• Scientists warned in a new study that the melting of Greenland’s ice sheet may have reached a “tipping point.”

From The New York Times

• The Business Roundtable, made up of CEOs of the nation’s top companies, warns in a national innovation agenda out later today that the U.S. focus on R&D is lagging, and other countries are gaining ground. “The United States cannot remain a global leader in innovation unless its policy and regulatory infrastructure is responsive.”

From Axios

• As the longest government shutdown in U.S. history stretches into a fifth week, millions of poor Americans who depend on food and rental assistance are becoming increasingly worried about the future.

From AP

• Three aviation unions — the National Air Traffic Controllers Association, the Air Line Pilots Association and the Association of Flight Attendants-CWA — warned that “the entire system” could “break” because of the shutdown.

From Axios

• In the past year, the availability of homes that a middle-class family could buy has declined in 86% of the largest metro areas, according to an analysis of 49 cities being released by the real estate brokerage Redfin.

From AP

• After Mr. Trump recognized Juan Guaidó as Venezuela’s legitimate interim president, Brazil, Argentina and other countries across South America quickly followed. The move is meant to pressure Nicolás Maduro—the autocratic president accused of staging a sham re-election last year—to step aside, leading to the restoration of democracy in a country traditionally close to Washington. Mr. Maduro, who received messages of support from Turkish President Recep Tayyip Erdoğan, Mexico and Bolivia, has been backed most importantly by China and Russia. He vowed to stay in office.