Editing IPCC:AR6/SRCCL/Chapter-2 (section)

==== 2.5.3.1 Effects of changes in land cover and productivity resulting from global warming ====

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In boreal regions, the combined northward migration of the treeline and increased growing season length in response to increased temperatures in those regions (Section 2.2) will have positive feedbacks both on global and regional annual warming ( ''high confidence'' ) (Garnaud and Sushama 2015 <sup>[[#fn:r1251|1251]]</sup> ; Jeong et al. 2014a <sup>[[#fn:r1252|1252]]</sup> ; O’ishi and Abe-Ouchi 2009 <sup>[[#fn:r1253|1253]]</sup> ; Port et al. 2012 <sup>[[#fn:r1254|1254]]</sup> ; Strengers et al. 2010 <sup>[[#fn:r1255|1255]]</sup> ). The warming resulting from the decreased surface albedo remains the dominant signal in all modelling studies at the annual timescale and during the snow season, while cooling is obtained during the growing season (Section 2.5.2.1 and Figure 2.21, right panel).

In the tropics, climate change will cause both greening and browning (Section 2.2). Where global warming provokes a decrease in rainfall, the induced decrease in biomass production leads to increased local warming ( ''high confidence'' ) (Port et al. 2012 <sup>[[#fn:r1256|1256]]</sup> ; Wu et al. 2016 <sup>[[#fn:r1257|1257]]</sup> ; Yu et al. 2016 <sup>[[#fn:r1258|1258]]</sup> ). The reverse is true where warming generates increases in rainfall and thus greening. As an example, Port e tal. (2012) <sup>[[#fn:r1259|1259]]</sup> simulated decreases in tree cover and shortened growing season in the Amazon, despite the CO <sub>2</sub> fertilisation effects, in response to both future tropical warming and reduced precipitation (Figure 2.21, left panel). This browning of the land decreases both evapotranspiration and atmospheric humidity. The warming driven by the drop in evapotranspiration is enhanced via a decrease in cloudiness, increasing solar radiation, and is dampened by reduced water vapour greenhouse radiation.

There is ''very low confidence'' on how feedbacks affect rainfall in the tropics where vegetation changes may occur, as the sign of the change in precipitation depends on where the greening occurs and on the season (as discussed in Section 2.5.2). There is, however, ''high confidence'' that increased vegetation growth in the southern Sahel increases African monsoon rains (Yu et al. 2016 <sup>[[#fn:r1260|1260]]</sup> ; Port et al. 2012 <sup>[[#fn:r1261|1261]]</sup> ; Wu et al. 2016 <sup>[[#fn:r1263|1263]]</sup> ). Confidence on the direction of such feedbacks is also based on a significant number of paleoclimate studies that analysed how vegetation dynamics helped maintain a northward position of the African monsoon during the Holocene time period (9–6 kyr BP) (de Noblet-Ducoudré et al. 2000 <sup>[[#fn:r1264|1264]]</sup> ; Rachmayani et al. 2015 <sup>[[#fn:r1265|1265]]</sup> ).

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'''Figure 2.21'''

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'''Schematic illustration of the processes through which the effects of global warming in (a) the Amazon (blue arrows and boxes), and (b) boreal regions (grey arrows and boxes) feedback on the regional climate change. In boreal regions, the sign of the feedbacks depends on the season, although annually global warming is further enhanced in those […]'''
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[[File:d22ae8a9968926035f16a50fcbc1f7d9 Figure-2.21-1024x691.jpg]]

Schematic illustration of the processes through which the effects of global warming in (a) the Amazon (blue arrows and boxes), and (b) boreal regions (grey arrows and boxes) feedback on the regional climate change. In boreal regions, the sign of the feedbacks depends on the season, although annually global warming is further enhanced in those regions. Dashed lines illustrate negative feedbacks, while solid lines indicate positive feedbacks. References supporting this figure can be found in the text.

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