Are we in the early stages of a sustained rise in commodity prices? And what does it mean for the US dollar?

We posed these questions a year ago when robust global economic growth was driving commodity demand and the US dollar was starting to tip over from a 15-year high. The two are inextricably linked, though which is the horse and which the cart is not always clear. The recent disruption in financial markets suggests it's worth a fresh look at the relationship.

Over the past couple of years, there has been a broad improvement in commodity prices, with indices up by around 50% on average since early 2016. It's been far from uniform, and different commodities bottomed at different times.

Iron ore and oil have seen the most spectacular rebounds, both up more than 100% from their lows.

The fundamentals in each commodity market are very different, but Principal Economist Jon Butcher identifies common factors behind the recovery.

First and foremost is growth in the global economy. GDP growth strengthened from a low of 2.3% in Q1 2016 to a six-year high of 3.1% in Q4 2017. The upswing has been broadly based with growth accelerating across Asia, Europe and the Americas. In 2016, emerging market growth was just 3.7%; this year we expect 4.6%, with China and India driving much of the improvement. This is doubly important for commodity demand, given the resource-intensive nature of emerging market growth.

Then there is the US dollar. The currency dropped 10% on a trade-weighted basis by end-January 2018, from its high of a year ago. The relationship between the US dollar and commodity prices is not straightforward, or indeed constant. But the dollar tends to be inversely correlated with commodity prices; a weaker dollar usually means stronger commodity prices, and that's what we've seen over the past six months.

The fall in the value of the dollar reflects strength in the emerging world rather than a weak US economy.

It's also sentiment: with confidence boosted by the global economic upswing, investors have shifted capital out of traditional safe havens like US treasuries into riskier assets with potentially higher returns.

Better prospects for growth in major trade partners like Europe and Canada, and with the expectation of monetary tightening in those economies, they have pushed their currencies higher against the dollar. We'd expect continued dollar weakness through 2018 given the prospects for a strong year of global economic growth.

Financial market volatility in the last fortnight has upset the apple cart. Commodity prices have corrected and the US dollar bounced by 4%, taking it back to December levels. US jobs data released on 2 February highlighted tightness in the US labour market.

Associated wage gains prompted fears of higher inflation and raised the prospect of accelerated US interest rate hikes. Uncertainty spiked, and equities and commodities dropped. Increased risk aversion effectively pulled capital back into safe havens like the US.

So, turning point or just a blip? More likely the latter.

Our view is that the global economy is set fair for growth at a healthy pace, perhaps a tad slower than in 2017-18. Developing economies in particular will do well.

This provides a backdrop for a sustained recovery in commodities over the next five years, though each commodity market has its own fundamental story. Oil, for example, is stuck in oversupply for the next two years before the market tightens into the early 2020s.

As commodities gradually recover, the US dollar should revert to gentle decline – though markets adjusting to the end of ‘easy money’ means it will doubtless be a bumpy ride for the currency and commodities alike. If we're right, then some commodity producers may be on a journey to a better place in the next few years – firmer prices and better margins.

On the other hand, it might not pan out this way. So producers have to learn from this tough down cycle and persevere with the relentless drive to keep costs down so they can still make money even at future cycle lows – and wherever the US dollar travels. That has to be the goal.