What you need to know about the environment this week

New York City Mayor Bill de Blasio declared a state of emergency on Wednesday after record-breaking rains caused flooding and dangerous road conditions. By the early hours of Friday, flash flooding had killed at least 44 people across four US states.

US President Joe Biden also approved the declaration of a state of emergency in California over the Caldor wildfire, which has burned since mid-August.

In Switzerland, ski resort staff have covered a glacier in blankets to block the sun and protect it from global warming.

Brazil's Vice President Hamilton Mourao said on Wednesday that energy might need to be rationed as a result of a severe drought affecting hydropower generation.

Almost a third of the world's tree species are at risk of extinction, according to a report published this week.

Hainan province in China has said it is considering setting up an international carbon emissions trading exchange.

The world's last remaining stocks of leaded petrol have been used, with UN Environment Programme calling the news a 'huge milestone'.

A blob of warm water in the southern Pacific is fuelling a decade-long megadrought in Chile, and climate change is at least partly to blame, scientists say.

Hurricane Ida struck the US state of Louisiana on Sunday. The Category 4 hurricane is one of the most powerful storms to ever hit the US Gulf Coast.

The storm caused widespread destruction, with more than 1 million homes and businesses left without power, at least six people killed, and countless homes destroyed and towns flooded. President Biden declared a major disaster in the state.

"The sky went black and what you could hear was a tornado," said Madeline Brewer, 30, shortly after being rescued by the US Army on Monday. "There was a whole tree that flew past."

Ida hit 16 years to the day after Hurricane Katrina, which killed more than 1,800 people in 2005 and devastated the Louisiana city of New Orleans. It's thought the damage from Ida would have been more severe in the city's metro area were it not for the $14.5 billion levee and floodwall system built after Katrina.

The number of disasters – such as floods and heatwaves – driven by climate change have increased fivefold over the past half a century, according to the World Meteorological Organization (WMO). More than 2 million people have been killed and there have been $3.64 trillion in total losses.

The WMO's Atlas surveys some 11,000 disasters from 1970-2019, which included Ethiopia's 1983 drought – the most deadly event, with 300,000 deaths – and Hurricane Katrina in 2005, the most costly at $163.6 billion.

"Thanks to our early warning service improvement we have been able to have a decrease of the casualties at these kind of events, but the bad news is that the economic losses have been growing very rapidly and this growth is supposed to continue," WMO Secretary-General Petteri Taalas told a press conference.

"We are going to see more climatic extreme because of climate change and this negative trend in climate will continue for the coming decades," he said.