How's this for global warming? Hotter summer temperatures could be a permanent fixture for half of the world by 2070.

Using data from more than 50 climate model experiments, a study by two Stanford University researchers predicts that the Northern Hemisphere will face extreme heat due to greenhouse gases.

"According to our projections, 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 the study's lead author, Noah Diffenbaugh, an assistant professor of environmental Earth science at Stanford University.

Diffenbaugh and his co-author researcher Martin Scherer predict that tropical areas, like Africa, Asia and South America will experience "the permanent emergence of unprecedented summer heat" within twenty years.

Europe, China and North America will see their summer temperatures shift within 60 years.

The study also utilized historical weather data to look at the accuracy of warming trends and predictions.

"It turns out that when we look back in time using temperature records, we find that this extreme heat emergence is occurring now, and that climate models represent the historical patterns remarkably well,” said Diffenbaugh.

The increased summer heat represents a very real threat to human health and crop production. The study points to the 2003 European heat waves that killed 40,000 people and experimental models that show summer temperatures having a significant impact on soy and wheat produced in the Midwestern United States.

"The fact that we're already seeing these changes in historical weather observations, and that they match climate model simulations so closely, increases our confidence that our projections of permanent escalations in seasonal temperatures within the next few decades are well founded," Diffenbaugh said.

The study was funded by the National Science Foundation, the Department of Energy, the National Institutes of Health and the World Bank.

The results of this study will be published in the June issue of Climatic Change.