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A spectroscopic comparison of ten hot-Jupiter exoplanets reveals that the difference between the planetary radius measured at optical and infrared wavelengths allows atmosphere types ranging from clear to cloudy to be distinguished; the difference in radius at a given wavelength correlates with the spectral strength of water at that wavelength, suggesting that haze obscures the signal from water. Diversity in the air on hot Jupiters David Sing et al . present a set of ten broadband exoplanet spectra from Hubble Space Telescope and Spitzer observations that resolve both the optical scattering and infrared molecular absorption spectroscopically. They find that the difference between the planetary radius measured at optical and infrared wavelengths provides a metric that can distinguish between different atmospheric types. Significantly, strong water absorption lines are seen in clear-atmosphere planets, while the weakest features are associated with clouds and hazes, strongly arguing against primordial water depletion during formation, and indicating that clouds and hazes are the cause of weaker spectral signatures. These results clarify the diversity seen in hot Jupiters and illustrate the interplay of clouds, hazes and metallicity in exoplanet atmospheres. Thousands of transiting exoplanets have been discovered, but spectral analysis of their atmospheres has so far been dominated by a small number of exoplanets and data spanning relatively narrow wavelength ranges (such as 1.1–1.7 micrometres). Recent studies show that some hot-Jupiter exoplanets have much weaker water absorption features in their near-infrared spectra than predicted 1 , 2 , 3 , 4 , 5 . The low amplitude of water signatures could be explained by very low water abundances 6 , 7 , 8 , which may be a sign that water was depleted in the protoplanetary disk at the planet’s formation location 9 , but it is unclear whether this level of depletion can actually occur. Alternatively, these weak signals could be the result of obscuration by clouds or hazes 1 , 2 , 3 , 4 , as found in some optical spectra 3 , 4 , 10 , 11 . Here we report results from a comparative study of ten hot Jupiters covering the wavelength range 0.3–5 micrometres, which allows us to resolve both the optical scattering and infrared molecular absorption spectroscopically. Our results reveal a diverse group of hot Jupiters that exhibit a continuum from clear to cloudy atmospheres. We find that the difference between the planetary radius measured at optical and infrared wavelengths is an effective metric for distinguishing different atmosphere types. The difference correlates with the spectral strength of water, so that strong water absorption lines are seen in clear-atmosphere planets and the weakest features are associated with clouds and hazes. This result strongly suggests that primordial water depletion during formation is unlikely and that clouds and hazes are the cause of weaker spectral signatures.

The Eocene–Oligocene transition (EOT) was a climate shift from a largely ice-free greenhouse world to an icehouse climate, involving the first major glaciation of Antarctica and global cooling occurring ∼34 million years ago (Ma) and lasting ∼790 kyr. The change is marked by a global shift in deep-sea δ18O representing a combination of deep-ocean cooling and growth in land ice volume. At the same time, multiple independent proxies for ocean temperature indicate sea surface cooling, and major changes in global fauna and flora record a shift toward more cold-climate-adapted species. The two principal suggested explanations of this transition are a decline in atmospheric CO2 and changes to ocean gateways, while orbital forcing likely influenced the precise timing of the glaciation. Here we review and synthesise proxy evidence of palaeogeography, temperature, ice sheets, ocean circulation and CO2 change from the marine and terrestrial realms. Furthermore, we quantitatively compare proxy records of change to an ensemble of climate model simulations of temperature change across the EOT. The simulations compare three forcing mechanisms across the EOT: CO2 decrease, palaeogeographic changes and ice sheet growth. Our model ensemble results demonstrate the need for a global cooling mechanism beyond the imposition of an ice sheet or palaeogeographic changes. We find that CO2 forcing involving a large decrease in CO2 of ca. 40 % (∼325 ppm drop) provides the best fit to the available proxy evidence, with ice sheet and palaeogeographic changes playing a secondary role. While this large decrease is consistent with some CO2 proxy records (the extreme endmember of decrease), the positive feedback mechanisms on ice growth are so strong that a modest CO2 decrease beyond a critical threshold for ice sheet initiation is well capable of triggering rapid ice sheet growth. Thus, the amplitude of CO2 decrease signalled by our data–model comparison should be considered an upper estimate and perhaps artificially large, not least because the current generation of climate models do not include dynamic ice sheets and in some cases may be under-sensitive to CO2 forcing. The model ensemble also cannot exclude the possibility that palaeogeographic changes could have triggered a reduction in CO2.

