New research into major climate change events of the past has found that we may have greatly underestimated the damage they caused.
In our efforts to understand climate change today, researchers look to major events of the past to predict the likely outcome of our future. However, new findings threaten to change what we know.
In a paper published to the international journal Geochemistry, Geophysics, Geosystems, NUI Galway’s Dr Audrey Morley and a team of researchers have found evidence that our previous calculations of past temperatures were wide of the mark by as much as 4C.
The findings came after the team studied an established geochemical tool for investigating sea surface temperatures in the past using marine plankton.
In the modern ocean, observations have shown that marine plankton will use more magnesium relative to calcium – which are elements freely available in seawater – when they form their shell in warmer waters.
This allows scientists to apply this modern relationship between magnesium, calcium and temperature to the past, by measuring magnesium-to-calcium ratios in fossilised marine plankton that are continually deposited in seafloor sediments.
New calculation model
The problem is, however, that this may not give a complete picture of the amount of magnesium in the shell – for example, higher carbon dioxide levels in seawater results in lower pH (potential of hydrogen) and lower carbonate ion concentrations.
With lower concentrations, organisms need to exert more energy for calcification, resulting in more magnesium than what would be predicted by temperature only, meaning the data is underestimated.
To counteract this, the study proposed a mathematical correction scheme that enables the carbonate ion concentration effect to be isolated from the temperature signal recorded in marine plankton via subtraction.
“This is particularly important for climate records from the subpolar/polar North Atlantic region that may have experienced abrupt changes in carbonate ion concentrations linked with abrupt climate events,” Morley explained.
“Correcting for low carbonate ion concentration values improves the fidelity of temperature reconstructions and allows a reassessment of the magnitude of climate events occurring during warm climates.”