Deforestation in mid- to high latitudes is hypothesized to have the potential to cool the Earth’s surface by altering biophysical processes1, 2, 3. In climate models of continental-scale land clearing, the cooling is triggered by increases in surface albedo and is reinforced by a land albedo–sea ice feedback4, 5. This feedback is crucial in the model predictions; without it other biophysical processes may overwhelm the albedo effect to generate warming instead5. Ongoing land-use activities, such as land management for climate mitigation, are occurring at local scales (hectares) presumably too small to generate the feedback, and it is not known whether the intrinsic biophysical mechanism on its own can change the surface temperature in a consistent manner6, 7. Nor has the effect of deforestation on climate been demonstrated over large areas from direct observations. Here we show that surface air temperature is lower in open land than in nearby forested land. The effect is 0.85 ± 0.44 K (mean ± one standard deviation) northwards of 45° N and 0.21 ± 0.53 K southwards. Below 35° N there is weak evidence that deforestation leads to warming. Results are based on comparisons of temperature at forested eddy covariance towers in the USA and Canada and, as a proxy for small areas of cleared land, nearby surface weather stations. Night-time temperature changes unrelated to changes in surface albedo are an important contributor to the overall cooling effect. The observed latitudinal dependence is consistent with theoretical expectation of changes in energy loss from convection and radiation across latitudes in both the daytime and night-time phase of the diurnal cycle, the latter of which remains uncertain in climate models8.
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- Supplementary Information (445K)
The file contains Supplementary Text and Data, Supplementary References, Supplementary Tables 1-3 and Supplementary Figures 1-4 with legends.
- Supplementary Data 1 (277K)
This file comprises: 1 Comparison between weather station and NARR screen height temperature (annual mean, Jan mean and July mean) in NARR cells in closest proximity to the station lat/long; 2 NARR diurnal temperature range for NARR cells in closest proximity to forest eddy covariance sites; 3 Summary of temperature statistics for forests and the closest matching weather stations & summary of net radiation data for the forest sites; 4 Year-by-year summary of temperature statistics for each forest/station pair; 5 Year-by-year NARR temperature data at NARR grid matching the paired weather station; 6 Data used for energy balance / factor separation analysis; 7 Data used for analysis of sensitivity to heat storage, FLUXNET cluster a.
- Supplementary Data 2 (29K)
The file contains monthly temperature data for the site pairs including lapse rates derived from NARR.