As mega-tornadoes, some over a mile wide, scythed through the American South, killing hundreds and smashing communities, AccuWeather, an American weather forecaster, blamed global warming.

This contradicted an early statement from Greg Carbin, a meteorologist with the US National Oceanic and Atmospheric Administration, who told Fox News "no scientific consensus" exists to link the tornadoes, the largest known outbreak in US history, to climate change, even as an escalating number of catastrophic droughts, storms and floods have wreaked havoc worldwide.

The world is in one of the strongest La Nina patterns ever recorded. Had it been tweaked by climate change? And had a warming world produced record amounts of warm, moist air?

The dispute sparked accusations that global-warming alarmists had exploited the tornadoes.

But it focused attention on what drives climate change: the carbons pumped into a warming atmosphere by our profligate use of fossil fuels.

Those carbons are brought to you by Big Oil, which has run into some wild weather of its own: in February Chevron was fined US$8 billion ($10.2 billion) in Ecuador, due to oil spills dubbed the "Amazon Chernobyl"; another spill, after a 2008 pipeline failure, has sparked a huge class action against Shell in Nigeria; and, most spectacularly, the explosion on BP's Macondo rig in the Gulf of Mexico on April 20, 2010 - killing 11 and spewing millions of gallons of crude in the Gulf of Mexico, America's worst spill - brought the industry's questionable safety standards into sharp relief.

A damning US government report found a "poor safety culture manifested in continued maintenance deficiencies, training and knowledge gaps, and emergency preparedness weaknesses."

In the US there is mounting concern about Big Oil's dark side, including protests against "fracking" - blasting water, sand and chemicals into subterranean rock to recover natural gas, a process that may contaminate groundwater.

Americans also fear gritty crude, extracted from Alberta tar sands, will corrode a 2375km pipeline to the Gulf, and pollute the Ogallala aquifer beneath the Great Plains.

Wild weather may be an end result of our fossil fuel addiction, but away from Tornado Alley it is business as usual for Big Oil. After the BP disaster the Obama Administration imposed a moratorium on offshore drilling, which was lifted in October.

As of April the Bureau of Ocean Energy Management, Regulation and Enforcement had approved 10 new deepwater permits. Scores of permits are pending. Republicans in Congress are pushing to drill off the Atlantic and Pacific coasts, in the Arctic, and in Alaska's Bristol Bay, once off limits.

This includes New Zealand. Petrobras is surveying drill sites in the Raukumara Basin, off East Cape. And Anadrako Petroleum says it will drill off Taranaki next summer. It is growing hard to ignore the brazen contradiction between drilling for oil and paying lip service to climate change.

Back in the Gulf, BP hopes to resume drilling later this year. Given the spill's contentious ecological legacy (plus litigation woes that include possible criminal charges for manslaughter) this will involve Herculean public relations.

The company has tried to burnish its image. Last May, BP pledged US$500 million for scientific research. A year after the spill some media reports painted a "striking recovery," with plant growth, pristine sand and clear water.

Yet despite assurance by Polaris Applied Sciences, engaged by BP to track the oil and orchestrate the clean-up, that residue oil only heavily affects 32 km of 5166km of surveyed beaches, with 373km said to have a light covering of oil, no one knows how the heavy use of chemical dispersants will affect the Gulf.

Last week, Greenpeace open-sourced 30,000 pages of confidential BP documents, acquired via the US Freedom of Information Act, at its PolluterWatch website. Greenpeace says the document cache show BP "wanted control of the science".

Documents discuss how to "direct" funding to specific studies, and ask "what influence do we have over the vessels/equipment driving the studies vs the questions?"

"There is a lot of uncertainty about the ecological impacts," explains Regan Nelson, senior oceans adviser with the National Resources Defence Council, a US environmental group. The Obama Administration has undertaken a Natural Resource Damage Assessment Process and its scientific conclusions are secret, pending litigation with BP.

