What's the Difference Between 1.5°C and 2°C of Global Warming?

Flames rise as a wildfire burns in the village of Galatsona, on the island of Evia, Greece, August 9, 2021. (Reuters)
Flames rise as a wildfire burns in the village of Galatsona, on the island of Evia, Greece, August 9, 2021. (Reuters)
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What's the Difference Between 1.5°C and 2°C of Global Warming?

Flames rise as a wildfire burns in the village of Galatsona, on the island of Evia, Greece, August 9, 2021. (Reuters)
Flames rise as a wildfire burns in the village of Galatsona, on the island of Evia, Greece, August 9, 2021. (Reuters)

Over and over at the UN climate summit in Glasgow, world leaders have stressed the need to limit global warming to 1.5 degrees Celsius.

The 2015 Paris Agreement commits countries to limit the global average temperature rise to well below 2°C above pre-industrial levels, and to aim for 1.5°C.

Scientists have said crossing the 1.5°C threshold risks unleashing far more severe climate change effects on people, wildlife and ecosystems.

Preventing it requires almost halving global CO2 emissions by 2030 from 2010 levels and cutting them to net-zero by 2050 -- an ambitious task that scientists, financiers, negotiators and activists at COP26 are debating how to achieve and pay for. But what is the difference between 1.5°C and 2°C of warming?

Reuters asked several scientists to explain:

Where are we now?
Already, the world has heated to around 1.1°C above pre-industrial levels. Each of the last four decades was hotter than any decade since 1850.

"We never had such a global warming in only a few decades", said climate scientist Daniela Jacob at the Climate Service Center Germany. "Half a degree means much more extreme weather, and it can be more often, more intense, or extended in duration."

Just this year, torrential rains flooded China and Western Europe, killing hundreds of people. Hundreds more died when temperatures in the Pacific Northwest hit record highs.

Greenland saw massive melting events, wildfires ravaged the Mediterranean and Siberia, and record drought hit parts of Brazil.

"Climate change is already affecting every inhabited region across the globe," said climate scientist Rachel Warren at the University of East Anglia.

Heat, rain, drought
More warming to 1.5°C and beyond will worsen such impacts.

"For every increment of global warming, changes in extremes become larger," said climate scientist Sonia Seneviratne at ETH Zurich.

For example, heatwaves would become both more frequent and more severe.

An extreme heat event that occurred once per decade in a climate without human influence, would happen 4.1 times a decade at 1.5°C of warming, and 5.6 times at 2°C, according to the UN climate science panel (IPCC).

Let warming spiral to 4°C, and such an event could occur 9.4 times per decade.

A warmer atmosphere can also hold more moisture, resulting in more extreme rainfall that raises flood risks. It also increases evaporation, leading to more intense droughts.

Ice, seas, coral reefs
The difference between 1.5°C and 2°C is critical for Earth's oceans and frozen regions.

"At 1.5°C, there’s a good chance we can prevent most of the Greenland and west Antarctic ice sheet from collapsing," said climate scientist Michael Mann at Pennsylvania State University.

That would help limit sea level rise to a few feet by the end of the century - still a big change that would erode coastlines and inundate some small island states and coastal cities.

But blow past 2°C and the ice sheets could collapse, Mann said, with sea levels rising up to 10 meters (30 feet) - though how quickly that could happen is uncertain.

Warming of 1.5°C would destroy at least 70% of coral reefs, but at 2°C more than 99% would be lost. That would destroy fish habitats and communities that rely on reefs for their food and livelihoods.

Food, forests, disease
Warming of 2°C, versus 1.5°C, would also increase the impact on food production.

"If you have crop failures in a couple of the breadbaskets of the world at the same time, then you could see extreme food price spikes and hunger and famine across wide swathes of the world," said climate scientist Simon Lewis at University College London.

A warmer world could see the mosquitoes that carry diseases such as malaria and dengue fever expand across a wider range.

But 2°C would also see a bigger share of insects and animals lose most of their habitat range, compared with 1.5°C, and increase the risk of forest fires - another risk to wildlife.

'Tipping points'
As the world heats up, the risk increases that the planet will reach "tipping points", where Earth’s systems cross a threshold that triggers irreversible or cascading impacts.

Exactly when those points would be reached is uncertain.

Droughts, reduced rainfall, and continued destruction of the Amazon through deforestation, for example, could see the rainforest system collapse, releasing CO2 into the atmosphere rather than storing it. Or warming Arctic permafrost could cause long-frozen biomass to decompose, releasing vast amount of carbon emissions.

"That's why it's so risky to keep emitting from fossil fuels ... because we're increasing the likelihood that we go over one of those tipping points," Lewis said.

Beyond 2°C
So far, the climate pledges that countries have submitted to the United Nations' registry of pledges put the world on track for 2.7°C of warming.

The International Energy Agency said Thursday that new promises announced at the COP26 summit – if implemented - could hold warming to below 1.8°C, although some experts challenged that calculation. It remains to be seen whether those promises will translate into real-world action.

Warming of 2.7°C would deliver "unlivable heat" for parts of the year across areas of the tropics and subtropics.

Biodiversity would be enormously depleted, food security would drop, and extreme weather would exceed most urban infrastructure's capacity to cope, scientists said.

