Yemen is gripped by civil war—and some experts say it could be the first of many “water wars” to come, as the planet grows hotter and drier. In This Is the Way the World Ends: How Droughts and Die-Offs, Heat Waves and Hurricanes Are Converging on America, Jeff Nesbit writes of the Yemeni conflict and many other geopolitical consequences of a warming world, including the precarious future of the Indus River, under the control of China, India and Pakistan, and why Saudi Arabia’s biggest dairy company is buying farmland in the Arizona desert. Nesbit joins Ira to discuss the future of our planet.  Our understanding of how protective the placenta is during pregnancy has been changing. Some ingested substances, like alcohol and pthalates, are known to cross the boundary and cause harm. And in the case of air pollution, a mother’s exposure is increasingly correlated with health problems in the infant, from cardiovascular to neurodevelopment. But how do inhaled particles lead to these problems? New research in the Journal of American Medicine this month points to one potential mechanism: changes in the thyroid hormones, which are critical to early development. What’s going on—and what can be done to protect the most vulnerable from potentially lifelong health effects?  NASA’s PMC Turbo mission sent up a balloon to capture images of one of the rarest clouds, polar mesospheric clouds. These clouds, called noctilucent clouds, only form during the summer 50 miles up in the atmosphere, and they nucleate around meteor dust. Researchers explain what these clouds tell us about climate change and the physics of gravity waves and turbulence.