The 20-year-old series of conferences has not fulfilled its main purpose of reducing the greenhouse gas emissions that some scientists say are warming the planet.
Attempts to create a new climate treaty failed in Copenhagen three years ago but countries agreed last year to try again, giving themselves a deadline of 2015 to adopt a new treaty.
Several issues need to be resolved by then, including how to spread the burden of emissions cuts between rich and poor countries. That is unlikely to be decided in the Qatari capital of Doha, where negotiators will focus on extending the Kyoto Protocol, an emissions deal for industrialised countries, and trying to raise billions of pounds to help developing countries adapt to a shifting climate.
"We owe it to our people, the global citizenry. We owe it to our children to give them a safer future than what they are currently facing," said South African foreign minister Maite Nkoana-Mashabane, who led last year's talks in Durban.
The UN process is often criticised, even ridiculed, both by climate activists who say the talks are too slow, and by those who challenge the view that the global temperature rise is at least partly caused by human activity, primarily the burning of fossil fuels like coal and oil.
Environmentalists found the choice of Qatar as host of the two-week conference ironic. The tiny Persian Gulf emirate owes its wealth to large resources of gas and oil and emits more greenhouse gases per capita than any other nation.
Yet it has not announced any climate action, and former Qatari oil minister Abdullah Bin Hamad Al-Attiyah did not do so when he opened the conference. "We should not concentrate on the per capita (emissions), we should concentrate on the amount from each country. I think Qatar is the right place to host" the conference, he said.
The concentration of greenhouse gases such as carbon dioxide has jumped 20% since 2000, according to a report released last week.
The goal of the talks is to keep the global temperature rise under 2C compared to pre-industrial times. But efforts taken so far to rein in emissions, reduce deforestation and promote clean technology are not working. A recent projection by the World Bank showed temperatures are expected to increase by up to 4C by 2100.