"So it's hard to get a good sense of what the impacts are."

The US government says 200 million gallons were spilled. BP contained 30 million gallons. The rest went into the Gulf. Less than 10 per cent was cleaned up, says Nelson.

One scientist, the University of Georgia's Samantha Joye - whose team first detected a huge plume of oil after the disaster, and who challenged government reports that downplayed the spill's size - found a scum of oil on the seafloor. Tarballs still wash ashore and wetlands lie devastated. The wider ecological implications are unknown.

"I think the BP disaster was a wake-up call," says Nelson.

"You're looking at billions of dollars in damages, lost jobs, and a long lasting impact over a wide area of the Gulf. People recognise the industry is not infallible. There are major accidents with major consequences. And for too long we didn't require enough vigorous oversight."

Oversight appears to be the last thing the Republicans in Congress want. Emboldened by last November's Tea Party led victory in the House of Representatives, conservatives seek to emasculate regulations and resume deepwater drilling.

But the Republicans' desire to hamstring budgets for the Environmental Protection Agency, charged with monitoring water and air quality, and eviscerate the landmark 2009 Supreme Court decision - that ruled greenhouse gases were a threat to public health - ran into strong opposition.

Efforts to curtail the EPA's authority, says David Doniger, policy director with the NRDC Climate Centre, passed the House but sank in the Senate. Similar GOP efforts to shrink the EPA's power, via a rider on the budget, also failed.

Republicans have introduced three oil industry-friendly bills into the House. One gives the government 60 days to approve or deny drilling permits. If the government fails to act by then the permit would be granted automatically.

"They seem to want to forget the Gulf spill ever happened," says Nelson. "They want to expand offshore drilling everywhere." Any GOP bills will likely stall in the Senate.

Although polls show over 60 per cent of Americans back the EPA's carbon regulations, Republicans still plug the "drill baby drill" mantra, as high prices and peak oil concerns propel Big Oil into frontier oil, regardless of safety concerns.

"The growing consumption of oil worldwide is outpacing discoveries," says Kert Davies, research director with Greenpeace USA. "We're using more oil than we're finding."

"The deepwater is the next place where there are big pots of oil. They know it's out there. And global demand will support the higher costs of getting it. When it was US$20 a barrel there was no way they would do operations like Deepwater Horizon. It's a multibillion-dollar risk. But at US$100 a barrel it's worth it. That's what driving the rush to go to the ends of the earth and drill in deep water; the price of oil and increased scarcity. The industry's increasingly risk-taking nature is driven by those things. And they're pretty desperate, actually, for new assets."

The deepwater wells include 70 in the Gulf of Mexico, 104 in South America, 97 in European waters, 48 off West Africa, 88 in the Middle East, and 110 in Asian and Australian waters.

The Macondo well was at 1524m, on the edge of "ultra deep water," where frontier oil is headed. The forensic report on BP's blowout preventer found it failed to close on the drill pipe.

Despite an ExxonMobil led effort, the Marine Well Containment System, to counter spills - and Davies notes the industry talks of "when" not "if" - there are no guarantees another blowout would would be quickly contained.

"A BP engineer told me that if the disaster had happened in shallow water they would have capped that well in two weeks," says Achenbach.

"When they went down the continental shelf into deep water, they didn't appreciate they were moving into a different world. It's a different engineering environment. Everything you do takes longer."

Working at such depths is like "going to outer space," he says

Down in the ultra deep realm, rig operators must deal with geological formations that are often highly pressurised and at high temperatures. In such a complex world, says Achenbach, a spill like the BP disaster "was bound to happen at some point, given the way the industry tries to balance efficiency with safety. They make decisions all the time for the sake of getting it done, rather than making sure everything is as safe as can possibly be. They want to be safe, but they want to make a profit. It's business."

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* 14,000 Deepwater wells have been drilled worldwide.

* 607 Rigs, out of a fleet of 799, are under contract.