Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data.

Area of Science:

• Paleoclimatology
• Climate Science
• Earth System Science

Background:

• Understanding past climate variability is crucial for contextualizing current climate change.
• Millennial-scale climate reconstructions inform natural climate variability and anthropogenic forcing.
• Previous reconstructions often relied on annual to decadal resolution data, potentially missing multicentennial trends.

Observation:

• A novel reconstruction of Northern Hemisphere temperatures for the past 2,000 years was developed.
• This reconstruction integrates low-resolution proxy data (lake/ocean sediments) with high-resolution tree-ring data.
• A wavelet transform technique was employed for timescale-dependent data processing.

Findings:

• The reconstruction reveals greater multicentennial temperature variability than most prior multi-proxy studies.
• Peak temperatures around 1000-1100 AD were similar to pre-1990 20th-century levels.
• Minimum temperatures around 1600 AD were approximately 0.7 K below the 1961-90 average.

Implications:

• The findings highlight a significant role for natural multicentennial climate variability.
• This natural variability is likely to persist, influencing future climate patterns.
• The results provide a valuable long-term perspective for climate modeling and prediction.