2.6 Does increasing atmospheric CO2 have any other effects?

Yes. The most important direct effect is exchange of atmospheric CO2 with the surface ocean waters, leading to an increase in CO2 in the oceans. The oceans have taken up 27–34% of CO2 emitted by human activity over the last 150 years. This ‘buffering’ capacity has effectively weakened the enhanced greenhouse effect. However, the continued uptake of CO2 by the oceans will lead to a slowdown in its capacity to absorb more CO2, meaning that in future more CO2 will remain in the atmosphere. In addition, there is growing concern about the possible impacts of increasing ocean CO2 on marine ecosystems. Increasing CO2 in the oceans raises the pH of the oceans – popularly referred to as ocean acidification. Increasing ocean pH impedes the ability of organisms to grow their external shells. This raises concerns about destabilising oceanic ecosystems where tiny shelly organisms (cocolithophores, a type of phytoplankton) form the base of the marine food web.

It is important to bear this in mind in evaluating geoengineering solutions to climate change. Putting to one side the proposed scale of interventions with various ecosystems (and potential problems arising as a result of that), many of these proposals aim to deal with the impacts of the enhanced greenhouse effect on global mean surface temperature (e.g. mirrors in space), but fail to address changes in the chemical composition of the oceans. See also ‘What about geoengineering? Won't that help us to control the climate?’ in Section 5.15.

These web-based resources provide additional information

  • A short note on CO2 and ocean acidification, with a link to a pdf file for a full briefing, can be found at the UK Marine Climate Change Impacts Programme.

  • RealClimate has a briefing and discussion on ocean acidification.

  • The Royal Society of London has an article on ocean acidification.

  • RealClimate has a collection of briefings and discussions on geoengineering.

2.5 What is happening to global temperatures?

2.7 What do all of these different measures and units mean?