"If we can keep warming below 3°C we likely remain within our adaptive capacity as a civilization, but at 2.7°C warming we would experience great hardship," said Mann.



Syrians Return to Homs, ‘Capital of the Revolution’ 

A girl holds an independence-era Syrian flag out of the window of a bus carrying displaced Syrians returning home after years of displacement in the northern Aleppo province, at the entrance of the central city of Homs on February 10, 2025. (AFP)
A girl holds an independence-era Syrian flag out of the window of a bus carrying displaced Syrians returning home after years of displacement in the northern Aleppo province, at the entrance of the central city of Homs on February 10, 2025. (AFP)
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Syrians Return to Homs, ‘Capital of the Revolution’ 

A girl holds an independence-era Syrian flag out of the window of a bus carrying displaced Syrians returning home after years of displacement in the northern Aleppo province, at the entrance of the central city of Homs on February 10, 2025. (AFP)
A girl holds an independence-era Syrian flag out of the window of a bus carrying displaced Syrians returning home after years of displacement in the northern Aleppo province, at the entrance of the central city of Homs on February 10, 2025. (AFP)

Once dubbed the capital of the revolution against Bashar al-Assad, Homs saw some of the fiercest fighting in Syria's civil war. Now, displaced people are returning to their neighborhoods, only to find them in ruins.

It was in Homs that the opposition first took up arms to fight Assad's crackdown on peaceful protests in 2011.

The military responded by besieging and bombarding rebel areas such as Baba Amr, where US journalist Marie Colvin and French journalist Remi Ochlik were killed in a bombing in 2012.

Since Assad's ouster, people have started returning to neighborhoods they fled following successive evacuation agreements that saw Assad take back control.

"The house is burned down, there are no windows, no electricity," said Duaa Turki at her dilapidated home in Khaldiyeh neighborhood.

"We removed the rubble, laid a carpet" and moved in, said the 30-year-old mother of four.

"Despite the destruction, we're happy to be back. This is our neighborhood and our land."

Her husband spends his days looking for a job, she said, while they hope humanitarian workers begin distributing aid to help the family survive.

The siege of Homs lasted two years and killed around 2,200 people, according to the Syrian Observatory for Human Rights.

During the siege, thousands of civilians and opposition fighters were left with nothing to eat but dried foods and grass.

In May 2014, under an evacuation deal negotiated with the former government, most of those trapped in the siege were evacuated, and two years later, Assad seized the last opposition district of Waer.

"We were besieged... without food or water, under air raids, and barrel bombings," before being evacuated to the opposition-held north, Turki said.

A boy walks past the debris of buildings in the Khaldiyeh district in Homs on February 10, 2025. (AFP)

- 'Precious soil of Homs' -

AFP journalists saw dozens of families returning to Homs from northern Syria, many of them tearful as they stepped out of the buses organized by local activists.

Among them was Adnan Abu al-Ezz, 50, whose son was wounded by shelling during the siege and who later died because soldiers at a checkpoint barred him from taking him to hospital.

"They refused to let me pass, they were mocking me," he said with tears in his eyes.

"I knew my house was nearly destroyed, but I came back to the precious soil of Homs," he said.

While protests and fighting spread across Syria over the course of the 13-year war, Homs's story of rebellion holds profound symbolism for the demonstrators.

It was there that Abdel Basset al-Sarout, a football goalkeeper in the national youth team, joined the protests and eventually took up arms.

He became something of a folk hero to many before he joined an armed group and was eventually killed in fighting.

In 2013, his story became the focus of a documentary by Syrian filmmaker Talal Derki named "The Return to Homs", which won international accolades.

Homs returnee Abu al-Moatasim, who remembers Sarout, recounted being detained for joining a protest.

When he saw security personnel approaching in a car, he prayed for "God to drop rocket on us so I die" before reaching the detention center, one of a network dotted around the country that were known for torture.

His father bribed an officer in exchange for his release a few days later, he said.

A vegetable vendor waits for customers in front of a damaged building in Homs on February 10, 2025. (AFP)

- 'Build a state' -

In Baba Amr, for a time early in the war a bastion of the opposition Free Syrian Army, there was rubble everywhere.

The army recaptured the district in March 2012, following a siege and an intense bombardment campaign.

It was there that Colvin and Ochlik were killed in a bombing of an opposition press center.

In 2019, a US court found Assad's government culpable in Colvin's death, ordering a $302.5 million judgement for what it called an "unconscionable" attack that targeted journalists.

Touring the building that housed the press center, Abdel Qader al-Anjari, 40, said he was an activist helping foreign journalists at that time.

"Here we installed the first internet router to communicate with the outside world," he said.

"Marie Colvin was martyred here, targeted by the regime because they did not want (anyone) to document what was happening," he said.

He described her as a "friend" who defied the "regime blackout imposed on journalists" and others documenting the war.

After leaving Homs, Anjari himself became an opposition fighter, and years later took part in the offensive that ousted Assad on December 8, 2024.

"Words cannot describe what I felt when I reached the outskirts of Homs," he said.

Now, he has decided to lay down his arms.

"This phase does not call for fighters, it calls for people to build a state," he said.