The Earth’s ecosystems are already strained. It is therefore not sufficient to just reduce the rate of GHG emissions. We should prepare for sequestering CO2 at a large scale to be on the safe side.
Man-made climate change is happening and its impacts and costs will be large, serious and unevenly spread. The impacts may be reduced by adaptation and moderated by mitigation, especially by reducing emissions of greenhouse gases. However, global efforts to reduce emissions have not yet been sufficiently successful to provide confidence that the reductions needed to avoid dangerous climate change will be achieved. This has led to growing interest in geo-engineering, defined here as the deliberate large-scale manipulation of the planetary environment to counteract anthropogenic climate change (Royal society, 2009)
On this background it seems that some kind of geo-engineering is inevitable to give us sufficient time for transforming economies and societies in an adequate direction. Whether we want to admit it or not, we humans have been involved in geo-engineering since at least 1750 by continuously adding greenhouse gasses into the atmosphere. Unfortunately the only solution to a problem of such magnitude is another form of deliberate geo-engineering. We must move this excess carbon dioxide back into the geological reservoirs where it originally came from.
According to the Royal Society there are two basic categories of geo-engineering methods:
- Carbon Dioxide Removal (CDR) techniques, which remove CO2 from the atmosphere. As they address the root cause of climate change, rising CO2 concentrations, they have relatively low uncertainties and risks.
- Solar Radiation Management (SRM) techniques, which reflect a small percentage of the sun’s light and heat back into space. These methods act quickly, and so may represent the only way to lower global temperatures quickly in the event of a climate crisis. However, they only reduce some, but not all, effects of climate change, while possibly creating other problems. They also do not affect CO2 levels and therefore fail to address the wider effects of rising CO2, including ocean acidification.
The solar radiation techniques as a rule will add chemicals like sulfuric acid aerosols to the stratosphere, thereby increasing the albedo. However, it is probably not very wise to combat one type of pollution with another type of pollution. Millions of tonnes of sulfuric acid “solar mirrors” would have to be sprayed throughout the stratosphere to produce a cooling effect. At some point in time these chemicals would deposit out of the atmosphere in wet or dry form, both on the continents and oceans. Addtional problems are that these small”mirrors” will follow air streams and spread unevenly. Some countries will resist this kind of pollution, and conflicts may arise. Less insolation over some regions will mean reduced photosynthesis, and less agricultural and biomass production. Some countries might perceive anything that threatens their agriculture as an act of war. Less photosynthesis is probably incompatible with producing food for a rising world population. We also risk a serious reduction in oxygen production on land and in the seas due to less photosynthesis.
The arguments for the CDR techniques are strong. Natural systems powerful enough to reverse the current trends of global warming, is massive growth in global reforestation. Another possibility might be the formation of marine snow. Earlier attempts in this direction, such as carbon capture and storage and fertilization on high nitrate low chlorophyll (HNLC) regions of the oceans by initiating large-scale phytoplankton blooms have failed.
Marine snow aggregates are ubiquitous components of all oceanic systems, appearing in different sizes and forms depending on the local oceanographic conditions. They appear to be self-contained and self-sustaining environments and can significantly contribute to sequestration, sedimentation and burial of newly produced organic matter from the water column. In specific conditions aggregates are not degraded, remineralized or colonized by zooplankton.
When sinking below the pycnocline (the layer separating upper and lower water in a water column) they efficiently bypass mid-water biota thus becoming perhaps the most important sequestration component of the marine biological pump (see figure) and the path of particulate organic carbon to the sea floor.
In some regions of the world, the surface waters of the oceans, notably the Southern Ocean, are deficient in iron, which limits the growth of phytoplankton. By fertilizing the oceans with the proper amount of iron, these microscopic plants would be encouraged to grow and absorb excess carbon dioxide from the atmosphere.
There are several experimental initiatives with carbon sequestration. So far none of them have been significant enough to make a clear indentation on the Keeling curve at Mauna Loa. Nevertheless, these experiments are of high importance and should continue at a much larger scale.
Sources / Read more
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