Irish sea temperatures rise more than previously thought

The temperature in the seas around Ireland has increased substantially more since the last ice age than previously estimated, according to a new international study led by University of Galway.

The implication is that the rise in sea temperatures around Ireland in the future will be significantly greater than currently predicted.

This has worrying consequences for the frequency, pattern and intensity of storms, rainfall and other extreme weather events in the years ahead.

The study suggests scientists have been underestimating the sensitivity of earth's climate system to greenhouse gases in the atmosphere.

It shows how large parts of the North Atlantic Ocean were up to 3C colder during the ice age than previously thought.

This means the water has heated up by 3C more since then.

The clear implication is that scientists have been underestimating the relationship between carbon dioxide added to the atmosphere and the resulting increase in ocean temperatures.

Scientists use estimates of the past response to the amount of energy added to our climate system to determine how much warming to expect in the future.

But if, as this study shows, that past relationship has been significantly underestimated, then the previous scientific estimates of future climate impacts have also been underestimated.

Research of tiny ocean organism

The research involved an innovative study of a tiny unicellular ocean organism called foraminifera.

These organisms, which are no bigger than a grain of sand, have been around for millennia.

They have miniscule shells made from calcium carbonate and other elements available in seawater.

When they die the tiny shells are deposited in sediment on the seafloor providing a treasure trove for scientists.

They can analyse the chemistry of those shells for indications of how climatic conditions in the ocean changed over billions of years.

Scientist have always used chemical analysis of foraminifera shells as a proxy for historical sea surface temperatures in the mid latitude Atlantic region.

But they have always known too that very cold seawater impacts on magnesium and calcium signals in shell formation.

This compromises the chemical analysis, and leaves scientist with no way to measure past polar seawater conditions.

Today’s study however solves that long-standing conundrum by identifying exactly how the carbonate chemistry of cold seawater impacts on the temperature signals recorded in the tiny shells.

This has enabled the scientists to make precise adjustments so the chemistry of polar foraminifera shells can truly reveal past polar sea surface temperatures globally.

North Atlantic cooling underestimated by up to 3C

When applied to last ice age, this method shows that current estimates of cooling over the mid-latitude North Atlantic have been underestimated by up to 3C.

That is according to Dr Audrey Morley, the University of Galway scientist and iCRAG Deputy Director who led the international team that made the breakthrough.

Her team had set out on several oceanographic cruises, including the Marine Institute’s RV Celtic Explorer in 2020, to collect living polar foraminifera together with the seawater that they lived in.

This is what allowed them to identify exactly how the carbonate chemistry of seawater impacts on the temperature signal recorded in the magnesium and calcium values of the tiny organism.

The team says their research method is invaluable.

It can now be applied to new and previously published datasets worldwide to re-evaluate the magnitude and extent of marine climate change in polar regions over millennia.

Dr Morley said: "In the future our new method will allow us to evaluate the ability of climate models to simulate polar amplified warming and cooling, which is especially important as climate model simulations targeting warmer than present climates have historically not captured the full extent of polar amplified warming.

"This information will enable a major leap forward in our ability to assess the sensitivity of Arctic climate and its role and variability within the global climate system. This will lay the foundation for an improved understanding of climate change."

The full study published in Nature Communications can be read here.