GLOBAL MARKETS-Stocks dip, investors twitchy about AI disruption

By Gregor Stuart Hunter and Amanda Cooper

SINGAPORE/LONDON, Feb 24 (Reuters) - Global shares tumbled for a second day on Tuesday, as sentiment suffered on a range of factors, from uncertainty over U.S. President Donald Trump's tariff policy and geopolitical tensions to renewed worries about the upheaval to the economy from AI.

After the Supreme Court ruled Trump's emergency tariffs were unlawful on Friday, the president announced a 10% across-the-board levy, which came into effect on Tuesday . Trump later said the tariff would be 15%, but it was unclear when, or if, this would apply.

Importers could be in line for billions of dollars in refunds, while trade partners and investors alike are in the dark about where many existing tariff agreements stand.

MSCI's All-World index .MIWD000000PUS eased for a second day. In Europe, the STOXX 600 .STOXX steadied, but remained in sight of record highs.

Markets in Asia got a boost from China and Japan, where traders returned from holiday. U.S. stock futures ESc1, NQc1 were up 0.2-0.3%.

BEARISH ANALYSIS ON EFFECTS OF AI GETS ATTENTION

On Monday, the S&P 500 .SPX slid 1.0%, erasing the past week of gains, as fears over the displacement effects of AI on software and other industries pushed the Nasdaq Composite .IXIC 1.1% lower. A bearish analysis from Citrini Research on the possible risks to the global economy took a further toll on jittery investor sentiment.

The report was "getting a lot of airplay", said Tony Sycamore, market analyst at IG in Sydney. "It does align with quite a few fears which are out there."

The article, which circulated at the weekend, is one of a number of recent "think pieces" on the long-term consequences of artificial intelligence - on employment, global growth and almost human existence itself - that have rattled investors.

In a note discussing a similar piece, Deutsche Bank strategist Jim Reid wrote: "The argument leans heavily on narrative and emotion rather than hard evidence. That doesn’t mean it will ultimately be wrong, but ... the vibes-to-substance ratio is undeniably high."

The sheer scale of corporate borrowing and spending on AI has been enough to make many nervous, not least because of the outsized market weight of companies at the heart of the boom. Yet, for all the recent volatility, the S&P itself is only around 2.5% below record highs.

"None of this, so far, has delivered the knock-out blow to equity markets, where the S&P 500 has gyrated in a narrow 6,775-7,000 range since the start of the year," said ING strategist Chris Turner. "Tomorrow evening's Nvidia release might be the next big story, however."

AI chipmaker Nvidia NVDA.O, which reports earnings after the bell on Wednesday, accounts for around 8% of the entire S&P 500.

FEDEX SUES FOR REFUNDS AFTER U.S. TARIFF RULING

On Monday, Trump warned countries against backing away from recently negotiated trade deals with the U.S. after the Supreme Court ruling, saying that he would impose much higher duties on them under different trade laws.

The new tariffs are based on Section 122 of the Trade Act of 1974, causing further confusion in markets trying to come to grips with U.S. protectionist policies. Global transportation company FedEx FDX.N on Monday sued for a refund.

In currencies, the dollar was a touch stronger, gaining most noticeably against the Japanese yen JPY=, which sank after a report from the Mainichi daily on Tuesday that said Prime Minister Sanae Takaichi had expressed her concern about further rate hikes when she met Bank of Japan Governor Kazuo Ueda last week.

The dollar was last up 0.75% at 155.79 yen and steady against the euro EUR= at $1.1791.

In commodities markets, Brent crude LCOc1 was up 0.1% at $71.57 per barrel as tensions continued to simmer between the U.S. and Iran while, in precious metals, safe-haven gold XAU= remained volatile, down 1.2% at $5,170 an ounce.

Bitcoin BTC= fell 2.2% to $63,172, while ether ETH= was last down 2.1% at $1,823.