When Helen Han and Dan Pan began having children, they quickly realized their apartment in Chicago wasn’t going to cut it much longer.

“We were there for seven years and it was perfect for the two of us,” said Mr. Pan, 36, who works in finance. But by 2018, with one child at home and plans to have a second, they sensed a pressing need for more space.

“It was a little too small with one kid, and definitely too small for two kids,” Mr. Pan said.

The effect could be potent, scientists say. Rivers contain carbon dioxide that is constantly escaping into the air, where it traps heat and warms the planet. But adding limestone converts some of that carbon dioxide into a stable molecule that instead stays underwater and washes into the sea, where it should remain trapped for thousands of years.

Until this year, only humans, dolphins and parrots were known to use names when communicating. In June, however, scientists reported that African elephants appeared to use names, too; researchers made the discovery by using artificial intelligence-powered software to detect subtle patterns in the elephants’ low-pitched rumbles.

So they began looking for a single-family home where they could live with their daughters, Eliza, now 6, and Astrid, 4. They wanted direct access to outdoor space, to be close to a neighborhood park, and “it needed to be light and bright,” said Ms. Han, 36, who also works in finance. “Light and the height of the ceilings were the most important things.”

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