Pacific multidecadal (50–70 year) variability instigated by volcanic forcing during the Little Ice Age (1250–1850)

The Pacific decadal oscillation (PDO) is the leading mode of decadal climate variability over the North Pacific. However, it remains unknown to what extent external forcings can influence the PDO’s periodicity and magnitude over the past 2000 years. We show that the paleo-assimilation products (LMR) and proxy data suggest a 20–40 year PDO occurred during both the Mediaeval Climate Anomaly (MCA, ~ 750–1150) and Little Ice Age (LIA, ~ 1250–1850) while a salient 50–70 year variance peak emerged during the LIA. These results are reproduced well by the CESM simulations in the all-forcing (AF) and single volcanic forcing (Vol) experiments. We show that the 20–40 year PDO is an intrinsic mode caused by internal variability but the 50–70 year PDO during the LIA is a forced mode primarily shaped by volcanic forcing. The intrinsic mode develops in tandem with tropical ENSO-like anomalies, while the forced mode develops from the western Pacific and unrelated to tropical sea surface temperature anomalies. The volcanism-induced land–sea thermal contrast may trigger anomalous northerlies over the western North Pacific (WNP), leading to reduced northward heat transport and the cooling in the Kuroshio–Oyashio Extension (KOE), generating the forced mode. A 50–70 year Atlantic multidecadal oscillation founded during the LIA under volcanic forcing may also contribute to the forced mode. These findings shed light on the interplay between the internal variability and external forcing and the present and future changes of the PDO.

Characterization of global wildfire burned area spatiotemporal patterns and underlying climatic causes

Wildfires are widespread disasters and are concurrently influenced by global climatic drivers. Due to the widespread and far-reaching influence of climatic drivers, separate regional wildfires may have similar climatic cause mechanisms. Determining a suite of global climatic drivers that explain most of the variations in different homogeneous wildfire regions will be of great significance for wildfire management, wildfire prediction, and global wildfire climatology. Therefore, this study first identified spatiotemporally homogeneous regions of burned area worldwide during 2001–2019 using a distinct empirical orthogonal function. Eight patterns with different spatiotemporal characteristics were identified. Then, the relationships between major burned area patterns and sixteen global climatic drivers were quantified based on wavelet analysis. The most significant global climatic drivers that strongly impacted each of the eight major wildfire patterns were identified. The most significant combinations of hotspots and climatic drivers were Atlantic multidecadal Oscillation-East Pacific/North Pacific Oscillation (EP/NP)-Pacific North American Pattern (PNA) with the pattern around Ukraine and Kazakhstan, El Niño/Southern Oscillation-Arctic Oscillation (AO)-East Atlantic/Western Russia Pattern (EA/WR) with the pattern in Australia, and PNA-AO-Polar/Eurasia Pattern-EA/WR with the pattern in Brazil. Overall, these results provide a reference for predicting wildfire and understanding wildfire homogeneity.

Global-scale interdecadal variability a skillful predictor at decadal-to-multidecadal timescales for Sahelian and Indian Monsoon Rainfall

In the present study, a sea surface temperature-based index named global-scale interdecadal variability (GIV) encompassing the combined variability of Atlantic multidecadal oscillation (AMO) and interdecadal Pacific oscillation (IPO) has been proposed. The warm phase of GIV exhibits a “cold AMO-like” pattern in the Atlantic basin and a “warm IPO-like” pattern in the Pacific basin. About 84% (R ~−0.914) of Sahelian and 42% (R ~−0.647) of Indian rainfall’s temporal variance is attributed to GIV, showing substantial improvement compared to the variance explained by AMO and IPO individually. The physical mechanism for GIV-rainfall teleconnection is related to a modification of the Walker circulation. Although there is a substantial degree of uncertainty in the current generation of state-of-the-art climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), some still replicate the observed GIV’s spatial structure, its teleconnection, and associated physical mechanism. The results presented herein advance our knowledge about rainfall’s interdecadal variability and have imperative ramifications for developing skillful decadal predictions.

