Global warming is irreversible without massive geoengineering of the atmosphere’s chemistry. This stark warning comes from the draft summary of the latest climate assessment by the Intergovernmental Panel on Climate Change.
Even if all the world ran on carbon-free energy and deforestation ceased, the only way of lowering temperatures would be to devise a scheme for sucking hundreds of billions of tonnes of carbon dioxide out of the atmosphere.
Since the last assessment, published in 2007Speaker, the IPCC has almost doubled its estimate of the maximum sea-level rise likely in the coming century to about 1 metre. They also conclude that it is now “virtually certain” that sea levels will continue to rise for many centuries, even if warming ceases, due to the delayed effects of thermal expansion of warming oceans and melting ice sheets.
The draft report says the available evidence now suggests that above a certain threshold of warming, the Greenland ice sheet will almost disappear within approximately 1000 years, which will result in 7 metres of global sea-level rise. It estimates that the threshold may lie between 1 °C and 4 °C of warming, but is not confident of this figure.
Carbon dioxide removal projects seek to remove greenhouse gases from the atmosphere. Proposed methods include those that directly remove such gases from the atmosphere, as well as indirect methods that seek to use natural processes(e.g. tree planting). Many projects overlap with carbon capture and storage and carbon sequestration projects.
* Creating biochar and mixing it with soil to create terra preta
* Bio-energy (biofuel) with carbon capture and storage to sequester carbon and simultaneously provide energy
* Carbon air capture to remove carbon dioxide from ambient air
* Planting trees to offset carbon emissions
* Ocean nourishment including iron fertilisation of the oceans
* Green concrete that absorbs carbon dioxide
There is also solar radiation management.
* Surface-based (land or ocean albedo modification); e.g. Cool roof—using pale-coloured roofing and paving materials.
* Troposphere-based, for example cloud whitening – using fine sea water spray to whiten clouds and thus increase cloud reflectivity.
* Upper atmosphere-based (e.g. stratospheric aerosols). Creating reflective aerosols, such as stratospheric sulfur aerosols, aluminum oxide particles, even specifically designed self-levitating aerosols.
* Space-based: E.g. Space sunshade—obstructing solar radiation with space-based mirrors, asteroid dust, etc.
Stratosphere based would be the cheapest method.
Biochar can cost a lot but would have the added benefit of improving topsoil for agriculture.
Having roofs and roads that are white are more contained interventions.
Reducing soot has the benefit of improving the health of billions and saving millions of lives per year and it reduces the darkening of ice and other surfaces.
Fixing soot and particulates is about ten times cheaper than fixing carbon dioxide and would work faster. The current contribution to global heating is nearly as large for soot and particulates as it is for existing levels of carbon dioxide.