LONDON- Global green bond issuance has surpassed the $100 billion mark already this year, the first time the milestone has been reached in the first half of this year, the Climate Bonds Initiative said on Tuesday.

Green bonds are a growing category of fixed-income securities, which raise capital for projects with environmental benefits.

Although green bonds make up a small fraction of the overall bond market, they are attracting more attention because meeting emissions-cut targets will need trillions of dollars of capital from public and private sectors.

Cumulative green bond issuance has reached nearly $107 billion, according to the Climate Bonds Initiative, a London-based non-profit which promotes investment in the low-carbon economy.

Issuance has now reached $100 billion three times - the last time was in Sept. 2018. Forecasts for the final amount of issuance this year range from $180 billion to $250 billion.

"Reaching $100 billion in green bond issuance for the third time and so early in the year is welcome. However, the global climate finance challenge is to reach a $1 trillion in annual green investment early in the 2020s," said Climate Bonds Initiative Chief Executive Sean Kidney.

The former United Nations climate chief, Christiana Figueres, has said the financial sector should be aiming to reach $1 trillion a year of green bond issuance by 2020 to support international goals to decarbonise economies.

So far this year, the largest corporate bonds issued have been by French utility Engie  at $1.7 billion, Korean petrochemicals firm LG Chem at $1.6 billion and the Industrial and Commercial Bank of China at $1.5 billion. 

In terms of country issuance, France and the United States have issued the most green bonds so far this year. Last month, the Netherlands launched a $6.7 billion green bond. 

(Reporting by Nina Chestney, editing by Louise Heavens) ((nina.chestney@thomsonreuters.com; +44 (0)207 542 8071; Reuters Messaging: nina.chestney.thomsonreuters.com@reuters.net))