We´re on track to exceed the 1.5C climate goal: what happens then?

• New IPCC report says action lacking to curb global warming
• World likely to breach 1.5C limit in early 2030s - experts
• Overshoot will require more drastic action to pull back

Despite many nations backing a target to limit global warming to 1.5 degrees Celsius (2.7 Fahrenheit), climate scientists say the planet is on track to breach that threshold in the early 2030s.

On Monday, the U.N.'s Intergovernmental Panel on Climate Change (IPCC) said governments have all the tools needed to make "deep, rapid and sustained greenhouse gas emissions reductions" to safeguard the 1.5C target.

What is lacking, it said, was political will.

About 40 environment ministers from around the world met this week in Copenhagen and reaffirmed their commitment to 1.5C after the IPCC report, delegates at the talks said.

Average global surface temperatures have already risen more than 1.1C above pre-industrial times, raising questions about what happens if and when 1.5C is passed.

Many climate scientists agree with a review by the Australian Academy of Science in 2021 that limiting warming to 1.5C is already "virtually impossible", and say too many governments are merely paying lip service to the target.

Here are questions about the 1.5C goal and options to keep it alive:

What is the 1.5C goal and what must be done to rescue it?

The Paris Agreement, adopted in 2015 by almost 200 nations, aims to limit warming to "well below 2C" (3.6F) above pre-industrial levels while "pursuing efforts" for 1.5C.

The 1.5 goal had been championed by small island states who fear rising seas and used the slogan "1.5 to stay alive".

The IPCC says the world has a better than 50% chance of limiting warming to 1.5C "with no or limited overshoot" if leaders can cut global emissions by 43% from 2019 levels by 2030. It defines "limited" as a tenth of a degree. 

But current government plans are insufficient, it said.

The planet is on target for warming of about 2.7C by the end of the century, according to the Climate Action Tracker research consortium.

Carbon dioxide emissions set record highs in 2022 despite tumbling prices of solar and wind energy, according to the International Energy Agency.

How will we know we have reached 1.5C?

It will be hard to know because temperatures vary significantly naturally, for instance with El Niño ocean warming events in the Pacific that can bring droughts, wildfires or floods in different regions of the world.

Last year, the U.N. World Meteorological Organization said there was a 50-50 chance that temperatures would reach 1.5C for at least one individual year between 2022 and 2026.

To smooth out freak blips of cold or heat, the IPCC uses 20-year averages.

"The occurrence of individual years with global surface temperature change above a certain level does not imply that this global warming level has been reached," it said.

Using 20-year averages, the world is on track to reach 1.5C in the first half of the 2030s in most emissions scenarios, the IPCC found.

Some nations may want to delay any declaration of failure on the goal even if temperature trends make it inevitable, said Glen Peters, a senior researcher at the Center for International Climate Research (CICERO) in Oslo.

"They may say: 'We're not over 1.5 yet'," he said.

"But it's like you have thrown a ball off the cliff and you say 'it hasn't hit the ground yet' ... You know by the law of physics that it is going to hit the ground."

Is the 1.5C goal dead if we exceed it?

Probably not, because IPCC scenarios foresee that temperatures could rise above 1.5C for a few decades and then fall again by 2100.

Only a few of the most ambitious models used by the IPCC for 1.5C predict there will be no overshoot at all.

"I would not bet on the IPCC calling 1.5C lost even in 6-7 years' time", when the panel is likely to issue its next report, said Bill Hare, chief executive of the Berlin-based Climate Analytics think-tank.

Allowing temperatures to overshoot 1.5, however, would require ever more "negative emissions" measures such as planting forests, which soak up carbon to grow, or expanding now-costly technologies to suck carbon from thin air.

What would happen with overshoot?

Since the Paris Agreement, ever more studies show that every tenth of a degree of temperature rise matters, from worsening the threats to coral reefs to accelerating ice melt in Greenland or Antarctica that is pushing up sea levels.

"Risks are increasing with every increment of warming," the IPCC said in its latest report, urging that any overshoot be as small as possible.

Among the risks, it said, are "increased wildfires, mass mortality of trees, drying of peatlands, and permafrost thawing".

Larger levels of overshoot would raise the need for bigger efforts to remove carbon emissions to return to 1.5C by 2100.

The focus should remain on meeting the 1.5C goal, said Lili Fuhr, deputy director of the climate and energy programme at the Center for International Environmental Law, a nonprofit environmental law firm.

She said it was "a whole lot better to fail at 1.5 and go slightly over" than to abandon that goal and claim success by limiting rising temperatures to 2C.