Countries will for the first time assess how far off track they are to curb global warming at this year's COP28 climate change summit, a process known as the "global stocktake".
Governments will look at progress so far as well as what action is still needed to get the world on track. The aim is to yield a plan by the end of the two-week U.N. conference in Dubai.
The assessment could become politically divisive as it sets the stage for the next few years of global action in cutting planet-warming emissions.
Here is what you need to know about the stocktake.
Why is a global stocktake important?
Each country sets its own targets and policies for meeting the 2015 Paris Agreement's overall goal of holding global warming to within 2 degrees Celsius of preindustrial times, and aiming for just 1.5 C of warming.
Under the 2015 pact, countries must gauge their progress as of this year, and then every five years afterwards. Based on the results, countries may be pressed to set more ambitious climate policies or to contribute more financing to help developing countries adopt clean energy.
This year's stocktake could also offer important guidance as countries prepare to update their emissions-cutting targets again by 2025. For example, the stocktake could advise that CO2-cutting targets should cover a country's entire economy, not just certain sectors.
Is the world off course in meeting climate goals?
In September, the United Nations offered an early stocktake assessment that revealed countries were far behind in meeting climate goals. It said action was required "on all fronts" to keep the global average temperature rise limited to 1.5 C - the threshold beyond which scientists say more severe and irreversible climate impacts will occur.
Despite a huge increase in the number of countries setting CO2-cutting targets since the Paris Agreement, current emissions plans still put the world on track to warm by at least 2.5 C, the U.N. estimates.
Many countries also have yet to set strong enough short-term policies to steer their economies towards emissions targets for 2030 and 2050.
The global average temperature has already warmed by 1.2 C since pre-industrial times, which is causing widespread drought along with more frequent deadly heat waves, wildfires and storms around the world.
How will the stocktake drive climate action?
Before the stocktake has even started, countries are squabbling over the scope of future plans - including whether they should commit to phase out fossil fuel use, end investments in new coal power plants or triple renewable energy capacity within this decade.
COP28 delegates will also need to decide if the stocktake should recommended action for specific sectors, such as the energy or manufacturing sectors.
The U.N.'s report in September urged countries to cut CO2-emitting coal power by 67% to 82% from 2019 levels by 2030.
The report also called for more finance to help poorer countries adopt clean energy, and noted that billions of dollars were still being invested in fossil fuels every year.
The European Union wants the stocktake to produce "concrete policy signals" for countries to follow.
Some developing countries have suggested the stocktake should focus on pressuring wealthy nations to do more, since they have contributed the most emissions to the atmosphere since the Industrial Revolution, diplomats said.
"This is where we take stock and see where we are - where are the gaps between the targets and our ambitions, and the actual action. What then needs to be decided... what do we then do from here," Dan Jorgensen, Denmark's Global Climate Policy Minister, told Reuters.
