‘One point five degrees’: Has global warming exceeded the much feared tipping point?

A paper published in Nature Climate Change this February by climatologist Malcolm T. McCulloch and his team has triggered intense debate. Their research claims that global warming has now exceeded 1.5°C above pre-industrial levels, a critical threshold that has been a focal point for climate scientists and activists. 

At the same time, global temperature data also shows that since the start of the post-industrial era, 2023 was recorded as the warmest year on Earth.

Following the publication, a series of reactions came from the scientific community and beyond. Articles were published in popular newspapers and journals, with experts either supporting or challenging McCulloch's findings. 

This uproar signifies the 1.5°C target, which originated from the Paris Climate Agreement which was signed in 2016. In this landmark agreement, nearly 200 nations decided to limit global temperature rise to below two degrees and to strive for a maximum increase of 1.5° Celsius. 

The significance of 1.5°

The 1.5° has been considered an important threshold as severe impacts such as the destruction of coral reefs, loss of Arctic sea ice, and thawing of permafrost may intensify beyond that point.

The Paris Climate Agreement does not specify the baseline very clearly. 

In their paper, McCulloch et al compared today’s temperature to the average from 1700-1860 arguing that the global increase in temperature during the 18th and early 19th has also been caused partly by human action.

By this measure, their research indicates we have surpassed the 1.5° Celsius mark.  

However, a more agreeable norm among climate scientists is considering the average temperature in 1850-1900 as the baseline for this purpose.

Disagreement over Paris agreement

Further, the Paris Agreement also does not specify the process of calculating the increase in temperature. That also contributes to confusion. 

For instance, if we take the average temperature for the period 1850-1900 as the base, last year the global average temperature was indeed 1.5° Celsius higher than the base (see the graph below). 

However, experts opined this does not necessarily signify a permanent crossing of the 1.5°C threshold.

To address annual temperature fluctuations, often influenced by phenomena such as El Niño Southern Oscillation (ENSO), scientists use a 20-year averaging method. 

This involves taking an average of the past 10 years and the projected temperature of the next 10 years, thereby smoothing out short-term variations. 

By this approach, the current average increase is about 1.3° Celsius (the red line in the graph above).

In conclusion

Despite these nuances, projections from the Intergovernmental Panel on Climate Change (IPCC) suggest that we will reach the critical 1.5°C threshold soon, probably by the year 2040. This necessitates the urgency for climate action and international cooperation to prevent the most catastrophic consequences.

In summary, it is clear that while we may not have technically crossed the 1.5°C threshold yet, we are very close. The debate itself is a strong reminder of the urgent need to mitigate climate change and protect our planet for future generations.

Views expressed are the author’s own and don’t necessarily reflect those of Down To Earth