GENEVA/GLASGOW, Oct 25 (Reuters) - Greenhouse gas concentrations hit a record last year and the world is "way off track" in capping rising temperatures, the United Nations said on Monday in a stark illustration of the task facing climate talks in Glasgow.

The Scottish city of Glasgow was putting on the final touches before hosting the climate talks, which may be the world's best remaining chance to cap global warming at the 1.5-2 degrees Celsius upper limit set out in the Paris Agreement.

Alok Sharma, the president of COP26, said developed nations are set to be three years late meeting a pledge to commit a total of $500 billion to help poorer countries tackle climate change.

He also said it would double the emissions cuts it plans to achieve by 2030.

A Reuters poll of economists found that hitting the Paris goal of net-zero carbon emissions will require investments in a green transition worth 2%-3% of world output each year until 2050, far less than the economic cost of inaction.

A "business-as-usual" trajectory leading to temperature rises of 1.6C, 2.4C and 4.4C by 2030, 2050 and 2100 respectively would result in 2.4% lost output by 2030, 10% by 2050 and 18% by 2100, according to the median replies to the survey.

"Greenhouse gas emissions are provoking climate catastrophes all over the planet