Whilst geological carbon sequestration remains an attractive climate change mitigation option there are uncertainties and complexities surrounding the legality of such projects. This working paper reviews the legal issues concerning geological carbon sequestration in the offshore waters surrounding the United Kingdom. Key international and European legislation that is relevant to CO2 storage is identified and we explore under which circumstances geological carbon sequestrations can currently take place. The underlying objectives of the Climate Change Convention and Kyoto Protocol are to prevent greenhouse gases (GHG) entering the atmosphere, as well as to remove GHG once they have been emitted. It is clear that geological carbon sequestration aims to prevent emissions from entering the atmosphere by capturing CO2 at source. It follows that as the CO2 does not enter the atmosphere, this will not classed as an 'emission' for the purposes of the Convention/Protocol, but as an 'emission reduction'. It is therefore dealt differently to other forms of sequestration projects such as CO2 take up in forests, which seeks to remove GHG already in the atmosphere. Emission reductions by carbon sequestration is not prohibited under the Convention/Protocol, which allow projects which reduce greenhouse gases at source. However, a potential problem is that the Convention/Protocol provides for transparent verification of emission reductions and there could still be concerns over its permanence, particularly concerning leakage and security. From a legal perspective, different locations of the sea are subject to different prescriptions under international law. Nations have the greatest amount of jurisdiction and control over the waters closest to shore with increasing responsibility to accommodate uses by other States as the distance from shore increases. The location of the CO2 site will therefore determine the legal responsibilities. A key legal question is whether CO2 is a waste, and whether it is dumped. The model for determining what is a waste in the marine conventions is to either list all the wastes that are prohibited for disposal, or to have a general prohibition on the dumping of all wastes except those listed. The position under the London Convention is that CO2 might fall under the 'industrial waste' category in the list of wastes prohibited for disposal. If it is not classed as industrial waste, C02 disposal will not be prohibited. It is clear that CO2 would probably not fall under the categories approved for dumping in the 1996 Protocol or OSPAR Convention, and should therefore be considered as waste. The definition of dumping is also a decisive factor in determining whether CO2 storage falls within the remit of the conventions. Dumping is defined in all the conventions as disposal, which is left undefined, but is often interpreted as the action of getting rid of something. Although there are some potential ambiguities, we conclude that long term storage of CO2 amounts to dumping under the conventions. If CO2 is considered to be a waste and dumped in the sea, another key legal issue is the pathway of the CO2 to the storage site. Under each marine convention it seems likely that if CO2 is transported by ship and then disposed of either directly from the ship, or from an offshore installation, this will be prohibited. In the case of a pipeline carrying CO2 to an installation, this will be prohibited under the London Convention and 1996 Protocol. This is not always the case under the OSPAR Convention, where there the prohibition against dumping only applies to installations carrying out activities concerning hydrocarbons. If CO2 is not a hydrocarbon, and in our view it is not, it is permissible under the OSPAR Convention to pipe CO2 to offshore installations provided they have not been already used for activities involving hydrocarbons. Both the London Convention and 1996 Protocol also only apply to activities using ships or platforms, and contain no further controls governing pipeline discharges from land-based sources. Under OSPAR, however, State's have general environmental obligations with respect to land-based pipelines. It is conceivable that some form of environmental assessment (EIA) might have to be undertaken under international or European law if a CO2 project is considered to have significant effects on the environment. The Law of the Sea Convention contains provisions concerning the environmental assessment of potentially damaging offshore activities, but the ESPOO Convention is the more specific international convention concerning EIA. It is doubtful whether CO2 storage falls under any of the categories listed requiring assessment under the Convention. Member States of the European Community are also required to ensure that the environmental consequences of projects identified in the EIA Directive are assessed before authorisation is given. There are no clear project categories contained in the Directive expressly covering CO2 storage offshore, but an EIA may be required for the modification of existing pipelines and offshore installations if these are modified to be used for CO2 transportation or disposal, then this might be caught under the Directive. The United Kingdom Government might also have to undertake a strategic environmental assessment (SEA) of the environmental implications of offshore CO2 disposal, from July 2004, when the European SEA Directive comes into force. SEA will also be required under international law in the future when the Kiev SEA Protocol is adopted, although this could take many years. Under the European SEA Directive the Government will be under a legal requirement to conduct an SEA if they prepare or adopt a plan or programme of a category listed in the annex to the Directive. It looks likely that C02 disposal in the sea might fall under one of the categories in the Directive and the Government could have to prepare an environmental report on the plan or programme's likely significant effects on the environment. A number of international and European legislation protecting marine habitat sites and species are likely to be relevant. The Biodiversity Convention urges contracting parties to take into account the environmental consequences of its programmes and they must prevent or minimize danger or damage to biological diversity. The legal teeth of the Convention is however limited in practice and it is unlikely to prevent CO2 storage projects taking place in practice. The OSPAR Convention, whose main focus is on marine pollution, also contains provisions relating to the protection of the ecosystems and biological diversity in marine waters, although these are in weak language. The Biodiversity Committee of the OSPAR Commission is charged with drawing up plans and programmes designed to control of human activities, and they can impose measures for instituting protective, conservation, restorative or precautionary measures related to specific sites or a particular species. It is possible that the OSPAR Commission could seek to protect habitats or species in an area where CO2 disposal is planned. The European Habitats Directive provides measures to protect habitats and species which are listed in the Directive. The Directive obliges Member States and the European Commission to select sites, known as special areas of conservation, where the habitats and species listed in the Directive can be found, and protected. The legal question therefore is whether the carbon sequestration projects might take place in sites that could be designated as special areas of conservation. In this study we identified only four habitats and seven species, listed in the Directive, that occur in United Kingdom waters, and many of these are rarely seen, making it quite unlikely that special sites will be designated. Even if an area has been designated as a special area of conservation, this still does not provide absolute protection against interference, only restrictions. Member States may permit interference for imperative reasons of overriding public interest, which expressly includes social, environmental or economic interests.