New research suggests that melting sea ice is weakening the Arctic Ocean’s ability to capture and store atmospheric carbon. The study, carried out at the Catlin Arctic Survey’s Ice Base in March and April 2010 by a team at the Department of Fisheries and Oceans, Canada, focuses on the efficiency of an important biological ‘pump’ that captures atmospheric carbon near the sea surface and then draws it down and stores it on the sea floor.

Phytoplankton (plant plankton), near the sea surface, capture atmospheric carbon and store it as non-sinking microscopic particles. Although these particles do not themselves sink, their sticky nature means they can capture heavier organic debris and become sufficiently dense that they fall to the ocean floor as ‘marine snow’, effectively removing significant amounts of atmospheric CO2 to the deep ocean for thousands of years.

The findings also show that carbon-rich gel-like particles (so-called transparent exopolymer particles or TEPs) are stored in the sea ice during winter and are released into the water column during early spring. TEPs are an important feature in the carbon cycle as they both capture carbon and also give ‘marine snow’ its stickiness, enabling it to attract organic debris and therefore sink.

Future increases in surface freshwater from melting sea-ice will likely further strengthen water layering and could change carbon draw-down in the Arctic Ocean. Coupled with the continuing retreat of sea-ice, this has implications for the capacity of the Arctic Ocean to mitigate increasing atmospheric CO2 emissions via carbon capture.

The oceans represent the largest active carbon sink on earth, absorbing more than a quarter of the carbon dioxide that humans put into the air. According to a recent estimate, the Arctic is responsible for 5% to 14% of the world’s CO2 uptake, although it accounts for only 3% of its ocean surface area.

The Catlin Arctic Survey, sponsored by global specialty insurer and reinsurer Catlin Group, involves an ‘Ice Base’ and an ‘Explorer Team’.

The Amazon rainforest, long regarded as a valuable carbon sink slowing climate change, is in danger of becoming a major source of greenhouse gas emissions. New research shows that the 2010 Amazon drought may have been even more devastating to the region’s rainforests than the unusual 2005 drought, which was previously billed as a one-in-100 year event. Analyses of rainfall across 5.3 million square kilometres of Amazonia during the 2010 dry season, published in Science, shows that the drought was more widespread and severe than in 2005.

The UK-Brazilian team also calculates that the carbon impact of the 2010 drought may eventually exceed the 5 billion tonnes of CO2 released following the 2005 event, as severe droughts kill rainforest trees. For context, the United States emitted 5.4 billion tonnes of CO2 from fossil fuel use in 2009.

The authors suggest that if extreme droughts like these become more frequent, the days of the Amazon rainforest acting as a natural buffer to man-made carbon emissions may be numbered.

Grim Future

Lead author Dr Simon Lewis, from the University of Leeds, explains: “Having two events of this magnitude in such close succession is extremely unusual, but is unfortunately consistent with those climate models that project a grim future for Amazonia.”

The Amazon rainforest covers an area approximately 25 times the size of the UK. University of Leeds scientists have previously shown that in a normal year intact forests absorb approximately 1.5 billion tonnes of CO2. This counter-balances the emissions from deforestation, logging and fire across the Amazon and has helped slow down climate change in recent decades.

In 2005, the region was struck by a rare drought which killed trees within the rainforest. On the ground monitoring showed that these forests stopped absorbing CO2 from the atmosphere, and as the dead trees rotted they released CO2 to the atmosphere.

The unusual drought, affecting south-western Amazonia, was described by scientists at the time as a ‘one-in-100-year event’, but just five years later the region was struck by a similar extreme drought that caused the Rio Negro tributary of the Amazon river to fall to its lowest level on record.

New Research

The new research, co-led by Dr Lewis and Brazilian scientist Dr Paulo Brando, used the known relationship between drought intensity in 2005 and tree deaths to estimate the impact of the 2010 drought.

They predict that Amazon forests will not absorb their usual 1.5 billion tonnes of CO2 from the atmosphere in both 2010 and 2011, and that a further 5 billion tonnes of CO2 will be released to the atmosphere over the coming years once the trees that are killed by the new drought rot.

Dr Brando, from Brazil’s Amazon Environmental Research Institute (IPAM), says: “We will not know exactly how many trees were killed until we can complete forest measurements on the ground. It could be that many of the drought susceptible trees were killed off in 2005, which would reduce the number killed last year. On the other hand, the first drought may have weakened a large number of trees so increasing the number dying in the 2010 dry season.”

Climate Change Models

Some global climate models suggest that Amazon droughts like these will become more frequent in future as a result of greenhouse gas emissions.

“Two unusual and extreme droughts occurring within a decade may largely offset the carbon absorbed by intact Amazon forests during that time. If events like this happen more often, the Amazon rainforest would reach a point where it shifts from being a valuable carbon sink slowing climate change, to a major source of greenhouse gasses that could speed it up,” Dr Lewis adds. “If greenhouse gas emissions contribute to Amazon droughts that in turn cause forests to release carbon, this feedback loop would be extremely concerning. Put more starkly, current emissions pathways risk playing Russian roulette with the world’s largest rainforest.”

The research was a collaboration between the Universities of Leeds, Sheffield and the Instituto de Pesquisa Ambiental da Amazonia (IPAM) in Brazil. The work was funded by the Royal Society, Gordon and Betty Moore Foundation and the US National Science Foundation.

Forests have a key role to play in combating climate change, both as a carbon sink and as a source of renewable energy, but initiatives to boost forestry for this purpose need to be subject to proper economic assessment, according to the findings of an inquiry by the British House of Lords Sub-Committee on Agriculture, Fisheries and the Environment.

The inquiry found that due to the diverse nature of forests across Europe it would not be practical for the EU to be given specific competence in this area. However, the Committee does recommend that the European Commission works with Member States in order to share experience of innovative economic mechanisms for forestry development and tackling climate change, and to ensure that afforestation initiatives are subject to proper economic assessment.

“We are concerned that the economics of forestry are the biggest obstacle to any further increase of forest cover in order to tackle climate change, as rewards can only be reaped over a long time-scale.  Wide public support for increased funding is unlikely given the current economic climate, but we know that some Member States take innovative approaches to the economics of forestry, through their tax systems for example,” remarks Committee chairman, Lord Carter of Coles. “We have also heard that it would be useful to value, and possibly trade, the public benefits provided by forestry.”

The findings of the inquiry have been submitted to the European Commission as a response to its Green Paper on ‘Forest Protection and Information in the EU: Preparing Forests for climate change,’ which was published on March 1st 2010.