2024 was the warmest year on record globally, with average temperatures exceeding 1.5 degrees. While often used interchangeably, this is not the same thing as breaching the Paris Agreement threshold of 1.5 degrees. 

The problem with the Paris agreement is that there was no formal definition of what 1.5 meant, but it is widely assumed that it refers to the IPCC’s definition – which defines this in terms of 20-year blocks of time relative to the average for 1850-1900. While that definition works for climate model projections, when it comes to yearly observations it means we won’t know if we’ve officially crossed the Paris line until a decade after it happens.

This new research attempts to overcome this problem using climate model simulations, and suggests that 2024 may indeed indicate that we have breached the Paris 1.5 mark. Whether we have or not, the fact remains that we only have about six years left in the global carbon budget emitting at current rates to give ourselves a 50/50 chance of still making the Paris target. If this new research is correct, 2024 may be the first sign that we have already overshot this target.

Recently we've seen individual days, months and even the year of 2024 exceed the 1.5°C global warming mark relative to pre-industrial levels. While this is very concerning, climate scientists have cautioned that this doesn't mean we've failed to meet the Paris Agreement goals. This is because the warming levels in the Paris Agreement refer to longer climate periods rather than short excursions over the 1.5°C level.

What these new studies highlight is how these single months and years over the 1.5°C mark are likely to be features of a longer period the world has entered in which the climate averages more than 1.5°C of global warming. In fact, without rapid decarbonisation it is hard to avoid the climate entering a longer phase of global warming above the 1.5°C level.

While this won't surprise too many climate scientists, these studies are a timely reminder of how far we really are from tackling climate change properly. Global greenhouse gas emissions remain at or near record levels and global warming has even accelerated in recent years. A major shift is needed to decarbonise our society and economy otherwise we will keep warming the planet and causing more and more damage.

Just published research that points to the most recent consecutive twelve months global average temperature at 1.5 °C [above pre-industrial levels] signals an earlier than expected breach of the Paris Agreement threshold while different research concludes that the most recent 12 months above 1.5 °C signals that Earth is most probably within the 20-year period that will reach the Paris Agreement limit.

Evidence supports the aforementioned research more strongly because using long-term temperature and rainfall averages of periods like 30 years, currently used to define climate by the World Meteorological Organization, or indeed 20 years, are now unsuitable for defining climate (see:- https://theconversation.com/unprecedented-climate-extremes-are-everywhere-our-baselines-for-whats-normal-will-need-to-change-24429)

In recent decades, there has been a glaring disconnect between the current definition of climate periods as the means [averages] of 30 consecutive years and the more appropriate means [averages] of decadal or shorter periods. It is generally known now that global warming (GW) and climate impacts have accelerated since the 1990s. As a result, global climate regimes are now increasingly being driven by GW, modulated by the phases of climate drivers relevant to the location of interest.

There is a need for a combined statistical-climate model approach to climate prediction. Climate models are needed to predict the future phases of the climate drivers based on updated climate drivers that can be attained over periods more appropriately comprising a few years.