Washington, June 7 (IANS) Tropical regions are likely to experience irreversibly hotter summers within the next 20 to 60 years, warns a climatologist.

"Large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years," said Noah Diffenbaugh of Stanford University, who led the study.

The Stanford University team concluded that many tropical regions in Africa, Asia and South America could see "the permanent emergence of unprecedented summer heat" in the next two decades, the journal Climatic Change reports.

"When scientists talk about global warming causing more heat waves, people often ask if that means that the hottest temperatures will become 'the new normal'," said Diffenbaugh, who is assistant professor of environmental earth system science at Stanford's Woods Institute.

"That got us thinking - at what point can we expect the coolest seasonal temperatures to always be hotter than the historically highest temperatures for that season," he said.

Accordingly Diffenbaugh and Stanford research assistant Martin Scherer, analyzed more than 50 climate model experiments and simulations of the 20th century that accurately "predicted" the Earth's climate during the last 50 years, according to a Stanford statement.

The analysis revealed that many parts of the planet could experience a permanent spike in seasonal temperatures within 60 years.

For instance, Diffenbaugh pointed to record heat waves in Europe in 2003 that killed 40,000 people.