Some 17,000 participants are due to attend the latest round of UN climate talks later in Qatar's capital, Doha.
Over the next two weeks they will be negotiating a new global deal on climate, but there are ongoing tensions between rich and poor countries.
The choice of venue has surprised many, as oil-rich Qatar has some of the highest per capita emissions of carbon dioxide (CO2) in the world.
A central divisive issue relates to the problem of "hot air" carbon permits.
The derisory term refers to attempts by some wealthy countries to carry over unused carbon permits so they can be offset against future cuts.
Developing nations say this is unfair and reduces the value of any commitment to reduce CO2.
Negotiators attending the 18th Conference of the Parties (COP18) of the United Nations Framework Convention on Climate Change have been piecing together a new approach since the failure of talks in Copenhagen in 2009.
In Doha, though, some hard facts have to be faced, says the BBC's environment correspondent, Matt McGrath.
A financial fund to help poorer countries runs out at the end of this year, as does the first commitment period of Kyoto Protocol, that legally binds around 30 richer countries to cutting carbon emissions.
In Doha, developing nations want to see new money and a new commitment to cutting CO2 by the better-off.
Some participants are worried that, as a result of their dependence on fossil fuels for their revenues, the Qataris may not push the talks in the right direction, adds our correspondent.