Carbon Footprints Today

80% of the world's current anthropogenic greenhouse gas emissions comes from 12 countries and Europe. National Geographic have produced this interactive graphic which examines the current emissions statistics. Scrolling over the graphic allows you to view stats for current emissions, cumulative emissions, emission intensity and emission (in tons) per capita.

Since 1850, nearly 1 billion tons of greenhouse gases has been added to the atmosphere. The PETM lasted 2000 years and resulted in the accumulation of 4.6 billion tons of carbon dioxide alone. This says that today's emissions are averaging a significantly greater intensity that those experienced in the 55mya.

Warming From the Wetlands

Here’s a quick podcast from CSIRO (Commonwealth Scientific and Industrial Research Organisation). Its a quick 5 minute interview that explains an alternative source of methane that may have ended the last glacial period 12 000 years ago.

The Carbon Conundrum

Dunkley Jones, T. et al. 2010 submitted a review of recent work into the PETM in an attempt to identify key components that contributed to the sudden warming, as well as to try and relate it to our modern world. 

The paper raises a few key issues, one that I will bring up today - the Carbon Conundrum. The amount of CO₂ released into the environment over the PETM is in the range of 4500PgC. That’s 4.5 billion tonnes of CO₂! Scientists know this because they have looked at the isotopic compositions of various sediments across the PETM from all carbon reservoirs - deep marine, shallow sea and terrestrial. All 3 show an sudden and significant divergence from the standard of roughly -4‰ - that is to say that across the PETM, the average weight of carbon in the environment decreased by 0.4%. That is a small number for such a significant change. Look at the graph below and you’ll see that change.

These δ¹³C values, as they are are known, give the ratios between two different types of C - ¹³C, a carbon atom with 13 nucleons and ¹²C, a carbon with 12 nucleons. As you’d expect, ¹²C is lighter. Each source of C in the world has its own signature δ¹³C. Every single plant on the planet makes CO₂ with a δ¹³C of -24‰, and volcanic outgassing produces CO₂ with a δ¹³C of -5‰. By extrapolating the data from other works, Dunkley Jones et al. managed to calculate the amount of CO₂ that you’d need to produce a global δ¹³C of -4‰ and the results were quite something!

By volcanic outgassing at -5‰, the rate of volcanic outgassing would have to increase over 100 times before it could explain the trends in the PETM - which is geologically unfeasible. More surprising still was that even when considering organic C at -24‰, over 75-90% of the total organic reservoir would be required. This clearly isn’t the case, where where is all the missing carbon?

Here is a diagram from the paper that shows the various sources and reservoirs of C and their relative  δ¹³C values. 

There are many conflicting theories over the source of this carbon, but the leading runner is methane hydrates. Methane hydrates are isotopically very ‘light’ in the carbon dioxide they can liberate with a δ¹³C of up to -60‰. The fear today is that as methane is such a potent greenhouse gas, some 10 times more so than CO₂, any release from clathrates with have a detrimental effect on our climate, accelerating global warming. Here is an article that goes further into the details of methane hydrate, and methane itself as a greenhouse gas. 

So what of the warming?

During the PETM, it has been estimated that somewhere between 2500 - 6800 gigatons of CO₂ were liberated into the atmosphere over the course of a few thousand years resulting in a 6°C. In the last 200 years, we have pumped 270 gigatons of CO₂. However, there it is a hotly-debated topic on when we should take the initial measurements. Most governmental organisations, including the IPCC, refer to the norm as pre-industrial levels. However, for a true reflection on the matter, I believe that the natural level of CO₂ in the atmosphere should be calculated from when humans first began altering their environment some 8000 years ago with the advent of sedentary culture and farming. CO₂ would therefore have been added through the loss of forests, other land uses changes, as well as the familiar burning for fires. This puts the amount of CO₂ we have released significantly higher. However, it is the rate of change that is most alarming. The 5°C changes over the course of the PETM happened over a period of thousands of years; the climate change we face today is happening within 200 years. The effects of climate change are expected to reach their peak by 2050 according to the IPCC, but with continued failure of inter-governmental agreement and the far from strict meeting of targets imposed by the UN, this prediction may quickly turn to a long lost ideal.  

For Starters…

The Paleocene-Eocene Thermal Maximum (PETM) is becoming an increasingly interesting and important period in the history of the Earth. It was a period in Earth’s history around 55 million years ago associated with rapid global warming and major ecological shifts over a period of a few thousand years. It is by no means the most infamous or dramatic event in the past; being easily overshadowed by the KT Extinction 65.5 million years ago that wiped out the dinosaurs, or the Permian extinction that almost annihilated life on Earth. However, our understanding of PETM in recent years has provided invaluable information for the anthropogenically-induced climate change of the Anthropocene. 

Over the course of this blog I hope to find out about the causes and effects of this sudden and intense shift in global environmental patterns and attempt to relate it to how we might best understand how our climate today will behave in the future. 

Here is a nice, quick video by the Smithsonian Center for Education and Museum Studies, which provides a brief introduction to the Paleocene-Eocene Thermal Maximum by paleontologist Scott Wing. Enjoy!