Two independent stories in New Scientist magazine this week show how tricky it is to determine whether we are in the start of a global warming episode or not.

Even if we are beginning to experience global warming, there’s still plenty of cause to think that man’s consumption of fossil fuels is just a pimple on the galaxy-wide surface of possible theories.

One story contrasts the opinions of ‘weather experts’ and reports: "The weather we've seen over the last few days is entirely consistent with what we're likely to see over the next few decades," says John Turnpenny, at the Tyndall Centre for climate change research in Norwich, UK. "We're likely to see such a heat spell in London every year."

The report contrasts this with: In July, the World Meteorological Organization warned that "extreme weather events might increase". But Ken Davidson, director of the World Climate Program and a contributor to the statement, says media reports linking such weather to climate change were overblown. "It certainly isn't clear at this point," he told New Scientist. "We were very careful to use the word 'might'."

While governments the world over (well, some anyway) are sensibly taking steps to cut carbon emissions to the Kyoto protocol, scientists still haven’t a clue to what is causing the world’s current weird weather.

Scientists do agree on one thing. They agree that no one yet knows the answer to this question, but they point out that an increase in the number and severity of extreme events is exactly what their models of a warmer world predict.

The UK's Hadley Centre in Bracknell, Berkshire has been showing off new climate change software recently. But Simon Brown, a climate change expert at the centre warns:

"People lump extreme events into one basket and use it to strengthen their arguments about climate change. But you can't do that.”

“We can't say that one causes the other. We're not at that point yet."

Another interesting theory about global warming rose to the top of the bubbling cauldron of theories this week. New Scientist reports the Sun's shifting magnetic field is set to focus a decade-long storm of galactic dust grains towards the inner Solar System, including Earth.

No one knows what this might do to the planet but speculation is already rife: some researchers have speculated that sustained periods of cosmic dust bombardment might be related to ice ages or mass extinctions.

Apparently, so the theory goes, the magnetic field of the sun sometimes acts like a shield, deflecting charged galactic dust away from the Solar System. However, the Sun's regular cycle of activity peaked in 2001.

As expected, its magnetic field then flipped over, so that south became north and vice-versa. Rather than deflecting the galactic dust, the magnetic field should now be channelling the dust inwards.

And it seems to be happening according to theory. New spacecraft measurements, collected by ESA scientist Markus Landgraf and colleagues at the Max-Planck-Institute in Heidelberg, show that three times more galactic dust is now entering the Solar System than during the 1990s.

Theories rage about the effects of space dust on the Earth and are hotly debated. However, about 40,000 tonnes of cosmic debris fall onto the planet every year, much of it creating ‘shooting stars’, properly called meteors.

If focussing of galactic dust towards the planets occurs then a strong argument, suggested by scientists recently, could gain credence. High dust inputs into the Earth's atmosphere, sustained for centuries or longer, could be responsible for ice ages and mass extinctions.

Langraf is cautious about such claims but told New Scientist: "Everything in interplanetary space eventually affects the planets, but exactly how is very speculative."