Rumours already swirling about the future of United States involvement in the Paris deal were further stoked when Mr Trump tweeted on Wednesday: "I will be announcing my decision on the Paris Accord over the next few days".
The matter has deeply divided the administration.
The White House has declined to comment on those reports, with spokesman Sean Spicer saying only that Trump would make it clear in the "next few days".
Word of Trump's expected decision came a day after the president met with Pruitt.
But the official says there may be "caveats in the language" that Trump uses to announce the withdrawal - and that could leave open the possibility that the decision isn't final.
"A USA withdrawal from Paris will be a disappointment to the climate community, but it may also embolden other countries to fill the void left by the US and take on a greater leadership role", said Glen Peters, a Norwegian scientist who tracks global carbon emissions.
The EU official involved in organizing the EU-China meeting said it would will "send important signals for the multinational system", as Trump moves to unpick some of the worldwide trade agreements the USA has signed up to.
Under Obama, Washington had pledged to reduce greenhouse gas emissions by 26-28 percent below 2005 levels by 2025. A long list of surprising people and companies-including ExxonMobil, several Republican senators, and Trump's secretary of state, Rex Tillerson (who was CEO of ExxonMobil before assuming his current role)-have all advocated for staying in the climate pact in one way or another. If President Trump calls it out for what it is, it will be a signal achievement of his administration.
This is what gives Mr Trump the authority to withdraw the USA from the agreement in a three-year process or take the U.S. out of the underlying United Nations climate accord all together - a process that would be much faster and in line with Mr Trump's ire towards the UN.
Moreover, the accord is flexible in the sense that it does not mandate that any nation achieve any particular level of emissions cuts. Accordingly, they are increasingly investing more in green technology.
Pope Francis presents Trump with papal writing on climate change
Asked about Spicer not being included in the group that met the Pope, a source close to the White House said: "Wow". Trump is the 13th president to visit the Vatican and, as part of his tour, he will view the Sistine Chapel.
California has also previously said it would help pick up the slack for any backdowns by the US President on climate change.
The 2015 agreement aims to prevent the Earth from heating up by 2 degrees Celsius (3.6 degrees Fahrenheit) since the start of the industrial age.
The Paris accord is meant to limit the global rise in temperature attributed to emissions.
The first option would be to exit the 2015 accord itself, but that would take almost four years to fully execute.
European leaders were especially dismayed by Trump's refusal to reaffirm USA support for last year's Paris climate change accord and his failure to publicly endorse NATO's mutual defense pledge.
Climate change, or global warming, refers to the damaging effect of gases, or emissions, released from industry and agriculture on the atmosphere.
Economists say a US pullout could give American exports an unfair price advantage compared to products from the European Union, where industries must pay penalties for emitting carbon dioxide.
Guterres said in that speech that "it would be very important for the US not to leave the Paris agreement".