Arctic Centre research professor Bruce Forbes has taken part in an expert assessment, published in Environmental Research Letters on 7 March 2016. The results go to the core of Arctic related climate discussion: what is actually happening with permafrost greenhouse gas releases? Are we talking about a tipping point, a time bomb or what?
Press release
Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment
published in Environmental Research Letters on 7 March 2016
• Tundra and boreal biomass may decrease in response to global warming due to drought stress, increased fire, and insect damage.
• First circumarctic projections of carbon export from rivers and
coastal erosion (nearly a doubling by 2100) and of tundra fire (3-fold
increase).
• The permafrost zone will be a net carbon source by 2100 but experts
predict 65-85% of carbon release may still be avoided if human emissions
start decreasing before 2050.
The permafrost carbon feedback has been portrayed in popular media and
to a lesser extent in peer-reviewed literature as an all-or-nothing
scenario. Permafrost greenhouse gas release has been described as a
tipping point, a runaway climate feedback, and most dramatically, a time
bomb. Though models predict that some portion of permafrost carbon
release will be offset by increased arctic and boreal biomass, estimates
of the permafrost carbon feedback vary by a factor of thirty. This
uncertainty means that permafrost carbon is currently not considered in
climate negotiations, increasing the risk of further overshooting
international emissions targets with serious societal and environmental
consequences.
Because precise empirical or model-based assessments of the critical
factors driving permafrost carbon balance are unlikely in the near
future, we used expert assessment techniques to collect quantitative
judgments from 98 permafrost-region scientists of the response of
high-latitude carbon balance to four warming scenarios. This approach is
complementary to traditional modeling techniques because it allows
consideration of a range of factors known to affect carbon balance but
insufficiently quantified for inclusion in models. For the permafrost
region these effects include nutrient dynamics, non-linear shifts in
vegetation, human disturbance, land-water interactions, and the
relationship of permafrost degradation with water balance.
Results suggest that, contrary to current model projections, total
permafrost-region biomass could decrease due to water stress and
disturbance in the boreal forest. Experts predicted major shifts in
hydrologic carbon flux and wildfire emissions, particularly for carbon
released into the ocean from collapsing coastlines and for tundra fire,
which could increase by 2- and 5-fold, respectively, by the end of the
century. In combination with previous findings, these results suggest
the permafrost region will become a carbon source to the atmosphere by
2100 regardless of warming scenario. However, because estimates of
change in biomass are similar across warming scenarios but permafrost
carbon release is strongly temperature-sensitive, the emissions gap
widens for warmer scenarios, resulting in five-times more net carbon
release under the business as usual scenario (RCP8.5) than for the
active reduction of human emissions scenario (RCP2.6). This suggests
that 65 to 85% of permafrost carbon release can still be avoided if
human emissions are rapidly reduced.
Our study does not support a runaway climate feedback scenario, but
instead indicates that the strength of the permafrost carbon feedback
depends on the amount of human emissions. That said, based on warming
events in the Eocene and the Holocene when permafrost was completely or
partially degraded, there could be a tipping point between 1.8 and 3.7°C
of warming (650 and 850 ppm CO2) after which permafrost degradation
becomes self-sustaining. What is clear from the spread of expert
responses and model simulations is that the rate and magnitude of
current warming is taking us into uncharted territory in regards to
permafrost carbon.
The article is freely downloadable at the following link: http://dx.doi.org/10.1088/1748-9326/11/3/034014
More information:
Ben Abbott on behalf of co-authors
+33624393704, benabbo(at)gmail.com