This is the concluding paragraph … download the pdf to read the entire paper.
The ultimate goal of our endeavours is planetary restoration: returning the Earth System to a healthy state for human posterity – a state which is guaranteed safe, sustainable, biodiverse and productive. Such a healthy state can only be guaranteed if it is close to pre-industrial norms. But planetary restoration will be impossible without reversing the most dangerous trends, which are apparent in the Arctic.
The problem we set ourselves was to find plausible methods for addressing the major crises emerging as a result of an accelerated Arctic meltdown. These crises could potentially manifest as abrupt and catastrophic climate change, sea level rise and multi-megaton methane release. The necessary action to quash these crises turns out to be nothing less than a refreezing of the Arctic: offsetting the heating that has resulted from lost albedo; cooling the Atlantic and Pacific water which continues to inject heat into the Arctic; restoring the sea ice whose retreat has boosted methane emissions; halting the ice mass loss from the Greenland Ice Sheet. We recommend a judicious combination of albedo enhancement, radiative cooling and physical constraint. But albedo enhancement using stratospheric and/or tropospheric aerosols turns out to be absolutely essential to provide the necessary basic cooling power if we have done our engineering assessment correctly. These techniques are commonly referred to as Solar Radiation Management (SRM).
With so much at stake, every effort has to be made to ensure a successful stabilisation of the Arctic situation. This is a huge operation which will require, for a decent chance of success: multinational collaboration; brilliant management; detailed planning; independent evaluations; multiple skills and expertise; and careful use of the resources available, since they could be a limiting factor for some techniques.
Parallel development of alternative technologies should be encouraged and parallel deployment allowed where there is no interference. For example, different MCB techniques could be applied in different areas of the ocean at the same time as SAI is deployed in the stratosphere.
However our assessment of the engineering techniques shows a wealth of expertise and ingenuity for tackling the problems. It suggests that there is a good chance of overall success if given proper backing for development and deployment, with appropriate systems for safety, monitoring and continuous evaluation.
But public opinion is heavily against SRM. Here are the predominant arguments against SRM:
• SRM is intrinsically dangerous. However, the proposed SRM methods are all based on naturally occurring processes which cool the planet’s surface without adverse side-effects. Additionally, much research has gone into identifying possible risks; and top modellers say that these risks can be circumvented or mitigated by appropriate careful application and monitoring.
• SRM is dangerous because, when stopped, the temperature will rebound – this is known as the termination problem. However, we urge that the levels of greenhouse gases in the atmosphere are reduced in parallel with the application of SRM, so that no such rebound is possible. SRM can be regarded as a stop-gap in this sense.
• SRM is morally wrong, because it allows polluters to continue polluting – it is a “get out of gaol free” card. This is the so-called “moral hazard” argument. However, reducing emissions is not going to save the Arctic, and saving the Arctic is not going to affect emissions; so that does not seem to be a valid argument.
• It would be morally wrong to rely on SRM when it is politically unacceptable, and so the world should prepare for what will happen without SRM – e.g. a metre of more of sea level rise this century. However the starting point should be what is possible from engineering considerations and what has to be avoided. If SRM is necessary to avoid passing points of no return leading to inevitable catastrophe, then this fact has to be faced by the international community. One such catastrophe would be the sudden destabilisation of major Greenland glaciers, with avalanches of kilometre-size chunks of ice leading to tsunamis and abrupt sea-level rise – complete disintegration of the Greenland Ice Sheet would produce 6-7 metres of sea level rise.
• SRM threatens biodiversity. However the opposite is true. For example refreezing the Arctic will help to preserve wildlife such as polar bears.
Although one could restrict SRM to application in the Arctic only, in order to avoid some of this criticism and acrimony, we have found that more globally applied SRM will almost certainly be necessary for refreezing the Arctic. On closer examination, global SRM could have huge benefits besides refreezing the Arctic, especially as regards sea level rise and reducing flood events.
• Countries like Bangladesh and mega-cities like Calcutta and Shanghai which lie on huge river deltas are already suffering heavily from a combination of sea level rise produced by ocean expansion and tidal surges produced by storms. Both sea level and storm intensity have risen due to global warming; global SRM would reverse these two trends.
• Over a billion people at mid and low latitude rely on meltwater from glaciers and their lives and livelihoods are threatened by glacier retreat. SRM applied at these latitudes would help to save these glaciers and prevent disastrous water shortages.
A basic requirement for planetary restoration will be SRM to reduce the global mean temperature below 0.5C, halt glacier retreat worldwide, and reduce intensity of tropical storms.
Complete planetary restoration, including a halt to sea level rise, is a realistic prospect to benefit future generations by returning the planet to a proven safe state.