The opening line of an October 2021 World Health Organization special report on climate and health put it starkly: "Climate change is the single biggest health threat facing humanity." The report, The Health Argument for Climate Action, follows publication last August of the first installment of the Intergovernmental Panel on Climate Change's Sixth Assessment Report, which documents unprecedented climate changes affecting every part of the planet as well as their implications for human health. At 2[degrees]C of global warming above preindustrial levels, which is predicted by the end of this century without stringent and sustained reductions in greenhouse gas emissions, heat extremes are expected to reach intolerable levels for agriculture and human health.

Extreme heat events are already widespread. Last July was Earth's hottest month on record. A rare and deadly heat wave in the Pacific Northwest required cooling measures for stricken residents unprecedented in that part of the country. Heat waves also set the stage for wildfires; Oregon experienced its third-largest fire in the state's history and California's second-largest fire burned from summer into fall.

At the opposite extreme, a winter storm in February led to record-setting cold in Texas, overwhelming the power grid and leaving millions without electricity, heat, and potable water. The remnants of Hurricane Ida caused severe flooding and infrastructure damage in the New York City area in early September. Based on federal disaster declarations, a Washington Post analysis that month concluded, "Nearly 1 in 3 Americans live in a county hit by a weather disaster in the past three months."

The challenges of preparing for such emergencies during the ongoing COVID-19 pandemic are myriad, from the difficulty of social distancing during a disaster response to hospital staffing shortages and extreme caregiving challenges. When Hurricane Ida came ashore in Louisiana in late August, causing widespread power outages during the state's fourth COVID-19 wave, nurses and physicians at one hospital had to provide manual breathing assistance to patients on ventilators until they could be moved to facilities with working generators.

In an open letter to world leaders in October, nurses and other health care providers emphasized the implications of failing to address the climate crisis. The signatories-more than 450 organizations, including the International Council of Nurses and Alliance of Nurses for Healthy Environments, and 3,400 individuals-noted, "As health professionals and health workers, we recognize our ethical obligation to speak out about this rapidly growing crisis that could be far more catastrophic and enduring than the COVID-19 pandemic."-Corinne McSpedon, senior editor