E2 Round-up: UN climate panel under review, de Boer concedes 2010 treaty unlikely, and Wal-Mart’s green supply chain.

The IPCC has been under attack over errors in its landmark 2007 report on climate change, but views of the problems’ severity diverge widely.

Climate skeptics – including some GOP members of Congress – say the panel’s credibility has been badly undercut.

But the UN and climate advocates say the flaws do nothing to undermine the core conclusions of the massive 2007 report – or the dominant view among scientists that human-induced warming is underway.

Nonetheless, it has been a rough few months for climate advocates. Yvo de Boer, the UN’s top climate official, tells the Associated Press that a global climate treaty isn’t in the cards this year.

De Boer is stepping down in July. And in announcing his resignation last week, he noted that “I have always maintained that while governments provide the necessary policy framework, the real solutions must come from business.”

Mega-retailer Wal-Mart ($405 billion in yearly sales) is a very big business, and Thursday rolled out plans to cut 20 million metric tons of greenhouse gases from its supply chain by 2015, the equivalent to taking 3.8 million cars of the road for a year, the New York Times and other outlets report.

Over at Greenbiz.com, Marc Gunther gives the plan two cheers (not three). He notes that until now, the company’s “bold sustainability efforts” around energy and waste reduction efforts haven’t included an emissions-cutting pledge.

“Today, Walmart made its first major commitment to reduce greenhouse gases -- although, in typical WMT fashion, rather than set a tough goal that might affect its own growth curve, the company plans to turn up the pressure on its thousands of suppliers to reduce their emissions,” he writes.

Elsewhere, two environmental groups fear EPA is dithering on action to impose new controls on coal ash, a waste product from power plants, the Baltimore Sun reports. They released a report showing contamination sites in 14 states.