Rise in UK carbon emissions disputed by report

Soil deposits of CO2 'not fuelling global warming yet – but will in future'
The Observer, Sunday 7 March 2010

A major study for the UK government has cast doubt over claims that rising temperatures are causing soil to pump greater amounts of carbon dioxide into the atmosphere, further fuelling global warming.
In 2005 it was reported in the science journal Nature that over the past 25 years 100m tonnes of carbon dioxide had been released by the soil of England and Wales. The figure cancelled out all emissions cuts in the UK since 1990.
However, a national survey of the soils of Great Britain, funded by the department for environment food and rural affairs, claims to have found no net loss of carbon over approximately the same period.
Scientists have now proposed that a special study group, with an independent statistical expert, should examine why the reports differ and which result is more likely to be correct.
The latest questions follow weeks of claims that predictions about the impacts of climate change have been overstated or miscalculated, including the melting of Himalayan glaciers, and separate allegations of bias based on leaked emails from scientists at the climate research unit at the University of East Anglia.
The author of the latest report, Professor Bridget Emmett of the UK Centre for Ecology and Hydrology (CEH), warned that finding there had been no loss of carbon so far should not be taken to mean the absence of a threat. In the long term, scientists predict a "tipping point" when the faster activity of microbes in warmer soils starts to generate more CO2 than can be absorbed by plants.
"That's when you start losing carbon as a whole," said Emmett. "Most of the models say that will be later this century."
The 2005 report in Nature was based on the National Soil Inventory, carried out initially between 1978 and 1983, and again from 1994 to 2003, by the National Soil Resources Institute at Cranfield University. That study said that from 1978 to 2003 there had been an estimated loss of 4m tonnes of carbon a year from the soils of England and Wales, and the researchers estimated that, because of the higher carbon content of Scotland's peaty soils, the annual loss from the UK as a whole was 13m tonnes a year. The fact that the losses occurred across all types of land use suggested a link to climate change, said the team.
At that time, one of the research team, Professor Guy Kirk of Cranfield University, told a conference: "It had been reckoned that the CO2 fertilisation effect was offsetting about 25% of the direct human-induced carbon dioxide emissions. It was reckoned that the soil temperature emission effect would catch up in maybe 10 to 50 years' time. We are showing that it seems to be happening rather faster than that."
The latest report by the CEH, just released as part of the ongoing analysis of the 2007 Countryside Survey of Great Britain, compared studies between 1978 and 2007. It found carbon concentration in the top 15cm of soil increased over the first two decades, and decreased between 1998 and 2007. The only exception was arable land, where there was a net loss of carbon, probably because of disruption by ploughing.
"Overall there was no change in carbon concentration ... and [we] cannot confirm the loss reported by the National Soil Inventory," states the report.
Kirk told the Guardian that the Cranfield team were still "confident in our results [that] there was a net loss of carbon". But he said subsequent studies had suggested that "at best" 10% of the loss of carbon was due to climate change, and the rest was due to changes in land use and management, such as conversion of grassland to crops.
Reasons being examined for the difference in results include where and how samples were chosen and analysed and how the data was compiled.
"The amount of carbon in topsoils across England and Wales is about 2bn tonnes, so detecting a change of even 4m tonnes per year is very challenging," said Emmett. "Small differences in methods between the two surveys can therefore have a large effect."