Potential for Climate Induced Methane Hydrate Dissociation Graham Macwilliams Pomona College
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Claremont Colleges Scholarship @ Claremont Pomona Senior Theses Pomona Student Scholarship 2018 Potential for Climate Induced Methane Hydrate Dissociation Graham MacWilliams Pomona College Recommended Citation MacWilliams, Graham, "Potential for Climate Induced Methane Hydrate Dissociation" (2018). Pomona Senior Theses. 179. http://scholarship.claremont.edu/pomona_theses/179 This Open Access Senior Thesis is brought to you for free and open access by the Pomona Student Scholarship at Scholarship @ Claremont. It has been accepted for inclusion in Pomona Senior Theses by an authorized administrator of Scholarship @ Claremont. For more information, please contact [email protected]. Potential for Climate Induced Methane Hydrate Dissociation Graham MacWilliams In partial fulfillment of a Bachelor of Arts Degree in Environmental Analysis, 2016-17 academic year, Pomona College, Claremont, California Readers: Branwen Williams Robert Gaines 1 Acknowledgements: I would like to thank my incredible readers Branwen Williams and Robert Gaines for their insightful guidance throughout this process. I would also like to thank my Mom and Dad for their steadfast love and tremendous support as I fought my way back to health during the writing of this thesis. 2 Abstract Methane hydrates are frozen deposits of methane and water found in high pressure or low temperature sediments. When these deposits destabilize, large quantities of methane can be emitted into the atmosphere. This is significant to climate change because methane has 25 times more greenhouse gas potential than Carbon Dioxide. Worldwide, it is estimated there are between 2500 and 10000 gigatons of methane stored in hydrate deposits. This represents more carbon than all fossil fuels on Earth. It is estimated that between 200 and 2000 gigatons of methane are stored in hydrates in Arctic waters acutely vulnerable to greenhouse warming. Over the last decade, researchers have identified instances of hydrate destabilization that have already begun. To gain insight into the potential climatic effects widespread hydrate dissociation would have, researchers have examined hydrate dissociation during the Paleocene Eocene Thermal Maximum 55 million years ago as a geologic precedent. In this period, large-scale hydrate dissociation contributed to 5-8 degree Celsius warming worldwide. If such a climatic shift were to transpire today, impacts on society would be enormous. There is currently a debate in the scientific community as to whether the risk of methane hydrate dissociation is relevant to the present generation. One side argues that not enough methane could be emitted into the atmosphere from today’s hydrate sources to have a meaningful impact on climate warming, where the other side contends that more than enough methane could be emitted from present day hydrate deposits to cause significant impacts to the global greenhouse effect. Given the information currently known about hydrates, it is reasonable to conclude there is a moderate risk of widespread destabilization that could impact global climate change in the coming decades. Significant acceleration of the conversion to alternative energies and implementation of geoengineering strategies should be considered. 3 Introduction 0.1 Introducing Methane Hydrates Since the second half of the 19th century, anthropogenic carbon emissions have resulted in greenhouse warming of the globe (IPCC, 2014). This warming has caused considerable environmental impact worldwide. The ice caps have lost 50 percent of their ice area and 80 percent of their ice volume since the middle of the 20th century, causing sea level rises of 10-20 centimeters (Berliner, 2003). Global precipitation has become more uneven, leading to either drought or flooding conditions. This has resulted in both droughts and flooding. Warmer ocean temperatures and a greater concentration of water vapor in the atmosphere are fueling more powerful hurricanes. Up from 270 ppm before 1880, the atmospheric Carbon Dioxide concentration is now 404 parts per million (Moss, 2010). This is projected to increase at a rate of 2 ppm per year for the foreseeable future, strongly suggesting that the 1 degree Celsius of greenhouse warming that has occurred since the industrial revolution will only further increase in the coming decades. This accelerating warming could potentially lead to several significant impacts that could exacerbate warming yet further. Among the most substantial of these impacts is the destabilization of methane hydrates. Methane hydrates are deposits of frozen methane occurring on the ocean floor. These deposits contain vast amounts of carbon, suggesting that their destabilization could