Climate change: Wildfires, hurricanes, drenching rains — as in India, above — and drought ravaged communities around the world. Temperatures reached new highs (check the change in your own area). Arctic ice melted more rapidly than ever. Will nations follow through on a global climate framework agreed upon in Poland?

Trade: The U.S. and China, the world’s two largest economies, spent the year engaged in a tit-for-tat trade war. The global economy appears to be slowing down, and rising U.S. interest rates are worrying markets.

Privacy: A Times investigation revealed that a consulting firm, Cambridge Analytica, used private Facebook data to help President Trump’s campaign, raising alarming questions about Silicon Valley’s privacy practices. Months later, we found that the social network gave Microsoft, Amazon, Spotify and others far greater access to people’s data than it had disclosed. And we learned that location data pulled from your phone apps is more personal (and public) than telecom companies say it is.

Migration: A record 68.5 million people, including people fleeing war in Syria and persecution in Myanmar, were forcibly displaced by the end of 2017. Venezuela’s misery is causing a refugee crisis in South America, and migrants are piling up at the U.S. border with Mexico. Migration may increase with climate change, and migrants are the targets of anti-immigration rhetoric around the world.

President Trump’s legal troubles: Many of the investigations into Mr. Trump’s business dealings, potential campaign finance violations and whether his campaign had connections to Russia could come to a head in the new year, particularly with Democrats taking control of the House.

Russia: The country’s increasingly aggressive behavior, including the attempted assassination of a former Russian spy, Sergei Skripal, and his daughter on British soil, worsened relations between the Kremlin and many Western countries.

Saudi Arabia: The brutal killing of a dissident journalist, Jamal Khashoggi, shined a harsh light on Crown Prince Mohammed bin Salman, who is believed to have ordered the assassination, and also on Saudi Arabia’s broader human rights abuses, particularly in the Yemen war. None of this was good optics for the prince’s plans to engage international investors and move the Saudi economy away from oil.