European leaders meeting in Brussels are set to endorse binding measures for cutting greenhouse gas emissions.
Slovenia's PM, who is chairing the summit, said the leaders had approved a timetable to implement an agreed 20% cut by 2020, compared with 1990 levels.
He likened the EU's plans to move to a low-carbon economy to a "third industrial revolution".
The summit is also discussing financial instability, as well as liberalisation of the bloc's energy markets.
Slovenian PM Janez Jansa said the leaders had taken note of a report by EU foreign policy chief Javier Solana warning of potential security concerns arising from global warming.
The report says climate change will have a growing impact on global security, multiplying existing threats such as shortages of food and water.
It warns that climate change could cause millions of people to migrate towards Europe as other parts of the world suffer environmental degradation.
EU'S 20/20/20 VISION: KEY AIMS AND POTENTIAL CHALLENGES
Mr Solana's report "enjoyed a lot of support", Mr Jansa told reporters.
The EU leaders are considering specific targets put forward by the European Commission in January on how to achieve the agreed 20% cut in greenhouse emissions by 2020.
The BBC's Paul Kirby in Brussels says an important barometer for the success of the summit is how far the leaders are prepared to go in implementing those targets.
The liberalisation of energy markets is another contentious issue, our correspondent says.
Germany and France lead a group of countries hostile to calls for the break-up of big energy companies which run both power stations and the distribution networks.
European Commission President Jose Manuel Barroso said there was a general understanding that a European energy market was linked to having a secure supply and promoting renewable energy.
'Med club'
Meanwhile a UK proposal to cut sales tax on "green" goods is unlikely to succeed.
The idea put forward by UK Prime Minister Gordon Brown would cover such products as low-energy light bulbs.
Mr Barroso said some countries did not agree with the idea which he described as "a very sensitive issue".
He went on to say that he did not want to dismiss the importance of positive discrimination for such products, but alternatives such as rebates might be more suitable.
HAVE YOUR SAY
EU leaders are also discussing the turmoil in financial markets.
They are expected to say that the European economy could ride out the current instability, as well as a downturn in the US.
Mr Barroso said it was clear that people felt it was yet "another reason not to allow complacency, but on the contrary to pursue the modernisation of the European economy".
French President Nicolas Sarkozy arrived at the talks having secured support from Germany for a watered-down proposal for a Mediterranean Union.
His aim is to forge closer ties between European countries bordering the Mediterranean and those beyond Europe, including Israel, Algeria and Tunisia.
The main objection to what some have dubbed "Club Med" was the cost, but there have also been complaints that a Euro-Mediterranean partnership already exists.
The compromise appears to be an "upgrade" on what already exists and hopes for its success have been carefully lowered.
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