The meeting of 196 countries, and the European Union, comes in the wake of increasingly dire warnings.
The latest round of United Nations climate talks get under way on Monday with governments facing pressure to ramp up action to cut emissions.
The meeting of 196 countries, and the European Union, comes in the wake of increasingly dire warnings about the state of the climate and at the end of a year which has seen severe weather extremes and increasing calls for action.
UN climate chief Patricia Espinosa (pictured) said: "This year, we have seen accelerating climate change impacts, including increased droughts, storms and heatwaves, with dire consequences for poverty eradication, human health, migration and inequality.
"The world's small window of opportunity to address climate change is closing rapidly."
She said the conference must be the "launchpad" for more climate ambition.
It was due to be held in Santiago, Chile, but was moved at short notice to Madrid, Spain, because of ongoing civil protests in the Chilean capital.
In the week leading up to the start of the talks, the World Meteorological Organisation revealed levels of climate-warming greenhouse gases including carbon dioxide had hit record levels in 2018.
And the UN Environment Programme (UNEP) exposed a dramatic "emissions gap" between the action countries had pledged to curb emissions that drive global warming and what is needed to avoid the worst of climate change.
UNEP said emissions would have to fall by 7.6 percent per year up to 2030 to keep the world on track to limit temperature rises to no more than 1.5C above pre-industrial levels - beyond which there will be severe impacts of rising seas, extreme weather and threats to water and food security.
Further reports released during the talks will reveal how hot the world has been in 2019, and the amount of carbon pollution countries have pumped into the atmosphere this year.
Despite the growing public concern over climate change, which saw millions of people take to the streets in September to demand urgent action on the crisis as part of the school strike movement, few new climate plans are expected.
But there will be pressure at the talks - attended by UN Secretary General Antonio Guterres - on governments to signal that they will be unveiling more ambitious targets and plans in 2020.
Next year sees the next major round of UN climate talks, which are set to be held in Glasgow towards the end of the year.
The Paris Agreement on tackling climate change comes into force in 2020 and countries are expected to come forward with more ambitious plans to meet their commitments under the deal to curb global warming.
The UK's former clean growth minister, Claire Perry O'Neill, who is set to be president of next year's talks, will be attending the meeting in Madrid, along with Lord Duncan and delegates from government and devolved administrations.
But the UK is unlikely to play a particularly high-profile role as the general election takes place on what is scheduled to be the penultimate day of the meeting.
Meanwhile Greta Thunberg, the teenage climate activist who inspired the global school strike movement, is sailing back across the Atlantic for the talks.
She had travelled to New York by yacht with plans to make her way down to Chile to attend the talks in Santiago without flying, but had to find a way home when the meeting was moved.
In the nitty-gritty of the negotiations, countries are trying to finalise rules around carbon markets, and agree how to help at-risk countries such as low-lying island nations cope with climate impacts they cannot adapt to.
And they will look at how to use recommendations in recent UN science reports on the world's land and oceans.
Emily Beament is the PA environment correspondent.