Expectations of what a warmer planet might mean range from the inconsequential to the much more dire, but researchers are working to bring more scientific data to the debate. For geologists at Florida State University (FSU), one way to learn more about the future is by visiting the past, 94 million years ago to be exact. By studying a major warming event at that point in the Earth's history, the researchers have found that it caused changes in ocean chemistry that were incompatible with vital nutrients needed to support life.

The end of the Cenomanian period, between 94 and 100 million years ago, was a pretty volatile time for the climate. Big swings in sea levels and temperatures, a lack of polar ice and Canadian palm trees were some of the defining features of a totally different time on this planet. Research from earlier this year has suggested that this major climatic event wiped out the ichthyosaurs, the highly adaptable marine reptiles that ruled the oceans for the 157 million years previous.

Looking to dive further into how these dramatic changes to the ocean's ecology unfolded, the FSU researchers obtained sediment samples from under the seafloor off the coast of Venezuela. They landed themselves a 10-meter (33-ft) slab which they linked to the massive climate turnover event through analysis of microfossils and shell organisms within.

Further examination of the sample revealed that changes in the ocean's nutrients at this time affected certain types of natural elements, or vitamins, causing some of them to die off completely. Two that vanished were vanadium and molybdenum, both of which are important trace metals that play a role in nitrogen fixation, a process that converts atmospheric nitrogen into ammonia and is essential to all life. Previous research has linked low molybdenum levels in the ocean to stunted evolution of animal life.

"These trace metals were drawn down to levels below where primary producing organisms, the base of the ocean food chain, can survive," says Assistant Professor of Geology at Florida University, Jeremy Owens. "This change inhibited biology."

The researchers also say that the absence of these trace metals is indicative of oxygen deficiency in the ocean water around the world, creating dead zones where it is difficult for life to exist.

Granted this all happened a very long time ago, but the scientists believe that by peering into the past of the world's oceans they can learn valuable lessons about the possible ramifications of global warming, a trend that has seen Earth sweat through 13 consecutive months of record temperatures.

"This is the best window to understanding future climate change," Owens says. "It gives us insight into the cascade of events that can affect the entire ocean."

The research was published in the journal Earth and Planetary Science Letters.