North Atlantic meltwater during Heinrich Stadial 1 drives wetter climate with more atmospheric rivers in western North America.

Atmospheric rivers (ARs) bring concentrated rainfall and flooding to the western United States (US) and are hypothesized to have supported sustained hydroclimatic changes in the past. However, their ephemeral nature makes it challenging to document ARs in climate models and estimate their contribution to hydroclimate changes recorded by time-averaged paleoclimate archives. We present new climate model simulations of Heinrich Stadial 1 (HS1; 16,000 years before the present), an interval characterized by widespread wetness in the western US, that demonstrate increased AR frequency and winter precipitation sourced from the southeastern North Pacific.

Tropical mountain ice core δO: A Goldilocks indicator for global temperature change.

Very high tropical alpine ice cores provide a distinct paleoclimate record for climate changes in the middle and upper troposphere. However, the climatic interpretation of a key proxy, the stable water oxygen isotopic ratio in ice cores (δO), remains an outstanding problem. Here, combining proxy records with climate models, modern satellite measurements, and radiative-convective equilibrium theory, we show that the tropical δO is an indicator of the temperature of the middle and upper troposphere, with a glacial cooling of -7.

Deciphering local and regional hydroclimate resolves contradicting evidence on the Asian monsoon evolution.

The winter and summer monsoons in Southeast Asia are important but highly variable sources of rainfall. Current understanding of the winter monsoon is limited by conflicting proxy observations, resulting from the decoupling of regional atmospheric circulation patterns and local rainfall dynamics. These signals are difficult to decipher in paleoclimate reconstructions.

Two annual cycles of the Pacific cold tongue under orbital precession.

The Pacific cold tongue annual cycle in sea surface temperature is presumed to be driven by Earth's axial tilt (tilt effect), and thus its phasing should be fixed relative to the calendar. However, its phase and amplitude change dramatically and consistently under various configurations of orbital precession in several Earth System models. Here, we show that the cold tongue possesses another annual cycle driven by the variation in Earth-Sun distance (distance effect) from orbital eccentricity.

Past climates inform our future.

As the world warms, there is a profound need to improve projections of climate change. Although the latest Earth system models offer an unprecedented number of features, fundamental uncertainties continue to cloud our view of the future. Past climates provide the only opportunity to observe how the Earth system responds to high carbon dioxide, underlining a fundamental role for paleoclimatology in constraining future climate change.

Past and future decline of tropical pelagic biodiversity.

A major research question concerning global pelagic biodiversity remains unanswered: when did the apparent tropical biodiversity depression (i.e., bimodality of latitudinal diversity gradient [LDG]) begin? The bimodal LDG may be a consequence of recent ocean warming or of deep-time evolutionary speciation and extinction processes.

Response to Comment on "Long-term climate forcing by atmospheric oxygen concentrations".

Goldblatt argues that a decrease in pressure broadening of absorption lines in an atmosphere with low oxygen leads to an increase in outgoing longwave radiation and atmospheric cooling. We demonstrate that cloud and water vapor feedbacks in a global climate model compensate for these decreases and lead to atmospheric warming.

CLIMATE CHANGE. Long-term climate forcing by atmospheric oxygen concentrations.

The percentage of oxygen in Earth's atmosphere varied between 10% and 35% throughout the Phanerozoic. These changes have been linked to the evolution, radiation, and size of animals but have not been considered to affect climate. We conducted simulations showing that modulation of the partial pressure of oxygen (pO2), as a result of its contribution to atmospheric mass and density, influences the optical depth of the atmosphere.