As Scotland sweltered in record atmospheric temperatures last week marine scientists were investigating the rise of a lesser-known but equally life-threatening heatwave.

Ocean heatwaves are a phenomenon which have, in recent years, led to the death of a mass of marine life in warmer climes.

Now colder countries like Scotland are facing up to the impending threat of this

silent killer, which occurs when water temperature is in the top ten per cent of the expected level for several consecutive days.

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Professor Mike Burrows, from the Scottish Association for Marine Science in Oban, is currently analysing data on global sea temperatures, with an international group of researchers, to determine the impact that ocean heatwaves can have.

Professor Burrows, 58, said: "We have been having this atmospheric heatwave, the weather drives heatwaves on land and everybody is talking about the weather at the moment because it has been so warm, but people can't see what is happening in the oceans, where currents drive heatwaves."

The number of ocean heatwaves has doubled in the last four decades. Professor Burrows said: "In the early 1980s the average was about two ocean heatwaves globally a year but in the last five years it's about four a year, they are becoming more frequent and more intense. In the early 80s, they lasted ten days, but now they are expected to last 20 days."

The marine ecologist is a member of a group of researchers from Australia, Canada, America, England, Spain and Scotland, currently investigating the subject.

The researchers have held regular virtual meetings by skype, over the last four or five years, discussing sea temperature data from around the globe and members have also met in Australia, Thailand and Plymouth.

The best-documented instance they have worked on occurred in the west coast of Australia in 2011, when ocean temperatures were the highest ever logged for the area.

These prolonged high sea temperatures caused the first-ever recorded bleaching on the World Heritage Ningaloo

Reef, resulting in the mass death of economically important fish species.

Professor Burrows said: "Seaweed around Perth, on that stretch of the coastline, died back and there was also a massive invasion of tropical fish, it was a massive change. Heatwave impact can be dramatic, things die in dramatic fashion."

He added that if a relative sea temperature rise occurred in Scotland, marine life used to living in cold water would definitely suffer.

The professor said: "At the end of May, beginning of June, last year it was quite hot here and the local sea temperatures were two to three degrees above what we would expect, the ocean did get warm.

"In Scotland, ten weeks of 4 to 5 degrees above normal sea temperature would mean big changes happening quite quickly.

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"The thing about heatwaves is they are a dramatic and immediate manifestation of climate change."

He added: "Short term heatwaves, when the water gets warm, can be bad for things like salmon farming."

Some species of fish can escape to deeper cooler water but Profesor Burrows said that cold-water fish,

like cod, could be the first casualty of a UK ocean heatwave.

He said: "Scotland hasn't had a really bad heatwave yet, but as heat becomes more intense the possibility increases and when it happens it's too late to stop it. Our heatwaves are increasing in frequency and intensity,

"Last summer those periods of higher than normal temperatures were getting longer and more frequent."

He added that there is evidence of some fish species moving north, mackerel shoals, for example, are moving to Iceland.

He said: "It's like an earthquake, it all works well before the earthquake happens. If we had 5% increase in Scottish water temperature it might have a detrimental effect and a significant impact on the species out there.

" If you are a sea angler there would be changes in the fish you are catching if you are a fisherman and you rely on a type of shellfish you would definitely be affected.

"Other species will come to replace things if the temperature changes. The next fifty years will be more about change, adapting to new climates."

The professor warned: "The worst is yet to come, where we have had really bad heatwaves elsewhere in the world impacts are immediate and dramatic.

"That's why looking at heatwaves across the globe is important, because we need to understand what will happen if a really big one happens."

The results of the group's work is being published in academic journals and is being sent to the IPCC (Intergovernmental Panel On Climate Change)

Professor Burrows said: ""We will obviously have to adapt to these things. The more these events occur fishermen may have to change

the sorts of fish they are fishing, but definitely, it's about cutting greenhouse gases and if we can reduce our carbon footprint.

"There is nothing we can do to stop this happening, apart from governments, desperate times need desperate measures.

"The more we look for the effects and the impacts of climate change the more we find - and the trends at the moment show no sign of slowing down.

It only reinforces the need for the government and society to take control of this problem. Renewable energy would be a good thing,

stop burning fossil fuels and potentially be self-sufficient in terms of energy."

He added: "If we don't do anything about it now our children will blame us and they have every right to be angry, while we are driving our big cars and waste these resources for future generations, it's a real issue.

"Ultimately we will be forced to change our lifestyles, the impact will be so great. Sea levels will rise and big cities next to oceans are going to have to spend a lot of money to keep the oceans out."