The sell-off came as weakening of the yuan led to worries that China's economy was slowing more than expected. The rest of Asia also recovered some losses after the dramatic plunge in Chinese shares had triggered a global sell-off. Markets in Europe and the US made steep losses overnight after trading in the world's second largest economy was closed within the first 30 minutes in the previous session, making it China's shortest trading day on record.

Regulators suspended the "circuit breaker" rule late on Thursday. Analysts said it was creating more panic selling instead of calming sentiment. "The fall in markets looks to have been exaggerated and driven more by fears and regulatory issues around the share market and currency rather than a renewed deterioration in economic indicators," said Shane Oliver, investment strategist at AMP Capital.

Investors were worried that China's moves to weaken the yuan would spark a currency war in the region as other countries tried to remain competitive.

Cameron is on a visit to Germany, where he met with chancellor Angela Merkel in Bavaria on Wednesday and will outline his reform ideas on Thursday at the annual conference of the sister party of Merkel's Christian Democratic Union, the Christian Social Union. The UK prime minister campaigned in the EU’s largest economy to enlist its support for his reform proposals ahead of an EU leaders’ meeting next month in Brussels.

If a deal is reached in February, Cameron could call for a referendum in June. In an article appearing in Germany’s biggest-selling newspaper, Bild, Cameron argued support for the UK’s membership has declined and the changes will help address the concerns of the British people. "But these changes will benefit the EU too, and Germany can help deliver them," he wrote.

"The problems in the EU that what we are trying to fix are problems for Germany and other European partners too," he argued. Cameron wants to cut EU bureaucracy and shift powers from Brussels to national capitals.

In August, Beijing decided to tweak its exchange rate peg with the dollar, making the renminbi float in a wider band against the greenback. This sparked immediate market panic that China was entering into the world's currency wars. But the devaluation in itself was small. Allaying fears further, the Chinese began to immediately intervene to prop up the RMB to stop it falling too fast by drawing down their reserves.

But devaluation fears are returning. The country's export performance has stuttered, while the dollar has rocketed on the back of a stronger US economy. Overall, the RMB has weakened by around 10 percent against the dollar over the last two years. "Over half of the weakness has come in the last four months," says Sean Yokota at SEB.

The Communist party has responded to mass capital outflows by using the full force of the state to punish those it accuses of "illegal cash transfers" out of the country. Some claim that the Chinese are beginning to lose control over their exchange rate and their economic policy. China's exchange rate policy, it could be said, has put the country in a bind.

In fact, the White House said the results from various monitors simply weren’t consistent with a hydrogen bomb, which can be far more powerful than an atomic bomb. But one top specialist says the monitor results and North Korea’s claims align fully with the scenario of a device designed for a low yield, yet emitting an enhanced amount of gamma rays.

Peter Pry, an expert on electromagnetic pulse weapons, told WND the explosion indeed was such a device. Pry said Pyongyang’s latest test, which followed three others each in the range of 10 kilotons or less, was “another kind of H-Bomb,” a neutron bomb, or enhanced radiation weapon such as a super-EMP weapon. Such weapons constitute, essentially, a “very low-yield H-Bomb that typically has yields of 1-10 kilotons, just like the North Korean device,” he said.

Pry, like other experts on EMP, was concerned that the North Koreans could launch a missile with a satellite that could constitute a nuclear device designed to explode on command at a high altitude over a highly populated area of a highly technical society such as the United States.

Instances of volcanic eruptions are their highest for 300 years and scientists fear a major one that could kill millions and devastate the planet is a real possibility. Experts at the European Science Foundation said volcanoes – especially super-volcanoes like the one at Yellowstone National Park, Wyoming, which has a caldera measuring 34 by 45 miles (55 by 72 km) - pose more threat to Earth and the survival of humans than asteroids, earthquakes, nuclear war and global warming.

The world's most dangerous active volcanoes include Yellowstone, Mount Vesuvius in Campagnia, Italy, and Popocatépetl near Mexico City. If any of them or other massive volcanic peaks suffered a major eruption the team said millions of people would die and earth’s atmosphere would be poisoned with ash and other toxins "beyond the imagination of anything man’s activity and global warming could do over 1,000 years."

Worryingly, scientists say research over the last 300 years of volcanic activity shows we are currently in a "volcano season" meaning increased activity. Volcanoes are also more likely from November to April in the northern hemisphere when ice, rain and snowfall can compress the bedrock.

So your doctor has essentially been deputized now with an Obama executive action.

Mental health professionals, therapists, if they detect that you might leave the office and go grab a gun and do something, they have to call and report you. And now doctors must do the same thing. "Doctors and other mental health professionals play an important role in protecting the safety of their patients and the broader community by reporting direct and credible threats of violence to the authorities."

"But there is public confusion about whether federal law prohibits such reports about threats of violence. The Department of Health and Human Services is issuing a letter," to doctors clarifying that no federal law prohibits them from reporting on potential dangerous behavior by their patients.

The executive action also protects the rights of health care providers to talk to their patients about gun safety. "Doctors and other health care providers also need to be able to ask about firearms in their patients’ homes and safe storage of those firearms, especially if their patients show signs of certain mental illnesses or if they have a young child or mentally ill family member at home."

Britain's FTSE 100 recovered slightly in late afternoon trading to finish the day down by just under 2 percent. It had fallen as much as 3 percent this morning, falling to lows last seen on Black Monday in mid-August. Today's sell off has seen around £30 billion wiped off its market capitalisation.

