Paleoclimatology Explained
Proxy Methods
Tree rings provide annual-resolution records spanning thousands of years. Width and density correlate with growing season conditions. Ocean sediment cores contain foraminifera shells whose isotope ratios record temperature and ice volume, spanning millions of years. Corals record tropical temperatures through skeletal chemistry. Speleothems preserve rainfall records through isotopes with precise uranium-thorium dating.
Major Discoveries
Deep-sea records confirmed regular glacial cycles paced by orbital variations (Milankovitch theory). Greenland ice cores revealed abrupt Dansgaard-Oeschger events with 8-16 degree swings in decades. The Paleocene-Eocene Thermal Maximum (56 million years ago) released massive carbon over 10,000 years, raising temperatures 5-8 degrees, the closest analog to current emissions but 10 times slower than today.
Temperature Reconstructions
Multi-proxy reconstructions show stable temperatures over the past millennium followed by sharp modern warming. Multiple independent analyses confirm recent warming is unusual in at least 2,000 years. Broader patterns are robust: warm periods correlate with high CO2, and current CO2 increase rate is unprecedented for at least 66 million years.
Multiple proxy records consistently show past warm periods had high CO2 and cold had low CO2. Current warming is unusual in 2,000+ years and CO2 increase rate is unprecedented in tens of millions of years.