Leaders of the world's top 20 economies are descending on the German city of Hamburg for this year's G20 Summit which takes place on July 7 and 8. 

The agenda suggests a continuation from the 2016 gathering in Hangzhou – a focus on free and fair trade, climate change and fighting terrorism. 

But a lot has changed in the world since last year, arguably most significantly the election of Donald Trump as US president.  

Here are five things to keep an eye out for as the two-day summit gets underway.

Trump meets Putin

Donald Trump's administration has been dogged by controversy and investigations over his presidential campaign's relationship with Russia. And on Friday, the world's media will be licking their collective lips as the US president sits down with his Russian counterpart Vladimir Putin on the sidelines of the summit.

Donald Trump and Vladimir Putin will meet face-to-face for the first time in Hamburg, as controversy over the Trump campaign's links to Russia continues in the US. /VCG Photo

Whether the men have met face-to-face before is unclear – Trump has previously claimed to have met, and to have not met, the Russian leader – but the body language between the leaders will be closely scrutinized.

The meeting is slated to last between 30 minutes and one hour, with Russia briefing that Syria and Ukraine will be the issues on the agenda. These should prove contentious enough, especially after Trump used a speech in Poland to call on Russia to stop "destabilizing" Ukraine and end support for "hostile regimes". Russia remains Syrian President Bashar al-Assad's main international supporter, while Trump ordered a missile attack against a Syrian military base.

US intelligence agencies believe Russia intervened in the 2016 presidential election to help Trump win, a claim the president has failed to unambiguously accept. Will he bring this up with Putin?

Way ahead for climate deal?

The Hangzhou G20 Summit is perhaps best remembered for an event that actually happened the day before its official opening – Chinese President Xi Jinping and then US President Barack Obama agreed to ratify the Paris Agreement on climate change. Heralded as a great step forward in the global battle against climate change, the deal has since been hampered by the Trump administration's decision to withdraw from the accord.

China and the US committed to the Paris climate deal in April 2016 ahead of the Hangzhou G20 Summit, but Donald Trump has since withdrawn the US from the agreement. /Xinhua Photo

China, along with other signatories and several US states, has restated its commitment to the pact. In fact, only the US, Nicaragua and Syria have not signed up to the deal. German Chancellor Angela Merkel, host of this year's summit, has called on the G20 to renew its focus on combating climate change and insists that Europe stands together on the issue.

The details of the final communique will be worth a look. Following a G7 meeting in late May, leaders acknowledged they had failed to bridge differences over climate change. With the remainder of the membership committed to the Paris goals, can the US agree on language that points to a way forward?  

Xi meets Trump

Chinese President Xi Jinping traveled to the US in April for talks with Trump at his Mar-a-Lago estate. After Trump's criticisms of China on the campaign trail – and on social media – there was intense interest about how the men would get on when they met face-to-face. 

Trump hailed the two-day visit as the start of "a very, very great relationship" and announced a 100-day action plan – in May the countries reached a 10-point trade deal.

Chinese President Xi Jinping held his first face-to-face talks with his US counterpart Donald Trump in April 2017. /Xinhua Photo‍

However, Trump's recent tweets have suggested a change in approach. The DPRK's escalation of missile tests (see below) is the main cause of conjecture, and the US last week announced sanctions against a Chinese bank with alleged links to the DPRK.  

The US also conducted a freedom-of-navigation operation in the South China Sea last week, and a major US arms sales to the Chinese region Taiwan was announced. China's ambassador to Washington Cui Tiankai warned the weapons deal "will certainly undermine the mutual confidence between the two sides and runs counter to the spirit of the Mar-a-Lago summit." Will Xi and Trump find common ground when they meet on the sidelines of the G20 Summit?

DPRK missile launches

Talks to address tensions on the Korean Peninsula are a constant, but the G20 Summit is the first opportunity for leaders to look for a solution face-to-face since the latest bout of tensions. These were amplified by the DPRK's launch of an intercontinental ballistic missile earlier this week.

DPRK leader Kim Jong Un celebrates after the test-launch of the intercontinental ballistic missile Hwasong-14 in this undated photo released by the DPRK's Korean Central News Agency in Pyongyang on July 5,  2017. /VCG Photo

While all parties have condemned the DPRK missile tests, proposed solutions have varied. China has recommended a resumption of the six-party talks and a deal whereby the DPRK halts its nuclear ambitions in return for the postponement of US-South Korea military drills, a suggestion Russia has agreed with. But the US has so far shown little appetite for compromise, and on Thursday Trump went as far as to say he was weighing up "pretty severe" options.

With the key leaders together in one place, will they be able to find a common voice on the DPRK?

Clash of ideas

And a clash of ideas on the global economic model is likely to be evident inside and outside the summit venue. Anti-capitalist protesters are a common site outside G20 meetings, and thousands rampaged on the streets of Hamburg on Thursday evening.   

A clash of ideas on the global economy is expected inside and outside the G20 Summit venue in Hamburg. /VCG Photo

Within the building, the "American First" rhetoric of Trump is set to meet the pro-globalization, free trade agenda of China and host country Germany. 

"Those who think that the problems of this world can be solved with isolationism or protectionism are terribly wrong," Merkel said in an address to the German parliament last week.

Reconciling the relative unity between China and European countries on issues such as globalization and climate change with the contrary stance taken by the US is likely to be the dominant theme over the next two days.