Abstract Stomata characteristics of two extinct conifer Cheirolepidiaceae species, Pseudofrenelopsis gansuensis and Pseudofrenelopsis dalatzensis , were used to reconstruct the atmospheric carbon dioxide concentration levels during the late Albian of the Cretaceous. A sequence of fossil samples was collected from five beds in the Dalazi Formation in the Zhixin and Luozigou basins of Jilin Province, northeastern China. The stomatal index was used to estimate the palaeo- p CO 2. The average stomatal index value of the two species was 4.1 and the atmospheric CO 2 content was c. 1200 ppmv by the average of Recent standardization and Carboniferous standardization. During the short interval from 104.8 ± 0.5 Ma to 104.0 ± 0.4 Ma in the late Albian, the atmospheric CO 2 content presents a decreasing tendency, with the highest value being c. 1300 ppmv in the Luozigou Basin. In addition, the higher atmospheric CO 2 values of the late Albian are likely linked to a ‘greenhouse climate’ during the time of Oceanic Anoxic Event 1c (OAE1c).

Abstract Permafrost is ground (soil or rock and included ice and organic material) that remains at or below 0 °C for at least two consecutive years. Permafrost terrain consists of an “active layer” at the surface that freezes and thaws each year, underlain by perennially frozen ground. The top of permafrost is at the base of this active layer. The base of permafrost occurs where the ground temperature rises above 0 °C at depth ( Osterkamp and Burn, 2002 ). In some cases, temperature measurements over a period of two years are required to determine the presence or absence of permafrost. Temperature measurements are also required to determine the status of the permafrost. Permafrost that is warm and/or warming is in danger of thawing. Approximately 25% of the exposed land area of Earth and ~80% of Alaska are underlain by permafrost. Mountain permafrost occurs at high elevations in western North America and on Mount Washington in New Hampshire. Permafrost has also been found near the summit of Mauna Kea in Hawaii. Permafrost is a product of cold climates. The first permafrost on earth must have existed prior to or formed coincidentally with the first glaciation, ~2.3 billion years ago. Permafrost occurrences, distribution, and thicknesses must have increased during periods of cold climates and decreased during warm intervals. Permafrost may have disappeared in the Arctic ~50 million years ago. The current permafrost in Alaska appears to have been initiated during the climatic cooling that began ~2.5 million years ago. During the past