in Europe”.

On the Spanish island of La Palma, firefighters were busy this past weekend battling a blaze which burned 5,000 hectares (12,355 acres), forcing the evacuation of 4,000 people.

Across the Atlantic, the US National Weather Service warned a “widespread and oppressive” heatwave in southern and western states was expected to peak, with more than 80 million people affected by excessive heat warnings or heat advisories.

Southern California is fighting numerous wildfires, including one in Riverside County that has burned more than 3,000 hectares (7,500 acres) and prompted evacuation orders.

In China, a remote township in the northwest region, a relatively arid part of the country, endured temperatures of more than 52C (126F) on Sunday.

Prolonged bouts of high temperatures in China have challenged power grids and crops, and concerns are mounting of a possible repeat of last year’s drought, the severest in 60 years.