Society faces a much greater threat from climate change than anyone has previously suggested, according to a new report that attempts to assess the cumulative impact of many factors.

It reveals 467 ways in which human health, food, water, economy, infrastructure and security already have been affected by multiple climatic changes, including warming, drought, heatwaves, wildfires, precipitation, floods, storms, sea level rise and changes in land cover and ocean chemistry.

Published in the journal Nature Climate Change, it is the work of 23 scientists, led by Camilo Mora from the University of Hawaii at Mānoa, US, who systematically reviewed thousands of scientific papers. Providing input was a team of other climate scientists, including several lead authors on the Intergovernmental Panel on Climate Change (IPCC) reports

The result, they say, is one of the most comprehensive assessments yet of how humanity is being impacted by the simultaneous occurrence of multiple climate hazards, strengthened by increasing greenhouse gas emissions.{%recommended 6635%}

“Greenhouse gas emissions pose a broad threat to humanity by simultaneously intensifying many hazards that have proven harmful in the past,” says Mora.

“Further, we predict that by 2100 the number of hazards occurring concurrently will increase, making it even more difficult for people to cope.”

In that year, for example, New York and Mexico City are projected to face up to four concurrent climate hazards, if greenhouse gas emissions are not mitigated, and Sydney and Los Angeles three. The Atlantic coast of Brazil will face five.

Even under strong mitigation scenarios, the researchers say, increasing cumulative exposure to the multitude of climate hazards will impact rich and poor countries alike and especially in tropical coastal areas.

“Our health depends on multiple factors, from clean air and water, to safe food and shelter and more,” says Jonathan Patz, director of the University of Wisconsin’s Global Health Institute. “So, without a real systems approach to climate change impacts, we cannot adequately understand the full risks.

“If we only consider the most direct threats from climate change, for example heatwaves or severe storms, we inevitably will be blindsided by even larger threats that, in combination, can have even broader societal impacts.”

To assess the reams of material, the researchers created a table with 10 climate hazards (such as drought) listed in columns and six aspects of human systems (water supply, for instance) in rows. This was used as a guide to possible combinations of keywords to search for publications reporting the impacts of climate hazards on key aspects of human life.

From more than 12,000 references assessed, 3280 relevant papers were identified and read in full to find case examples of climate hazards impacting human systems. To qualify for selection, impacts had to be observed and supported with traceable evidence, including place and time.

The documented case examples, with supporting papers, are available at purpose-built website, which also contains a global map of cumulative climate hazards.