For hundreds of years, an ancient type of sponge that produces a rigid skeleton has been monitoring fluctuations in ocean temperature at depths ranging from 30 to 90 meters below the Caribbean Sea’s surface.

Now those sponges are at the centre of a bold and controversial claim made in a leading scientific journal that, since the start of the Industrial Revolution, the planet may have already warmed by 1.7C – half a degree more than estimates used by the United Nation’s climate panel.

A group of prominent scientists advised against jumping to conclusions, expressing concern that the study may have gone too far. They also raised doubts about the validity of making such a strong statement based on just one type of sponge found in a specific area.

However, according to Professor Malcolm McCulloch from the University of Western Australia, the findings published in the journal Nature Climate Change are reliable.

According to our research, the effects of global warming are more severe than previously believed. This serves as a reminder that we must take action to reduce CO2 emissions. The negative consequences of global warming will occur sooner than expected.

Using the assistance of underwater explorers, six examples of Ceratoporella nicholsoni were extracted from locations near Puerto Rico and the US Virgin Islands. This sponge species has a slow growth rate and can reach sizes of 10cm to 15cm over hundreds of years.

As sponges increase in size, they accumulate strontium and calcium in a proportion that corresponds to the surrounding water temperature.

McCulloch and his team used data from sponges to reconstruct ocean temperatures from the last 300 years. They then combined these findings with land-based temperature data to approximate global warming.

According to the authors, the sponges grow at a depth that shields them from changes in temperature and in a specific section of the ocean, the temperature variations align with the overall global average.

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Upon reviewing their data, McCulloch and his colleagues from Indiana State University and the University of Puerto Rico found that the sponges aligned with the fluctuations in global temperature observed through recent measurements.

The sponges also documented a significant decrease in temperatures due to a large volcanic eruption in Indonesia in 1815, providing assurance that the sponges were an accurate representation of temperature.

McCulloch stated that the use of sponges has helped to address the limitations of 19th century ship-based measurements of ocean temperatures, which were often lacking and unreliable.

However, the sponges also demonstrate that the onset of current warming occurred in 1860. The United Nations’ Intergovernmental Panel on Climate Change defines the “pre-industrial” era as spanning from 1850 to 1900, and the rate of global warming is measured against this 50-year timeframe.

According to Prof Amos Winter from Indiana State University, the main point to remember is that our current temperatures are significantly higher than those of the pre-industrial era. This realization could potentially shift our perspective on the state of the planet and motivate us to take immediate action.

According to Professor Helen McGregor, a specialist in utilizing proxy data to analyze past climate patterns, the study holds significance due to its unique observation of ocean warming at a depth not previously examined by other proxy records, like corals.

‘Extremely sceptical’

Several top climate scientists disputed the authors’ findings and assertions that the Earth had reached a significant warming milestone.

According to Professor Michael Mann, a climate scientist at the University of Pennsylvania, he doubts the possibility of disregarding the instrumental global surface temperature record in favor of paleo-sponges from a single location. He believes this idea does not hold up to scrutiny.

According to Mann, there is limited proof that the Earth experienced a temperature increase of approximately 0.2C in the late 19th century. However, it is now recognized that using this time period as a baseline is already assumed when discussing the thresholds of 1.5C and 2C, making it irrelevant.

Gavin Schmidt, the head of the Nasa Goddard Institute for Space Studies, stated that the sponges are a valuable inclusion in paleo-climate records, providing insight into temperatures from before the use of modern instruments.

He cautioned against assuming that proxies from one area of the Atlantic accurately represent the overall global average.

“Estimates of the global mean temperatures before 1850 require multiple proxies from as wide a regional variation as possible, thus claims that records from a single record can confidently define the global mean warming since the pre-industrial are probably overreaching.”

According to Dr. Andrew King, a climate expert from the University of Melbourne, the IPCC’s selection of the time period between 1850 and 1900 as the “pre-industrial” era was a practical decision due to the limited amount of recorded data before 1850.

King expressed doubts about the assertion that the planet has already experienced a 1.7C increase in temperature since the beginning of the industrial revolution.

According to the speaker, when comparing computer simulations of the climate from 1850 to 1900 with and without the addition of human-generated CO2, there was minimal variation.

Only in the 20th century, when there is a notable increase in atmospheric carbon dioxide levels, does a distinction become evident. This implies that the time period of 1850-1900 can serve as a decent, though not flawless, representation of a pre-industrial climate.

The University of Oxford’s Professor Yadvinder Malhi expressed concerns about the way the journal presented the findings, stating that it could potentially mislead the public about the progress being made to limit global temperature increase to 1.5 degrees Celsius.

Although the [journal] headline may suggest otherwise, the findings of this paper do not indicate that we have surpassed the Paris climate goals.

According to Dr. Friederike Otto, a climate expert from Imperial College London’s Grantham Institute, the research does not provide any information on whether we have surpassed the 1.5C temperature threshold outlined in the Paris Agreement.

“The limit was set as the point at which dangerous warming becomes unacceptable and refers to the increase in temperature compared to the late 19th century. Therefore, if this research has indeed discovered warming occurring before the mid-1800s, it does not necessarily indicate that the planet is closer to surpassing the 1.5C limit, as commonly believed.”

“Climate change is killing people now; the slower emissions are cut, the worse the consequences will be. The world will indeed warm by 1.7C in the coming years, the level identified by the paper, if fossil fuel use is not rapidly halted.”

Source: theguardian.com