Flash floods in Europe and India, devastating heatwaves across the USA, and even the British summer is wetter - all because of a change to the northern jet stream. A result of man-made global warming? Scientists looking for an answer may be on a fool's errand writes Robert Matthews
Forget the arguments about the reality of global warming. Our planet is now in the grip of something over which there can be no argument: global weirding.
Record-breaking heatwaves in cities from Tulsa, Oklahoma, to Toronto, Canada; devastating floods in Russia and India, hundreds dead, millions affected. These are not gloomy scenarios put about by eco-warriors; when thousands of local weather records are simultaneously broken in many countries, you know something weird really is happening.
But is it just a temporary glitch in the global weather machine, or has it gone permanently awry?
Meteorologists lay much of the blame with the malfunctioning of a key part of that machine, the northern polar jet stream.
Identified by the pioneering Japanese atmospheric scientist Wasaburo Oishi in the 1920s and exploited by pilots ever since, jet streams are "rivers" of air that whip around the Earth at altitudes of around 10 kilometres or so, at speeds of around 200kph.
Their ferocious energy comes from the combined effects of the Earth's rotation and the temperature difference between the equator and the poles. And this leads to their crucial role in determining weather, as they serve to separate the cold air of the poles from the warmer air closer to the equator.
The effectiveness of the jet streams in keeping these two vast regions of air apart depends on a host of factors in ways that aren't fully understood.
But what is clear is that a weakened jet stream can meander far from its usual course, allowing warm air to seep much closer than normal to the poles, and cold air to head towards the equator - triggering outbreaks of weird weather for those on either side.
The dramatic effects of what a weakened jet stream can do have been all too visible this year. Measuring around 4,000km coast-to-coast, the United States is so vast that it can sit below one whole wave-like meander of the northern polar jet stream.
In March that led normally mild south-western states like Arizona to end up on the colder, northern side of the jet stream - and blasted with dramatic snow storms. Meanwhile, further east, usually bitterly cold states like Minnesota found themselves on the warmer, southern side of the jet stream, and experienced sweltering heat.
Now similar upheaval is being experienced elsewhere. The same meandering jet stream has passed south over Britain, leading to record-breaking rainfall, no sign of summer - and mounting concern for the London Olympics. Even the lethal flooding in southern Russia and India has been linked to misbehaving jet streams.
Inevitably all this has led to attempts to link the upheaval to global warming. After years of having little more than statistics to make the case, could we finally be seeing the symptoms of an overheating planet?
On the face of it, a link does seem plausible. The strength of the jet streams is determined by the temperature difference between the equator and the poles, so if the poles warm up - as is predicted by most global warming models - the jet streams might be expected to get weaker.
That, in turn, should make them more susceptible to wandering off their normal paths, triggering "global weirding".
But mere plausibility isn't a sound basis for explaining the world's climate. It certainly sounds plausible that the reason it's so hot at this time of year is because the Earth is at its closest to the sun.
But the Earth was, in fact, at its farthest from the sun on July 4. In any case, it's currently winter in the southern hemisphere.
The true explanation for the heat of summer lies in the seemingly trivial fact that the Earth's axis is tilted to its orbit.
In July, the northern hemisphere is tilted towards the sun, whose rays then strike the Earth's surface less obliquely. As a result, the sun's heat is more concentrated over the northern hemisphere, with more striking each square metre of ground, resulting in higher average temperatures. And, surprisingly, that counts for more than the distance of the Earth from the Sun.
In the same way, the putative link between global warming and the jet stream could be undermined by some less-than-obvious natural phenomena.
To find out more, two researchers at the University of Reading in England, Dr Tim Woollings and Dr Mike Blackburn, turned to sophisticated computer simulations of the atmosphere.
Using 22 such simulations, developed by leading teams around the world, they compared the effect of raising global temperatures with the natural variation recorded since the late 1950s.
In results recently published in the Journal of Climate, they found that - as expected - global warming does indeed affect the jet streams, pushing them closer to the poles.
But what about those meanders, which have caused so much havoc? Are they just natural variation, or the product of global warming?
Veterans of the global warming debate will not be surprised by the answer: maybe. Despite being based on state-of-the-art theory and run on some of the world's most powerful computers, the simulations just refused to reach a consensus on the response of the jet streams to global warming. Both the size and direction of the response were lost in the error-bars of the predictions.
In short, scientists remain stuck under the curse of climate research: the Butterfly Effect, according to which ignoring even tiny effects - perhaps even the flap of a butterfly's wing - can lead to drastically different conclusions.
There was a time when humans knew they couldn't predict climate change, and simply braced themselves for an unknown future. But climate scientists dreamed of a time when they would have the technology needed to crunch the numbers and find the answers.
Now they have the technology, but reliable answers remain elusive. Perhaps it's time to redirect that intellectual firepower to boost one thing we humans are good at: adapting to the vagaries of nature.
Robert Matthews is visiting reader in science at Aston University, Birmingham, England.