New data showing that the US had its 12th-hottest summer on record may not, at first glance, appear particularly significant or alarming.



But in announcing the news, climate scientists have pointed out that, of the 11 American summers that were recorded as warmer than 2015’s, seven have occurred in the last 15 years; the other four were all during the “Dustbowl” 1930s heatwaves that plagued the US during the Great Depression.

And, as part of the climate warming trend globally, next Thursday a federal agency is set to announce the latest worldwide figures that are likely to show that it was officially the hottest summer ever recorded on the planet, and the hottest first eight months of the year to date.



The summer of drought, fires and heat for large parts of the western US dominated the news and pushed national temperatures up, even though the central states were cooler than average for the season.



The average temperature in the lower 48 states for June to August 2015 was 72.7F (22.6C), 1.3 degrees above the 20th-century average, according to the latest data from the National Oceanic and Atmospheric Administration (NOAA), where the records go back to 1895.



California, Nevada, Oregon and Washington states have experienced their hottest year on record and the north-east nudged record warm temperatures for August.

On 1 September, 30% of the contiguous US was suffering drought conditions, up 3.3% since July, according to a NOAA report released on Friday.



Scientists are watching with interest the combined effect of the El Niño cyclical weather pattern warming the surface waters of the equatorial region of the Pacific Ocean at the same time as the northern reaches of that ocean have also been unusually warm this summer.



The state of Alaska has experienced its warmest year recorded to date, with temperatures four degrees fahrenheit (2.2 degrees celsius) above average, the NOAA report said.

“We do have a long-term warming trend for the globe and the US and it’s manifesting itself in the lower 48 as more and more summers, and years, and individual months being warmer than average and warmer than they were in the past,” said Jake Crouch, a climate scientist at NOAA.

Washington state’s historic wildfires this summer have charred more than 300,000 acres, the largest burning on record for the state.

“It’s becoming more common to see record or near record temperatures,” said Crouch.

He warned that the drought in California was expanding into the north-west and another warm winter for the region would worsen the drought.

The island village of Kivalina in Alaska is at risk from rising sea levels. Alaska has experienced its warmest recorded year to date. Photograph: Jonathan Ernst/Reuters

El Niño is expected to bring huge storms to California but limited rain to Oregon and Washington and NOAA does not expect any of it to be enough to offset the serious effects of the severe long-term drought in the region.

On Thursday, NOAA will release climate data for the globe for August.

“I’m assuming that August is going to be another warm month for the globe,” said Crouch, while declining to go into further detail or confirm that it will officially cap the warmest summer and warmest eight months on record worldwide.

However, the data has been heading in that direction. NOAA had previously predicted that there was “almost no way” that 2015 would not prove to be the warmest on record globally.

On Thursday it’s expected officially to be confirmed that the first eight months have been the warmest on record so far and the warmest three-month period June to August, constituting the hottest summer ever logged for the northern hemisphere.

Crouch pointed out that in the first seven months of 2015, worldwide figures had shown that the globe was almost a degree warmer than average and August figures are likely to have been boosted by the strengthening El Niño pattern.

“It’s extraordinary how much of the ocean is at record warm temperatures – about 75% to 80% of the world’s oceans are at record or near record warmth,” he said.

“I’m at a loss for words. It’s definitely not good.”