Everything essential to know about COP26

The United Nations says the COP26 summit is "the world's best last chance to get runaway climate change under control".

There's still a window of opportunity to avoid chaos but it's narrow.

What is or isn't achieved by about 2030 is considered crucial to success or failure.

Here's what is what is essential to know about the summit, what's riding on it and Australia's position.

WHAT IS COP26:

It's short-hand for the 26th annual Conference of Parties to the UN Framework Convention on Climate Change.

It begins on October 31 and will be attended by thousands of delegates from most countries, including 120 world leaders. Australian Prime Minister Scott Morrison will be among them.

The summit is essentially a global stocktake on climate action.

Have countries kept the promises they made under the 2015 Paris pact to limit warming to well below 2C and preferably to 1.5C? And what will they do next?

A key requirement of the Paris pact is that countries recommit every five years to increasingly ambitious climate action including the critical task of slashing greenhouse gas emissions.

This will happen for the first time at COP26.

WHAT'S ON THE LINE:

Everything, according to the world's top climate scientists.

In August, the Intergovernmental Panel on Climate Change released its sixth assessment report on climate action.

It warned the world is dangerously close to runaway warming.

The planet has already warmed about 1.1C since the Industrial Revolution and the IPCC said it's likely to hit or exceed the 1.5C limit in about a decade from now.

Without rapid, deep cuts to emissions from fossil fuels the IPCC warned the world would also sail past 2C. Yet there is still hope.

Under a scenario of very low emissions, Earth is still likely to reach 1.5C but the IPCC believes it will still be possible to drop back below that after a few decades.

WHY HALF OF ONE DEGREE MATTERS:

Scientific modelling shows every fraction of a degree will have an exponential effect on the health and livability of the planet.

Australia is already feeling climate change in the form of higher temperatures and more extreme weather.

Every additional fraction of a degree will increase its risk of more frequent and severe bushfires, droughts, cyclones and storms, coastal inundation and, if warming hits 2C, the loss of the Great Barrier Reef.

Globally, 2C would expose 37 per cent of the world's population to severe heatwaves at least once every five years, compared to 14 per cent at 1.5C.

It would expose 61 million additional urban dwellers to drought. And small island states and low-lying countries would sink further into the rising sea, among many other devastating effects.

THE OBJECTIVES OF COP26:

The headline objectives of the Glasgow summit are to ensure the world achieves net zero emissions by 2050 and between now and then take enough action to keep 1.5C "within reach".

Countries have been urged to present ambitious 2030 emissions reductions targets by phasing out coal, rapidly switching to electric vehicles, limiting deforestation and investing heavily in renewable energy.

Another key objective is for developed countries including Australia to honour a decade-old pledge to provide $100 billion annually to help developing countries deal with climate change and decarbonise.

WHAT AUSTRALIA WILL OFFER:

Prime Minister Scott Morrison is yet to say what new climate policy commitments he will take to Glasgow.

For weeks he's been locked in a stand-off with junior coalition partner the Nationals trying to secure their support for a 2050 target of net zero emissions.

Observers believe he will get that across the line if he grants a National Party wishlist for regional communities dependent on fossil fuel industries.

But the prime minister has ruled out what allies and neighbours have been demanding of Australia - a formal and ambitious increase to its existing pledge to cut emissions by 26-28 per cent by 2030.

Mr Morrison is expected to offer an update on projections in Glasgow showing Australia will achieve cuts of 32 per cent or higher.

But that's well short of what other developed economies have pledged for 2030 who've roughly promised to cut their emissions by about half by then. That's true of the US and EU, with the UK promising a reduction of at least 68 per cent by 2030.

UN Secretary-General Antonio Guterres says countries need to cut carbon emissions by 45 per cent by 2030 to be carbon neutral by the middle of the century.

UN climate envoy Selwin Hart who advises Gutteres had a blunt message for Australia earlier this year: "If G20 countries including Australia choose business-as-usual, climate change will soon send Australia's high living standards up in flames."

Australia is the world's largest coal exporter and second-largest gas exporter.

Australian Associated Press