Fast climate change

There has been a fair amount of discussion that I have seen in the popular scientific press, that climate change can occur much more quickly than the tepid pace that is often sited.

 

What is a little alarming is that these current finding relate to an event that is often sited as being most comparable to our situation today. 

 

What is alarming, is that some unusually granular sedimentary deposits seem to indicate that it all happened in a very fast acting cyclical time frame.

Climate change, 55 million years ago
Dave Ansell, Naked Scientist, 10 October 2013

Historically, Earth was much warmer. About 55 million years ago, temperatures were, on average, 8 degrees Celsius higher than they are now. There were crocodiles living off Greenland, and palm forests in Wyoming.

Suddenly, the levels of carbon-dioxide doubled and global temperatures increased by 5 degrees.

Previously, scientists had thought this warming had taken tens of thousands of years.

But now researchers Morgan Schaller and James Wright have been studying offshore clays dating from this period from Maryland and Delaware. They discovered a repeating pattern in the clay, resembling tree-rings, corresponding to a yearly cycle of rivers dropping more and less sediment into the ocean.

By looking at different isotopes of carbon present in each of the clay layers, including carbon-12, which is more easily taken up by living things, and carbon-13, which is more common in inorganic carbon sources, they found evidence for a huge injection of about 3000 billion tonnes of carbon into the atmosphere over a period of a few months.

Over the next 13 years, this dissolved into the shallower parts of the sea causing it to become acidic, killing off more deep sea species than at the end of the cretaceous which killed off the dinosaurs. It then took 150 000 years for things to return to normal.

New Finding Shows Climate Change Can Happen in a Geological Instant
Ken Branson, Rutgers Today, 6 October 2013 (hat tip: Crazy Eddie)

Rapid” and “instantaneous” are words geologists don’t use very often. But Rutgers geologists use these exact terms to describe a climate shift that occurred 55 million years ago.

In a new paper in the Proceedings of the National Academy of Sciences, Morgan Schaller and James Wright contend that following a doubling in carbon dioxide levels, the surface of the ocean turned acidic over a period of weeks or months and global temperatures rose by 5 degrees centigrade – all in the space of about 13 years.

The Abstract:
Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum
James Wright, Morgan Schaller, Preceedings of the National Acadamy of Science, 5 August 2013

(PETM) and associated carbon isotope excursion (CIE) are often touted as the best geologic analog for the current anthropogenic rise in pCO_2. However, a causal mechanism for the PETM CIE remains unidentified because of large uncertainties in the duration of the CIE’s onset. Here, we report on a sequence of rhythmic sedimentary couplets comprising the Paleocene/Eocene Marlboro Clay (Salisbury Embayment). These couplets have corresponding δ¹⁸O cycles that imply a climatic origin. Seasonal insolation is the only regular climate cycle that can plausibly account for δ¹⁸O amplitudes and layer counts. High-resolution stable isotope records show 3.5‰ δ¹³C decrease over 13 couplets defining the CIE onset, which requires a large, instantaneous release of ¹³C-depleted carbon. During the CIE, a clear δ¹³C gradient developed on the shelf with the largest excursions in shallowest waters, indicating atmospheric δ¹³C decreased by ∼20‰. Our observations and revised release rate are consistent with an atmospheric perturbation of 3,000-gigatons of carbon (GtC).

Thirteen years (versus the previously thought ~10,000) is a really short period of time for that type of change. 

 

That the whole question has been so politicized means that some will jump to quickly to make the specific analogy with our current situation, while others will dismiss or ignore the entire issue.

 

I have generally put climate change as a secondary driver of future problems.  Human population growth toward ~10 billion seemed like it was getting to us much faster, and would be far more problematic.  Arguably climate change (or at least half of it) is a secondary effect of population growth in any case.  But it appears that it is at least possible for climate growth to overtake the primary cause on the timeline:  Oh joy!