Environment pressure group Friends of the Earth Scotland says the average monthly temperature was 12.9C, nearly half a degree above the previous hottest records for the same quarter in 2014 and 2006.
The average monthly sunshine for May, June and July 2018 was 212.1 hours; May was the hottest and sunniest May “ever”, June was the third warmest and fifth sunniest June “ever”, and July was the fourth warmest and eighth sunniest July ever.
Friends of the Earth Scotland’s Director Dr Richard Dixon said: “Heatwaves like these threaten to kill thousands every year in the future.
“With record temperatures, widespread wildfires and continuing droughts around the world, this summer has been a wake-up call on climate change.
“Scotland has seen crops wilting in fields, trains running at reduced speed and water shortage warnings, while other countries have seen much worse, including hundreds of deaths.
“Holidaymakers died on the beach in Greece, California looks set for another record-breaking fire season and temperatures in Spain and Portugal were forecast to reach above 45C.”
He added: “The weather is sending us very clear signals that our climate is changing in major ways.
“As records break we enter new territory for the planet and we should be worried.
“Some extra summer heat is no doubt welcome for many but the bigger picture is of bigger storms, more floods and more severe heatwaves.
“To avoid the worst consequences of climate change, we need to reduce the climate emissions from transport, industry and farming as rapidly as possible.
“With a new climate bill already in the Scottish Parliament we need politicians from all parties to set tougher targets and put in place the policies that will move us rapidly towards a fossil-free Scotland”.