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.