1.5 deg climate threshold breached — temporarily.
According to EU Copernicus 2023 was the first year of the instrumental record in which the global temperature exceeded 1.5 deg C above the pre-industrial baseline. This is a politically significant threshold as it was defined in 2015 by the Paris COP meeting as a limit beyond which we should avoid crossing to prevent increasing extreme climatic events.
The year 2023 however was an unusual one and is not the start of a prolonged period above the Paris threshold and global temperatures are expected to stall or fall. The latest estimates are that the threshold may be breached persistently in the 2030s according to some climate models.
The record warmth of 2023 needs to be seen in perspective.
The later-half of the year was exceptionally warm. According to one climate scientist the record warmth seen in the latter half of 2023 was “gobsmackingly bananas?”
Mika Rantanen, a climate researcher at the Finnish Meteorological Institute, said at the time: “I’m still struggling to comprehend how a single year can jump so much compared to previous years,” and Ed Hawkins, at the University of Reading, UK, said the heat seen this summer was ‘extraordinary.’
As we recently pointed out the effects of the Hunga-Tonga explosion and the policy change in the burning of ship fuels in addition to the natural El Nino, were the main causes of the warmth. But as the year continued, and especially at the climate retrospectives of the year, many of the qualifications as to why it was so warm, were sidelined in favour of the role of 2023’s record heat in the climate crisis.
But writing in the journal Nature recently, Rantanen and Laaksonen (2024) have told us what we already knew - that the exceptional warmth seen in the latter part of 2023 was not due to an acceleration of global warming. They look at two climate models, specifically MPI-GE and CESM2-LE, which they say are “known for their reliable simulations of both internal climate variability, such as El Nino, and the forced response due to greenhouse gas warming.”
They say that September 2023 - which broke the previous record by a remarkable 0.5 deg C - could not be explained by internal climate variability (less than 1 per cent probability) and they suggest that the Hunga-Tonga explosion and the release of the aerosol burden due to cleaner ship fuels could be major factors. Curiously there was a similar spike in temperatures in February 2016, by 0.47 deg C which they say was ten times more likely to be due to internal climate variability (El Nino) than the September 2023 jump, which perhaps shows an inconsistency in the climate models.
So, dramatic headlines aside as to the climate catastrophe that was 2023, what the latter part of that year has really shown us is the magnitude of climate variability that can occur that is unrelated to anthropogenic greenhouse gasses and cannot be represented by climate models. Mika Rantanen says that “the question arises as to whether other external forcing, those that may not be accurately represented in the models, have contributed to the record.”
Far from being a vindication of climate models 2023, taken alongside the fact that it is well-known that in general such models forecast a future that is unrealistically hot and incompatible with the data, the year represents somewhat of a disaster for them highlighting their limitations.
Feedback: david.whitehouse@netzerowatch.com