High hopes for COP26 climate summit

Representatives from almost 200 countries will gather in Scotland from Sunday to confront the threat posed by climate change.

The United Nations says Glasgow's 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 an overview of the summit, what's riding on it, and Australia's position.

WHAT IS COP26?

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

It begins on Sunday 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.

The UN's Environment Programme this week warned the world is off course and won't achieve 1.5C, let alone 2C, without dramatic action.

It said nations must present much stronger plans to reduce emissions. Otherwise the planet is on track for "catastrophic" warming of at least 2.7C this century.

However, 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.

Fractional degree increases have been linked to more frequent and severe bushfires, droughts, cyclones and storms, coastal inundation.

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 until then takes 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 WILL AUSTRALIA OFFER?

Mr Morrison will go to COP26 with a new promise that Australia will achieve net zero emissions by 2050, a pledge matching those offered by some other countries several years ago.

Australia's position is short of what international allies wanted - a much stronger formal commitment to cut emissions by 2030.

Mr Morrison will provide "updated projections" showing Australia is on track for a 30 to 35 per cent reduction by the end of the decade.

That's below what the IPCC says the nations of the world must achieve - an overall 45 per cent cut in order to keep warming to 1.5C.

Mr Morrison's plan to achieve net zero was released on Tuesday. It said Australia would continue exporting coal and gas "through to 2050 and beyond", for as long as demand continues.

Emissions will be reduced through a focus on clean hydrogen and a $20 billion investment in low-emissions technologies to build a greener economy that will create 62,000 new regional jobs while saving existing industries.

Mr Morrison has ruled out new taxes and mandates, and the net zero commitment will not be enshrined in law.

The modelling that underpins emissions abatement strategies, including carbon capture and storage, has not yet been released.

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