A century of reforestation in the Eastern United States (EUS) has contributed to a cooling effect that helps explain the lack of warming in the region during the 20th century, contrasting with warming trends in much of North America. The study shows that forests in the EUS have a significant cooling effect on surface temperatures, and for the first time, it demonstrates that this benefit also extends to near-surface air temperatures. Reforestation in temperate regions can provide biophysical climate adaptation benefits by cooling surface and air temperatures, offering a complementary set of benefits: mitigating climate change by removing carbon dioxide from the atmosphere and helping with adaptation to rising temperatures by cooling surface and air temperatures over large areas. The research used new cross-scale approaches and multiple independent data sources to uncover links between reforestation and temperature responses 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. 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. 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. The study also found that the cooling effect of reforestation is most pronounced in forests around 20–40 years old, with the strongest cooling effect observed in tall forests. The results indicate that 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. The findings highlight the importance of reforestation in mitigating climate change and adapting to rising temperatures, particularly in temperate zones. The study provides a comprehensive understanding of the biophysical impacts of reforestation on temperature trends, demonstrating its potential as a key climate adaptation strategy.A century of reforestation in the Eastern United States (EUS) has contributed to a cooling effect that helps explain the lack of warming in the region during the 20th century, contrasting with warming trends in much of North America. The study shows that forests in the EUS have a significant cooling effect on surface temperatures, and for the first time, it demonstrates that this benefit also extends to near-surface air temperatures. Reforestation in temperate regions can provide biophysical climate adaptation benefits by cooling surface and air temperatures, offering a complementary set of benefits: mitigating climate change by removing carbon dioxide from the atmosphere and helping with adaptation to rising temperatures by cooling surface and air temperatures over large areas. The research used new cross-scale approaches and multiple independent data sources to uncover links between reforestation and temperature responses 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. 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. 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. The study also found that the cooling effect of reforestation is most pronounced in forests around 20–40 years old, with the strongest cooling effect observed in tall forests. The results indicate that 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. The findings highlight the importance of reforestation in mitigating climate change and adapting to rising temperatures, particularly in temperate zones. The study provides a comprehensive understanding of the biophysical impacts of reforestation on temperature trends, demonstrating its potential as a key climate adaptation strategy.