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OKLAHOMA CITY (AP) - With the planet heating up, many scientists seem fairly certain some weather elements like hurricanes and droughts will worsen. But tornadoes have them stumped.

These unpredictable storms plague the United States more than any other country. As tornado season nears, scientists have been pondering a simple question: Will there be more or fewer twisters as global warming increases?

There is no easy answer. Lately, tornado activity in America has lurched from one extreme to the other. And scientists are unsure if climate change has played a role in recent erratic patterns.

In 2011, the United States saw its second deadliest tornado season in history, with nearly 1,700 twisters that killed 553 people. The following year had twice as many tornadoes as usual through April. Then the twisters suddenly disappeared.

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