Bubbles of air trapped in polar ice cores let scientists sample the atmosphere of past centuries. Ice forms as snow piles up and compresses, capturing soot, pollen and tiny pockets of the air of its time. Willi Dansgaard, a Danish meteorologist, began studying this in the late 1950s, working from a fishing boat in the Arctic. In 1967 he obtained cores from Camp Century, a US Army base in Greenland, that reached back about 100,000 years. Those records showed that carbon dioxide levels were about 280 parts per million before industrial emissions, and they now exceed 420. Today, researchers face a new problem: ice in sensitive regions is melting and refreezing, which pushes out bubbles and degrades the record. Scientists such as Dorothea Moser are working out what can still be learned from that damaged ice.

Hampi is a UNESCO World Heritage Site in Karnataka, India, with more than 1,600 surviving remains spread over 4,100 hectares. It was the capital of the Vijayanagara Empire from 1336 to 1565. Travellers from Persia and Portugal described it as a prosperous, wealthy and grand city with temples, markets and farms along the Tungabhadra River. By 1500 it was estimated to be the world's second-largest city after Beijing, and probably India's richest at the time. In 1565 a coalition of Muslim sultanates defeated the Vijayanagara Empire, its capital was conquered and destroyed, and the city was left in ruins. Hampi remains a religious centre, with the active Virupaksha Temple at its heart.