Mega Methane

Reading BBC news is one of my habits, but it was only yesterday did I find out that BBC actually provides a lot more than news! Under the section of Nature, there are theories of prehistoric life including some about mass extinction ones. So I decided have a look for some ideas to the blog.

First idea that I came across was the Catastrophic methane release. Methane clathrate forms when temperature is approximately at the freezing point, and the pressure of overlying water and sediment creates the right condition. A simple theory as to how it may lead to mass extinction: temperature increases and causes methane in the clathrate to be released as gas. As a result, global warming occurs and causes further methane release. This creates a vicious cycle. The change of the environment caused by rising temperature brings plant and animal life onto the route of extinction.

A theory cannot be valid without evidence. Kemp, Coe, Cohen and Schwek conducted a quantitative research in UK. Carbon-isotope (δ13C_org) shifted A, B and C in Toarcian (Early Jurassic) as shown below. The only reason why it happened was through methane hydrates. The stratigraphic relationship established (Left of Figure 1) between the three pulses and the cyclostratigraphy (Right of Figure 1.) shows a direct link of methane hydrate to astronomical forcing. In addition, the shifts of A and B, studied by the authors, coincided with losses of 67% and 50% respectively of marine invertebrate species in Yorkshire. These data, together with a proportion of terrestrial organisms being extinct, can be identified as mass extinction being caused by methane release. Great increases in atmospheric methane and CO₂ caused severe greenhouse effects after the first pulse of methane release. This is similar to the state of present world. As we are experiencing global warming, is it therefore a precursor to the next mass extinction?

Figure 1. Data are from Hawsker Bottoms and Port Mulgrave in Yorkshire in Kemp et al, 2005

One of the five extinctions, Permian extinction, directly relates to methane release. Ryskin explained that if the water were prone to stagnation and anoxia, dissolved methane accumulated in oceanic water would be explosive. Large part of the ocean was anoxic and possibly stagnant at the Permian-Triassic boundary. These parts constituted the eruption region, which consisted of large amounts of methane and other gases in the atmosphere. Methane concentration between 5%-15% would cause explosions and destroy most of the terrestrial life. It is believed that either the explosion caused firestorms with dust and smoke and result in darkness and global cooling, or resulted in global warming with carbon dioxide and remaining methane. Both cooling and warming can contribute to the extinction.

Theories and empirical studies show that methane can be a cause of extinction. But can it be the reason for our next approaching one?

Interestingly, concerns about extinction are very widespread that The New Indian Express published a relevant article recently. They argued that methane could be the key contributor to the 'Sixth Mass Extinction. However, the difference today is the root of recent rise in methane concentrations lies with human activity.

This next extinction, if we are impending one soon, methane will definitely not be the only reason.