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15 January 2024 Expert commentary

The European Union's Copernicus Climate Change Service (C3S) announced on 9 January 2024 that 2023 was officially the hottest year in recorded history. 

The announcement follows a preliminary press release, 30 November, by the World Meteorological Organization (WMO) which showed that data even up to the end of October 2023 meant that the year 2023 was about 1.40 degrees Celsius above pre-industrial temperatures.     

Copernicus’ full record, which now includes November and December data, saw that record temperature updated to 1.48 degrees Celsius above pre-industrial temperatures. 

CSIRO experts, who are undertaking a wide range of research to help governments, industries and communities tackle climate change, respond. 

All quotes below are available for use by media.

Was this consistent with climate projections of climate warming? 

Dr Jaci Brown, Climate Intelligence Director, explains: 

“The warming rate is within the range of what scientists expect – last year was not a surprise. We won’t see even warming each year, instead we will continue to see fluctuations between cool and warm years – like we have with three years of La Niña and now an El Niño. What is clear is that the Earth and Australia are warming, will continue to warm, and subsequent El Niño years will push us into new extremes of heat.” 

Dr Michael Grose, Research Scientist says: 

“Very much so. The trend of global average temperature, and the possibility of years this warm are included in climate projections as far back as 1980, and with assessments such as from the Intergovernmental Panel on Climate Change (IPCC) ever since." 

Is 2024 likely to be even hotter?  

Dr Jaci Brown, Climate Intelligence Director, explains: 

“2024 may be hotter or it may be cooler. It depends on how our climate variability such as El Niño tracks into the year. What is more certain is that next decade will be hotter than this one.

“The heat in 2023 is a useful glimpse of our not-too-distant future. In a few decades this won’t look like a hot year, it will be a normal year or possibly even a cool year. We need to be asking ourselves – how do we prepare for that?” 

What factors contributed to 2023 being the hottest year on record?  

National Environmental Science Program Climate Systems Hub Leader, Dr Simon Marsland, says: 

“2023 coincided with the highest levels of greenhouse gas concentrations in our atmosphere. There is a very clear and explicable reason for 2023 being the hottest year on record - global warming, as a result of human-induced climate change. 

“There are always hotter years and colder years for the global average surface temperature. El Niño years tend to be warmer overall and happen every 3-5 years or so.”  

What kind of climate extremes took place in 2023? 

Dr Simon Marsland, National Environmental Science Program Climate Systems Hub Leader,  says:  

“2023 opened our eyes to new climate extremes from massive wildfires in Canada to ferocious fires in Southern Europe and Hawaii, and from Cyclone Jasper’s torrential and extended rains to the devastating rush of the Libyan floods. These types of events are the signature of more hazardous weather under global warming.

“The ocean in 2023 also had chart-toppers, with a hot northern hemisphere summer that played out in the ocean.  

“Antarctic sea ice was at a record minimum over the 2023 winter. Around a million square kilometres of the usual sea-ice cover was missing across the winter, an area the size of the Murray Darling Basin.” 

Was it the hottest year everywhere? 

Dr Michael Grose, Research Scientist says: 

“It was the warmest year on record for the global average, the global ocean, the global land, North America, South America and Africa. It was the second warmest for Europe and Asia. But it was only 15th warmest for Australia, and down the list for some other places too. This is entirely expected due to the variability in the climate, which is never completely uniform in space.” 

Why were global sea surface temperatures so significant in 2023? 

National Environmental Science Program Climate Systems Hub Leader, Dr Simon Marsland, says:  

“Global average sea surface temperatures reached new highs, and marine heatwaves covered a record area. By October 2023, 37 per cent of the global ocean was experiencing marine heat wave conditions. We are seeing the signal of climate change very clearly and very profoundly in the global ocean system.

“About 90 per cent of the heat generated by global warming is stored in the ocean. As sea surface temperatures warm up, the ocean draws down even more heat.

“The ocean acts like a great heat reservoir, so when new heat is added to the ocean it expands, and sea level rises. Continued emissions mean we are locking in global warming for future generations.” 

