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A Derby woman claims that the frequency of "bizarre weather" phenomena like pink skies is on the up - and that they are caused by chemical or biological agents left in the sky by high-flying aircraft.

Liz Bywater says the spraying of "chemtrails" are behind the "increasingly bizarre weather".

Those who subscribe to the theory speculate that the purpose of the chemical release may be solar radiation management, weather modification, psychological manipulation and human population control.

Others say the purpose of such covert operations is to make people sick to benefit drug companies.

The arguments have been dismissed by the scientific community. There is no evidence that purported chemtrails differ from normal water-based contrails routinely left by high-flying aircraft under certain atmospheric conditions.

Theories such as is began to circulate in the USA in the late 1990s.

Ms Bywater said in a letter to us: "Has the Derby Telegraph, along with the BBC, ITV etc, pledged to be silent about what is really going on in the skies – how else could they remain silent about the increasingly bizarre weather pictures they show and the heavily chemtrailed skies?

"Are people now so completely hypnotised by their phones and dumbed down by strontium, barium and aluminium falling to the earth from jets that they rarely even look skywards?"

However Professor of Climate Change at the University of Reading, Ellie Highwood, who is also the vice-president of the Royal Meteorological Society, said there was no evidence of chemtrails.

She said: "People have looked for ages for any such thing as chemtrails. There’s no evidence.

"You do get water-vapour trails – the lines that come out the back of aircraft. It’s the same kind of principle as on a cold winter morning, when you get a cloud form in front of your face in the dry, cold air."

Professor Highwood also pointed out that there is no evidence that the frequency of "bizarre weather" incidents has increased because no-one is recording that data.

She added that the appearance of the sky is very dependent on one's viewpoint - so someone may see a pink sunset in Derby but another person in Nottingham may not.

However, she did explain that there is sometimes a connection between pink skies and man-made pollution.

She said: "You get red skies when the blue light from the sun is scattered.

"The effect is strongest during sunrise or sunset. That’s an entirely natural thing that happens every day.

"At certain times of year it will get more scattered. That can be from pollution from greenhouse sources – traffic pollution and things like that.

"Or it can be particularly noticeable if you have calm weather with not much wind blowing things around."

Are you a believer in chemtrails - despite what the experts say? Let us know in the comments below.