China is already the world's largest manufacturer and user of solar panels and the largest investor in renewable energy. It also plans to start a carbon-trading market.

The same day in July that US President Donald Trump controversially met in private with Russian President Vladimir Putin in Helsinki, another meeting was underway among global leaders. Held in Beijing, it too was unconventional, at least from the perspective of 20th century history. It concluded with China signing an agreement with the EU that will see the world's biggest coal user and notorious polluter step to the forefront in the global initiative to protect the environment.

Premier Li Keqiang led the Chinese delegation that met with European Council President Donald Tusk and European Commission President Jean-Claude Juncker at the 20th EU-China Summit. A range of issues were discussed, but the breakthrough was a signed memorandum of understanding and statement outlining joint ambitions on clean energy initiatives to support the 2015 Paris Agreement. The EU and China aim to increase cooperation in emissions trading, low carbon cities, energy efficiency and renewable energy.

"We have underlined our joint, strong determination to fight climate change and demonstrate global leadership," Junker said. "It shows our commitment to multilateralism and recognises that climate change is a global challenge affecting all countries on Earth. There is no time for us to sit back and watch passively. Now is the time for decisive action."

Bill Hare, Director and Senior Scientist at Climate Analytics headquartered in Berlin, says "clearly the US has vacated this geopolitical territory and the EU has stepped up to in effect replace it".

"During the Obama years, the US was the bigger player with China and much more influential," he says. "For both China and the European Union climate change is a major issue, and one which decision-makers in both regions recognise as posing major threats to the future wellbeing of their peoples and economies. Both see the Paris Agreement as enduring and long-term architecture to help the world prevent dangerous climate change."

And for China the impacts are indeed close to home. Long battling desertification and heavily polluted cities, its northern plain could become virtually uninhabitable within this century, according to a just-released study by the Massachusetts Institute of Technology (MIT).

"This spot is going to be the hottest spot for deadly heatwaves in the future," said MIT Professor Elfatih Eltahir, who led the new study. "China is currently the largest contributor to the emissions of greenhouse gases, with potentially serious implications to its own population. Continuation of current global emissions may limit the habitability of the most populous region of the most populous country on Earth."

Hare says the "big question is whether the EU and China will increase their level of ambition and action by 2020".

"There has been a big question about whether China would be prepared to do that in the absence of the United States," he says. "With both the EU and China now working together, and both working internally toward the possibility of raising their ambition by 2020, there are grounds for optimism that both these important actors will move forward, and in the process encourage many others to do so even without United States."

The EU and China account for around one-third of global greenhouse gas emissions and both share a vision of a prosperous, energy-secure future. A 2015 climate declaration between Beijing and Brussels already agreed to intensify cooperation in mitigation policies, carbon markets, low-carbon cities, greenhouse gas emissions from the aviation and maritime industries, and hydrofluorocarbons.

Even though the goals set out in the Paris Agreement are voluntary - so-called nationally determined contributions (NDC) - the accord creates a binding framework for countries to progressively move forward to meet increasingly stringent targets.

"China seems set to meet its NDC, however the ambition level is not yet sufficient and nor is that from the European Union," says Hare.

"One of the areas to watch is how the most-recent agreement between the EU and China begins to play in relation to coal investments," says Hare. "A number of countries are still investing in coal, including China externally, so if China begins to switch its position as it moves forward with the European Union, switching its foreign investments toward cleaner technology would have a big impact on others such as Japan, South Korea and countries looking for cleaner ways of developing, particularly in Southeast Asia and Africa."

China is already the world's largest manufacturer and user of solar panels and the largest investor in renewable energy. It also plans to start a carbon-trading market in Beijing. Europe's cutting edge environmental technology and China's increasing will and vast government spending seem a good fit.

The two sides said they remained committed to creating a mechanism to transfer $100 billion a year from richer to poorer nations to help them adapt to climate change. The fund has been a major bone of contention for the Trump administration.

As Europe sweltered through record temperatures last week - surpassing 45 C in Portugal - and China reflects on a possible desolate future for its north, climate change seems far from just a theory. Rational leaders are moving to see if it can be stopped from becoming inevitable.

Jon Van Housen and Mariella Radaelli are editors at the Luminosity Italia news agency in Milan