People in developing countries will need to make big cuts in greenhouse gas emissions if "dangerous" climate change is to be avoided, a report warns.
Researchers at the Third World Network calculate that even if rich nations make deep cuts, the developing world will face per-capita reductions of 60%.
It suggests this would pose challenges to these countries' development.
Meanwhile, another report warns that current proposals for cutting developed world emissions do not go far enough.
The Global Climate Network, an alliance of research groups, says that current pledges by the EU and by US President-elect Barack Obama will not put the world on track to halving emissions by 2050.
Both reports have been under discussion here at the United Nations Framework Convention on Climate Change (UNFCCC) conference in Poznan, Poland.
"The figures are very grim," said Martin Khor, director of the Malaysia-based Third World Network.
"They're grim if we go for a 50% [global] cut by 2050, and we may need more - I think we only went for a 50% figure so as not to scare politicians."
Halving global emissions by 2050 (relative to a 1990 baseline) would mean that they are unlikely to rise more than 2.5C above the pre-industrial average, according to calculations by the Intergovernmental Panel on Climate Change (IPCC).
Further IPCC analyses suggest this would avoid some of the most serious potential climate impacts.
The leaders of the G8 major industrialised nations endorsed the global target at their summit this year in Japan.
A number of countries, including the UK, want to keep their own emissions in 2050 80% below the 1990 baseline.
If the entire industrialised world took on this commitment, the Third World Network calculates, developing nations would have to cut their emissions by 23% in order for the world to hit its 50% target.
But because the populations of developing countries are growing, this 23% figure translates to a per-capita cut of 60%.
If the developing world made a more modest commitment, to keep its per-capita emissions constant at 1990 levels, population growth would still mean that the total emissions from these countries would double by 2050, scuppering any chance of a global 50% cut.
Although some developing countries have established plans for improving energy efficiency and curbing the rate at which their emissions are rising, there is no appetite within the bloc for an actual cut, and industrialised nations are not pressing them to take on firm targets.
Without such a commitment, this report suggests, there is little chance of avoiding temperature rises that are likely to bring major impacts, if the IPCC is right.
Ewah Eleri, executive director of the International Centre for Energy, Environment and Development based in the Nigerian capital, Abuja, said there were some obvious easy ways for the poorest developing countries to reduce emissions.
One would be to replace traditional open wood-burning stoves with more efficient models.
"Being able to introduce efficient wood stoves is not rocket science," he told BBC News.
"But it holds a lot of promise in terms of reducing the health hazard to men, women and children who work in the kitchen."
Making the switch across Nigeria could probably reduce the country's emissions by 20-30%.
Experts believe Mr Obama's plans for cutting emissions do not go far enough
Globally, he said, about two billion people use wood as their primary fuel; and switching them all to locally-made efficient stoves would cost about $6bn.
Mr Eleri said that although developing countries could do more, the lead has to be taken by the West.
The EU has staked a claim to that lead by vowing to cut its emissions by 20% by 2020, or by 30% if there is a global deal.
Mr Obama has proposed a more modest goal - bringing US emissions down by 2020 to the level they were at in 1990.
The analysis by the Global Climate Network suggests these pledges are not enough to halve global emissions by 2050, even if they are implemented.
There is, it says, a "mitigation gap".
"We have got to unlock emissions growth in developing countries," said the organisation's co-ordinator Andrew Pendleton, who is based at the Institute for Public and Policy Research (IPPR) in London.
"But we have got to find an equitable way of doing that."
The clear message from putting these two reports together was, he said, that richer nations will have to get finance and clean technology into the developing world if they want to turn the goal of a 50% cut into reality.