The impacts I just summarised are already upon us and even without increasing their severity they will nevertheless increase their impacts on our ecosystems, soils, seas and our societies over time. It is difficult to predict future impacts. But it is more difficult not to predict them. Because the reported impacts today are at the very worst end of predictions being made in the early 1990s - back when I first studied climate change and model-based climate predictions as an undergraduate at Cambridge University. The models today suggest an increase in storm number and strength (Herring et al, 2018). They predict a decline of normal agriculture, including the compromising of mass production of grains in the northern hemisphere and intermittent disruption to rice production in the tropics. That includes predicted declines in the yields of rice, wheat, and corn in China by 36.25%, 18.26%, and 45.10%, respectively, by the end of this century (Zhang et al, 2016). Naresh Kumar et al. (2014) project a 6–23 and 15–25% reduction in the wheat yield in India during the 2050s and 2080s, respectively, under the mainstream projected climate change scenarios. The loss of coral and the acidification of the seas is predicted to reduce fisheries productivity by over half (Rogers et al, 2017). The rates of sea level rise suggest they may be soon become exponential (Malmquist, 2018), which will pose significant problems for billions of people living in coastal zones (Neumann et al, 2015). Environmental scientists are now describing our current era as the sixth mass extinction event in the history of planet Earth, with this one caused by us. About half of all plants and animal species in the world's most biodiverse places are at risk of extinction due to climate change (WWF, 2018). The World Bank reported in 2018 that countries needed to prepare for over 100 million internally displaced people due to the effects of climate change (Rigaud et al, 2018), in addition to millions of international refugees.
Despite you, me, and most people we know in this field, already hearing data on this global situation, it is useful to recap simply to invite a sober acceptance of our current predicament. It has led some commentators to describe our time as a new geological era shaped by humans
- the Anthropocene (Hamilton, et al, 2015). It has led others to conclude that we should be exploring how to live in an unstable post-Sustainability situation (Benson and Craig, 2014; Foster, 2015). This context is worth being reminded of, as it provides the basis upon which to assess the significance, or otherwise, of all the praiseworthy efforts that have been underway and reported in some detail in this and other journals over the past decade. I will now offer an attempt at a summary of that broader context insofar as it might frame our future work on sustainability.
The politically permissible scientific consensus is that we need to stay beneath 2 degrees warming of global ambient temperatures, to avoid dangerous and uncontrollable levels of climate change, with impacts such as mass starvation, disease, flooding, storm destruction, forced migration and war. That figure was agreed by governments that were dealing with many domestic and international pressures from vested interests, particularly corporations. It is therefore not a figure that many scientists would advise, given that many ecosystems will be lost and many risks created if we approach 2 degrees global ambient warming (Wadhams, 2018). The IPCC agreed in 2013 that if the world does not keep further anthropogenic emissions below a total of 800 billion tonnes of carbon we are not likely to keep average temperatures below 2 degrees of global averaged warming. That left about 270 billion tonnes of carbon to burn (Pidcock, 2013). Total global emissions remain at around 11 billion tonnes of carbon year (which is 37 billion tonnes of CO2). Those calculations appear worrying but give the impression we have at least a decade to change. It takes significant time to change economic systems and so if we are not already on the path to dramatic reductions it is unlikely we will keep within the carbon limit. With an increase of carbon emissions of 2% in 2017, the decoupling of economic activity from emissions is not yet making a net dent in global
emissions (Canadell et al, 2017). So, we are not on the path to prevent going over 2 degrees warming through emissions reductions. In any case the IPCC estimate of a carbon budget was controversial with many scientists who estimated that existing CO2 in the atmosphere should already produce global ambient temperature rises over 5°C and so there is no carbon budget – it has already been overspent (Wasdell, 2015).
That situation is why some experts have argued for more work on removing carbon from the atmosphere with machines. Unfortunately, the current technology needs to be scaled by a factor of 2 million times within 2 years, all powered by renewables, alongside massive emission cuts, to reduce the amount of heating already locked into the system (Wadhams, 2018). Biological approaches to carbon capture appear far more promising (Hawken and Wilkinson, 2017). These include planting trees, restoring soils used in agriculture, and growing seagrass and kelp, amongst other approaches. They also offer wider beneficial environmental and social side effects. Studies on seagrass (Greiner et al, 2013) and seaweed (Flanery, 2015) indicate we could be taking millions of tonnes of carbon from the atmosphere immediately and continually if we had a massive effort to restore seagrass meadows and to farm seaweed. The net sequestration effect is still being assessed but in certain environments will be significant (Howard et al, 2017). Research into “management-intensive rotational grazing” practices (MIRG), also known as holistic grazing, show how a healthy grassland can store carbon. A 2014 study measured annual per-hectare increases in soil carbon at 8 tons per year on farms converted to these practices (Machmuller et al, 2015). The world uses about 3.5 billion hectares of land for pasture and fodder crops. Using the 8 tons figure above, converting a tenth of that land to MIRG practices would sequester a quarter of present emissions. In addition, no-till methods of horticulture can sequester as much as two tons of carbon per hectare per year, so could also make significant contributions. It is clear, therefore, that our assessment of carbon budgets must focus as much on these agricultural systems as we do on emissions reductions.
