The Pliocene Epoch (∼5.3–2.6 million years ago, Ma) was characterized by a warmer than present climate with smaller Northern Hemisphere ice sheets, and offers an example of a climate system in long-term equilibrium with current or predicted near-future atmospheric CO₂ concentrations (pCO₂). A long-term trend of ice-sheet expansion led to more pronounced glacial (cold) stages by the end of the Pliocene (∼2.6 Ma), known as the “intensification of Northern Hemisphere Glaciation” (iNHG). We assessed the spatial and temporal variability of ocean temperatures and ice-volume indicators through the late Pliocene and early Pleistocene (from 3.3 to 2.4 Ma) to determine the character of this climate transition. We identified asynchronous shifts in long-term means and the pacing and amplitude of shorter-term climate variability, between regions and between climate proxies. Early changes in Antarctic glaciation and Southern Hemisphere ocean properties occurred even during the mid-Piacenzian warm period (∼3.264–3.025 Ma) which has been used as an analog for future warming. Increased climate variability subsequently developed alongside signatures of larger Northern Hemisphere ice sheets (iNHG). Yet, some regions of the ocean felt no impact of iNHG, particularly in lower latitudes. Our analysis has demonstrated the complex, non-uniform and globally asynchronous nature of climate changes associated with the iNHG. Shifting ocean gateways and ocean circulation changes may have pre-conditioned the later evolution of ice sheets with falling atmospheric pCO₂. Further development of high-resolution, multi-proxy reconstructions of climate is required so that the full potential of the rich and detailed geological records can be realized.

中文翻译：

---

北半球冰川作用的爆发和加剧导致的气候演变

上新世（约5.3-260万年前，Ma）的特点是气候比现在温暖，北半球冰盖较小，并提供了气候系统与当前或预测的近期大气长期平衡的一个例子CO ₂浓度 ( p CO ₂）。冰盖扩张的长期趋势导致上新世末期（∼2.6 Ma）出现更明显的冰川（冷）阶段，称为“北半球冰川作用强化”（iNHG）。我们评估了上新世晚期和更新世早期（3.3 Ma 至 2.4 Ma）海洋温度和冰量指标的时空变化，以确定这一气候转变的特征。我们确定了区域之间和气候代理之间的长期手段以及短期气候变化的节奏和幅度的异步变化。南极冰川和南半球海洋特性的早期变化甚至发生在皮亚琴兹中期温暖期（∼3.264–3.025 Ma），这已被用作未来变暖的类比。随后气候变化加剧，同时出现了更大的北半球冰盖（iNHG）。然而，一些海洋区域并未感受到 iNHG 的影响，特别是在低纬度地区。我们的分析证明了与 iNHG 相关的气候变化的复杂性、不均匀性和全球异步性。海洋门户的变化和海洋环流的变化可能预先调节了冰盖后来随大气层下降的演化pCO ₂。_ 需要进一步发展高分辨率、多代理气候重建，以便充分发挥丰富而详细的地质记录的潜力。