Long-Term Lake Area Change and Its Relationship with Climate in the Endorheic Basins of the Tibetan Plateau

Lakes are sensitive indicators of climate change in the Tibetan Plateau (TP), which have shown high temporal and spatial variability in recent decades. The driving forces for the change are still not entirely clear. This study examined the area change of the lakes greater than 1 km2 in the endorheic basins of the Tibetan Plateau (EBTP) using Landsat images from 1990 to 2019, and analysed the relationships between lake area and local and large-scale climate variables at different geographic scales. The results show that lake area in the EBTP has increased significantly from 1990 to 2019 at a rate of 432.52 km2·year−1. In the past 30 years, lake area changes in the EBTP have mainly been affected by local climate variables such as precipitation and temperature. At a large scale, Indian Summer Monsoon (ISM) has correlations with lake area in western sub-regions in the Inner Basin (IB). While Atlantic Multidecadal Oscillation (AMO) has a significant connection with lake area, the North Atlantic Oscillation (NAO) does not. We also found that abnormal drought (rainfall) brought by the El Niño/La Niña events are significantly correlated with the lake area change in most sub-regions in the IB.

The Cyclical Sine Model Explanation for Climate Change

This paper will show that the global warming/climate change underway on Earth today is a totally natural occurrence with solid scientific and historical support. The Earth is currently in the upswing part of its normal temperature cycle. Very warm (Medieval Warming) and very cold (Little Ice Age) cycles have been historically documented on Earth for at least the last 3,000 years. This cyclicity has a repeated period of approximately every 1,500 years [1]. The explanation for the Earth’s temperature increases since 1850 is captured in a mathematical model called the Cyclical Sine Model. This model fits past climate cycles, measured temperatures since 1850, and correlates closely with the thousand year cyclicity of solar activity from 14C/12C ratio studies [2], and Bond [3] Atlantic drift ice cycles. This model also agrees with sunspot history, the Atlantic Multidecadal Oscillation, and the Pacific Decadal Oscillation. In addition, this model quantitively explains the time span 1945-1975 when an impending ice age was feared [4]. Earth temperatures are controlled by three solar cycles of approximately 1,000, 70, and 11 years. The Cyclical Sine Model is the best explanation for the Earth’s recent temperature increases.

Modulation of Atlantic Multidecadal Oscillation on the Interdecadal Variation of South Asian High and Somali Jet in Summer

As two important components of the Asian summer monsoon system, the intensities of South Asian High (SAH) and Somali jet (SMJ) in summer exhibit both interannual and decadal variabilities. On the interdecadal timescale, the temporal evolution of the SAH intensity is in phase with that of the SMJ intensity. By comparison, we find that both of them evolve synchronously with the Atlantic Multidecadal Oscillation (AMO), with AMO cold/warm phases corresponding to the weakening/strengthening of SAH and SMJ. Further diagnoses indicate that the interdecadal variabilities of the SAH and SMJ intensities in summer may be modulated by the AMO phase. Mechanistically, this modulation appears to be achieved via an interdecadal Silk Road pattern (SRP)-like wave train along the Asian westerly jet and Matsuno–Gill tropical atmospheric response. The cold SST anomaly over extratropical North Atlantic related to the AMO firstly induces an anomalous high over Western Europe and produces a well-organized wave train between 30°N and 60°N. The anomalous Iranian Plateau low along with the wave train path leads to a weakened SAH. Besides, the AMO-related cold SST anomalies over tropical North Atlantic cool the tropical tropospheric atmosphere through the moist adjustment process and produce a Matsuno–Gill-like atmospheric response covering the tropical Indian Ocean. Due to the Matsuno–Gill response, subsidence motion anomalies over the central tropical Indian Ocean corresponding to a result in increased lower-level divergence and upper-level convergence are excited over the tropical Indian Ocean. Finally, the tropical Indian Ocean divergence in the lower troposphere leads to the weakened summer SMJ, and the tropical Indian Ocean convergence in the upper troposphere results in the decrease and northward displacement of SAH in summer.