How can a world population of 8 billion be more sustainable?

• Population has doubled to 8 billion over last 50 years
• Major lifestyle changes will be needed to protect planet
• States and companies need to price in environmental harm

LONDON - The global population will reach a new milestone of 8 billion on Nov. 15, the United Nations has projected, with the number of people on earth having doubled in less than 50 years.

That figure is expected to reach 9.7 billion in 2050 and peak at about 10.4 billion during the 2080s amid dwindling growth rates, the World Population Prospects report said.

This comes at a crucial time for the planet as climate change and nature loss caused by human activities - from the food that people eat to the fossil fuels burned for energy - are having an increasingly significant impact on life.

"How will we answer when 'Baby 8 Billion' is old enough to ask: what did you do for our world and for our planet when you had the chance?" U.N. Secretary-General Antonio Guterres said at the COP27 climate summit in Egypt on Monday.

The U.N. Environment Programme (UNEP) has warned that "unprecedented" action to cut greenhouse gas emissions will be needed to reach global targets of limiting warming to 1.5 degrees C above pre-industrial temperatures.

Meanwhile, as forests continue to be cleared and oceans polluted, human impacts are destroying nature and biodiversity: wildlife populations have fallen by more than two-thirds since 1970, according to the World Wildlife Fund (WWF).

As negotiators discuss nature protection at COP27, climate advocates have called for the global economic system to put a price on planet-heating emissions, and to value the services provided by nature - from storing carbon to regulating rainfall.

With the number of people living on the planet only set to soar further in the coming decades, what can be done to make human life more sustainable?

Accelerate renewable energy

Despite the rise in renewable energy technologies such as solar panels and wind farms, most of the energy that people use to power industry, transport and buildings is still polluting.

Fossil fuels account for around 80% of energy production, according to the International Energy Agency (IEA), and global demand for energy is surging as the population grows and economies continue to develop.

The IEA says the path to net zero planet-heating emissions by 2050 requires a "massive deployment" of all available clean energy technologies, with investment needing to more than triple by 2030.

Renewable energy technologies have become much cheaper over the past decade.

In 2021, two-thirds of newly installed renewable power had lower costs than the cheapest fossil fuel-fired option in G20 countries, the International Renewable Energy Agency said.

Make buildings greener

Another change needed to work towards a sustainable future concerns the buildings where people live and work.

From the construction of buildings with cement, steel and other materials, to the energy used within them, buildings account for 38% of global energy-related carbon dioxide emissions, according to UNEP.

New technologies are being developed for low-carbon cement and steel, while research suggests that substituting these materials for timber could significantly cut building emissions.

Meanwhile, existing buildings need to be retrofitted to become more energy efficient, such as with more effective insulation and the installation of heat pumps.

If implemented worldwide, using heat pumps instead of traditional boilers and furnaces could cut CO2 emissions by 3 billion metric tonnes each year, according to consulting firm McKinsey & Company.

Reduce meat in diets

With the United Nations estimating that there will be nearly 2 billion more mouths to feed by mid-century, changing global diets is also considered vital to protecting the planet.

From agricultural production to transport and packaging, the food system is responsible for around one-third of human-caused greenhouse gas emissions.

Scientists say one of the best ways to protect nature and the global climate is to consume less meat.

About 70% of the world's agricultural land is used for producing meat and dairy goods, even though the products amount to less than 20% of the total food calories available globally.

This is piling pressure on forests and other natural areas.

Experts say governments can encourage the shift to plant-based diets through public procurement of meat alternatives, national dietary guidelines and banning advertising of meat.

Promote cleaner transport

In order to reduce emissions from traditional vehicles, automakers are doubling spending on electric vehicles and batteries to $1.2 trillion by 2030.

But experts say a "modal shift" is also needed to encourage people to abandon their private vehicles for public transport, walking or cycling - especially in cities - such as in Germany and Spain where cheap rail tickets have cut emissions.

As well as reducing pollution, more active transport can tackle physical inactivity and obesity - which causes one million deaths per year in Europe, according to the World Health Organization.

Countries also need to cut down on flying to reach net zero. The aviation sector accounts for around 2.8% of global CO2 emissions, and just 1% of the population cause half of all aviation emissions, says the NGO Transport & Environment.

Tackle fast fashion

The fashion industry is the second biggest consumer of water after agriculture, and accounts for up to a tenth of greenhouse gas emissions, according to UNEP.

In Britain, the charity Oxfam said that around 13 million items of used clothing end up in landfills every week.

To make the industry greener, analysts say more must be done to curb production and keep clothes in use for longer - such as through repair, renting and repeated use.

End damaging subsidies

One of the biggest barriers to these changes are government subsidies for fossil fuels and other industries like agriculture and fisheries which are damaging the climate and nature.

From cash payments to tax breaks, research by the Business for Nature coalition found that at least $1.8 trillion is being spent on environmentally harmful subsidies each year.

Climate activists and conservationists have been pushing governments for decades to reform damaging subsidies and repurpose them towards more sustainable practices - such as regenerative agriculture instead of intensive farming.

At the upcoming U.N. COP15 meeting on biodiversity in Montreal in December, a new global framework is being drafted that aims to redirect $500 billion of these subsidies each year.

(Reporting by Jack Graham; Editing by Kieran Guilbert)