much of the rest of Russian Siberia, the world's greatest temperature-variation between summer's highs and winter's lows, often well over between the seasons. Southwesterly winds bring warm air from Central Asia and the Middle East. The climate in West Siberia (Omsk, or Novosibirsk) is several degrees warmer than in the East (Irkutsk, or Chita) where in the north an extreme winter subarctic climate (Köppen Dfd or Dwd) prevails. But summer temperatures in other regions can reach . In general, Sakha is the coldest Siberian region, and the basin of the Yana has the lowest temperatures of all, with permafrost reaching . Nevertheless, Imperial Russian plans of settlement never viewed cold as an impediment. In the winter, southern Siberia sits near the center of the semi-permanent Siberian High, so winds are usually light in the winter. Precipitation in Siberia is generally low, exceeding only in Kamchatka, where moist winds flow from the Sea of Okhotsk onto high mountains – producing the region's only major glaciers, though volcanic eruptions and low summer temperatures allow only limited forests to grow. Precipitation is high also in most of Primorye in the extreme south, where monsoonal influences can produce quite heavy summer rainfall. Global warming Researchers, including Sergei Kirpotin at Tomsk State University and Judith Marquand at Oxford University, warn that Western Siberia has begun to thaw as a result of global warming. The frozen peat bogs in this region may hold billions of tons of methane gas, which may be released into the atmosphere. Methane is a greenhouse gas 22 times more powerful than carbon dioxide. In 2008 a research expedition for the American Geophysical Union detected levels of methane up to 100 times above normal in the atmosphere above the Siberian Arctic, likely the result of methane clathrates being released through holes in a frozen "lid" of seabed permafrost around the outfall of the Lena and the area between the Laptev Sea and East Siberian Sea. Since 1988, experimentation at Pleistocene Park has proposed to restore the grasslands of prehistoric times by conducting research on the effects of large herbivores on permafrost, suggesting that animals, rather than climate, maintained the past ecosystem. The nature reserve park also conducts climatic research on the changes expected from the reintroduction of grazing animals or large herbivores, hypothesizing that a transition from tundra to grassland would lead to a net change in energy emission to absorption ratios.