result in substantial additional greenhouse warming should this gas be emitted into the atmosphere. This is because methane is 25 times more potent a greenhouse gas than CO2 . Enough carbon is stored in methane hydrates that if even a small fraction of it were to be released into the atmosphere, resulting warming would potentially rival all anthropogenic warming since the industrial revolution. Perhaps what 4 renders methane hydrate destabilization one of the most significant environmental impacts of existing climate change is that initial releases of methane would cause warming that would lead to further hydrate destabilization and methane release. This would cascade in a positive feedback loop that would result in considerable climate warming (Smith, 2006). Such global temperature increases could potentially occur very rapidly depending on the rate of venting from these methane deposits, resulting in considerable cost to both the biosphere and human society. While hydrates have been studied since their discovery in the early 19th century, naturally occurring deposits have only been seriously investigated by the scientific community since the 1990’s. It is only since the onset of this thorough investigation that researchers have acknowledged the possibility that hydrate methane venting could result in considerable climate change. To assess the potential environmental effects a hydrate methane release would have, investigators have looked at instances in the geologic past in which hydrate destabilization has taken place before, namely 56million years ago at the end of the Paleocene Epoch. To determine the extent of hydrate destabilization today, investigators have launched repeated expeditions to the Arctic Ocean, in which they have found instances of destabilization at the West Spitzbergen Continental Margin and the East Siberian Arctic Shelf (Westbrook et al., 2009, Shakhova et al., 2010). The scientific community is currently attempting to assess the risk hydrate destabilization could take place in the present day. To do this, they are actively debating several key characteristics of hydrates, such as how much of the hydrate reservoir worldwide is vulnerable to destabilization, how much methane that is vented from destabilizing hydrates is actually emitted into the atmosphere, and the timescales that destabilizing hydrates emit methane 5 (Ruppel, 2011). The extent of hydrate carbon vulnerable to destabilization and the fraction of vented methane emitted into the atmosphere suggest at least a moderate risk that significant emissions could transpire in the 21st century. Based on parallels of hydrate dissociation at the Paleocene Eocene Thermal Maximum 56million years ago, a present day hydrate methane release would result in warming between 5-8 degrees Celsius. This would cause significant environmental impacts around the world. 0.2 What are methane hydrates? Methane hydrates are frozen cubic lattice structures found at the bottom of the ocean. They form under conditions of either high pressure or low temperature. As a result, they are found in either the deep ocean or in shallow water at the poles. They are less stable than ice due to fewer supports in their molecular structure, making them more prone to rapid melting. These hydrates hold vast amounts of methane, containing 164 volumes of methane gas for every volume of hydrate. Hydrates are highly significant because there are between 2500 and 10000 gigatons of methane contained in hydrates globally (Dickens, 1994). This represents more carbon than all fossil fuel reserves combined. While the vast majority of hydrate deposits occur in deep ocean not susceptible to climate warming, between 250 and 2000 gigatons of methane are present in shallow Arctic waters vulnerable to climate change (Dickens, 2003). These hydrates are more susceptible to dissociation because they formed due to the freezing temperatures of the Arctic climate. When this climate warms, rising temperatures spread rapidly through the shallow ocean water column, destabilizing frozen methane hydrates on the sea floor. This hydrate destabilization increases the likelihood of a significant release of methane that would be emitted into the atmosphere. 6 0.3 When have hydrates destabilized before? In order to determine the climatic and environmental effects of a large scale methane release from Arctic hydrates, it is important to examine when such a release has occurred in the geologic past. One of the most significant of these instances is large scale hydrate destabilization at the end of the Paleocene Epoch 56 million years ago, known as the Paleocene Eocene Thermal Maximum. The climate warming was so significant that the event serves as the demarcation between the Paleocene and Eocene Epochs. Initially, greenhouse warming was caused by a combination of volcanism due