One in seven funds branded as sustainable has a carbon emissions intensity higher than the average across all investment funds, and no climate-labelled fund has a portfolio fully aligned with the Paris Agreement's goal, a study showed on Tuesday.

The analysis, conducted by sustainability data and technology platform ESG Book, is the latest to question the reliability of funds marketing themselves on environmental, social and governance (ESG) grounds.

ESG and climate-labelled funds have boomed in recent years as trillions of dollars are looking for products that are deemed more socially and environmentally friendly, prompting regulators to increase scrutiny of investment managers' claims.

"If you are an investor in a fund, you can see your daily financial performance, but hardly anybody tells you 'is the fund actually delivering on (its) climate targets?'," ESG Book CEO Daniel Klier told Reuters in a call.

Among the 515 climate and ESG funds the study analysed, 73 showed a greater emissions intensity ratio than the average recorded across the 36,000 funds ESG Book tracks, and 15 funds exceeded 400 tons of carbon dioxide equivalent per million dollars of revenue - more than twice as high as the wider average.

Klier, previously global head of sustainable finance at HSBC, said there was a need for a better labelling system and greater understanding that some companies are closely managing how they perform on ESG metrics but not improving their climate performance.

The analysis also found that many of the 95 climate funds ESG Books examined invested in fossil fuel and mining companies, including in Shell, Exxon Mobil and BHP Group.

While such companies might have a place in climate transition funds, ESG Book said including them in 'climate aware' or 'climate care' funds seemed "at odds with the definition of a climate fund".

"Always check the label," ESG Book wrote.

The landmark 2015 Paris accord set a goal of limiting a rise in the world's average surface temperatures to "well below" 2 degrees Celsius and ideally below 1.5.

(Reporting by Juliette Portala; Editing by Tommy Reggiori Wilkes and Mark Potter)