Can world leaders reach agreement on a deal to cut carbon emissions?

Has the moment of truth arrived? A traumatised Paris will be in lockdown this week as more than 140 world leaders, including Barack Obama and President Xi Jinping of China, fly into the city for the start of two weeks of climate change negotiations that the UN hopes will lead to a historic new global deal to reduce carbon emissions.

No demonstrations will be allowed in France but hundreds of thousands of people are expected to march on Sunday in Britain, Australia, the US, South Africa, Brazil and mainland Europe.

An unprecedented security operation following the terrorist attacks in Paris will see 2,800 police guarding the 40,000 delegates and diplomats and 6,000 journalists who will pack the conference venue at Le Bourget airport north of the city.

A further 8,000 police will guard French borders. “Mobile units, riot squads and gendarmerie units will all be called on at an unprecedented level,” said the interior minister, Bernard Cazeneuve.

The mayor of Paris, Anne Hidalgo, urged Parisians not to use their cars on Sunday or Monday when much of the city will be virtually impassable as world leaders host bilateral meetings in hotels and embassies.

The summit, which hopes to secure a deal to hold global warming to a 2C rise, opens to a warning by World Bank chiefs that climate change destabilises countries and allows terrorism and conflict to flourish.

“We are quite certain that the impact of climate change will be to destabilise countries,” Jim Yong Kim, the World Bank president, told the Observer. The bank claimed that terrorist movements such as Boko Haram in Nigeria and al-Shabaab in Somalia have taken root because of long-running droughts and growing competition for scarce resources fuelled by climate change. “Whenever there is a scarcity of water, when there is erosion of soil, people are competing for these scarce resources. That is the main source of conflict,” said Makhtar Diop, the World Bank’s vice-president for Africa. “These disputes have spawned instability that has allowed movements such as Boko Haram to take root.”

Prince Charles will give the keynote speech at the summit of 195 countries and is expected to warn that there is little time to avoid climate catastrophe.

The state of emergency in France, which is due to last three months, has resulted in hundreds of events around the conference being been called off. However, some demonstrators are expected to defy police in the name of free speech.

Nine French climate activists have been placed under house arrest, accused of flouting a ban on organising protests. Naomi Klein, the Canadian writer and climate change campaigner, accused French authorities of “a gross abuse of power that risks turning the summit into a farce. The French government, under cover of anti-terrorism laws [is] shamefully banning peaceful demonstrations and using emergency powers to pre-emptively detain key activists.”

Greenpeace said people would make themselves heard, whatever the obstacles. Jean-François Julliard, executive director of its French arm, said: “March or no march, in Paris thousands of people will use their collective imagination to project their voices into the UN climate talks. When they do so, voices will ring loud in the ears of the politicians inside.”

John Jordan, a prominent British activist, said: “At the moment, a demonstration is legally defined as more than two people who share a political message. We are trying to find creative ways around these laws.”

UN bodies, international charities and academics have all urged governments to act boldly. “Climate change is the defining issue for the 21st century. We estimate that it is already causing tens of thousands of deaths every year – from shifting patterns of disease, from extreme weather events, and from the degradation of air quality, food and water supplies, and sanitation,” said a spokesman for the World Health Organisation

Mark Goldring, the UK chief executive of Oxfam, warned that developing countries’ economies could be wrecked by climate change – they faced losing $1.7tn (£1.1tn) annually by the middle of the century if global average temperatures rise by 3C.

“World leaders need to put aside their self-interest and do what is best for the world,” he said. “That means greater cuts to emissions and more climate funding so vulnerable communities already facing hunger, floods and droughts can survive.”