Written by Laure Poncet
For the first time, global temperatures have consistently surpassed 1.5°C of warming over the past 12 months, according to data from the EU’s Copernicus Climate Change Service.
This warming trend raises concerns about our progress towards meeting the goals of the Paris Agreement, which aims to limit global warming to well below 2°C above pre-industrial levels.
Climate scientist Dr Kim Reid from the ARC Centre of Excellence for Climate Extremes explained that while this year-long exceedance of 1.5°C doesn’t break the commitments made in the Paris Agreement, it does bring us closer to the red line.
“This breach of 1.5°C for the last 12 months isn’t a death knell for the Paris Agreement, but it is a fire alarm, and we need to wake up and put out this fire.”
What does the 1.5°C value mean and where does it come from?
In 2015, world leaders of 195 nations agreed to limit global warming to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5°C. Pre-industrial levels refer to the period between 1850 and 1900, which scientists use as a baseline because it precedes the time when humans started burning large amounts of fossil fuels.
While 1.5°C is not a binding target of the agreement, Reid explained that limiting global warming to as close to this value as possible is crucial if we want to avoid the worst impacts of climate change.
“The risks associated with extreme weather events, sea level rise, biodiversity loss, and disruptions to ecosystems and human societies are significantly larger in a 2°C warmer world compared to a 1.5°C warmer world. Humanity’s ability to adapt to climate change will become increasingly challenging above 2°C,” she said.
She explained that there are different mechanisms behind this. “In the case of extreme weather events, for example, the warmer the atmosphere, the more water vapour it can hold. This, in turn, increases the potential for heavy rainfall events, tropical cyclones and severe thunderstorms.”
The probability of passing crucial tipping points also increases with every fraction of a degree of warming. Tipping points are critical thresholds in the climate system which can lead to abrupt and potentially irreversible changes. One example of such a tipping point is the West Antarctic Ice Sheet.
“If the West Antarctic Ice sheet passes a tipping point, its collapse could accelerate the flow of ice into the ocean, leading to global sea level rise. Once initiated, this process could be hard to stop, and it would take thousands of years to restore an ice sheet of that size,” Reid explained.
“However, we are unlikely to exceed an Antarctic climate tipping point this century,” she added.
Why did temperatures exceed 1.5°C in the past year?
The warming trend over the past decades is caused by the burning of fossil fuels. This human-caused warming is also responsible for much of the rise in temperatures observed over the past 12 months.
On top of that, El Niño – a natural climate phenomenon associated with the increase in ocean temperatures in the central and eastern tropical Pacific Ocean – gave global surface temperatures an extra boost.
“Annual temperatures vary from year to year due to factors such as El Niño and La Niña. During typical El Niño years, we tend to get warmer than average global temperatures, while La Niña years tend to be colder than average.”
“We had an El Niño at the end of 2023 which may explain, at least in part, why we saw these record temperatures,” explained Reid.
“As we shift to neutral and potentially a La Niña, temperatures will likely decrease a little relative to the last 12 months. However, the background warming is still there. So, unless we stop emissions, temperatures will continue to rise over the next decades.”
Have we passed 1.5°C global warming already?
In the period from July 2023 to June 2024, global temperatures hit record highs, peaking at 1.64°C above the pre-industrial average. Does this mean we have failed to meet the aspirational goal of limiting global warming to 1.5°C?
The answer is no. To iron out the influence of year-to-year natural variations, such as those caused by El Niño or volcanic eruptions, the 1.5°C value is defined as the first 20-year period when we exceed 1.5°C of global warming. This means that the 1.5°C value is considered breached if the average temperature change over 20 years exceeds 1.5°C.
“While temperatures exceeded 1.5°C over the past year, a single year above the limit doesn’t mean we breached 1.5°C. However, we are likely at the start or the early middle of this 20-year period,” said Reid.
“If we continue burning fossil fuels, we’ll see more and more years above 1.5°C and we’ll move closer and closer to warming exceeding 1.5°C on average. This will generally elevate climate risk leading to increased costs of adapting to climate change.”
Can we remain below 1.5°C?
While the past year does not formally breach 1.5°C, scientists warn that we are getting close. As the world continues to warm, years exceeding 1.5°C will likely be more common, which could push us beyond 1.5°C sooner than we expect. At the current rate of emissions, scientists estimate we could cross it within the next decade.
“We do need to ramp up our efforts to make sure we do not cross that line. And this can only be done by drastically reducing our emissions. Forget 2050, we need net zero by 2035 if we want to stay below 1.5°C,” said Reid. “That means any further fossil fuel exploration is utterly incongruent with maintaining a safe climate.”
However, if we do overshoot the 1.5°C limit – which is probably inevitable now due to failure to reduce global emissions over the last few decades – Reid urged not to give up on climate action.
“1.5°C is bad. 2°C would be significantly worse. 3°C would be catastrophic. Every extra increment matters and every action to reduce emissions reduces the risk of dangerous climate change.”