Angela Merkel needed a photo to recognise Australia’s latest Prime Minister Scott Morrison, but her fellow G20 participants required no help to recognise that the global body regulating international trade disputes is in deep trouble.

The German chancellor was spotted using a cheat sheet featuring a mugshot of Mr Morrison – and it is easy to understand why.

Ms Merkel, who has led her nation for 13 years, has seen Australian prime ministers come and go, from John Howard to Kevin Rudd, Julia Gillard and Mr Rudd again, then Tony Abbott, followed by Malcolm Turnbull and now Mr Morrison.

The meeting came a day after Mr Morrison’s first meeting with US President Donald Trump, who quizzed him about Mr Turnbull’s ouster.

Angela Merkel reveals her Morrison cheat sheet during an unguarded moment. Photo: AAP

The mystery of Australia’s revolving-door leadership aside, there was no disagreement about the urgent need to fix the brewing trade war between the US and China.

The threats and counter-threats traded between the superpowers represented the most obvious symptom of global discord.

In a potentially significant compromise, struck over a steak dinner at the G20, Mr Trump and Mr Xi agreed to a 90-day truce. The US promised to halt new tariffs in exchange for China buying more US goods.

Mr Trump had originally threatened to impose a tariff of 25 per cent, up from 10 per cent, on $US200 billion worth of Chinese imports to the US, from January 1.

The deal, struck in what the White House termed a “highly successful meeting”, may reassure financial markets and ease fears about the economic implications of reduced trade between the two economic powers.

Mr Trump put a smiley face on the trans-Pacific contretemps, claiming he has an “incredible relationship” with Mr Xi.

“The relationship is very special – the relationship that I have with President Xi,” he said.

“I think that’s going to be a very primary reason we’ll probably ending up getting something good for China and good for the United States, so we very much appreciate it.”

Mr Xi replied: “Only with co-operation between us can we serve the interest of world peace and prosperity.”

President Xi smiles as President Donald Trump looks grim at the G20. Photo: Getty

A final statement from a two-day gathering in Argentina recognised trade as an important engine of global growth.

“The system is currently falling short of its objectives and there is room for improvement,” the statement read.

“We therefore support the necessary reform of the WTO to improve its functioning. We will review progress at our next summit.”

The WTO is on the verge of becoming dysfunctional, just when it is most needed to fulfil its role as umpire in trade disputes and as the watchdog of global commerce.

The US is unhappy with what it says is the WTO’s failure to hold Beijing to account for not opening up its economy as envisioned when China joined the body in 2001.

To force reform at the WTO, the US has blocked new appointments to the world’s top trade court. The European Union is also pushing for reform at the WTO.

G20 delegates said that negotiations on the final summit statement proceeded more smoothly than at a meeting of Asian leaders two weeks ago that ended without a consensus, thanks to a decision to avoid any reference to protectionism and unfair trading practices.

On climate change, the US once again marked its differences with the rest of the G20 by reiterating its decision to withdraw from the Paris Agreement and its commitment to using all energy sources.

The other members of the group reaffirmed their commitment to implement the Paris deal – although that undertaking was marked by a “wiggle room” aside that actions to reduce greenhouse gas emissions would take into account “national circumstances and relative capabilities”.

“We will continue to tackle climate change, while promoting sustainable development and economic growth,” the statement said.

-with AAP