Global warming is causing more than 300,000 deaths and about $125 billion in economic losses each year, according to a report by the Global Humanitarian Forum, an organization led by Kofi Annan, the former United Nations secretary general.

The report, to be released Friday, sifted data sets and existing studies of health, disaster, population and economic trends. It found that human-influenced climate change  mainly by exacerbating flooding and drought  was elevating the global death rates from illnesses including malnutrition, diarrheal disease, malaria and heat-related ailments. But even before its release, the report drew criticism from some experts on climate and risk, who questioned its methods and conclusions.

Along with the deaths, the report said that the lives of 325 million people, primarily in poor countries, were being seriously affected by climate change. It projected that the number would double by 2030.

Roger A. Pielke Jr., a political scientist at the University of Colorado, Boulder, who studies disaster trends, said the forum’s report was “a methodological embarrassment” because there was no way to distinguish deaths or economic losses related to human-driven global warming amid the much larger losses resulting from the growth in populations and economic development in vulnerable regions. Dr. Pielke said that “climate change is an important problem requiring our utmost attention.” But the report, he said, “will harm the cause for action on both climate change and disasters because it is so deeply flawed.”