Air quality, aviation fuel and Australia's koalas: Everything you need to know about the environment this week 

The World Economic Forum's Sustainable Development Impact Summit took place this week. You can check out the highlights here.

South Africa has adopted a more ambitious emissions reduction target ahead of COP26.

British Prime Minister Boris Johnson used an address at the United Nations General Assembly to urge the world to "grow up" and tackle climate change.

The US Environmental Protection Agency has finalized a rule that will slash the use of hydrofluorocarbons, commonly used in refrigerators and air conditioners.

Despite the impact of COVID-19 on air quality, most European Union countries broke at least one air pollution limit last year, according to provisional data.

Australia has lost about 30% of its koalas over the past three years, with drought, bushfires and deforestation all hitting numbers.

Sixty companies have pledged to accelerate the supply and use of sustainable aviation fuel to reach 10% of global jet aviation fuel supply by 2030.

A new set of case studies and best practice examples to help cities reduce emissions has been launched by the World Economic Forum and Accenture.

At an event on the sidelines of the UN General Assembly, philanthropists and investors committed $5 billion to nature restoration and conservation.

The $8.2 billion MacArthur Foundation said on Wednesday it would divest from fossil fuel holdings with changes to its equity indexes, becoming the largest foundation to move money away from the oil and gas sector.

The World Health Organization (WHO) tightened its air quality guidelines this week, marking the first change in them since 2005. The new recommendations could save "millions of lives", the organization said.

The WHO hopes that the changes will encourage member countries towards actions that slash fossil fuel emissions.

Scientists applauded the new guidelines but worried that some countries would have trouble implementing them, given that much of the world was failing to meet the older, less stringent standards.

Chinese President Xi Jinping announced on Tuesday that the country would not build any new coal-fired power projects abroad. He used an address at the UN General Assembly to add to pledges to tackle climate change.

"China will step up support for other developing countries in developing green and low-carbon energy, and will not build new coal-fired power projects abroad," Xi said in his pre-recorded video address at the annual UN gathering, in which he stressed China's peaceful intentions in international relations.

Xi provided no details, but depending on how the policy is implemented, the move could significantly limit the financing of coal plants in the developing world.

The announcement follows similar pledges by South Korea and Japan earlier this year.