HONG KONG — When industrialized nations pledged in 2009 to mobilize $100 billion a year by 2020 to help the poorest countries deal with climate change, it won over some skeptics in the developing world who had argued that rich nations should pay up for contributing so much to the problem.

But the money has been slow to materialize, with only $3.5 billion actually committed out of $10.3 billion pledged to a prominent United Nations program called the Green Climate Fund. President Trump’s decision last year to cancel $2 billion in promised aid did not help.

At a climate change conference in Thailand this past week, some delegates reached by telephone said that the setting — the heart of Southeast Asia, a region where challenges relating to warming are readily apparent — was grimly fitting. They described the United Nations program’s shortcomings as a symbol of a broken promise.

“The fund of hope is becoming a fund of hopelessness,” said Meena Raman, legal adviser to the Third World Network, an advocacy group in Malaysia, and a former nonvoting member of the Green Climate Fund’s board.