There is an 80% chance that the world will temporarily cross the 1.5 degree Celsius threshold in the next five years. A long-term breach would accelerate and intensify the catastrophic impacts of climate change.
This May was the warmest May ever. In fact, each of the last 12 months have set a new warming record for that particular month, Europe’s Copernicus Climate Change Service (C3S) said last week.
The average global temperature last month was 1.5 degree Celsius above the estimated May average for the 1850-1900 pre-industrial reference period. For the 12-month period (June 2023 – May 2024), the average temperature stood at 1.63 degree Celsius above the 1850-1900 average.
The World Meteorological Organization (WMO), in a separate report published on June 6, said there is now an 80% chance that at least one calendar year between 2024 and 2028 would see its average temperature exceed 1.5 degree Celsius above the pre-industrial levels — for the first time in history. Just a year ago, the WMO had predicted a 66% chance of the same.
Scary as these facts are, they do not imply that the world is about to breach the commonly talked about 1.5 degree Celsius temperature threshold. That threshold refers to a warming over a longer period, with usually a two or three decade average taken into consideration.
What is the 1.5 degree Celsius threshold?
In 2015, 195 countries signed the Paris Agreement, which pledged to limit global temperatures to “well below” 2 degree Celsius above pre-industrial levels by the end of the century. It also said countries would aim to curb warming within the safer 1.5 degree Celsius limit.
While the Agreement did not mention a particular pre-industrial period, climate scientists generally consider 1850 to 1900 as a baseline, since it is the earliest period with reliable, near-global measurements. Some anthropogenic global warming had already taken place at that time — the Industrial Revolution began in England in the mid-1700s. Nonetheless, a reliable baseline is crucial to measure the rising temperatures today.
Why 1.5 degree Celsius?
The safer 1.5 degree Celsius limit was chosen based on a fact-finding report, which found that breaching the threshold could lead to “some regions and vulnerable ecosystems” facing high risks, over an extended, decades-long period.
The 1.5 degree Celsius was set as a “defence line”, to ensure that the world avoids the disastrous and irreversible adverse effects of climate change which would begin to unfold once the average temperature increases by 2 degree Celsius above the pre-industrial levels. For some regions, even a smaller spike will be catastrophic.