General view of Chilean Calbuco volcano from Puerto Montt, located at 1000 km southern Santiago de Chile, Chile, 22 April 2015. Due to the eruption of the volcano with a smoke column 20 km high, authorities declared a red alert and ordered the evacuation of around 1500 inhabitants of Ensenada, Alerce, Colonia Río Sur and Correntoso towns. (Photo by Alex Vidal Brecas/EPA)

Models painted in camouflage colours to blend in with the background pose for Chinese artist Liu Bolin's artwork “Dongji”, or Winter Solstice, on the second day after China's capital Beijing issued its second ever “red alert” for air pollution, in Beijing, China, December 20, 2015. In this artwork, Liu wants to express his concerns about China and its people, including air pollution problem, Liu told Reuters. (Photo by Kim Kyung-Hoon/Reuters)

Revellers hit the town on Saturday, February 19, 2022 for a pub crawl despite the snow in Leeds, United Kingdom. The UK capital was placed under its first ever “red” weather warning, meaning there is “danger to life”. The same level of alert was in place across southern England and South Wales, where schools were closed and transport paralysed. (Photo by Nb press ltd)

Popocatepetl volcano spews incandescent material as seen from Paso de Cortés on May 23, 2023 in Amecameca, Mexico. The second highest volcano in the country increased its activity while Mexican authorities raised the alert to yellow phase 3. Popocatepetl volcano caused the fall of ashes in different municipalities in Puebla, Estado de Mexico and Mexico City. Mexican army has spread forces as a preventive measure while the 3 levels of government are in coordination to observe the activity of the volcano and the situation in the surroundings. (Photo by Cristopher Rogel Blanquet/Getty Images)

A woman carries an umbrella during a heat wave in Rome, Italy, 16 July 2023. Italy is facing the third heatwave of the summer on 16 July bringing record temperatures. The new heatwave is forecast to peak on 18 July, when temperatures in areas of southern Sardinian may reach 48 degrees Celsius, according to forecasts. On 15 July, the health ministry has put on red alert major Italian cities. (Photo by Massimo Percossi/EPA)

Beachgoers are hit by a wave in La Libertad May 3, 2015. El Salvador emergency authorities declared a green alert along the pacific coats due to a large swell that affected the Salvadoran coast and originated from the extra-tropical storms that formed in New Zealand and the Southern hemisphere, according to El Salvador's ministry of environment and natural resources. (Photo by Jose Cabezas/Reuters)

The city of Meroë laid undiscovered for two millennia before British archaeologist John Garstang excavated it in the early 20th century. Garstang took the radical decision to document his discoveries with photography – and immortalised an ancient world. “Meroë: Africa’s Forgotten Empire” is being shown until 14 September at Garstang Museum of Archaeology, Liverpool. Here: A group visiting the excavations at Meroë, including (from left) Midwinter Bey, director of Sudan Railways; Lord Kitchener; General Sir Francis Reginald Wingate, Sirdar of the Egyptian Army; Professor Archibald Sayce; John Garstang; and Lady Catherine Wingate, 1911. (Photo by Garstang Museum of Archaeology)

Members of the new BFEplus anti-terror unit of the German federal police holds a G36C automatic weapon after taking part in a capabilities demonstration at a police training facility on December 16, 2015 in Ahrensfelde, Germany. The BFEplus, whose acronym stands for Beweissicherungs und Festnahme Einheit, or Evidence Safeguarding and Arrest Unit, is to support the GSG9 police special forces unit in containing domestic terror threats. Germany is on high-alert following the November Paris terror attacks and a credible threat at the Germany vs. Holland football match in Hanover. (Photo by Sean Gallup/Getty Images)