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The Intergovernmental Panel on Climate Change has published major climate assessment reports six times since 1990. The most recent was last years. The results are clear that human influence is contributing to global warming, and may soon be irreversible.
But are we looking at the wrong data or not?
A large amount of the work in the more than 14,000 scientific papers which went into the 2021 IPCC report is based on comparing climate data gathered since the industrial revolution with climate data from Earth’s ancient past. By analysing fossil records, rocks, and ice core samples, we can get a better understanding of climate change and its impacts.2, There has been a sharp decline in biodiversity.
But are we looking at the right periods of Earth’s history for our comparison?
An international team believes that we haven’t. The researchers’ Paper, publishedIn the Proceedings of the National Academy of Sciences (PNAS) journal, argues that we have wrongly been comparing today’s climate to historical episodes known as “greenhouse” phases. And the modelling would be more accurate if we compared modern climate data with data from previous “icehouse” periods in Earth’s history.
More about the climate: A barcode of Earth’s climatic past
The researchers’ results suggest that human-induced climate change will be worse and even more rapid than we thought.
The term icehouse refers to periods in Earth’s history in which the planet has large reserves of ice – like we currently do with the Arctic and Antarctic ice sheets.
“The research comes down to the different environments the Earth is operating under,” says University of Waikato, New Zealand, scientist and team member Terry Isson. “At the moment, we’re in an ‘icehouse’ phase, with glaciers and ice caps. The data we look at for forecasting the effects of global warming come from a period of ‘greenhouse’ when the Earth didn’t have massive stocks of ice.”
A major effect of global warming is the reduction of dissolved oxygen in the oceans – marine anoxia – leading to mass death of underwater life and marine dead zones. The ocean surface is flooded with fresh water from melting ice caps or glaciers, which prevents circulation and cuts off oxygen supply for deeper water.
The authors note in beginning the paper: “Warming-mediated increases in marine anoxia may be more pronounced in a glaciated versus unglaciated climate state.”
“We know that global warming affects oxygen levels and how acidic our oceans are. This has led to a
flow-on effect to the kind of life that our oceans can sustain,” says Isson.
Instead of looking at greenhouse periods, the team looked at an event 304 million years ago – in an ice-capped world much like today – known as the Kasimovian–Gzhelian Boundary (KGB). The atmospheric CO has been decreasing for about 300,000.2The levels rose by two-thirds, the oceans became anoxic and the biodiversity fell on the land as well as in the oceans.
Scientists believe that the massive carbon release may have been caused by volcanic eruptions that ripped through coal beds during the carboniferous period. The eruptions would have set off fires and heated the ground, releasing more organic carbon.
“It was one of the fastest warming events in Earth’s history,” says Isabel Montañez, professor in the University of California’s Davis Department of Earth and Planetary Sciences, and a member of the research team. This is the first known rapid warming event in an Icehouse Earth. The team’s results show that an icehouse climate may be more sensitive to warming than greenhouse phases when carbon dioxide levels are already higher.
Researchers used carbon isotopes to calculate the amount of carbon released into the atmosphere in the time period before the KGB. “We don’t have a rate, but it was one of the fastest in Earth’s history,” Montañez says. The atmospheric CO increased by two-fold2From 350 parts per million (similar to levels before industrialisation) to 700 ppm.
The team also studied rocks from China today to determine oceanic oxygen levels that existed 304 million years ago. Increased uranium levels in rocks on the ocean floor can indicate an absence of oxygen. The team estimates that about 23% of the world’s oceans became anoxic dead zones after the KGB, matching the fossil record showing mass extinctions on land and in the sea around the time.
“If you raised CO2 by the same amount in a greenhouse world, there isn’t much effect, but icehouses seem to be much more sensitive to change and marine anoxia,” Montañez says.
The new research doesn’t discount the decades of work that has already sounded the alarm about human-induced climate change, but rather it strengthens it.
Modelling is not a perfect science that will give you an exact, infallible answer. Understanding the infinitely complex system which is the Earth’s climate historically, and then making predictions about the future is gruelling. The data we collect is vital to building models.
However, the trends are clear. The trends are clear. The climate is changing and the planet is warming due to human activity. This is reinforced by the new research. Comparing the current icehouse periods with previous ones may help to see where our ice-capped world might be heading. “This research indicates that this process may be more rapid and more severe in our current
Climate. We may be seriously underestimating global warming’s rate and effects if we
continue to rely on greenhouse comparisons,” says Isson.
