Climate change is contributing to the inequitable suffering of billions of people around the world. Driven by human greenhouse gas emissions, climate-related hazards -- including heat waves, floods, wildfires, and disease outbreaks -- are accelerating more rapidly and having more direct effects than previously anticipated. Indeed, health is increasingly an important lens through which to measure the effects of climate change -- making climate change more salient and tangible to the public and policymakers.

The health crisis posed by climate change is enormous. But how big exactly? According to the World Health Organization's (WHO) Climate Change and Healthopens in a new tab or window webpage, "Between 2030 and 2050, climate change is expected to cause approximately 250,000 additional deaths per year." This number is one of the first you'll encounter if you research online the impact of climate change on health, yet, it seems wholly inconsistent with the Lancet's characterizationopens in a new tab or window of climate change as the greatest global health threat of the 21st century.