Clearly a massive campaign and policy agenda to transform agriculture and restore ecosystems globally is needed right now. It will be a huge undertaking, undoing 60 years of developments in world agriculture. In addition, it means the conservation of our existing wetlands and forests must suddenly become successful, after decades of failure across lands outside of geographically limited nature reserves. Even if such will emerges immediately, the heating and instability already locked into the climate will cause damage to ecosystems, so it will be difficult for such approaches to curb the global atmospheric carbon level. The reality that we have progressed too far already to avert disruptions to ecosystems is highlighted by the finding that if CO2 removal from the atmosphere could work at scale, it would not prevent massive damage to marine life, which is locked in for many years due to acidification from the dissolving of CO2 in the oceans (Mathesius et al, 2015).
Despite the limitations of what humans can do to work with nature to encourage its carbon sequestration processes, the planet has been helping us out anyway. A global “greening” of the planet has significantly slowed the rise of carbon dioxide in the atmosphere since the start of the century. Plants have been growing faster and larger due to higher CO2 levels in the air and warming temperatures that reduce the CO2 emitted by plants via respiration. The effects led the proportion of annual carbon emissions remaining in the air to fall from about 50% to
40% in the last decade. However, this process only offers a limited effect, as the absolute level of CO2 in the atmosphere is continuing to rise, breaking the milestone of 400 parts per million (ppm) in 2015. Given that changes in seasons, temperatures extremes, flood and drought are beginning to negatively affect ecosystems, the risk exists that this global greening effect may be reduced in time (Keenan et al, 2016)
These potential reductions in atmospheric carbon from natural and assisted biological processes is a flickering ray of hope in our dark situation. However, the uncertainty about their impact needs to be contrasted with the uncertain yet significant impact of increasing methane release in the atmosphere. It is a gas that enables far more trapping of heat from the sun’s rays than CO2 but was ignored in most of the climate models over the past decades. The authors of the 2016 Global Methane Budget report found that in the early years of this century, concentrations of methane rose by only about 0.5ppb each year, compared with 10ppb in 2014 and 2015. Various sources were identified, from fossil fuels, to agriculture to melting permafrost (Saunois et al, 2016).
Given the contentiousness of this topic in the scientific community, it may even be contentious for me to say that there is no scientific consensus on the sources of current methane emissions or the potential risk and timing of significant methane releases from either surface and subsea permafrost. A recent attempt at consensus on methane risk from melting surface permafrost concluded methane release would happen over centuries or millennia, not this decade (Schuur et al. 2015). Yet within three years that consensus was broken by one of the most detailed experiments which found that if the melting permafrost remains waterlogged, which is likely, then it produces significant amounts of methane within just a few years (Knoblauch et al, 2018). The debate is now likely to be about whether other microorganisms might thrive in that environment to eat up the methane – and whether or not in time to reduce the climate impact.
The debate about methane release from clathrate forms, or frozen methane hydrates, on the Arctic sea floor is even more contentious. In 2010 a group of scientists published a study that warned how the warming of the Arctic could lead to a speed and scale of methane release that would be catastrophic to life on earth through atmospheric heating of over 5 degrees within just a few years of such a release (Shakhova et al, 2010). The study triggered a fierce debate, much of which was ill considered, perhaps understandably given the shocking implications of this information (Ahmed, 2013). Since then, key questions at the heart of this scientific debate (about what would amount to the probable extinction of the human race) include the amount of time it will take for ocean warming to destabilise hydrates on the sea floor, and how much methane will be consumed by aerobic and anaerobic microbes before it reaches the surface and escapes to the atmosphere. In a global review of this contentious topic, scientists concluded that there is not the evidence to predict a sudden release of catastrophic levels of methane in the near-term (Ruppel and Kessler, 2017). However, a key reason for their conclusion was the lack of data showing actual increases in atmospheric methane at the surface of the Arctic, which is partly the result of a lack of sensors collecting such information. Most ground-level methane measuring systems are on land. Could that be why the unusual increases in atmospheric methane concentrations cannot be fully explained by existing data sets from around the world (Saunois et al, 2016)? One way of calculating how much methane is probably coming from our oceans is to compare data from ground level measurements, which are mostly but not entirely on land, with upper atmosphere measurements, which indicate an averaging out of total sources. Data published by scientists from the Arctic News (2018) website indicates that in March 2018 at mid altitudes, methane was around 1865 parts per billion (ppb), which represents a 1.8 percent increase of 35 ppb from the same time in 2017, while surface measurements of methane increased by about 15 ppb in that time. Both figures are consistent with a non-linear increase - potentially exponential - in atmospheric levels since 2007. That is worrying data in itself, but the more significant matter is the difference between the increase measured at ground and mid altitudes. That is consistent with this added methane coming from our oceans, which could in turn be from methane hydrates.
This closer look at the latest data on methane is worthwhile given the critical risks to which it relates. It suggests that the recent attempt at a consensus that it is highly unlikely we will see near-term massive release of methane from the Arctic Ocean is sadly inconclusive. In 2017 scientists working on the Eastern Siberian sea shelf, reported that the permafrost layer has thinned enough to risk destabilising hydrates (The Arctic, 2017). That report of subsea permafrost destabilisation in the East Siberian Arctic sea shelf, the latest unprecedented temperatures in the Arctic, and the data in non-linear rises in high-atmosphere methane levels, combine to make it feel like we are about to play Russian Roulette with the entire
human race, with already two bullets in the chamber. Nothing is certain. But it is sobering that humanity has arrived at a situation of our own making where we now debate the strength of analyses of our near-term extinction.