Cultivated land releases laughing gas – nitrous oxide (N2O) – to the atmosphere. As a greenhouse gas, laughing gas is 300 times more powerful per molecule than carbon dioxide (CO2). Paul Crutzen and his associates calculated that global emissions of laughing gas nitrogen from cultivated land represents about 3-5 percent of the total amount of nitrogen supplied to the land. He then calculated how great laughing gas emissions from cultivating biofuels might be in comparison with the reduction of CO2 emissions resulting from biofuels replacing fossil fuels. The comparison revealed that laughing gas emissions may contribute more to global warming than to cooling down the climate. However, Crtuzen’s findings were critically based on the calculation that 3-5 percent laughing gas nitrogen is released to the atmosphere from the nitrogen supplied to the cultivated land, a percentage that differed considerably from the IPCC’s corresponding estimate of only one percent.

Destouni and Darracq have investigated the reason for the gap between Crutzen’s and the IPCC’s results and which percentage is the most accurate regarding emissions of laughing gas from cultivated land.

In their study Destouni and Darracq calculated the flow of nitrogen on and under the surface of the ground throughout the entire Norrström catchment area, a 22,000 square km area comprising the whole Mälardalen region, whose waters flow out to the Baltic Sea via the Norrström in Stockholm. Destouni’s research team has long used this area as a field laboratory for their studies of the water’s and water-borne nutrient (nitrogen and phosphorous) fluxes, flow routes, and flow times from various parts of the area to the Baltic. This cumulative knowledge could now be used to calculate the total amount of nitrogen flowing through the cultivated land as well as the amount of water-borne nitrogen from cultivated land that at each point in time is being transported through the catchment area, distributed across the different surface waters (streams, lakes, wetlands) and subsurface (soil, ground-, sediment) waters of the area.

Both the primary flow through cultivated land and the secondary water-borne nitrogen that originates from cultivated land entail emissions of laughing gas nitrogen to the atmosphere. To calculate these emissions, Destouni and Darracq used the IPCC’s relatively low values of 0.75-1 percent of laughing gas nitrogen being released into the atmosphere from cultivated land and the various surface and subsurface water systems in the catchment area. The total sum of cultivation-related primary and secondary emissions of laughing gas nitrogen was about 3 percent of the primary nitrogen in the cultivated land, a figure that corresponds to Crutzen’s global estimate.

“The difference between the IPCC’s and Crutzen’s estimates is due to the fact that the IPCC, even though using reasonable local values, did not factor in all the localities and water systems on and beneath the land surface that at every point in time contain nitrogen and release laughing gas originating from cultivated land. Crutzen’s global mass balance calculation showed how great the total laughing gas emissions from cultivated land needed to be to complete the balance, but could not break down the total emissions into their local components,” says Georgia Destouni.

For further information please contact: Georgia Destouni, professor of hydrology, phone: +46 (0)8-16 47 85; cell phone: +46 (0)70-4532366; e-mail georgia.destouni@natgeo.su.se

For pictures please contact: press@su.se or phone: +46 (0)8-16 40 90

Link to the article: http://stacks.iop.org/1748-9326/4/035008