ThinkLONG

Using the Oceans to Reduce Atmospheric CO2 Levels

02 Dec 2008 0 comment(s)

Prof Gideon Henderson, co-Director of the 21st Century Oceans Institute with Prof David Marshall, spoke at the School on 27 November about the relationship between the oceans, the carbon cycle and climate change. His lecture highlighted the work of oceanographers who are using physics and chemistry to explore how oceans can be used to absorb the high levels of CO₂ humans are putting into the atmosphere.

The atmospheric concentrations of CO₂ have risen dramatically in the last 300 years due to human activity, and their greenhouse effect is connected to climate change scenarios. Not all CO₂ goes into the atmosphere, however. The oceans absorb about a third of the carbon pushed into the atmosphere over time. 2.2 gigatons of carbon go into the oceans every year, although where it is absorbed depends on the ocean temperature, biology, and circulation patterns. As the oceans absorb more carbon, they become more acidic.

Because the oceans naturally absorb carbon, they have been seen as a way to adapt to higher CO₂ emissions and avoid extreme scenarios of climate change. One proposal has been to store carbon in the deep ocean (most carbon is naturally absorbed at the surface). Others have focused on geo-engineering, or manipulating natural systems to enhance carbon uptake by the ocean.

The first geoengineering proposal involves dropping iron into areas of the ocean. Some parts of the ocean don't absorb much carbon because low iron levels limit the amount of life on the ocean surface. Fertilising the oceans with iron can promote the growth of life, which will sequester carbon from the atmosphere. Some companies have already tried to implement this process to sell carbon credits, but they have been prohibited from doing so by international law. Not enough is known yet about iron fertilisation, and the Oceans Institute is using sophisticated modelling to examine the chemical and biological processes involved and their wider implications.

A second proposal is to make the oceans more alkaline to balance the acidity resulting from carbon absorption - this would enable the oceans to absorb even more carbon from the atmosphere. Adding alkalinity involves producing massive volumes of calcite from limestone and dissolving this calcite into the oceans. Like the iron fertilisation proposal, not enough is yet known about the impacts of this process on a wide scale: What would it do to biota? How can it be mixed evenly? How do we engineer the large-scale extraction, processing and dilution of limestone/calcite?

Attendees raised several questions about the ethics of implementing geoengineering plans without full knowledge of their biological impact. Prof Henderson argued that although geoengineering may be inherently unpredictable, research is needed to clearly identify possible risks and drawbacks associated with a variety of approaches. Although it would naturally be desirable not to ‘mess' with the oceans, climate change will likely place increasing pressure on governments to implement technical solutions. Prof Henderson added, "By the time we get to this point we need to be informed by good science."

This blog comes from the seminar series on 21st Century Challenges