Madrid, Spain - As alarm bells ring ever louder worldwide over climate change, some 25,000 delegates will meet for the next two weeks in Spain for COP25, the annual United Nations international conference on a global challenge that shows little signs of being resolved.
Last Monday, a World Meteorological Organization report indicated that greenhouse gas concentrations rose again in 2018, with carbon dioxide levels hitting 407.8 parts per million, a new record in human history.
COP25 begins on Monday in a trade fair park in the Spanish capital, Madrid, days after the European Union collectively declared a "climate emergency", echoing a joint, equally grim crisis warning issued in early November by more than 11,000 scientists from 150 countries.
"The confirmation that we've exceeded the records for CO2 levels in the atmosphere indicates that the measures governments are currently taking are not sufficient," Alberto Mataran Ruiz, who specialises in environmental science at the Spain's University of Granada, told Al Jazeera.
"One key question is probably changing those measures. There's another big issue with the United States, which is pulling out of the 2015 Paris climate change agreement altogether... [It] is a big problem as the US is one of the most important producers of CO2."
Initially, COP25 was scheduled to be held in Brazil. It then moved to Chile after Brazil's right-wing President Jair Bolsonaro, widely criticised by environmentalists for his policies on the Amazon region, took office last January.
However, following lengthy spells of civil unrest in Chile, the Sebastian Pinera government there announced in early November that the country was ceding the hosting of COP25 to Spain, four weeks before it was set to start.
While Chile remains the overall in charge of COP25 this year, the event is being held at the sprawling grounds on the eastern edge of Madrid under the auspices of the Spanish government.
Spain's Minister for Ecological Transition, Teresa Ribera, told a news conference earlier this week that the overall cost of COP25 would be about 50 million euros ($55m), 10 million euros ($11m) less than anticipated, while roughly 200 million euros ($220m) of local economic activity is likely to be generated during the event.
More than 50 high-ranking authorities, including heads of states, are expected to attend, while grassroots climate activists will join parallel events, and in some cases, organising protests elsewhere in Madrid.
"Article 6 of the 2015 Paris climate agreement is the most important and most controversial question that needs to be resolved in COP 25," Javier Andaluz Prieto, a representative for climate and energy of the Ecologistas en Accion movement, told Al Jazeera.
"Last year, in COP24, they completed a kind of rulebook in which each country had to include its pledges on renewable energy and reduction of greenhouse gases," he said.
"But very different points of view still exist on carbon 'markets'" - emissions trading schemes covered in Article 6 - "while the Clean Development Mechanisms [CDMs]" - a global, environmental investment and credit project - "remain even more problematic", he said.
Huge wind farms built on lands belonging to indigenous communities in countries like Mexico, sometimes through CDMs, are one particular concern.
"It's these communities that are best adapted to climate change, who conserve biodiversity, but who are suffering the effects, on their land, of such mechanisms," Mataran Ruiz said.
A US delegation - despite the country already having given formal notice on withdrawing from the Paris Agreement - is one surprise attendant in Madrid.
Meanwhile, teenage Swedish environmental activist, Greta Thunberg, is still crossing the Atlantic in a catamaran on her way to Spain.
Last year, negotiations between different nations over the Katowice rulebook for climate change went down to the wire, and cliffhanger deals are expected in Madrid too.
"Last-minute obstacles have been the norm at several previous COPs," Andaluz Prieto said. "It would be unusual if this one was any different."
Mataran Ruiz said meetings like the COP25 should take place, "no matter how much energy they themselves use".
"They put climate change onto the media's agenda, they push governments to take measures, and they act as a loudspeaker to warn us about what's happening."