The UN secretary general has warned that the planet is close to “the point of no return” and branded global efforts to combat climate change “utterly inadequate”, as world leaders gather for a vital conference on the Paris Agreement.

Antonio Guterres issued the stark warning ahead of the fortnight-long UN climate change conference (COP25) in Madrid.

Rulers and delegates from almost 200 countries will attempt to firm up the commitments made in 2015, establish new international rules for emissions trading, and broker systems of compensation for poorer countries already affected by global warming.

The Alliance of Small Island States, representing nations most at risk from rising seas, views the talks as the last chance to avert potential "catastrophe", while Save the Children warns that 33 million African children are facing hunger as a result of cyclones and droughts made more likely by climate change.

“The point of no return is no longer over the horizon,” Mr Guterres told reporters in Madrid. “It is in sight and hurtling towards us.”

Climate change: Decade's defining issue in pictures Show all 20 1 /20 Climate change: Decade's defining issue in pictures Climate change: Decade's defining issue in pictures California In this decade, humans have become ever more aware of climate change. Calls for leaders to act echo around the globe as the signs of a changing climate become ever more difficult to ignore Getty Climate change: Decade's defining issue in pictures Athens, Greece Fierce wildfires have flared up in numerous countries. The damage being caused is unprecedented: 103 people were killed in wildfires last year in California, one of the places best prepared, best equipped to fight such blazes in the world AFP/Getty Climate change: Decade's defining issue in pictures Redding, California Entire towns have been razed. The towns of Redding and Paradise in California were all but eliminated in the 2018 season AP Climate change: Decade's defining issue in pictures Athens, Greece While wildfires in Greece (pictured), Australia, Indonesia and many other countries have wrought chaos to infrastructure, economies and cost lives AFP/Getty Climate change: Decade's defining issue in pictures Carlisle, England In Britain, flooding has become commonplace. Extreme downpours in Carlisle in the winter of 2015 saw the previous record flood level being eclipsed by two feet AFP/Getty Climate change: Decade's defining issue in pictures Hebden Bridge, England Hebden Bridge in West Yorkshire has flooded repeatedly in the past decade, with the worst coming on Christmas Day 2015. Toby Smith of Climate Visuals, an organisation focused on improving how climate change is depicted in the media, says: "Extreme weather and flooding, has and will become more frequent due to climate change. An increase in the severity and distribution of press images, reports and media coverage across the nation has localised the issue. It has raised our emotions, perception and personalised the effects and hazards of climate change." Getty Climate change: Decade's defining issue in pictures Somerset, England Out west in Somerset, floods in 2013 led to entire villages being cut off and isolated for weeks Getty Climate change: Decade's defining issue in pictures Dumfries, Scotland "In summer 2012, intense rain flooded over 8000 properties. In 2013, storms and coastal surges combined catastrophically with elevated sea levels whilst December 2015, was the wettest month ever recorded. Major flooding events continued through the decade with the UK government declaring flooding as one of the nation's major threats in 2017," says Mr Smith of Climate Visuals Getty Climate change: Decade's defining issue in pictures London, England Weather has been more extreme in Britain in recent years. The 'Beast from the East' which arrived in February 2018 brought extraordinarily cold temperatures and high snowfall. Central London (pictured), where the city bustle tends to mean that snow doesn't even settle, was covered in inches of snow for day PA Climate change: Decade's defining issue in pictures London, England Months after the cold snap, a heatwave struck Britain, rendering the normally plush green of England's parks in Summer a parched brown for weeks AFP/Getty Climate change: Decade's defining issue in pictures New South Wales, Australia Worsening droughts in many countries have been disastrous for crop yields and have threatened livestock. In Australia, where a brutal drought persisted for months last year, farmers have suffered from mental health problems because of the threat to their livelihood Reuters Climate change: Decade's defining issue in pictures Tonle Sap, Cambodia Even dedicated climate skeptic Jeremy Clarkson has come to recognise the threat of climate change after visiting the Tonle Sap lake system in Cambodia. Over a million people rely on the water of Tonle Sap for work and sustinence but, as Mr Clarkson witnessed, a drought has severley depleted the water level Carlo Frem/Amazon Climate change: Decade's defining issue in pictures Addis Ababa, Ethiopia In reaction to these harbingers of climate obliteration, some humans have taken measures to counter the impending disaster. Ethiopia recently planted a reported 350 million trees in a single day AFP/Getty Climate change: Decade's defining issue in pictures Morocco Morocco has undertaken the most ambitious solar power scheme in the world, recently completing a solar plant the size of San Francisco AFP/Getty Climate change: Decade's defining issue in pictures London, England Electric cars are taking off as a viable alternative to fossil fuel burning vehicles and major cities across the world are adding charging points to accomodate AFP/Getty Climate change: Decade's defining issue in pictures Purmerend, The Netherlands Cities around the world are embracing cycling too, as a clean (and healthy) mode of transport. The Netherlands continues to lead the way with bikes far outnumbering people Jeroen Much/Andras Schuh Climate change: Decade's defining issue in pictures Xiamen, China Cycling infrastructure is taking over cities the world over, in the hope of reducing society's dependency on polluting vehicles Ma Weiwei Climate change: Decade's defining issue in pictures Chennai, India Despite positive steps being taken, humans continue to have a wildly adverse effect on the climate. There have been numerous major oil spills this decade, the most notable being the BP oil spill in the Gulf of Mexico in 2010 AFP/Getty Climate change: Decade's defining issue in pictures Amazon rainforest, Brazil More recently, large swathes of the Amazon rainforest were set alight by people to clear land for agriculture AFP/Getty Climate change: Decade's defining issue in pictures California This decade may have seen horrors but it has led to an understanding that the next decade must see change if human life is to continue Getty

