It’s hard to grasp the magnitude of the ecological catastrophe unfolding in the Gulf of Mexico as a result of the Deepwater Horizon/BP oil spill. At this point no one is certain how much oil is pouring from the well into the surrounding ocean. BP, adopting an early government estimate, has claimed that it amounts to a mere 5,000 barrels a day, but some scientists say the amount is closer to 60,000 or 70,000 barrels. Taking the lesser of these estimates, that would translate into the equivalent of an Exxon Valdez spill every four days. Given that this has been going on for five weeks at the time of this writing, the gulf has by now absorbed nine such spill equivalents, with more to come. But picturing the 1989 Exxon Valdez spill—until now the largest in US waters—and multiplying by nine does not begin to convey the scale of the disaster. For the first time in history, oil is pouring into the deep currents of a semi-enclosed sea, poisoning the water and depriving it of oxygen so that entire classes of marine species are at risk of annihilation. It is as if an underwater neutron bomb has struck the Gulf of Mexico, causing little apparent damage on the surface but destroying the living creatures below.

Who bears responsibility for this unmitigated catastrophe? What should be done in response?

Beginning with the first question, it is evident that a host of actors bear responsibility, from the drilling managers aboard the Deepwater Horizon rig to the BP officials who oversaw their work to the government regulators who awarded the corporations blanket waivers to ignore required environmental assessments. But, as in all matters that derive from broad strokes of policy, this disaster bears the imprint of the ultimate deciders: presidents George W. Bush and Barack Obama.

What can be determined from the information available is that the April 20 explosion occurred because BP managers were in a hurry to seal off the well so they could move the rig (which BP leased from Transocean for $500,000 per day) to another drilling location. To speed up the move, BP’s managers evidently approved the risky exit procedure that led to the lethal explosion. At one level, then, responsibility can be laid at the feet of the managers involved in that decision as well as of Cameron International, the manufacturer of the rig’s blowout preventer, which appears to have been defective. These managers operated in a corporate culture that favored productivity and profit over safety and environmental protection.

BP, which has boasted of its success in boosting oil production in the gulf, has a sordid history when it comes to safety. Last October it was fined $87 million by the Occupational Safety and Health Administration for failing to correct safety problems discovered after a 2005 explosion that killed fifteen workers at BP’s Texas City refinery—the largest such fine ever levied by OSHA. Like other firms operating in the gulf, BP has also sought a blanket exemption from requirements that it conduct an environmental impact assessment for each new offshore well it drills.

But corporate officials and their parent companies did not operate in a political vacuum. BP and its subcontractors were able to drill in this location, some forty miles off the Louisiana shore, because the government, first under Bush and then under Obama, has been keen to increase production in the deep waters of the Gulf of Mexico. Ever since it became clear, in the 1990s, that oil output at Prudhoe Bay in northern Alaska was in irreversible decline and that no other onshore location in the continental United States could provide increased levels of petroleum, the government has sought to boost output from the deepwater gulf to moderate the nation’s growing dependence on imported energy. To that end, the Bush administration proposed to open up new areas for drilling, including the Arctic National Wildlife Refuge (ANWR) and the Outer Continental Shelf, and to facilitate the efforts of giant energy firms to exploit these resources.

Bush was never able to persuade Congress to approve drilling in ANWR. But he did succeed in expanding drilling in other areas, including the deepwater gulf. Bush’s principal instrument in these endeavors was the Minerals Management Service (MMS), the branch of the Interior Department responsible for providing leases for offshore drilling as well as collecting the fees and royalties the companies paid for operating in federal waters.

Intended largely to promote offshore drilling, the MMS was also responsible for ensuring that all such operations complied with the National Environmental Policy Act, the Endangered Species Act and other environmental laws. Full adherence to these laws could have slowed the expansion of drilling or blocked it altogether—but the MMS provided the leases without making the companies, including BP, obtain required environmental permits. MMS officials routinely ignored warnings from the agency’s own scientists and from those at the National Oceanic and Atmospheric Administration that this sort of deepwater drilling posed a risk of massive oil spills with devastating consequences for protected marine species. Such preferential treatment for industry is hardly surprising, given the cozy—in some cases criminal—relationships that developed between senior MMS officials and their corporate counterparts.

Enter the Obama administration. Obama has been deeply critical of his predecessor’s environmental policies and has promised to place fresh emphasis on developing alternative fuels—but he has shown little inclination to reverse the nation’s growing reliance on offshore oil. As it did under Bush, the MMS has continued to award leases for offshore drilling in the gulf without requiring environmental scrutiny. In October the agency gave Shell Oil preliminary approval to drill in the Beaufort Sea, off Alaska’s northern coast, despite warnings from scientists within and outside the agency that any spill in these far northern waters would have catastrophic environmental repercussions. Then on March 30—three weeks before the Deepwater Horizon disaster—Obama announced he would permit offshore drilling in additional areas of the gulf as well as in the Beaufort and Chukchi seas above Alaska and off the East Coast. Although Obama supposedly took this step in part to win support from Senate Republicans for the proposed climate-protection bill, it also reflects his belief, inherited from Bush, that the United States must produce more domestic oil to reduce its reliance on imports.

Since the gulf explosion, the administration has taken several halfhearted steps to slow the drive for increased deepwater drilling. It placed a moratorium on awarding new offshore leases, although the MMS reportedly has continued to give these away. It has also announced plans to break up the MMS into several independent agencies—with separate bodies responsible for awarding leases, collecting revenues and providing environmental oversight—in order to prevent a future conflict of interest. All these bodies, however, will remain within the Interior Department, and it is unclear if the White House really has the will to curb risky offshore drilling.

What can we learn from all this? It should be obvious that merely tightening safety and environmental procedures on offshore rigs will not be enough to prevent further environmental ruin. As long as the major energy firms continue to rest future profits on wells in ever-deeper waters—and government regulators collude with them in this—more catastrophes are inevitable. Clearly, it’s policy that has to change, not its implementation.

To prevent more ecological disasters, President Obama has to acknowledge the fallacy of his offshore-drilling plan and place a moratorium on all drilling in the Arctic, the Atlantic and new areas of the Gulf of Mexico while the government and industry determine whether it will ever be safe to operate in these waters. As BP’s inept response to the crisis shows, the giant firms lack the capacity to control leaks in deep offshore waters, and so any approval of new wells in the gulf must be contingent on developing safety and cleanup technologies equal to the task. In the meantime, every effort must be made to speed the introduction of alternative fuels that pose fewer threats to the natural environment.