The terrestrial biogenic fluxes of individual greenhouse gases have been studied extensively, but the net biogenic greenhouse gas balance resulting from anthropogenic activities and its effect on the climate system remains uncertain. Here we use bottom-up (inventory, statistical extrapolation of local flux measurements, and process-based modelling) and top-down (atmospheric inversions) approaches to quantify the global net biogenic greenhouse gas balance between 1981 and 2010 resulting from anthropogenic activities and its effect on the climate system.

The terrestrial biosphere can release or absorb the greenhouse gases, carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O), and therefore has an important role in regulating atmospheric composition and climate. Anthropogenic activities such as land-use change, agriculture and waste management have altered terrestrial biogenic greenhouse gas fluxes, and the resulting increases in methane and nitrous oxide emissions in particular can contribute to climate change.

The news is really bad on the climate change front lately. I don't usually report on that stuff, but occasionally a new result comes along which is too impressively bad to pass on. A recent Nature Letter met that criteria. It's called The terrestrial biosphere as a net source of greenhouse gases to the atmosphere . Here's the abstract.

We are talking about the most important greenhouse gases here, including methane and nitrous oxide. The effective "radiative forcing" (surface warming) produced by those GHG gases is discussed in terms of carbon dioxide-equivalence, which is abbreviated as CO 2 e.

Here's the result. Read it and weep.

We find that the cumulative warming capacity of concurrent biogenic methane and nitrous oxide emissions is a factor of about two larger than the cooling effect resulting from the global land carbon dioxide uptake from 2001 to 2010. This results in a net positive cumulative impact of the three greenhouse gases on the planetary energy budget, with a best estimate (in petagrams of CO 2 equivalent per year) of 3.9 ± 3.8 (top down) and 5.4 ± 4.8 (bottom up) based on the GWP100 metric (global warming potential on a 100-year time horizon).

Long story short, due to human activity, mostly land use, the terrestrial biosphere is a net source of greenhouse gases expressed in CO 2 -equivalence.

That's a Big Deal because for a long time now scientists have thought of the terrestrial biosphere as a carbon sink (net absorber of anthropogenic carbon emissions, e.g., trees take up carbon). That's still true in terms of carbon dioxide alone, but when you add in methane and nitrous oxide, the terrestrial biosphere becomes a greenhouse gas source, not a sink (pictured below).

As of 2013, we were at 478 CO 2 e parts-per-million (ppm) in the atmosphere if you include all greenhouse gases. It's hard to believe that this kind of GHG accounting has never been done before.

Here's the last part of the abstract.

Our findings suggest that a reduction in agricultural methane and nitrous oxide emissions, particularly in Southern Asia, may help mitigate climate change.

Good luck with that.