Noting that the world has the scientific knowledge and the technical means to limit global warming, the UN chief denounced policymakers’ lacklustre response in the face of a “global climate emergency”.

Mr Guterres said: “The signals of hope are multiplying. Public opinion is waking up everywhere, young people are showing remarkable leadership and mobilisation.

“More and more cities, financial institutions and businesses are committing to a 1.5C pathway … what is still lacking is political will.

“Political will to put a price on carbon. Political will to stop subsidies on fossil fuels. Political will to stop building coal power plants from 2020 onwards. Political will to shift taxation from income to carbon. Taxing pollution instead of people.”

He said that for the leaders of all countries to show “anything less” than accountability and responsibility, and a willingness to commit to ambitious targets “would be a betrayal of our entire human family and all generations to come”.

But he insisted his message was “one of hope, not of despair. Our war against nature must stop and we know that that is possible.”

Some 70 countries – many of them among the most vulnerable to climate change – have pledged to stop emitting more greenhouse gases by 2050. But some of the world’s largest emitters are yet to do so.

Mr Guterres said he hoped the Madrid meeting would prompt governments to aim for net-zero emissions by 2050, ahead of a deadline to do so at COP26 in Glasgow next year.

Last week, the UN’s World Meteorological Organisation warned that the level of greenhouse gases had reached another all-time high, “with no sign of a slowdown, let alone a decline”.

Four years after the Paris Agreement, negotiators are still to tackle the contentious issue of creating a worldwide market for emissions – a key element of the sixth article of the 2015 accord.

“We are here to find answers for article six, not to find excuses,” Mr Guterres said.

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While these talks represent the last chance for countries to keep the Paris Agreement alive by firming up their targets for 2050 after a five-year grace period, the conference also marks the first since Mike Pompeo’s announcement that the US would turn its back on the accord, as Donald Trump had long threatened.

The US will be represented by Marcia Bernicat, the assistant state secretary for international environmental affairs, while House speaker Nancy Pelosi will also lead a delegation of Democratic lawmakers.

Organisers expect about 29,000 visitors in total, including 50 heads of state and government for Monday’s opening, as well as scientists, seasoned negotiators and activists during the two-week meeting.

The talks were initially to be hosted in Chile, but deadly anti-government protests in its capital, Santiago, saw the conference relocated to Spain.