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. 2010 Jan 26;107(4):1295-300.
doi: 10.1073/pnas.0913846107. Epub 2010 Jan 7.

Changes in Arctic vegetation amplify high-latitude warming through the greenhouse effect

Abigail L Swann  1 , Inez Y Fung, Samuel Levis, Gordon B Bonan, Scott C Doney
Affiliations

Changes in Arctic vegetation amplify high-latitude warming through the greenhouse effect

Abigail L Swann et al. Proc Natl Acad Sci U S A. .

Abstract

Arctic climate is projected to change dramatically in the next 100 years and increases in temperature will likely lead to changes in the distribution and makeup of the Arctic biosphere. A largely deciduous ecosystem has been suggested as a possible landscape for future Arctic vegetation and is seen in paleo-records of warm times in the past. Here we use a global climate model with an interactive terrestrial biosphere to investigate the effects of adding deciduous trees on bare ground at high northern latitudes. We find that the top-of-atmosphere radiative imbalance from enhanced transpiration (associated with the expanded forest cover) is up to 1.5 times larger than the forcing due to albedo change from the forest. Furthermore, the greenhouse warming by additional water vapor melts sea-ice and triggers a positive feedback through changes in ocean albedo and evaporation. Land surface albedo change is considered to be the dominant mechanism by which trees directly modify climate at high-latitudes, but our findings suggest an additional mechanism through transpiration of water vapor and feedbacks from the ocean and sea-ice.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Map showing the land area converted to broad-leaf deciduous trees in V-FO and V-IO in units of 104 km2. The converted area totals 3,000,000 km2.
Fig. 2.
Fig. 2.
(A) The anomaly (ΔV - IO) in near-surface atmospheric temperature in degrees Celcius (deg C) between a model experiment where trees are introduced on bare ground north of 60 °N and a corresponding control run with no added trees. (B) The same as (A) for column water vapor in percent. (C) The difference δ(ΔV - IO-ΔV-FO) in near-surface atmospheric temperature in deg C between two anomalies where trees are introduced on bare ground north of 60 °N, one with an interactive ocean model (V-IO), and the other with fixed ocean and sea-ice (V-FO). (D) The same as (C) for column water vapor in percent.
Fig. 3.
Fig. 3.
(A) Albedo anomalies averaged over land area north of 60 °N (Green solid line), ocean area north of 60 °N (Blue dashed line). Plus signs represent results from the interactive ocean model (ΔV - IO) and open circles represent results from the fixed ocean model (ΔV-FO). (B) Same as for (A) for latent heat flux anomalies and transpiration averaged over land area north of 60 °N (Red dashed-dot line).
Fig. 4.
Fig. 4.
The top-of-atmosphere net radiative imbalance (ΔF) caused by adding trees. Terms shown (from Left to Right) are ΔF due to changes in land albedo, water vapor changes from evapo-transpiration (ET), ocean albedo, water vapor changes from ocean evaporation (OE). The total value of each column shows the full ΔF from ΔV - IO. The dark color shows the direct response of ΔV-FO and the light color shows the additional feedback δ(ΔV - IO-ΔV-FO) when the ocean and sea-ice are allowed to respond.
Fig. 5.
Fig. 5.
Diagram representing the response and feedback of vegetation and sea-ice processes on climate at high-northern latitudes.
See this image and copyright information in PMC

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