Organizers expect around 29,000 visitors to the meeting, including around 50 heads of state and government for Monday's opening session.
While there is scant global action and no binding multilateral treaties to tackle the "global climate emergency", there is robust, even overwhelming agreement in the scientific community that human impact on climate has been enormous in recent years and that "we may have crossed tipping points".
"Our delegation is here to send a message that Congress's commitment to take action on the climate crisis is iron clad", she said, flanked by Democratic Congressional representatives.
"It's about applying pressure to those governments who don't think climate change is worth taking seriously". The blue zone will also host events and activities run by NGO actors and side events organised by participating countries.
Over the next fortnight, negotiators, business leaders and civil society members from nearly 200 countries, meeting in Madrid for the 25th round of the annual UN-sponsored climate talks, will focus on finalising the framework and modalities that will permit and ensure collaborative action among nations towards the common goal of slowing down global warming.
In order to do this almost 200 countries signed the Paris agreement in 2015 - this agreement meant that the countries pledged to try and keep the warming of the planet below 2 degrees Celsius, 1.5 is the number that scientists say that we should hit by 2050.
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The Paris process faces a moment of truth next year when governments are due to unveil more ambitious proposals to cut the production of planet-warming gases in time to stop the climate careering past risky tipping points. The adoption of such system would either move forward the Paris climate accord implementation or jeopardise the achievement of its goals in case of a weak deal.
Mr Guterres noted some 70 countries - many of them among the most vulnerable to climate change - have pledged to stop emitting more greenhouse gases by 2050. "This is Chile's COP: it is Chile that has organized the leadership and that has worked for an alliance against climate change and the success of this event will belong to Chile".
The COP25 conference takes place at the IFEMA convention center on the outskirts of the Spanish capital.
"And without them, our goal is unreachable", he said.
The Climate Change Conference is held annually within the framework of the UNFCCC.
Some 250,000 representatives from 200 countries are taking part.
The Paris Agreement aims to combat climate change by keeping the global temperature rise this century well below 2ºC above pre-industrial levels. The accord has since been ratified by 187 parties to the UNFCCC.