The UKOA programme was active between 2010-2016, with supported research completed in mid-2015 and knowledge exchange work in early 2016.
This website now has archive status.

How much variability is there in oceanic CO2 uptake and what are the trends for the future?

“Acidification” of ocean waters is a consequence of the rising concentration of carbon dioxide (CO2) in the atmosphere. It is calculated that surface ocean pH has decreased on average by about 0.1 units since pre-industrial times due to the ocean’s uptake of CO2. By 2100 this decrease may reach 0.3 units, with potentially serious consequences for some marine ecosystems. 

However, acidification is not occurring uniformly everywhere; evidence from the scattered measurements available suggests that surface pH varies substantially. Variations are from place to place, season to season, year to year and decade to decade. These natural variations form a scale against which human-caused changes may be measured. Acidification that moves the natural system beyond the natural variations is likely to be more damaging than changes that remain within natural bounds. It is important therefore to establish this natural variability, by increasing systematic measurements.

The aims of this project are:

  • To quantify the rate of change of ocean pH in the north Atlantic and European shelf (UK coastal waters in particular) and also parts of the Southern Ocean.
  • To gather pH observations from commercial “ships of opportunity”, small research vessels, and the regular surveys undertaken by the Centre for Environment, Fisheries and Aquaculture Science (CEFAS).
  • To collaborate with marine scientists worldwide, who are researching ocean acidification, to obtain a much wider and more complete picture of the issue. We will therefore take a lead in the “Surface Ocean CO2 atlas”, which has recently begun to synthesise global data on changing carbonate chemistry that controls ocean pH. By this means we will synthesise the best available estimates of how pH has changed in the past, as well as how it is currently changing and predict likely changes in the future, for the ocean regions of interest.


The outputs of this programme will:

  • Feed into the cross-government Climate Change Adaptation programme
  • Make a significant contribution to the Living With Environmental Change programme
  • Provide evidence to the IPCC 5th Assessment Report on Climate Change
  • Provide information to marine bioresource managers, policy makers negotiating CO2 emissions reduction and other stakeholders


Results from this project will leave a lasting legacy, including:

  • Existing observation systems, which measure the uptake of CO2 by the oceans, will be maintained and upgraded, to ensure that data can be used to accurately calculate pH.
  • New observations round much of the coastal waters of the UK using surveys undertaken by CEFAS.
  • Collaboration and co-ordination with international partners in Europe and the US to instrument several other shipping routes covering the North Atlantic.
  • A leading role will be taken in the international marine science community, to make a database available under the “Surface Ocean CO2 atlas (SOCAT)” project, documenting observations relevant to the pH of the surface oceans, and use these to synthesise the best available picture of how pH has varied in the past over the global ocean, but particularly in our regions of interest. SOCAT is aimed primarily at calculating the changing CO2 content of the surface ocean, but from this and with additional information, pH can be calculated.
  • An update of the presently rather schematic notion of how acidification will proceed, under given increases in CO2 later this century. We should be able to answer what pH change and variability the regions in our study have seen in the recent past and what they will see in the near future, enabling more accurate predictions about the more distant future.
  • Data will be made as widely available as possible via the British Oceanographic Data Centre (BODC) and the Carbon Dioxide Information Analysis Center (CDIAC).