Dr Chris Chapman, Ocean Dynamics Team Leader, adds: 

“The world’s warmest year coincides with record breaking ocean temperatures. Preliminary data from satellites indicate that the global average sea surface temperature was, on average, almost 1 degree Celsius above normal. Many regions of the global experienced marine heatwaves with disastrous effects. For example, coral reefs in the Caribbean Sea and Eastern Pacific suffered widespread bleaching due to sustained marine heatwaves.

“Ocean temperatures were so high due to two factors: the development of a significant El Niño event, which has certainly pushed global sea surface temperatures higher; and ongoing global warming.

“The Earth’s oceans act as a giant sponge for heat, having absorbed more than 90% of the additional heat in that is in the Earth system due to rising concentrations of greenhouse gases.

“The amount of heat in the ocean has been rising year-on-year since at least the early 2000s. The current El Niño event on top of the climate change trend has led to the record-breaking temperatures that we have been seeing over the last 8-10 months.” 

Did record-breaking temperatures affect sea surface temperatures in 2023, or vice-versa?  

Dr Chris Chapman, Ocean Dynamics Team Leader, explains:

“The ocean, atmosphere and land surface are all connected, and separating one component of the Earth system from the others is always tricky. Take El Niño for example: El Niño is a complicated dance between ocean and atmosphere: atmospheric winds drive heat in the depths of the Pacific Ocean to the surface, which warms the atmosphere, and changes the wind patterns, which then acts to bring more of that heat from the deep ocean to the surface.

“The record air temperatures and corresponding sea surface temperatures are entirely consistent. However, within the climate system the oceans act as a ‘fly-wheel’ and the vast amount of heat that have absorbed over the last several decades will remain with us for a very long time to come.” 

What sea surface temperatures records were broken in Australia in 2023? 

Dr Chris Chapman, Ocean Dynamics Team Leader, explains: 

“It is still too early to assess if record temperatures were broken in and around Australia in 2023. However, late spring saw the development of a strong marine heatwave between the Victorian board and southern Tasmania that may rival the infamous 2015/2016 event.

“Very warm temperatures were found across the Great Barrier Reef region between July and September. Australia’s west coast experienced very high temperatures between the southwest and northwest capes from November through to mid-December, likely due to an intensified Leeuwin current.” 

What bearing will this record have on the global climate system and our ability to limit warming to well below 2 degrees?  

Dr James Risbey, Climate Variability and Hazards Team Leader says:  

“Rising temperatures bring into play a range of feedbacks in the climate system that can further increase greenhouse gas concentrations and global temperature.

“As temperatures move towards the 2 degree and above level, the main factor that can limit that is rapid reductions in emissions of greenhouse gases.” 

The year was around 1.4 °C above the pre-industrial temperature. Does this mean we are almost at the ambitious 1.5 °C limit from the Paris Agreement? 

Dr Michael Grose, Research Scientist says: 

“Not quite. The limits in the Paris Agreement are about the long-term trend in temperature, not one particular year. The Earth warmed by around 1.1 degrees Celsius up to the last decade, and if we look at trends up to 2023, we are at between 1.2 and 1.3 degrees Celsius. We are on track to reach the 1.5 degrees Celsius limit in the early 2030s, but we will see years above this (and below) before we do.” 

What does the 2023 record underscore about the urgency of the climate challenge and the need to mitigate rising greenhouse gas emissions? 

Dr Zoë Loh, Observations – Greenhouse Gases Team Leader says:  

“It is both critical and urgent that we reduce greenhouse gas emissions. Climate change is driven by rising concentrations of greenhouse gases in the atmosphere.

“Until we cut anthropogenic emissions to zero, greenhouse gas concentrations will continue to rise, driving further warming. To avoid smashing heat records year on year, we must reduce emissions as a matter of priority.” 


Last year, 2023, was officially the hottest year in recorded history.
Near global ocean heat content reconstruction. Taken from the 2022 Australian State of the Climate report. ©  CSIRO and Bureau of Meteorology
Copernicus’ full record, which now includes November and December data, saw that record temperature updated to 1.48 degrees Celsius above pre-industrial temperatures.
Forecasting released during spring in Australia suggested above-average ocean temperatures were likely to occur around Australia over summer.

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