Research was published last week showing the financial cost of methane being released from Earth’s permafrosts. But the risks go beyond financial – Earth’s history shows that releasing these stores could set off a series of events with calamitous consequences.
The sediments and bottom water beneath the world’s shallow oceans and lakes contain vast amounts of greenhouse gases: methane hydrates and methane clathrates (see Figure 1). In particular methane is concentrated in Arctic permafrost where the accumulation of organic matter in frozen soils covers about 24 per cent of northern hemisphere continents (see Figure 2a) and is estimated to contain more than 900 billion tonnes of carbon.
Methane, a greenhouse gas more than 30 times more potent than CO2, is released from previously frozen soils when organic matter thaws and decomposes under anaerobic conditions (that is, without oxygen present).
Most of the current permafrost formed during or since the last ice age and can extend down to depths of more than 700 metres in parts of northern Siberia and Canada. Thawing of part of the permafrost has not yet been accounted for in climate projections.
The Siberian permafrost is in particular danger. A large region called the Yedoma could undergo runaway decomposition once it starts to melt. This is because elevated temperatures cause microbes in the soil to decompose, which causes heat, which creates a self-amplifying process.
Palaeoclimate studies of stalagmite cave deposits across Siberia indicate they grew faster during the warm periods 424,000 and 374,000 years ago, due to permafrost melt. At that time, mean global temperatures rose by approximately 1.5 degrees Celsius above pre-industrial temperatures. Thus Vaks et al state: “Growth at that time indicates that global climates only slightly warmer than today are sufficient to thaw extensive regions of permafrost.”
Evidence of melting of permafrost has also been reported from the dry valleys of Antarctica, where development of thermokarst (small surface hummocks formed as ice-rich permafrost thaws) has been reported, reaching a rate about 10 times that of the last ~10,000 years.
Arctic air temperatures are expected to increase at roughly twice the global rate. A global temperature increase of 3 degrees celsius means a 6 degree rise in the Arctic, resulting in an irreversible loss of anywhere between 30 to 85 per cent of near-surface permafrost. According to the United Nations, warming permafrost could emit 43 to 135 billion tonnes CO2 (GtCO2) equivalent by 2100, and 246 to 415 GtCO2 by 2200.
The geologically unprecedented rate of CO2 rise (~2.75 ppm/year during June 2012-2013) may result in faster permafrost collapse.
Already measurements along the Siberian shelf uncover enhanced methane release. In 2010 a Russian marine survey conducted more than 5000 observations of dissolved methane showing that more than 80 per cent of East Siberian shelf bottom waters and more than 50 per cent of surface waters are supersaturated with methane. Atmospheric methane levels (during glacial periods: 300–400 parts per billion; during interglacial periods: 600–700 ppb) have recently reached 1850 ppb – the highest in 400,000 years (see Figure 2b).
Hansen refers to the 'Venus Syndrome', drawing an analogy between the enrichment of Venus’ atmosphere in CO2 (its atmosphere is 96.5 per cent CO2 and its surface temperature is 462 degrees) and potential terrestrial runaway greenhouse effects. This needs to be placed in context.
On Earth, weathering processes and oceans draw down the bulk of atmospheric CO2 to be deposited as carbonates. It’s therefore impossible for Earth to develop Venus-like conditions. But the onset of a hyperthermal – a huge release of carbon such as happened during the Paleocene-Eocene Thermal Maximum 55 million years ago, with an attendant mass extinction of species – is possible.
Extraction and combustion of the current fossil fuel reserves (more than 20,000 billion tonnes of carbon – Figure 4) would inevitably lead to a hyperthermal commensurate with or exceeding the PETM. If that happens, CO2 would rise to above 500ppm (see figure 4), temperature would rise by about 5 degrees (figure 5) and the polar ice sheets would melt – it’s a future we could face if emissions continue to accelerate.
Not that the above features too much in the Australian elections, where the reality of climate change has been replaced with pseudoscience notions, including by some who have not consulted basic climate science text books, and by hip-pocket-nerve terms such as 'carbon tax', 'emission trading scheme' or 'direct action'. The proposed 5 per cent reduction in emissions relative to the year 2000 represent no more than climate window dressing.
Nor are coal exports mentioned too often, despite current exports and planned future exports, which represent carbon emissions tracking toward an order of magnitude higher than local emissions.
According to Dr Adam Lucas of the Science and Technology Studies Program at University of Wollongong, Australia (with ~0.3 per cent of the global population) currently contributes domestic emissions of about 1.8 per cent of global emissions. The total domestic and overseas consumption of Australian coal is responsible for more than 2 per cent of global emissions. Plans to triple or even quadruple coal export volumes over the next 10 years would raise Australia’s total contribution to global GHG emissions to toward 9 to 11 per cent by 2020 – an order of magnitude commensurate with that of Middle East oil.
Which places the “Great moral challenge of our generation” in perspective.
Dr Andrew Glikson, a Earth and paleoclimate scientist, is a Visiting Fellow at the School of Archaeology and Anthropology, Australian National University, where he is reviewing the effects of climate on prehistoric human evolution.