The 12-day talks under the UN Framework Convention on Climate Change (UNFCCC) seek to breathe life into a quest to forge a pact on heat-trapping greenhouse gases.
Troubled by bickering, nit-picking and defence of national interests, the process coincides with the rise of carbon dioxide (CO2) to historic levels.
UNFCCC chief Christiana Figueres told delegates that US scientists in Hawaii last month had detected more than 400 parts per million (ppm) of CO2 in the atmosphere for the first time in human history.
After discussions among two technical bodies today, the talks get down to tougher business tomorrow.
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They will try to flesh out commitments for the deal, expected to be signed in late 2015, and to beef up action in the years before the pact takes effect in 2020.
The negotiations lead up to the UNFCCC's annual minister-level talks, which this year will take place in Warsaw from November 11 to 22.
Political interest on tackling climate change at a global level peaked in the runup to the 2009 Copenhagen Summit.
In the meantime, carbon emissions are reaching new record highs, driven by emerging countries that are devouring coal, oil and gas to power their economic growth.
The 195 UNFCCC parties have pledged to limit warming to two degrees Celsius compared to pre-industrial temperatures, when CO2 levels were 270 ppm.
But carbon concentrations are escalating at around two or three ppm each year, placing Earth on track for warming of as much as two degrees C by century's end, a figure that many scientists say would be catastrophic.