Leaders of the world's top economies will gather on Friday (July 7) in Germany for perhaps one of the stormiest G20 summits in years, with disagreements over issues ranging from global trade to measures to battle climate change.

Here's a look at what the organisation is about, and the issues on its agenda during the two-day summit.

What is G-20?

The Group of 20 leading industrialised and emerging powers hold annual summits on economic governance, with wars and crises often overtaking the official agenda.

Grouping the United States and other G7 members with giants such as China, India and Russia, it represents two thirds of the world population, three quarters of world trade and about 80 per cent of economic output.

The other members are Argentina, Australia, Brazil, Britain, Canada, France, Germany, Indonesia, Italy, Japan, Mexico, Saudi Arabia, South Africa, South Korea, Turkey and the European Union.

The G-20, with its ministerial-level beginnings in 1999, first met for a summit in 2008 in Washington to discuss ways to achieve balanced and sustainable world economic growth.

Critics charge that the "self-appointed" club undermines the role of the international bodies, such the United Nations, International Monetary Fund (IMF) and World Bank.

The grouping has often been a magnet for protesters, including at this year's meet in Hamburg, Germany.

At the 2010 summit in Toronto, thousands of anti-capitalist protesters clashed with Canadian police, leaving dozens injured on both sides and sparking mass arrests.

The list of G-20 members does not strictly reflect the world's 20 biggest economies. Some non-members like Switzerland have bigger economies than, for example, member Argentina.

The leaders mostly meet behind closed doors and lack the power to enforce binding decisions or rules.

The heads of global and regional bodies are invited to the summits - among them the chiefs of the UN, IMF, World Bank, WTO, African Union, Apec and South-east Asia's Asean.

Rotating G-20 summits also invite guest nations, including "permanent guest" Spain and, this year, partner countries the Netherlands, Norway and Singapore.

Next year's G-20 host will be Argentina.

Key issues and personalities

- North Korea

North Korea's first successful test of an intercontinental ballistic missile on Tuesday (July 4) is likely to overshadow all other
trade and diplomatic rows. The reclusive state's relentless pursuit of its nuclear ambitions comes as a slap in the face for US President Donald Trump, who vowed Pyongyang's goal of possessing an ICBM "won't happen". The tough-talking property tycoon has so far failed to persuade China to bring its rogue neighbour to heel.

- Storm clouds

Germany has made climate protection a priority of its G-20 presidency. It had hoped to get the world's biggest industrialised and emerging economies to commit to taking the lead in implementing the landmark 2015 Paris climate deal on keeping the global rise in temperatures "well below" 2 deg Celsius from pre-industrial times.

But Trump dashed those hopes after vowing in early June that he would pull the world's second biggest carbon emitter out of the Paris accord.

Host Chancellor Angela Merkel admitted that after Trump's announcement, she "knew that we could not expect discussions to be easy". But she and European allies have vowed to defend the climate pact at the summit, setting them on a collision course with Trump.

- Looming trade war

Signing up to an anti-protectionist pledge used to be routine at G-20 meetings, but not this time.

Trump, swept to power by popular anger over deindustrialisation in vast parts of the United States, has pledged to "follow two simple rules: buy American and hire American". That has put him at odds with many US trading partners, including export giants Germany and China, which he has criticised over their massive trade surpluses.

Trump's threats may soon materialise, as Washington is reportedly preparing to impose punitive tariffs on steel imports - something that
G-20 exporters would be keen to ward off.

The United States in April launched a probe into whether steel imports posed a danger to national security, with the result due within days. Trump is reportedly waiting to hear from trading partners before announcing his decision on whether to limit imports of the metal.

According to news website Axios, the US leader is leaning towards imposing tariffs as high as 20 per cent on the metal - a move that would likely unleash retaliatory measures.

- Antagonistic pairs

With accusations of Russian meddling in the US elections and contacts between Trump's senior aides and President Vladimir Putin's men, the vexed relationship between the two will be closely scrutinised when they meet face to face for the first time on Friday.

The two leaders face an array of contentious foreign policy issues, from Syria to Ukraine and North Korea. Trump has struck a tough tone on Russia's ally Syria, while Washington's decision to toughen sanctions over the conflict in Ukraine has angered Moscow.

Another meeting to watch will be Trump's talks with China's President Xi Jinping, particularly after Trump, in a tweet, accused Beijing of not doing enough to rein in North Korea. Meanwhile, Trump infuriated Beijing last week when he approved a US$1.3 billion (S$1.8 billion) arms sale to Taiwan, while China lashed out after a US warship sailed close to an island claimed by China, Taiwan and Vietnam in the South China Sea.

Merkel also faces a testy meeting with Turkey's President Recep Tayyip Erdogan, particularly after Berlin refused him permission to address ethnic Turks on the sidelines of summit. Berlin and Ankara's relations have been fraught, deteriorating sharply
over Turkey's mass crackdown after a failed coup last year and a host of other rights controversies.

- Street protests

Outside the conference rooms, anti-globalisation activists, including an anticipated 8,000 potentially violent extremists, are squaring up for a showdown with police. Germany has deployed 20,000 officers from across the country. The authorities have also banned rallies in a vast area of the city during the summit and stopped protesters from setting up camp.

But the measures have only angered far-left activists, who complain that the city is being turned into a "fortress" and say they still plan to disrupt the summit.

Source: AFP