Continental-scale temperature variability during the past two millennia, Pages 2k consortium Not enough data in Africa

Location of the data:

Location of the data

Common feature: long term cooling trend, end 1900 All region are cooling until ~1900 then warming, except Antarctica

Cooling significant Cooling trend significant (p<0.05) except in North America when it is weakly significant (p<0.10) in tree rings, and not significant in pollen. Trend is 0.1 to 0.3°C/1000 years, also significant, except for Europe

Cooling trend to 1900 Sign (positive or negative) and statistical significance of the slope of least-squares linear regression through each site-level proxy record within the PAGES 2k data set. The fraction of records that exhibit significant (P < 0.05) or non-significant cooling trends was evaluated for records extending back different lengths in 30-year steps. The longer the record, the more likely it is to exhibit a significant long-term cooling trend. For illustration purposes, the fraction of positive trends with magnitude smaller (light red) and larger (red) than the one-sided P = 0.05 level is also included.

Cause: solar/volcanic? Potential causes: solar irradiance, volcanic, land use changes, obitally driven insolation Solar and volcanic are the most important In Arctic and Scandinavia, orbitally driven insolation is also important Southern hemisphere: summer cooling is a delayed response to the decrease in local spring insolation modulated by S. Ocean thermal inertia (Renssen, 2005)

Centenial scale variability: not uniform NH has a sustained warmth South America and Australasia is warm later, Transition to colder temp is evident in Arctic/EU/Nam starting , It is probably unforced By 1580, all regions except Antarctica are cold No uniform Medieval warm /Little ice age, instead, (unforced) centennial scale variability superimposed on a long term (forced) cooling trend. NH has a sustained warmth South America and Australasia is warm later, Transition to colder temp is evident in Arctic/EU/Nam starting , It is probably unforced By 1580, all regions except Antarctica are cold No uniform Medieval warm /Little ice age, instead, (unforced) centennial scale variability superimposed on a long term (forced) cooling trend.

Forcing Periods of most negative solar/volcanic correspond to cold temperature (P<0.01) These periods include the coldest 30 year of each reconstruction. Not all the regions cooled during the volcanic/solar downturns

20 th century 20 th century includes the warmest 30 year period in all records except Antarctica Surrounding ocean may be damping Antarctic response (Stouffer and Manabe, Nature, 1989) Excluding Antarctica, 20 th century temp is 0.4°C warmer than last 500 year average Stronger for land regions than ocean dominated regions (Australaisia, S.Am)

20 th century

20 th century is warm The proportion of warmest 30 years in individual proxy records The proportion of warmest 100 years Area weighted best estimate of past surface temperature (30-year average): is the warmest since 1400 A.D. Hard to say anything for the first millenium because of fewer data

Comparison with other methods

Conclusion Long term cooling trend visible in all records, ended in 1900 Centennial scale variability is uncorrelated, and likely unforced No uniform Medieval warm /Little ice age, instead, (unforced) centennial scale variability superimposed on a long term (forced) cooling trend. Antarctica is doing something different The last 30 years are warmer than any time since Long term cooling trend visible in all records, ended in 1900 Centennial scale variability is uncorrelated, and likely unforced No uniform Medieval warm /Little ice age, instead, (unforced) centennial scale variability superimposed on a long term (forced) cooling trend. Antarctica is doing something different The last 30 years are warmer than any time since 1400.