Welcome to The Environmentalist, your column for understanding the natural world. Today, we will be asking what happens and what does it mean when we cross 1.5°C.
The United Nations Environment Programme (UNEP) recently released a new report confirming a fear that climate scientists have harbored for years: 1.5°C above pre-industrial levels is likely to be surpassed in the next few years. It will potentially stay above that level for decades to come, challenging the global community to devise a path to return to below 1.5°C in due course. For years, 1.5°C has been the number that humanity has strived to protect and preserve. But what does this threshold mean?
The 1.5°C threshold refers to the increase in average global temperature since the pre-industrial period, but does not represent a uniform temperature increase across the globe. Under the 2015 Paris Agreement, countries aim to keep warming safely beneath 2°C while “pursuing efforts” to limit it to 1.5°C. However, the threshold is often mistakenly viewed as a tipping point separating a safe climate from a dangerous one. Climate change impacts are already being felt worldwide, and each additional fraction of a degree of warming brings greater risks of negative impacts.
The possibility of the world exceeding the 1.5°C temperature limit has been frequently flagged over recent years. 2024 was the first time the global average temperature was more than 1.5°C above the pre-industrial average for a calendar year. However, that single year does not constitute an overshoot of the Paris temperature goal. It will take decades to determine whether 1.5°C has been exceeded in the long-term. New research suggests that we may have already entered the period in which long-term warming finally reaches 1.5°C, adding urgency to UNEP’s latest report. While that report warns of the dangers of an overshoot and whether or not it can be limited, it also shifts the focus onto how much of that overshoot can still be limited.
Overshoot doesn’t just matter in terms of degree, the length of time that we are above 1.5°C also matters greatly, as higher temperatures lead to more extreme weather, greater ecosystem loss, more sea level rise, and greater impacts on food and water security. Once the temperatures return to below 1.5°C, it won’t undo the negative effects. Some of the losses, like species extinctions, ice loss, and changes to ecosystems, could be irreversible or long lasting even after temperatures decrease. The goal, therefore, is to keep our time above 1.5°C as short as possible and to minimize the extent of the overshoot.
Although we are still on course for around 2.8°C of warming this century, the extent to which we can limit the overshoot still remains in our hands. Every fraction of a degree of warming we can prevent will save lives, species, and ecosystems. As the Lorax once said, “Unless someone like you cares a whole awful lot, nothing is going to get better.” So, let’s care.
