[JAMA Forum]
By Howard K. Koh, MD, MPH, and Gina A. McCarthy, MS

Three developments in late 2017 heightened attention to the critical intersection between science, climate change, and health:

• The US Global Change Research Program’s Fourth National Climate Assessment (NCA4) identified the last 3 years as the warmest in modern history, with human activities related to greenhouse gas emissions (carbon dioxide, methane, hydrofluorocarbons) extremely likely to be the dominant cause. The NCA4, the authoritative assessment from the nation’s leading climate scientists, found no convincing alternative explanation for such warming.

• Leaders from nearly 200 countries met at the United Nations Framework Convention on Climate Change 23rd Conference of the Parties (COP23) to advance guidelines and procedures for implementing the 2015 Paris Agreement pledges to collectively limit global warming to 2^oC (3.6^oF) higher than preindustrial levels by 2025. Of note, COP23 took place during a season of extreme US weather events. These included Hurricanes Harvey and Maria (ranked as the second and third costliest tropical cyclones ever recorded) and the 2017 California wildfires (the costliest wildfire event on record).

• The Lancet Countdown on health and climate change urged the global health community to shift away from 25 years of inaction, pledging to report regularly on health outcomes related to Paris Agreement commitments. Because US health care activities contribute substantially greenhouse gas emissions (resulting in nearly 10% of greenhouse gas emissions in 2013), more research should focus on detecting and attributing the health effects of climate change. A 2017 modelling analysis, part of evolving scientific studies in this area, provides early evidence that the carbon footprint of US health care activities can be linked to 123 000 to 381 000 disability-adjusted life-years lost annually from 5 factors affecting health (malaria, floods, malnutrition, diarrhea, and cardiovascular disease).

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