3 June, 2025

Martha Henriques This week, we discover that the world's oceans aren't just getting warmer, they're getting darker too. As life in the shallows changes, more and more light is absorbed in the ocean's upper layers. The dark zone of the ocean is therefore growing from below, leaving scientists scrambling to understand the consequences. Plus: China's electric two-wheelers are charging ahead on batteries entirely free from lithium, as Xiaoying You reports.

CLIMATE CONVERSATION China's scooters powered by salt batteries Electric scooters are powering China's salt battery drive. Credit: Getty Images Lithium-based batteries power the vast majority of the 40 million or so electric vehicles on the roads today. But the lithium-ion battery is facing a growing number of contenders. An emerging industry is exploring alternative potentially cheaper and more sustainable power sources for electric vehicles. ‌ One promising alternative is the "salt battery", which uses sodium instead of lithium. The raw materials for a sodium-ion battery are cheaper than for a lithium-ion battery, and they avoid the need for critical minerals. In China, the leader in the technology, small vehicles like scooters have begun to speed ahead on salt batteries. ‌ Click the button below to see why China is betting on salt batteries as a competitor to lithium, and whether the rest of the world will catch up. Read more

THE BIG PICTURE Why the oceans are getting darker Changes in the upper layers of the ocean are having far-reaching effects in the depths. Credit: Reuters The lower depths of the ocean are getting darker with climate change, researchers have found. As warmer waters change the chemistry of the ocean's upper layers, light can't penetrate as deeply. In 9% of the ocean – an area about the size of Africa – light is reaching 50m (160ft) shallower depths compared with two decades ago. Scientists are still working to understand the implications.  Read more