Extreme heat and drought disrupt Europe's nuclear power plants and energy supply

A hot and exceptionally dry summer has disrupted Europe's nuclear power plants, prompting governments to take extraordinary measures to keep energy supplies running.

In Romania, the state-owned nuclear power producer Nuclearelectrica on Thursday began disconnecting its sole operating reactor from the power grid due to low water levels on the Danube River — a vital economic artery that stretches 1,770 miles.

That's despite the southeastern European country's government taking some unprecedented measures in recent days, including dredging the channel and sinking rock-filled barges. Romanian naval forces also carried out a controlled underwater explosion on the riverbed last week, seeking to improve water flow to the cooling systems of its Cernavoda power plant.

The two reactors of Romania's one active nuclear power plant, operated by Nuclearelectrica, typically supply about a fifth of the country's electricity.

In Hungary, the government has enjoyed something of a reprieve as rainfall has helped lift water levels on the Danube, allowing it to restart another turbine at its Paks nuclear power plant.

Two of the power plant's eight turbines are now producing electricity again, Hungarian Prime Minister Péter Magyar said via social media on Monday, offering some relief to a facility that supplies nearly half the country's electricity.

In France, where nuclear provides about 70% of the country's electricity, utility provider EDF said Wednesday that it had reduced output at multiple reactors due to environmental issues.

EDF also shut down three reactors at its Gravelines nuclear power plant in northern France earlier in the week due to a "massive influx of jellyfish," triggering automatic preventative measures.

It marked the second successive year that a jellyfish swarm shuttered reactors at the facility, which is one of the largest in the country.

France has reportedly been forced to shut down a record number of nuclear power plants this summer amid a prolonged bout of extreme heat, wildfires and droughts. To be sure, nuclear power plants are often built near rivers or coastlines, so they use nearby water sources to cool their reactors.

European governments are exploring a range of options to mitigate the impact of nuclear power's vulnerability to heat waves and low water levels, such as additional or upgraded cooling systems or scheduling maintenance around periods of extreme heat.

In the U.K., Prime Minister Andy Burnham on Wednesday called a meeting of the government's emergency Cobra committee in response to extreme heat, wildfires and drought.

The move marks the second Cobra meeting this year on heat waves and comes as the country braces for temperatures of up to 38 degrees Celsius (100.4 degrees Fahrenheit) on Thursday.

"I think many would suggest that treating this as an emergency is perhaps a little overdue," Gareth Remond-King, head of international program at the Energy and Climate Intelligence Unit, told CNBC's "Squawk Box Europe" on Wednesday.

"What this extreme heat and all of these knock-on impacts, including the wildfires as well as the drought that's affecting the rivers, what they tell us is that our climate system is in crisis. This is not something that is simply going to pass," Remond-King said.

"This promises to continue not just as we're seeing it this summer but continue to get worse and worse, if we continue to burn fossil fuels, add greenhouse gases to the atmosphere and drive that temperature even higher, then we push the climate system into even greater crisis," he added.

Europe's summer of weather extremes is not just threatening its energy infrastructure. The fallout is also likely to hamper its economic growth.

An analysis published by Dutch bank Triodos on Aug. 8 found that the adverse effects of Europe's searing summer heat could amount to an economic cost of 180 billion euros ($207.7 billion), driven primarily by weaker labor productivity.

This is the equivalent to about 1% of the European Union's gross domestic product, which is exactly the expected level of economic growth for the 27-nation bloc this year.

"The main ways in which heat affects EU GDP are lower agricultural output and higher food prices, constrained energy production and higher electricity prices, transport disruption and increased transportation costs, and reduced labour productivity," Triodos said in the report.