Freak weather has pushed more than half of all US counties into a state of primary natural disaster, raising questions about whether climate change predictions are now coming true.

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This is the biggest drought in America's history in terms of the area it covers.

As of last week, more than half of all the counties in the US were deemed to be in a state of primary natural disaster. The designation, by the US Department of Agriculture, allows drought-stricken farmers to apply for emergency aid.

The drought has accompanied a spate of temperature records being broken across the US starting as early as March. Taken together, people in the US are beginning to ask whether their freak weather could be linked to the changing climate scientists have long warned of.

The warming planet

It is a reasonable question. A new report from the National Oceanic and Atmospheric Administration, written with the help of UK Met Office scientists, concluded some of last year's drought conditions in Texas were 20 times more likely to have occurred now than in 1960. The reason being the atmosphere is just that much warmer now.

While no one particular drought, flood or cold snap can be definitely attributed to climate change, the current thinking is that a warming planet loads the dice in favour of more extreme events.

"We have shown that climate change has indeed altered the odds of some of the events that have occurred," said Peter Stott, from the UK Met Office, one of the report's authors. "What we are saying here is we can actually quantify those changing odds."

Extreme weather

This year the US heatwave has been accompanied by record wet weather in the UK and other parts of northern Europe. Similarly the US and Europe have seen some exceptionally cold winters. There is evidence beginning to emerge that these climatic "anomalies" could be linked to increasing ice melt in the Arctic.

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Ice is melting at the North Pole (Reuters)

The whiteness of the polar ice caps reflect the sun's rays back into the atmosphere - effectively cooling the planet. At the North Pole (though not at the South Pole, which is actually icier than normal) this ice is retreating. As the ice melts, a positive feedback sets in as the ocean warms and more ice melts.

"The water warms up. That begins a positive feedback because the warm water now melts more ice and we lose more of the reflective medium, the ice, and we get more water, more open water, absorbing more solar radiation and warming up," said Prof Martin Jeffries, US Office of Naval Research, in Arlington,Virginia.

"On a global scale this has consequences because we're changing - by losing the sea ice in the summer - we are changing the global reflectivity and absorbing more solar radiation in the arctic which then feeds out into the global environmental system," he said.

The USA is experiencing a historic drought (ITN)

Solar energy

But all that extra solar energy that is not being reflected into space ends somewhere else in the climate system. New research is beginning to emerge that links this to extreme weather and it is that which loads the weather dice.

Although this drought is the most widespread, the US has seen more extreme dry spells before. The dust bowl of the 1930s was more intense and devastated agriculture in some states for years.

Many farmers don't think their world is changing: "I'm not one for knee-jerk reactions" said Jeff Beasley, a cattle farmer in southern Illinois. "We've seen droughts before in the 1930s and the 1950s and I believe were seeing just another of those cycles," he told Channel 4 News.

But if the scientists are right and the frequency of weather extremes is increasing, the weather - on which places like the midwest depend - will not be as reliable as it used to be.