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Map by U.S. National Waather Service shows expected temperatures at 8 p.m. on Sunday

Thousands of miles away, a cadre of international Nobel laureates assembled to discuss global warming were having a, if you will, heated debate, arguing over data that the vast majority of scientists the world over say shows clear evidence of manmade climate change.

But in the steaming streets of Brooklyn, the crowded public pools of Atlanta, the burning mountainsides of Colorado and the power outage-hit suburbs of Washington, D.C., it took no Einstein to figure it out.

It was really, really hot again on Sunday as the heat wave that has been frying most of the East Coast, Southeast and Midwestern U.S. states went into its fourth day.

Twenty states were under excessive heat warnings or heat advisories on Sunday, the National Weather Service said, with temperatures driving the mercury above 100 degrees Fahrenheit across much of the Southeast. All-time temperature records have been exceeded in 140 locations over the past week, the Weather Service said.

One of those places is the city of Atlanta, where thermostats maxed out at 106 degrees Saturday. Sunday's highs were expected to be around three degrees cooler. The hot, humid air hanging over the Southern city prompted environmental officials to declare a code purple air quality alert, meaning the local atmosphere was considered very unhealthy for most people.

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A vendor at Turner Field in Atlanta, GA places ice on his head to cool off during and Atlanta Braves game

Elsewhere, the South was broiling, with temperatures reaching 109 in Columbia, S.C. Firefighters issued a barbecue ban in Jasper, Ala., where 100-plus degree temperatures have dried out the vegetation, making most open flames an extremely risky proposition. Temperatures record also were set over the weekend in Louisville, Ky., and Nashville, Tenn.

In Raleigh, N.C., where temperatures were expected to hit 106 on Sunday, a radio station found people at the local farmer's market trying to hydrate by chowing on chilled cantaloupes and watermelon, while trying to remain stoic.

It's very hot, but air conditioning's only been around for a few years, 60 years probably, Lisa Lee, a farmer at the market, told WRAL.

While the Southeast was the hottest, most of the attention was focused on a swath of the East Coast between Washington, D.C., and Atlantic City, N.J. There, a powerful cluster of thunderstorms Friday had knocked out power to hundreds of thousands in the region, leaving them unable to turn on the air conditioner to cool down. Power-sapped water pumps, also a result of the mass outage, led to water interruptions. In suburban Maryland, authorities declared residents should stop all outside water use, take shorter showers and limit flushing toilets to avoid exacerbating the situation.

Virginia Gov. Robert McDonnell said the combination of continuing high temperatures, power outages and water restrictions meant this is a very dangerous situation.

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Municipal workers clear debris in Washington, D.C. following a violent series of thunderstorms Friday. The storms knocked out power to hundreds of thousands in the region.

Another place where a dangerous situation was brewing was in New York City, where a labor dispute between Consolidated Edison Inc. and thousands of its workers led to a lockout of 8,500 employees Sunday. That left just managers and, possibly scab crews, to deal with any problems that might arise as 8.2 million New Yorkers tax the power grid.

But even the four days of extreme heat still did not make the sweltering eastern half of the United States the hottest place in the nation. That distinction belonged to the mountains of Colorado, according to a map released by NASA, where wildfires spread across thousands of acres.

NASA

NASA image showing divergences from average surface temperatures

All those facts did not seem to affect the discussion across the Atlantic, where Nobel laureates in physics were set to kick off a six-day conference at Lindau, an island in a Bavarian lake, with a lively debate on the current state of global warming science. (Global warming, for the record, is much more about the planet's average temperature rising by a few degrees over decades, and not about heat waves, although certain extreme weather events such as the cluster of thunderstorms that hit the East Coast can be spurred by warmer climate.)

There, some of the most intelligent people on Earth were buzzing about comments from Ivar Giæver, a Norwegian physicist and 1973 Nobel Prize winner who claims scientific evidence proves the temperature has been amazingly stable over the past 150 years and that he is terrified by the one-sided propaganda in the media.

In particular I am wor­ried about all the money wasted on alternate energies, when so many chil­dren in the world go hungry to bed, Giæver wrote in a summary of a speech he is set to deliver Monday.

Such statements are anathema to the scientific consensus on climate change, which are closer to the views expressed by Mario Molina, a Mexican chemist who shares a 1995 Nobel for his work on the ozone layer and is also speaking at the conference to explain why climate change is the most serious environmental challenge facing society in the 21st century.