Data and code for: A century of reforestation reduced anthropogenic warming in the eastern United States

Restoring and preserving the world’s forests are promising natural
pathways to mitigate some aspects of climate change. In addition to
regulating atmospheric carbon dioxide concentrations, forests modify
surface and near-surface air temperatures through biophysical processes.
In the eastern United States (EUS), widespread reforestation during the
20th century coincided with an anomalous lack of warming, raising
questions about reforestation’s contribution to local cooling and climate
mitigation. Using new cross-scale approaches and multiple independent
sources of data, we uncovered links between reforestation and the response
of both surface and air temperature in the EUS. Ground- and
satellite-based observations showed that EUS forests cool the land surface
by 1–2 °C annually compared to nearby grasslands and croplands, with the
strongest cooling effect during midday in the growing season, when cooling
is 2 to 5 °C. Young forests (20–40 years) have the strongest cooling
effect on surface temperature. Surface cooling extends to the near-surface
air, with forests reducing midday air temperature by up to 1 °C compared
to nearby non-forests. Analyses of historical land cover and air
temperature trends showed that the cooling benefits of reforestation
extend across the landscape. Locations surrounded by reforestation were up
to 1 °C cooler than neighboring locations that did not undergo land cover
change, and areas dominated by regrowing forests were associated with
cooling temperature trends in much of the EUS. Our work indicates
reforestation contributed to the historically slow pace of warming in the
EUS, underscoring reforestation’s potential as a local climate adaptation
strategy in temperate regions.

修复与保护全球森林，是缓解气候变化部分影响的极具前景的自然路径。除调节大气二氧化碳浓度外，森林还可通过生物物理过程改变地表及近地表气温。美国东部（Eastern United States, EUS）在20世纪曾开展大规模再造林运动，同期却出现了异常的增温停滞现象，这引发了学界关于再造林对局地降温及气候缓解的贡献的疑问。本研究采用全新的跨尺度研究方法，并依托多组独立数据源，揭示了美国东部再造林与地表及气温响应之间的关联。基于地面与卫星的观测结果显示，与周边草地和农田相比，美国东部的森林可使地表年均降温1~2℃，在生长季正午时段降温效果最为显著，可达2~5℃。林龄20~40年的幼龄林对地表温度的降温效果最强。地表降温效应可延伸至近地表大气，与周边非林区相比，森林可使正午气温最高降低1℃。对历史土地覆被与气温趋势的分析表明，再造林的降温效益覆盖整个研究区域。被再造林覆盖的区域，较未发生土地覆被变化的邻近区域最高可降温1℃；而在美国东部大部分区域，以再生林为主的区域均伴随气温降温趋势。本研究表明，再造林是美国东部历史增温速率偏缓的成因之一，这也凸显了再造林作为温带区域局地气候适应策略的潜力。