Nearly 1,000 children a day are now dying because of climate change, according to a path-breaking study published Wednesday (PDF), and the annual death toll stands at 400,000 people worldwide.

Climate change also is costing the world economy $1.2 trillion a year, the equivalent of 1.6 percent of economic output, reports the Climate Vulnerability Monitor, a study commissioned by 20 of the world’s governments whose nations are most threatened by climate change and released on the sidelines of the U.N. General Assembly meeting in New York.

Most of the 400,000 annual deaths are “due to hunger and communicable diseases that affect above all children in developing countries,” concludes the study, written by 50 scientists and policy experts from around the world.

Separately, the U.N. Food and Agriculture Organization has warned that the record heat and drought that struck the United States and other key global food producers during the summer of 2012 will slash crop yields, raise food prices, and, unless urgent action is taken, “turn into a catastrophe hurting tens of millions over the coming months.”

“The new report is another reminder that climate change’s most savage impact is hunger and poverty,” said Jeremy Hobbs, executive director of Oxfam International, in a statement. “Behind the statistics are the stories of real families and communities, for whom climate change means putting children to bed with empty stomachs.”

A Reuters report on the new study, however, dramatically overstated the projected death toll, stating, “more than 100 million will die…by 2030 if the world fails to tackle climate change.” But the 100 million figure includes deaths not only from climate change but also from air pollution and indoor cooking smoke, long major killers in developing countries, where women often cook with wood in poorly ventilated structures.

What is new about the Climate Vulnerability Monitor report is its calculation of 400,000 annual deaths from climate change. That is a significant increase over previous estimates. The U.N. Intergovernmental Panel on Climate Change, the gold standard for climate science, said in its Fourth Assessment Report in 2007 that climate change caused 150,000 extra deaths a year.

But the 150,000 figure took into account only deaths from malnutrition, malaria, and diarrhea caused by contaminated water, a common result of floods. Excluded were the effects of heat waves, crop losses due to an increase in pests, and a range of other deadly diseases, which can be substantial. For example, the record-breaking heat wave that blanketed Europe for six weeks in summer 2003 caused at least 71,449 excess deaths, according to a 2008 study sponsored by the European Union.

As global warming intensifies in the coming years, the death toll could rise to 700,000 a year by 2030, the new report calculates, while the economic costs, if the effects of air pollution are included, could increase to 3.2 percent of global output. These economic costs arise not only from stunting of crops, flooding, and wildfires, as Americans experienced this summer, but also from the lower productivity of workers when they labor under hotter conditions.

Although most of the human suffering and economic damage will occur in the world’s poorest nations, which have contributed little to the greenhouse gas emissions that are overheating the planet, the United States is by no means immune. Climate impacts could cut the U.S. GNP by 2 percent by 2030, according to the report.

Yet climate change continues to be the great unmentionable on Capitol Hill and the presidential campaign trail. Mitt Romney has mocked President Obama for even caring about the issue. For his part, Obama rarely mentions the C-word—aka, climate change—even as he frequently touts his “all-of-the-above” energy strategy that includes massive increases in oil and natural gas production.

The Economist, in a 2011 article cited in the new report, opined that 100 years from now, looking back, the only important question about our historical moment will be “whether or not we did anything to arrest climate change.”

Governor Romney? President Obama? Are you listening?