90 per cent of earth's land will face extreme summer heat wave

Earth's northern hemisphere, which comprises of 90 per cent of the planet's land has become much more likely to experience an extreme summer heat wave compared to a base period from 1951 to 1980, the scientists said.

Over the past 30 years the northern hemisphere has seen more "hot" (orange), "very hot" (red) and "extremely hot" (brown) summers. The study shows how the area experiencing "extremely hot" summers grows from nearly nonexistent during the base period to cover 12 per cent of land in the Northern Hemisphere by 2011.

The statistics show that the recent bouts of extremely warm summers, including the intense heat wave afflicting the US Midwest this year, could be due to global warming, lead author James Hansen of NASA's Goddard Institute for Space Studies (GISS) has claimed.

"This summer people are seeing extreme heat and agricultural impacts," Hansen said. "We're asserting that this is causally connected to global warming, and in this paper we present the scientific evidence for that."

Researchers analyzed mean summer temperatures since 1951 and showed that the odds have increased in recent decades for what they define as "hot," "very hot" and "extremely hot" summers.

The researchers detailed how "extremely hot" summers are becoming far more routine. Since 2006, about 10 per cent of land area across the Northern Hemisphere has experienced these temperatures each summer.

Specifically, an average of 75 per cent of land area across Earth experienced summers in the "hot" category during the past decade, compared to only 33 per cent during the 1951 to 1980 base period.

Other regions around the world also have felt the heat of global warming, according to the study. Global maps of temperature abnormalities show that heat waves in Texas, Oklahoma and Mexico in 2011, and in the Middle East, Western Asia and Eastern Europe in 2010 fall into the new "extremely hot" category.