A new reconstruction of Southern Hemisphere temperature for the last one thousand years, which uses almost double the number of records of previous attempts, highlights the difference in temperature fluctuations between the Northern and Southern hemispheres. This analysis, published in a Letter in Nature Climate Change this week, reports that the current (post-1974) warm phase is the only period during the past millennium when both hemispheres experienced synchronous warm anomalies.

The paleoclimate temperature record is dominated by Northern Hemisphere reconstructions. Raphael Neukom and colleagues used 277 terrestrial and 48 marine records from the Southern Hemisphere to reconstruct the temperature fluctuations for the years 1000-2000 and compared this with both published Northern Hemisphere reconstructions and the instrumental record since 1850. The authors find that the Northern Hemisphere had a greater temperature variation range, compared with the Southern Hemisphere, over the years 1000-1850.

These results suggest that climate models currently overestimate the correlation between Northern Hemisphere-Southern Hemisphere temperatures by underestimating internal variability, such as the role of ocean-atmosphere dynamics in the ocean-dominated Southern Hemisphere. These effects buffer temperature changes, which are delayed relative to the Northern Hemisphere, but there is no consistent lag period. They propose that internal variability needs to be taken into consideration for climate predictions.