Fishy use of data to claim oceans are cooling

A Facebook post claims the oceans are cooling, despite an increase in the atmospheric concentration of carbon dioxide over the past decade.

This claim is false. Even when assessing the post’s two arbitrary dates which are just eight years apart, ocean temperatures have risen. However, experts told AAP FactCheck this is too short a time frame for accurate analysis and that trends need to be viewed over many decades to account for natural variations and other factors.

Looking at the data over a longer period of time shows a clear increasing trend in line with the rise in atmospheric CO2.

The claim was made in a December 26 post (screenshot here) shared on the “Climate change is natural” Facebook page.

“Despite the continued increase in atmospheric #CO2 concentration over the last decade or so, the planet, including the oceans, has slightly cooled. Highlighting the relative insensitivity of global surface temperature to changes in atmospheric CO2 concentration,” the post states.

The post includes three graphs which illustrate atmospheric, global and ocean temperatures from 2014 to 2022.

It is copied from a December 24 tweet from Matthew Wielicki, an assistant professor in geological sciences at the University of Alabama and self-described “skeptic on climate alarmism”.

AAP FactCheck has previously addressed claims global temperature, which is calculated from measurements taken in the troposphere above the land and ocean, is cooling – see here, here and here.

Evidence shows a consistent warming trend in global temperatures over the past 25 years, with the eight years prior to 2022 being the hottest on record.

Data from the National Oceanic and Atmospheric Administration (NOAA), the University of East Anglia Climate Research Unit, NASA’s Goddard Institute for Space Studies and Berkeley Earth all show sustained warming since the 1970s.

The claim oceans have been cooling over the past decade is also false.

The third graph in the post, titled “Oceans: Cooling Since January 2014”, appears to be based on NOAA’s global monthly sea surface data on temperature anomalies.

However, experts told AAP FactCheck the graphs were misleading due to the use of cherry-picked data.

“It is a significant error to just look at a few years data and draw any conclusions about long-term trends as natural variability will lead to shorter term (e.g., decadal) variations in things like global temperatures and sea surface temperatures,” Meric Srokosz, a professor of physical oceanography at the National Oceanography Centre, said in an email.

Josh Willis, an oceanographer at NASA's Jet Propulsion Laboratory, agreed.

"Data going back 100 years shows clear warming in all three things: global temperature, air temperature and ocean temperature," Dr Willis told AAP FactCheck in an email.

"Eight years is just a little bit too short a time to see the human-caused warming against the natural cycles in these surface temperature plots.

"But if you took the average temperature over this 8 year period and compared it to the previous 8 years (or the one before that, or the one before that), you'd see that this warming is relentless. Just like attempts to pretend it's not happening."

Professor Srokosz said long-term trends showed sea surface temperatures were rising.

"Note that temperatures do not rise in a nice linear fashion due to various sources of natural variability," Prof Srokosz said.

"If you look at the end of the sea surface temperature record things have flattened out a bit (the last few years that the post looks at), but the long-term trend is upwards."

Other experts AAP FactCheck contacted confirmed sea surface temperatures are increasing.

"Overall, the sea surface temperature is warmer in the last decade (2013-2022) than the previous decade (2003-2012)," Boyin Huang, an oceanographer who specialises in sea surface temperature reconstruction at NOAA, said in an email.

John Abraham, a professor of thermal sciences at the University of St Thomas, said oceans were warming "both at the surface (sea surface temperature) as well as throughout the depth well below 2000m".

"Long term trends show a mild warming from late 1950s-1990s and then a rapid increase after (the) 1990s," Professor Abraham said in an email.

Dr Willis said ocean warming was even more evident by looking at ocean heat content, which is the amount of heat stored in the ocean.

"This shows that the oceans are (getting) warmer each and every year," he said.

Oceans have absorbed more than 90 per cent of the excess heat trapped by greenhouse gases due to human-caused global warming.

About two thirds of this heat is stored in the upper layer of the ocean - from zero to 700 metres - and the rest is stored in deeper layers.

Measurements of sea surface temperature reflect the amount of heat stored in the ocean at a particular time. This means as oceans absorb more heat, sea surface temperature will continue to rise.

Three different ocean heat content data sets from NOAA, the Institute of Atmospheric Physics (IAP), and the Japan Meteorological Agency (JMA) show a warming trend for the top 2000 metres of the ocean globally.

Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research, said ocean heat content showed warming at all layers of the ocean.

"Warming globally is at all levels down to 2000m which is all we have measurements for," Dr Trenberth told AAP FactCheck in an email.

"The top 100m the top 300m the layer 300 to 700m etc. All are warming."

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