Global warming and the limits of linear projection

While the debate over global warming continues in the U.S.A., it appears several other countries are weighing the threat posed by climate change in the near term:

Chinese planners have been concerned since 2003 that climate change may hamper construction and stability of the Qinghai-Tibet railway, partially built over permafrost. More recently, a Chinese climatologist warned that safety of the railyay may be compromised by 2050 given current trends; i.e. assuming a linear continuation of the trend

Russian researchers have observed that large areas of frozen peat bog in Siberia are melting, threatening to release a massive amount of methane, a greenhouse gas. Such a release may have a nonlinear impact, accelerating global warming.

Linearity may not be an accurate model of what is yet to come.