Most of the world's indices have rebounded after the announcement that China would no longer be imposing its emergency trading laws. Europe's biggest faller was Germany's Dax index which declined by 2.3 percent. Contrary to those devaluation fears, latest reserves data for December suggests the Chinese authorities have been intervening on a massive scale to prop up the renminbi.

Reserves fell by around $108 billion in December, leaving the country's war chest at $3.3 trillion. Analysts are divided on how long Beijing can burn through its reserves to keep the exchange rate stable.

"There's a large risk that we are going to see this continue tomorrow," Amy Zhuang of Nordea Bank told the BBC. "Chances are that there's again some major volatility, I would be extremely surprised to see a calm opening. And probably, this nervousness will last all of next week."

Introducing what's called a "circuit-breaker" to stop trading in the case of a sharp fall appears to be yet another example that hasn't really worked in the way intended. The idea is that a plunge of 5% will lead to a 15-minute pause to allow the mood to cool down, so that trading can resume more level-headed after the break.

But what happened on Monday and then again on Thursday did not quite go according to that plan. "Once you have that 15-minute pause, every trader in the market is just going to be sending out a ton of "sell" orders and so as soon as the market reopens, it is flooded with those orders and quickly hits that 7% percent threshold," Angus Nicholson of IG Trading told the BBC.

It would, of course, be madness to assume that one day’s trading can enlighten us in any way on the outlook for 2016 as a whole. But the stock market is being plagued by unanswered questions and buffeted by powerful, global trends. Here are five I expect to be following especially closely as the year progresses.

Iran and Saudi Arabia

The increasingly angry dispute pitting Iran against Saudi Arabia has emerged as one of the early Black Swans of 2016: it is the sort of event that could have been predicted but by and large wasn’t. It could turn out to be a major event, or could subside almost as quickly as it flared up. The real danger from this latest bust-up is that it will delay any resolution to the Syrian quagmire.

Company profits

Corporate profits in the West could be at a turning point. For years, they outperformed, feeding into a simplistic narrative that “capital was seizing all the gains of growth” – but 2015 was actually a grim year for corporate America in particular. It may well be that the US and other Western economies are past peak profitability, at least when it comes to this economic cycle.

US Presidential election

The US elections will cast a gloomy shadow over the world economy. Donald Trump, a nasty populist who is no friend of free trade or of genuine, free market capitalism, continues to do dangerously well in the Republican party’s nomination context. At the very least, Trump could cling on for a while longer, rattling investors in the process; or he could win the nomination and help give Hillary Clinton the keys to the White House.

Brexit

The Brexit debate will also spook the markets. Yet while investors, economists and firms are right to be concerned by Trump, too many are acting irrationally when it comes to the EU referendum question. Axel Weber, the chairman of UBS, the Swiss bank, was far more sensible last year when he argued that “the UK would get a very favourable deal with the EU to maintain a large part of market access to the EU” in the event of a Brexit.

Pay in the UK

Wages and salaries will be the key question for the British economy. The Fed finally bit the bullet last year and hiked US interest rates; but the Bank of England may easily decide to do nothing all year. If salaries shoot up, the Bank will hike rates; if pay rises start to look vanishingly small again, it will keep rates on hold.

The mayor suggested women keep “at arm’s length” from strangers, travel in groups, and to ask bystanders for help. “It is important to prevent such incidents from ever happening again,” Reker said, the Independent reported Wednesday. Reker’s comments appear to ignore the fact that victims, often traveling in groups, were systematically targeted by gangs. “I don’t think much of the how-to-behave tips for women such as arm’s length. It is not women who are responsible, but the perpetrators,” German Justice Minister Heiko Mass responded Wednesday on Twitter.

Pamela Geller, president of the American Freedom Defense Initiative, told Breitbart News on Wednesday that “Europe is doomed” because there is “a break between the people and the EU elites.” “People are going to rise up or they’re going to succumb” said Geller, WND’s Woman of the Year. Cologne’s police department has received more than 100 criminal complaints since last Friday. Similar attacks happened in Duesseldorf, Hamburg and Stuttgart, CNN reported Wednesday.

Bild accused German media seven days ago of ignoring stories that make Chancellor Angela Merkel look bad. Merkel ushered in 1.1 million migrants from the Middle East and North Africa in 2015. The aftermath of the New Year’s Eve attacks convinced a reporter for Huffington Post Deutschland that a cover-up was attempted. “The media’s handling of this issue is a slap in the face for every victim,” Anabel Schunke said Monday, WND reported.

The Diagnostic and Statistical Manual of Mental Disorders: Fifth Edition (DSM-5), which the American Psychiatric Association uses for psychiatric diagnosis, defines “oppositional defiant disorder” as a “recurrent pattern of negativistic, defiant, disobedient, and hostile behavior toward authority figures” which typically begins at a young age but can survive into adulthood.

“Adults with Oppositional Defiant Disorder feel misunderstood and disliked, hemmed in and pushed around,” according to Russell Barkley, PhD. “Some feel like mavericks or rebels.” In other words, an Obama-supporting psychologist could potentially diagnose conservatives and libertarians with “Oppositional Defiant Disorder” due to their criticism of authority, particularly the federal government, and then report them to the FBI as too “mentally unfit” to purchase a gun.

But even scarier, the newest version of the DSM-5 is so broad that almost every form of human behavior could be considered some type of mental illness. In fact, over the past 50 years, the number of mental illnesses defined by sequential editions of the DSM have grown from 130 to over 350.