Speaking to reporters in Nanjing, eastern China, just over a week before the start of UN climate talks in Copenhagen on 7 December, Barroso said that taken as a whole, the proposed curbs were encouraging.
However, he said they fell short of the minimum scientists believed was needed to avoid future temperature rises of two degrees Celsius or more above the pre-industrial average, which could lead to dangerous climate disruptions.
"If you sum up all the commitments made so far, according to our estimates, we are not yet where we should be if we want Copenhagen to succeed," said Barroso, who will attend a European Union-China summit in Nanjing on Monday.
"Everyone has a good reason not to do more, and it's legitimate, but at the end if we just concentrate on the reasons not to do more, we'll not achieve the necessary result."
Barroso's calls were echoed by Swedish Prime Minister Fredrik Reinfeldt, who said on Monday that countries were not being ambitious enough in their proposals to reduce carbon emissions.
"The global efforts put on the table for mitigation are not enough [...] More needs to be done," Reinfeldt, whose government holds the rotating presidency of the 27-member European Union, told reporters during a regular EU-China summit days before crucial climate change talks in Copenhagen.
Reinfeldt also said the two sides had agreed to fight protectionism and keep their markets open.
The European Union has pressed for countries to agree on ways of cutting greenhouse gas emissions by 50% of recent global levels by 2050, a goal that scientists have said is likely to avoid temperature rises of 2C or more.
In July, the Group of Eight leading industrial countries failed to get the biggest developing countries plus China and India to sign up to the goal of halving world greenhouse gas emissions by 2050.
"I believe it should be possible and we are working for it, for the 50% by 2050," said Barroso. "Certainly, we would like to see that result, but it's too soon to say if the different partners are ready."
The world's biggest greenhouse gas emitter, China, said on Thursday it would try to slow its growing greenhouse gas emissions by aiming to cut the amount of carbon dioxide emitted to generate each unit of economic output by between 40 and 45% by 2020 compared with 2005 levels (EurActiv 26/11/09).
The United States has promised to cut 2005 emissions by 17% by 2020. EU leaders agreed in December 2008 to cut emissions by 20% below 1990 levels by 2020 and by 30% if other developed countries followed suit.
"What I can tell you is that I certainly ask the Chinese and all our partners for the outer limits of their positions," said Barroso.
Barroso urged all parties in Copenhagen to aim for an "ambitious, operational" accord to fight global warming.
(EurActiv with Reuters.)