Understanding the evolution of the permafrost extent and active layer thickness (ALT) in the Northern Hemisphere (NH) is critical for global carbon flux simulation, climate change prediction, and risk assessments in engineering. The temporal variation characteristics of the permafrost extent and ALT for the NH have not been studied. We used the Kudryavtsev method, integrating a 0.5 degrees x 05 degrees spatial resolution of air temperature, soil texture, snow depth, vegetation type, volume moisture content, and organic content to simulate the distribution of permafrost extent and ALT in the NH from 1969 to 2018. The results indicated that permafrost extent decreased from 23.25 x 10(6) km(2) (average from 1969 to 1973) to 21.64 x 10(6) km(2 )(average from 2014 to 2018), with a linear rate of -0.023 x 10(6) km(2)/a. Siberia had the highest degradation rate of 0.014 x 10(6) km(2)/a , followed by Alaska, the Mongolian Plateau, the Qinghai-Tibet Plateau, Northern Canada, and Greenland, with linear rates of -0.012 x 10(6), -0.005 x 10(6), -0.004 x 10(6), -0.0014 x 10(6), and - 0.0004x 10(6) km(2)/a , respectively. The average ALT in the NH increased at a linear rate of 0.0086 m/a. Alaska and the Mongolian Plateau had the highest thickening rate of 0.024 m/a, followed by the Qinghai-Tibet Plateau, Siberia, Northern Canada, and Greenland, which had linear rates of 0.009, 0.008, 0.0072, and 0.003 m/a, respectively. The uncertainty of the results could be attributed to the inaccurate forcing data and limitations of the Kudryavtsev model. (C) 2021 Elsevier B.V. All rights reserved.

来源平台：SCIENCE OF THE TOTAL ENVIRONMENT