An environmental advocate dressed in a furry, head-to-clawed-paw polar bear suit defied Philadelphia's staggering heat wave on Sunday and prepared to join thousands of more comfortably dressed protesters at the March for a Clean Energy Revolution.

The march, aimed at banning the natural gas drilling practice known as fracking, promised thousands of participants from all 50 states on the eve of the Democratic National Convention. At least 1,000 people gathered at Broad and Market as the march began and police estimates at 2 p.m. ranged between 5,000 and 10,000 as the march proceeded.

At the same time, another 3,000 supporters of Sen. Bernie Sanders planned to assemble in a rally and march, energized by the announcement that DNC Chairman Debbie Wasserman Schultz would resign as party head and not preside over the convention. Hours earlier, Sanders called outright for her resignation on ABC's "This Week," telling host George Stephanopoulos the DNC "was not running a fair operation, that they were supporting Secretary Clinton."

Sanders said he was "not shocked" but was "disappointed" by the DNC emails leaked by the WikiLeaks last week. The Washington Post reported that WikiLeaks had revealed about 20,000 emails apparently favoring Hillary Clinton's candidacy over Sanders.

One dejected Sanders loyalist, Paula Iasella, 61, of southern New Hampshire, lugged a 3-foot by 4-foot double-faced sign on a 7-foot-tall aluminum pole. The front of the sign was a portrait painted of Sanders with the message #stillBernie; the back, a silhouette of Sanders with his fist raised and the words "US DemExit."

Iasella said she is leaving the Democratic Party after 42 years.

Another Sanders supporter, Ian O'Malley, 24, of Media, said he was especially angry over the WikiLeaks email news. "When will this madness end," he asked.

O'Malley carried an elaborate, bamboo frame flag contraption with several colorful quilt square signs lashed to it. "This party's over," and "Not Afraid to Go Green," it said.

Participant Jessica Griffith of Las Vegas held aloft a sign lettered with DNC in red, with the words "Does Not Care about Democracy" in black.

The environmentalists said they were pushing for the nation's "current and future leaders" to ban fracking now, keep fossil fuels in the ground, stop dirty energy, transition to 100% renewable energy and ensure environmental justice for all."

Their march, which began at City Hall and headed east down Market toward Independence Hall, prompted Philadelphia police to block off Market Street at 16th, resulting in a giant traffic jam at 16th and Race.

SEPTA riders - themselves seeking to reduce fossil fuel consumption by taking mass transit, as one said - faced big detours. Buses scheduled near City Hall or the Navy Yard or those that try to cross Broad Street were being delayed and rerouted.

The polar bear character, who drew lots of attention in the stifling 95-degree heat before the Energy march began, was a counterpoint to the oppressive heat that descended on the city as DNC delegates poured in, preparing for the convention to open on Monday.

The man sweltering inside the bear suit, American University professor Bill Snape, made it to the end of the march - not in costume, but on message.

"I'm in much better shape than the polar bears of the Arctic," Snape said while standing in the shade at Independence Mall. "Their habitat is literally melting, melting precipitously. So this is our lighthearted way to remind people we need to stop climate change now. Not tomorrow. Not next week. Now."

City officials were so concerned about the dangerous health conditions from the heat and high humidity - with the heat index expected to exceed 100 degrees - that Mayor Kenney urged visitors to limit their time outdoors as much as possible and to take advantage of city-provided cooling centers, spray ground or public pools. He also warned of thunderstorms and said safety personnel would direct demonstrators to shelter areas until storms passed.

"For the safety of demonstrators during the DNC, two medic tents, two misting tents and bottled water will be available in FDR Park," he said. Medics were being assigned to marches.

In addition, free bottles of water were prepared for demonstrators and sprinkler caps were affixed to fire hydrants along Broad Street.

Hundreds of Sanders supporters gathered in New Jersey - setting up mostly in several campsites throughout South Jersey towns - to gain easy access to Philadelphia for rallies this week. While some traveled with groups of people they knew, others found each other on Facebook to connect when they arrived.

Andrea Hafley, 30, of Chicago, traveled with a few of her friends to camp out at the Four Seasons Campground in Pilesgrove. She said she is motivated by Sanders and like-minded people who want to rally at the DNC.

"This is about the movement, and having everybody come together and still standing strong together for Bernie," she said.

Nathan Shuffield, 22, walked about 250 miles from his hometown of Malvern, Ark., then hitched rides with other Sanders supporters across the journey. One family from Indiana helped him get to Pilesgrove.

"I've never been super politically active, but the FBI suggestion not to indict Hillary kind of set me forward and let the path for me here," he said.

Shuffield loaded up a bus with 40 others Sunday morning, leaving Four Seasons to get to rallies in Philadelphia.

At Parvin State Park, dozens of campsites were filled with hundreds of people camping out for the week. From Seattle, Shanda Masta, 42, traveled cross-country with a large group of about 20 people.

"We came here to support Bernie, and most of us have been passionate and involved for months," she said. "We've seen the horrific things that we've seen . . . Democrats change the rules every time - we knew we had to get out here to support."