While nuclear energy experts disagree on just how bad the situation is at Japan’s stricken nuclear plants, there is one thing that they are all certain of: things could get worse. Over the last few days, various media reports about the nuclear crisis have shown that the only certainty is uncertainty. Yesterday’s explosion and fire at Fukushima Dai-ichi heightened concerns and precautions, but the long term effects are still hard to pin down.

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The International Nuclear and Radiological Event Scale (INES) ranks incidents from Level 1 — the lowest, meaning their is very little threat to the general population — to Level 7, the highest, meaning that a major accident has occurred, large amounts of radioactive material have been released, and their will be widespread health and environmental issues.

A French nuclear official told CNN that he believes yesterday’s complications put the situation just below Chernobyl on the INES, making it a “serious accident” with major concerns. “It’s clear we are at Level 6, that’s to say we’re at a level in between what happened at Three Mile Island and Chernobyl,” said Andre-Claude Lacoste, president of France’s nuclear safety authority.

In 1986, a nuclear reactor at a plant in Chernobyl exploded. Thirty people died and hundreds more became sick. It should be made clear, though, that the reactor had no protective vessel like the plants do in Japan. The meltdown at Three Mile Island caused no sickness, and only trace amounts of radiation were found in plants and animals.

Immediately after the earthquake hit and the Fukushima Dai-ichi plant experienced problems, the International Atomic Energy Agency said the situation was a Level 4, which classifies as a minor release of radioactive material and only food should be tested for contamination. After yesterday’s development, the IAEA did not give a rating, but the Japanese chief of the IAEA insisted there was no comparison to Chernobyl.

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However, other experts believe the situation is well beyond a Level 4. Joseph Cirincione, author of Deadly Arsenals: Nuclear, Biological and Chemical Threats, told CNN that the situation is at least a 5 or 6 and will most likely turn into a 7. “This is not going to end well,” he said. “At the very least, we’re going to have a very expensive mess to clean up, and the worst is that we we spread radioactive particles across hundreds or thousands of square miles of Japan.”

The Institute for Science and International Security issued a statement with similar sentiments: “This event is now closer to a level 6, and it may unfortunately reach a level 7.”

Still, many believe that the situation is nowhere near Chernobyl. James Acton, an associate in the Nuclear Policy Program at the Carnegie Endowment, said Fukushima is probably a Level 2, and others, like Tom Cochran of the National Resource Defense Council, have resisted rating the incident because there are too many variables. Cochran has concerns about a possible core meltdown, but he’s more concerned about the bigger picture:

“We’ve watched Exxon Valdez, the BP oil spill, numerous coal mining accidents, Chernobyl, TMI, now Fukushima, slag ponds, TVA (Tennessee Valley Authority) reactors giving way,” he told CNN. “You have got to ask yourself, how many wake-up calls do you need before you get serious about building a safe, renewable-energy economy?”

How many, indeed.