• Europe is suffering under extreme temperatures and fires exacerbated by drought and winds.
• "Yesterday was the busiest day for the fire service in London since the Second World War," Sadiq Khan, the mayor of London, told Sky News on Wednesday.
• Beyond the U.K., firefighters in France, Spain and Greece firefighters are fighting to keep back wildfires.

Europe is suffering under an unprecedented heat wave, leaving firefighters in London dealing with a huge surge in emergency calls.

"Yesterday was the busiest day for the fire service in London since the Second World War," Sadiq Khan, the mayor of London, told Sky News on Wednesday.

On a normal day, the fire service will get 350 calls, Khan said. On a busy day, the London fire service would get 500 calls. On Tuesday, the London fire service received more than 2,600 calls, Khan said. There were 41 properties destroyed in London due to wildfires and 16 firefighters were injured battling the blazes, Khan said.

"It is important for us to recognize that one of the consequences of climate change and these sorts of temperatures that lead to the fires you are seeing," Khan said. "The challenge in London is we have a lot of grass, a lot of green spaces and a lot of that impinges on properties. And when you have not had rain for a long period, when the grass is incredibly dry, fires can start very quickly and spread even faster because of wind and that leads to properties being destroyed."

"A lot of the problems we have here today are a direct consequence of climate change, excess death because of the heat wave," Khan said. "A lot of these problems can be solved by tackling climate change expediently, rather than kicking the can down the road."

Beyond the U.K., firefighters in In France, Spain and Greece are fighting to keep back wildfires exacerbated by heat and dry conditions.

"High temperatures and ongoing drought are two primary factors that contribute to wildfire conditions, and southern Europe has had both of those lately," Alexandra Naegele, a researcher at the Woodwell Climate Research Center, told CNBC.

"Combined with high wind days, these conditions have resulted in the rapid spread of wildfires across the continent," Naegele told CNBC. 

"In the future, this kind of heatwaves are going to be normal. We will see stronger extremes," said Petteri Taalas, the Secretary General of the World Meteorological Organization, part of the United Nations.

"We have pumped so much carbon dioxide in the atmosphere that the negative trend will continue for decades. We haven't been able to reduce our emissions globally," Taalas said in a statement published Tuesday. "I hope that this will be a wake-up call for governments and that it will have an impact on voting behaviors in democratic countries."

The high temperatures have been influenced by a meteorological event called a "heat dome," Alyssa Smithmyer, a meteorologist with weather forecasting company, AccuWeather, told CNBC. A heat dome has been causing the record-high temperatures in western and central Europe, she said.

"A heat dome is a term used when a widespread area of high pressure sits over a region or country and lingers for days or even weeks, trapping a very warm air mass beneath it. An area of high pressure will push air to the surface, and this process will warm the air through compression," Smithmyer told CNBC.

The heat dome conditions make rain unlikely.

"Due to the influence of the high pressure, there is often minimal chances of precipitation or even clouds as the heat dome lingers over a region. As the high pressure lingers over a region for an extended period of time, temperatures can rise to extreme values," Smithmyer told CNBC. "The lack of precipitation or cloud cover will further exacerbate temperatures under these conditions." 

Apart from the heat itself, the high temperatures also bring high levels of harmful ozone pollution, according to scientists at The Copernicus Atmosphere Monitoring Service.

"The potential impacts of very high ozone pollution on human health can be considerable both in terms of respiratory and cardio-vascular illness," Mark Parrington, a senior scientist from Copernicus, said in a written statement published Tuesday.

"Higher values can lead to symptoms such as sore throat, coughing, headache and an increased risk of asthma attacks. The Climate and Clean Air Coalition estimates that ozone pollution causes approximately one million additional deaths per year. This is why it is crucial that we monitor surface ozone levels," Parrington said.