Tropes

ScienceDaily_2013 17422.txt

#Understanding Earths climate prior to the industrial eraclimate signals locked in the layers of glacial ice preserved in the annual growth rings of trees or fingerprinted in other so-called proxy archives such as lake sediments speleothems and corals allow researchers to quantify climate variation prior to instrumental measurements. An international research team has investigated now hundreds of these proxy records from across the globe and compared them with both simulations of the Earth s climate and instrumental measurements of temperature and precipitation. Climate extremes not always recognized in proxy archivesthe scientists learned that these proxy archives provide an incomplete record of climate variation. The annual width or density of tree-rings is influenced not only by temperature while the ring is developing but also from the climate of the past years and other factors like tree age. This makes it difficult to extract pure temperature signals from these natural archives. Importantly the researchers found out that proxy data underestimate climate fluctuations of for example air temperature over the land surface where large year-to-year variability is common. In contrast long-term trends in precipitation tend to be exaggerated by the proxy records. These findings indicate that the proxy data often result in a#oeblurry picture#of climate variation. The researchers were able to conclude from their work that short-term extreme climate events such as individual years with hot summers are captured not well by the proxy reconstructions. Temperature trends can t be used to understand rainfallinvestigations on the individual factors and processes fingerprinted in tree-ring ice-core and speleothem records are needed to develop a more accurate history and understanding of the climate system. The authors explicitly warn that proxy records that predominately reflect temperature variation should not be used to make conclusions about precipitation change and vice versa. Our results point to uncertainties in the global climate system that were recognized previously not says David Frank co-author of this study. He continues: This might be surprising because we know more about the Earth s climate now than say 20-years ago. Part of the scientific process is to confront and uncover these unknowns while developing climate reconstructions. There is still a lot of basic research needed to reduce uncertainties about how the Earth s climate system operated prior to the industrial era and how it may operate in the future. Story Source: The above story is provided based on materials by Swiss Federal Institute for Forest Snow and Landscape Research WSL. Note: Materials may be edited for content and length. Journal Reference f

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