PAGES: Two Millennia Global Temperature Reconstruction confirms Hockeystick
PAGES (Past Global Changes), an international network of climate scientists has released a paper with a two millennia global temperature reconstruction (), the most sophisticated one so far. It shows a long-term little by little cooling followed by a sudden upturn over recent 100 years, a manifestation of modern global warming. Both of it is in common with earlier reconstructions. Long-lasting cooling trend was caused by decreasing angle of Earth´s axial tilt (obliquity) and by changes in volcanic and solar activity.
Global Temperature for last 2000 years from PAGES (a) compared to earlier reconstructions (b). Running count of the number of regional reconstructions (c). For each 30-year interval: Proportion of individual proxy records within each Continental-scaled region indicating highest temperature during that 30-year period (d). For each century: Proportion of individual proxy-records indicating highest temperature during that century (e). Volcanic (black) and solar (red) climate forcing (f). All climate forcings together (g). Change in summer Insolation (July, January) at 65°N/S (both hemispheres) over last 2000 years. Source: PAGES, 2013
In mid and high latitudes high obliquity implies:
1) Warm summers with increased ice melting. 2) Cold winters with decreased evaporation leading to less snowfall. As a result the polar ice sheets are shrinking!
And low obliquity: 1) Cool summers with decreased ice melting. 2) Mild winters with increased evaporation leading to intensified snowfall. As a result polar ice sheets are spreading!
Temperatures were traced back in 7 continental-scale regions using proxies, historical documents and instrumental data. Values derived from proxy-data are matching close on with modern instrumental data!
The seven Continental-scale regions and the proxies used for global temperature reconstruction. Source: PAGES, 2013
The main result of the study is:
Current global surface temperatures are higher than at any time in the past 1400 years! The hockey stick curve a result of Michael E. Mann´s pioneering global temperarature reconstruction from 1999 – attacked by climate sceptics over and over again – is effectively vindicated!
Calibration of temperatures derived from proxies with instrumental temperature record from Climate Research Unit of Hadley Centre (HadCRUT). Both curves are matching well. Source: PAGES, 2013.
Some more results:
Roman Warm Period (RWP), Medieval Warm Period (MWP) and Little Ice Age (LIA) really happened but in different regions at different times. In Europe temperature peaks in Roman Warm Period (RWP) and Medieval Warm Period exceed 30-year interval 1971-2000. A scrap of comfort for climate sceptics but is it important to note: Over the last 30-year average for 1982-2012 global temperature has risen once again (about 0,2°C) compared with average for 1970-2000!
Continental-scale temperature reconstructions depicted as colors for anomalies of a standard-period from 1190-1970. Dashed outlines enclose intervals of strong negative forcing by volcanic eruptions and weak solar activity (above). Running count of number of individual proxy records by r egion (below). Source: PAGES, 2013
Continental-scale temperature reconstructions depicted as curves for anomalies of a standard-period from 1190-1970. Instrumental data (in cyan) always for comparison. Source: PAGES, 2013
Warming in the Northern Hemisphere was twice as rapid than in the Southern Hemisphere due to ocean dampening. The portion of sea compared to landmass is higher in the latter.
The Arctic had fastest warming through ice-albedo feedback. After melt of highly reflective sea-ice sunlight is absorbed by the dark water. Surprisingly the Arctic was warmer during 1941-1970 compared to 1971-2000. I think a possible explanation for this cooling is the increased melting of sea-ice during the latter period consuming a lot of energy.
Jens Christian Heuer
Source: PAGES 2k Consortium: Continental-scale variability during the past two Millennia, NatureGeoscience, March 2013