Back to the greenhouse world of the Cretaceous?

A look back into the history of the earth allows a scenario of the future

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CO2 emissions trading is flourishing, new ideas for reducing greenhouse gases in the atmosphere are heating up the home, but even with the greatest efforts, climate change seems inevitable. New impulses to describe and understand the future scenario now give a look back into the dinosaur era.

Sea level 200 meters higher than today

A period characterized by a greenhouse climate was the Cretaceous period 145-65 million years ago. Their research is the focus of the paleozoanographers, paleontologists and sedimentologists around Jörg Mutterlose and Adrian Immenhauser of the Ruhr-Universität: The analysis of deposits from this period shows that the sea level must have been at least 200 meters higher than today about 93 million years ago. Such global sea-level rise is explained inter alia by the melting of the polar ice caps as a result of an increase in the CO2 concentration. What did the climate look like at the time?


Carbon sink regulated

An interesting find that the researchers have been able to make in core drilling almost anywhere in the world is several black mudstone benches dating back to the Cretaceous. These dark rocks have a high accumulation of organic carbon, which consists of unicellular algae. "Due to lack of oxygen in the oceans, the organisms that degrade the dead protozoa and reintroduce the carbon they contain into the material cycle can not survive, " explains Maternity.

Since these dark rocks have been found almost worldwide, it is called an oceanic anoxic event (Ocean Anoxic Event, OAE). An OAE represents a geologically short section of about 500, 000 years, in which there was an interruption of the carbon cycle. The rocks of the OAE are carbon sinks, as carbon is bound in them for a long time and thus removed from the material cycle. "This phenomenon has a regulating effect on the increased CO2 content in the warm phase, " says Mutterlose. "However, this binding of CO2 begins only a few million years late, so that only about 85 million years ago began to cool again." Display

Cretaceous conditions in the year 2200

A global OAE indicates a completely different climatic regime for the period 99 to 89 million years ago than today. At that time, the oceanic circulation patterns were not driven by cold deep waters as they are today: since polar ice was missing, one has to assume very sluggish ocean currents. The lack of circulation probably caused the oxygen deficit in the ocean basins. For the Cretaceous, we assume globally balanced, tropical-warm conditions. The marine environment responded to these conditions with great diversity and at the same time a low number of individuals.

"If the increase in the proportion of CO2 documented in our atmosphere continues around 1960, then chalk-time CO2 levels can be expected around 2200, " estimates the motherless. Then probably similar stable equilibrium conditions would be set again as in the Cretaceous period. Estimating the response of our biosphere is more difficult. The proliferation of cold-loving forms will be significantly reduced, the researchers estimate. In the seas, primary producers with siliceous skeletons (diatoms) will be pushed back in favor of those with calcareous, ie carbonaceous skeleton (coccoliths) and organically modified algae (dinoflagellates). So it would create a completely different structure of the food chains in the oceans.

(Ruhr-University Bochum, 10.04.2007 - NPO)