The research, conducted mostly by scientists based at the University of New South Wales, examined hot days starting in 1979 and then compared them with observations for 1997-2012 – a period when average global temperatures have generally plateaued.

The trend of rising temperatures over land continued through the whole period, with the strongest increase showing up in extremely hot days.

“The available evidence suggests that the most 'extreme' extremes show the greatest change,” the report, published in Nature Climate Change on Wednesday, found.

Debate over a so-called “hiatus” in temperature rises has intensified in recent years, with scientists blaming the pause on more heat being absorbed by the oceans, more active volcanoes, and a weaker solar radiation cycle. Some media outlets argue the slowdown in temperature increases reduces the urgency to curb greenhouse gas emissions that are blamed for global warming.

“The average temperatures mask something that's going on” over land, said Markus Donat, a post-doctoral researcher at UNSW, and one of the report's authors.

Not only is there no pause in temperatures increases over land but “the hot extremes, which mostly occur in summer, are getting hotter”, he said.

The effect of hotter spells during summers can be significant since that is when the impact on society of warmer conditions is greatest, Dr Donat said.

Farming is also affected since hotter conditions tend to increase evaporation, drying out the soil, he said.

While the study covered the years to 2012, the trend continued last year, Dr Donat said.

Last year was Australia's hottest in more than a century of records, with hot conditions extending in 2014 for many regions. Adelaide, Canberra and Melbourne all set summer heatwave records this year, while record heat over inland parts of Queensland and NSW exacerbated drought conditions.

Extreme heat events are now affecting on average more than twice the land area compared with similar events three decades ago, the study found.