Extreme warming rates affecting alpine areas in SW Europe deduced from algal lipids

Alpine ecosystems of the southern Iberian Peninsula are among the most vulnerable and the first to respond to modern climate change in southwestern Europe. While major environmental shifts have occurred over the last ~ 1500 years in these alpine environments, only changes in the recent centuries have led to extreme responses, but factors imposing the strongest stress have been unclear until now. To understand these environmental responses, here, for the first time, we calibrated algal lipids (long-chain diols) to instrumental data extending alpine temperatures backward 1500 years. These novel results highlight the enhanced effect of greenhouse gases on alpine temperatures during the last ~ 200 years and the long-term modulating role of solar forcing. This study also shows that warming rates during the 20th century (~ 0.18 ºC/decade) increased ~ 2.5 times with respect to the last stage of the Little Ice Age (~ 0.07 ºC/decade), even exceeding temperature trends of the high-altitude Alps during the 20th century. As a consequence, temperature exceeded the pre-industrial threshold in the 1950s, being one of the major forcings of the enhanced recent change in the alpine ecosystems from southern Iberia. Nevertheless, other factors reducing the snow and ice albedo (i.e. atmospheric deposition) may have influenced local glacier loss, since steady climate conditions predominated from middle 19th century to the first decades of the 20th century.