Climate researchers said Thursday the planet could warm by more than 3.5 degrees Celsius (6.3 degrees Fahrenheit), boosting the risk of drought, flood and rising seas.
The UN's target is a 2 C (3.6 degree Fahrenheit) limit on warming from pre-industrial levels for manageable climate change.
In a report issued on the penultimate day of new UN talks in Bonn, scientists said Earth's average global temperature rise could exceed the dangerous 3.5 C (6.3 F) warming they had flagged only six months ago.
Marion Vieweg, a policy researcher with German firm Climate Analytics, told AFP the 3.5 C (6.3 F) estimate had been based on the assumption that all countries will meet their pledges, in themselves inadequate, to reduce greenhouse-gas emissions.
New research has found this is not "a realistic assumption," she said, adding that right now "we can't quantify yet how much above" 3.5 C (6.3 F) Earth will warm.
The monitoring tool is called Climate Action Tracker (CAT), a joint project of Climate Analytics, Ecofys and the Potsdam Institute for Climate Impact Research in Germany.
Her colleague, Bill Hare, said the gap between countries' promised interventions and the reality was "getting bigger."
Projections are for greenhouse-gas overshoot of between nine and 11 billion tonnes per year beyond the annual 44-billion-tonne ceiling needed by 2020 to achieve the 2 C (3.6 F) target.
At the moment, the world emits about 48 billion tonnes of these gases, including CO2 and methane.
The United States accounts for six billion tonnes, China seven and the European Union (EU) five, the CAT said.
The 195 parties to the UN Framework Convention on Climate Change (UNFCCC) are meeting in the former German capital of Bonn for the first time since they agreed in Durban, South Africa, last December to forge a new global pact.
The accord would be completed by 2015 and take effect in 2020.
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