Search Results
Mid-Pleistocene transition in glacial cycles explained by declining CO2 and regolith removal
Variations in Earth's orbit pace the glacial-interglacial cycles of the Quaternary, but the mechanisms that transform regional and seasonal variations in solar insolation into glacial-interglacial cycles are still elusive. Here, we present transient simulations of coevolution of climate, ice sheets, and carbon cycle over the past 3 million years. We show that a gradual lowering of atmospheric CO2 and regolith removal are essential to reproduce the evolution of climate variability over the Quaternary. The long-term CO2 decrease leads to the initiation of Northern Hemisphere glaciation and an increase in the amplitude of glacial-interglacial variations, while the combined effect of CO2 decline and regolith removal controls the timing of the transition from a 41,000- to 100,000-year world. Our results suggest that the current CO2 concentration is unprecedented over the past 3 million years and that global temperature never exceeded the preindustrial value by more than 2°C during the Quaternary.
Detecting and quantifying causal associations in large nonlinear time series datasets
Identifying causal relationships and quantifying their strength from observational time series data are key problems in disciplines dealing with complex dynamical systems such as the Earth system or the human body. Data-driven causal inference in such systems is challenging since datasets are often high dimensional and nonlinear with limited sample sizes. Here, we introduce a novel method that flexibly combines linear or nonlinear conditional independence tests with a causal discovery algorithm to estimate causal networks from large-scale time series datasets. We validate the method on time series of well-understood physical mechanisms in the climate system and the human heart and using large-scale synthetic datasets mimicking the typical properties of real-world data. The experiments demonstrate that our method outperforms state-of-the-art techniques in detection power, which opens up entirely new possibilities to discover and quantify causal networks from time series across a range of research fields. Copyright © 2019 The Authors,
Agreement between reconstructed and modeled boreal precipitation of the Last Interglacial
The last extended time period when climate may have been warmer than today was during the Last Interglacial (LIG; ca. 129 to 120 thousand years ago). However, a global view of LIG precipitation is lacking. Here, seven new LIG climate models are compared to the first global database of proxies for LIG precipitation. In this way, models are assessed in their ability to capture important hydroclimatic processes during a different climate. The models can reproduce the proxy-based positive precipitation anomalies from the preindustrial period over much of the boreal continents. Over the Southern Hemisphere, proxy-model agreement is partial. In models, LIG boreal monsoons have 42% wider area than in the preindustrial and produce 55% more precipitation and 50% more extreme precipitation. Austral monsoons are weaker. The mechanisms behind these changes are consistent with stronger summer radiative forcing over boreal high latitudes and with the associated higher temperatures during the LIG.
Stabilizing the West Antarctic Ice Sheet by surface mass deposition
There is evidence that a self-sustaining ice discharge from the West Antarctic Ice Sheet (WAIS) has started, potentially leading to its disintegration. The associated sea level rise of more than 3m would pose a serious challenge to highly populated areas including metropolises such as Calcutta, Shanghai, New York City, and Tokyo. Here, we show that the WAIS may be stabilized through mass deposition in coastal regions around Pine Island and Thwaites glaciers. In our numerical simulations, a minimum of 7400 Gt of additional snowfall stabilizes the flow if applied over a short period of 10 years onto the region (−2 mm year−1 sea level equivalent). Mass deposition at a lower rate increases the intervention time and the required total amount of snow. We find that the precise conditions of such an operation are crucial, and potential benefits need to be weighed against environmental hazards, future risks, and enormous technical challenges. Copyright © 2019 The Authors,
Gold-DNA nanosunflowers for efficient gene silencing with controllable transformation
The development of an efficient delivery system for enhanced and controlled gene interference–based therapeutics is still facing great challenges. Fortunately, the flourishing field of nanotechnology provides more effective strategies for nucleic acid delivery. Here, the triplex-forming oligonucleotide sequence and its complementary strand were used to mediate self-assembly of ultrasmall gold nanoparticles. The obtained sunflower-like nanostructures exhibited strong near-infrared (NIR) absorption and photothermal conversion ability. Upon NIR irradiation, the large-sized nanostructure could disassemble and generate ultrasmall nanoparticles modified with c-myc oncogene silencing sequence, which could directly target the cell nucleus. Moreover, the controlled gene silencing effect could be realized by synergistically controlling the preincubation time with the self-assembled nanostructure (in vitro and in vivo) and NIR irradiation time point. This study provides a new approach for constructing more efficient and tailorable nanocarriers for gene interference applications