Climate Action
Decoding 1.5 Degrees Celsius
December 12, 2025
1.5 degrees Celsius isn’t just a number. It has become a symbol of the climate fight. For years, world governments, environmental activist groups, and figures like Greta Thunberg and Leonardo DiCaprio have spotlighted 1.5 degrees as a critical threshold. Stay below it (compared to pre-industrial levels) and the planet fares far better; exceed it, and the consequences worsen. Over time, 1.5 °C has come to represent not just a target, but the urgency, struggle, and collective effort driving the movement to protect our collective future.
Its repeated use has given it an almost symbolic quality — rather than being a goal of the climate fight, it represents the fight itself, and the urgency behind it.
The United Nations’ Environment Programme announced last month that we will overshoot this number, The United Nations Secretary General, António Guterres, describes it as a “moral failure,” and urges world leaders to “lead,” or, “be led to ruin.” So, what does all of this mean? It’s time to decode 1.5 degrees Celsius.
One Number, Different Meanings
Due to its ubiquitousness nowadays, you may not know that small island nations first advanced the “below 1.5 °C” goal. Most nations agreed that limiting world temperatures between 1-2 °C above pre-industrial levels was fitting. But small island nations adopted the phrase “1.5 to stay alive”, to highlight the disproportionate dangers their states would face if level reached 2 °C, compared to the rest of the world.
In 2015, 195 nations signed the Paris Climate Agreement to keep global temperatures “well below” a 2 °C increase, and, hopefully, limit it to 1.5 °C. Since then, it’s come to define the environmental movement.
As research exposed the dangers of a 2 °C world, nations pledged action to stay below this threshold. Even now, activists cling to it, not just as a goal, but as a beacon of hope. To abandon it entirely would feel like admitting defeat, risk shaking public faith in the fight for our planet and studies suggest, demotivate people.
In May, Extinction Rebellion activists held a “funeral” for the Earth, which included blood-red outfits and a symbolic casket. They made speeches about how politicians had failed to keep Earth at “livable” temperatures. At first glance, it seems contradictory, if the Earth is already dying, why act? But the spectacle makes the point: recognizing the crisis doesn’t mean giving up; it’s exactly why we must fight harder.
Lots of Room to Improve…Don’t Give Up
That’s why it’s important to realize that 1.5 °C is not an absolute threshold. We have been experiencing climate-related natural disasters for years, even though we only met this 1.5 threshold this year.
What is true though is that a permanent 1.5 °C increase would have alarming consequences for the planet. In estimates from 2021, in terms of biodiversity, by 2100, 70-90% of coral reefs will likely perish, and 14% of the world’s species will be at risk of extinction. And in terms of environmental changes, sea levels will rise by roughly 0.26 to 0.77 meters (0.85 to 2.52 feet) by 2100, exposing 31 to 69 million people to dangerous floods, while 950 million people will also experience water and heat stress. It will also make intense natural disasters — including heatwaves, droughts, and wildfires — much more common.
But a temperature increase of 2 °C would be significantly worse. At 1.5 °C above pre-industrial levels, 14% of people would experience heat waves at least once every five years, but at 2 °C, it increases to 37% of people. By 2100, at 2 °C, the percentages of insects, plants, and vertebrates that would lose half of their habitats would double or triple, and sea levels would rise by up to 0.87 meters, or 2.85 feet.
It may seem odd that just a half degree difference results in this much difference but every 0.1 °C change above present levels could leave 140 millions people vulnerable to dangerous heat and increase local area temperatures and precipitation levels. This means we can’t stop fighting because 1.5 °C is over, or because 2 °C seems far away — because every change, positive or negative, matters.
So, What Now?
The most important thing to remember is that passing 1.5 °C doesn’t mean we stop caring or acting. In fact, environmental activism matters more now, than it ever has. So get involved!
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