For economists and investors, the globe hasn't been this confusing in at least three decades

Uncertainty around what will happen next with the global economy and how governments will respond is troubling Wall Street as investors and economists chase a moving target of possible trade wars and monetary policy shifts.

An index designed to measure policy-related uncertainty around the world is hovering at its highest level ever. The Economic Policy Uncertainty Index hit its second-highest level of all time, 340, in June. The index spiked to 341 at the end of last year when the market suffered its worst December since the Great Depression amid the intensified U.S.-China trade war and an ill-advised rate increase from the Federal Reserve, with the major stock averages briefly dipping into bear market territory.

“We found that high levels of policy uncertainty tended to depress investment, depress hiring, in industries that are most exposed to that government behavior,” one of the index’s founders Scott Baker told CNBC.

The EPU Index tracks the amount of times newspaper articles use buzzwords related to economic and political uncertainty. Additionally, it measures the number of tax laws set to expire and the spectrum of disagreement among economists, the more dissent, the higher the index goes. Tracking began in the 1990s.

The track record of the index speaks for itself. The metric has spiked during almost every important political and economic moment since its inception, from the terrorist attacks of 9-11 to the 2008 financial crisis to the vote that passed Brexit.

Populist uprisings seem to be the agents of change around the world lately. The index average rose 78% when President Donald Trump defeated left-wing political veterans in the 2016 election. Uncertainty also reigned when the UK voted in a nation-wide referendum to leave the European Union.

This time is no different. Concerns about global economic uncertainty caused the Federal Reserve to cut interest rates for the first time since the 2008 financial crisis. After a 25 basis point reduction in the overnight lending rate, Fed Chairman Jerome Powell said “implications of global developments for the economic outlook as well as muted inflation pressures” contributed to the Fed’s decision.

The confluence of Trump’s America-first agenda and China’s comfortability with long-standing unfair trade practices have kept a trade deal between the U.S. and China tied up for more than a year.

Since the Chinese trade officials reneged on a nearly finished trade deal in May, the U.S. and China have engaged in a tit-for-tat tariff war, weighing on business and investor sentiment.

On Thursday, Trump said in a tweet the U.S. is putting an additional 10% tariff on the remaining $300 billion dollars worth of Chinese goods, effective September 1, driving markets, the dollar and oil prices lower.

It is unclear how the trade talks will go when they resume in early September. China may stall a resolution until after the 2020 election, another source of uncertainty overhang, as Democrats juggle twenty plus candidates, some with socialist agendas.

Global central banks have been easing at unprecedented levels, with debt in Europe and Japan at zero or negative interest rates, while still producing weak economic data. Last week, European Central Bank President Mario Draghi signaled that the ECB will likely lower interest rates before the end of the year as “a significant degree of monetary stimulus continues to be necessary to ensure that financial conditions remain very favorable and support the euro area expansion.”

“The risk of a European uncertainty shock remains elevated,” said Societe Generale global head of research Brigitte Richard Hidden. “The much greater risk is Brexit, or more specifically a no-deal Brexit.”

A populist uprising in Britain landed a nation-wide referendum with plans to leave the European Union and a new British Prime Minister make it even more unclear if the U.K. will make a plan before the deadline.

Last week, GDP data showed that economic growth is slowing, although not entirely, thanks to strong consumer spending.

A standout number in the GDP report was the 5.5% tumble in gross private domestic investment. Worries over the tariff war with China have been a major driver of business sentiment, with executives expressing concern throughout this quarter’s earnings season.

If the EPU is any gauge, the decline in capex spending makes sense.

The creators of the EPU Index, Scott Baker of Northwestern University, Nicholas Bloom from Stanford University and Steven Davis, of the University of Chicago, have also shown that an economic policy uncertainty shock of 90 points reduces gross fixed investment in the U.S. by 6% within two quarters and lowers GDP by just over 1%.

“Uncertainty is the enemy of the business cycle,” said Morgan Stanley’s Chetan Ahya in a note to clients, and “uncertainty still reigns.”

— with reporting from CNBC’s Michael Bloom