- 55 million years ago, the earth’s climate warmed by 5 to 8oC.
- New evidence suggests that two massive releases of carbon occurred.
- The first was similar in size to modern-day man-made green house gas emissions, and may have been the trigger of the second larger release, where global temperatures warmed by 8oC, and remained so for 90’000 years.
- If true, this will be the first geological evidence for a process that is not yet included in climate models for future warming.
As our politicians debate how to limit global warming to 2oC, our current activities are on track for 6 to 8oC warming by the end of the century. Now scientists suggest that an ancient global warming, may have been triggered by a previously unknown carbon release that was similar to our current green house gas emissions. The implications are deeply worrying.
Fifty-five million years ago, global temperatures rose between 5 and 8oC and oceans acidified, in a global warming event known as the Paleocene-Eocene Thermal Maximum or PETM. Up to 50% of non-migrating marine life became extinct, unable to adapt to a rapidly warming world.
Researchers from the USA have new evidence to suggest that this massive global warming event may actually have been a direct response to a previously unknown, carbon release event.
The scientists identified both events in the carbon isotopes of a sediment core drilled in the Bighorn Basin in Wyoming, USA. They used a computer model to simulate the timing, size, and duration of the two events, and narrowed down the likely culprits to carbon released from marine gas hydrates. These ice-like deposits buried deep under the ocean floor destabilise as the deep ocean warms, releasing methane, and carbon to the atmosphere.
The researchers suggest that the first smaller carbon release occurred at similar rate to our present day carbon emissions. It warmed the atmosphere and eventually this heat was transferred to the deep oceans, destabilising gas hydrates and enabling the larger, second carbon release event to occur. The global warming that followed lasted up to 90’000 years.
Worryingly, these ancient events may have been caused by carbon emissions similar to our own. Scientists are currently monitoring the deep oceans to find any signs of warming, and so far, our climate models do not include carbon emissions from such rapid marine gas hydrate release. Given the recent evidence for upper ocean warming and methane leakage from the Arctic Ocean and off the northern coast of the USA, this may be something important to revisit.
Photo credit: Flickr US Geological Survey
Time for some extra info? Read on:
This research paper is available free to view in Nature Geoscience. In addition to the paper, you can also view and download supplementary information (this is extra information that is not crucial to the central arguments set out in the paper, and so provided as supplementary information).
This study touches on some hot topics in climate science, including:
Feedbacks in the climate system, refers to some climatic event or trend that occurs as a result of underlying changes in global temperature.
Climatic thresholds or tipping points are changes to the system such that it enters into a new state where so-called “normal” or “mean/average” conditions are different for a sustained period, e.g. mean global temperature.
If the PETM did occur as a feedback to a smaller carbon release event, similar to current carbon emissions, then this is deeply concerning. These feedbacks are not built into our climate models, but this study offers evidence that perhaps they should be, and that we may need to consider such feedbacks as a potential long-term result of current warming trends.
However, it is worth bearing in mind that the Paleocene climate was already likely to be substantially warmer than mean-global temperatures today. In addition, the continents were arranged very differently which means that internal climate variability would be different to today (i.e. ocean-atmosphere interactions which drive our climate system). None-the-less, the mechanics of methane and carbon release are entirely plausible, and so their implications are still relevant to the modern-day world.
Why not judge for yourself by reading the original article? Can you find any other factors, not yet considered by the study that would also influence their results? How might the scientists refine their interpretations? What other data sources would be useful? For example, marine cores, ice cores, or land-based sediment cores as used here.
See this months extra info (to follow shortly) for some definitions of the terminology used throughout this paper.
Any questions? Post them here or get in touch, and we will try our best to answer them.