Abstract The Piacenzian stage of the Pliocene (2.6 to 3.6 Ma) is the most recent past interval of sustained global warmth with mean global temperatures markedly higher (by ~2–3 °C) than today. Quantifying CO 2 levels during the mid-Piacenzian Warm Period (mPWP) provides a means, therefore, to deepen our understanding of Earth System behaviour in a warm climate state. Here we present a new high-resolution record of atmospheric CO 2 using the δ 11 B-pH proxy from 3.35 to 3.15 million years ago (Ma) at a temporal resolution of 1 sample per 3–6 thousand years (kyrs). Our study interval covers both the coolest marine isotope stage of the mPWP, M2 (~3.3 Ma) and the transition into its warmest phase including interglacial KM5c (centered on ~3.205 Ma) which has a similar orbital configuration to present. We find that CO 2 ranged from $${{\\bf{394}}}_{{\\boldsymbol{-}}{\\bf{9}}}^{{\\boldsymbol{+}}{\\bf{34}}}$$ 394 − 9 + 34 ppm to $${{\\bf{330}}}_{{\\boldsymbol{-}}{\\bf{21}}}^{{\\boldsymbol{+}}{\\bf{14}}}$$ 330 − 21 + 14 ppm: with CO 2 during the KM5c interglacial being $${{\\bf{391}}}_{{\\boldsymbol{-}}{\\bf{28}}}^{{\\boldsymbol{+}}{\\bf{30}}}$$ 391 − 28 + 30 ppm (at 95% confidence). Our findings corroborate the idea that changes in atmospheric CO 2 levels played a distinct role in climate variability during the mPWP. They also facilitate ongoing data-model comparisons and suggest that, at present rates of human emissions, there will be more CO 2 in Earth’s atmosphere by 2025 than at any time in at least the last 3.3 million years.

The Sahara is the largest hot desert on Earth. Yet the timing of its inception and its response to climatic forcing is debated, leading to uncertainty over the causes and consequences of regional aridity. Here we present detailed records of terrestrial inputs from Africa to North Atlantic deep-sea sediments, documenting a long and sustained history of astronomically paced oscillations between a humid and arid Sahara from over 11 million years ago. We show that intervals of strong dust emissions from the heart of the continent predate both the intensification of Northern Hemisphere glaciation and the oldest land-based evidence for a Saharan desert by millions of years. We find no simple long-term gradational transition towards an increasingly arid climate state in northern Africa, suggesting that aridity was not the primary driver of gradual Neogene expansion of African savannah C 4 grasslands. Instead, insolation-driven wet–dry shifts in Saharan climate were common over the past 11 Myr, and we identify three distinct stages in the sensitivity of this relationship. Our data provide context for evolutionary outcomes on Africa; for example, we find that astronomically paced arid intervals predate the oldest fossil evidence of hominid bipedalism by at least 4 Myr. Pulses of Saharan dust have been entering the North Atlantic since at least 11 Ma, a result of astronomically paced cycles between arid and humid conditions in northern Africa, according to a terrigenous input record from an ocean core off west Africa.

RNA interference (RNAi) is a powerful tool for post-transcriptional gene silencing. However, the siRNA guide strand may bind unintended off-target transcripts via partial sequence complementarity by a mechanism closely mirroring micro RNA (miRNA) silencing. To better understand these off-target effects, we investigated the correlation between sequence features within various subsections of siRNA guide strands, and its corresponding target sequences, with off-target activities. Our results confirm previous reports that strength of base-pairing in the siRNA seed region is the primary factor determining the efficiency of off-target silencing. However, the degree of downregulation of off-target transcripts with shared seed sequence is not necessarily similar, suggesting that there are additional auxiliary factors that influence the silencing potential. Here, we demonstrate that both the melting temperature (Tm) in a subsection of siRNA non-seed region, and the GC contents of its corresponding target sequences, are negatively correlated with the efficiency of off-target effect. Analysis of experimentally validated miRNA targets demonstrated a similar trend, indicating a putative conserved mechanistic feature of seed region-dependent targeting mechanism. These observations may prove useful as parameters for off-target prediction algorithms and improve siRNA 'specificity' design rules.

Atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks; these feedbacks involve the erosion of silicate rocks and organic-carbon-bearing rocks. The integrated effect of these processes is reflected in the calcium carbonate compensation depth, which is the oceanic depth at which calcium carbonate is dissolved. Here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial Pacific Ocean. The carbonate compensation depth tracks long-term ocean cooling, deepening from 3.0–3.5 kilometres during the early Cenozoic (approximately 55 million years ago) to 4.6 kilometres at present, consistent with an overall Cenozoic increase in weathering. We find large superimposed fluctuations in carbonate compensation depth during the middle and late Eocene. Using Earth system models, we identify changes in weathering and the mode of organic-carbon delivery as two key processes to explain these large-scale Eocene fluctuations of the carbonate compensation depth. A detailed reconstruction of the calcium carbonate compensation depth—at which calcium carbonate is dissolved—in the equatorial Pacific Ocean over the past 53 million years shows that it tracks ocean cooling, increasing as the ocean cools. A history of carbon cycles and climate change The carbonate compensation depth — the oceanic depth at which carbonate is dissolved — reflects the amount of carbon dioxide present in the atmosphere, and thus gives clues about climate on geological timescales. This paper reports a detailed reconstruction of the carbonate compensation depth in the equatorial Pacific over the past 53 million years. The compensation depth is found to track ocean cooling, deepening from 3.0–3.5 kilometres during the early Cenozoic (56–53 million years ago) to 4.6 kilometres today. Rapid fluctuations observed in the carbonate compensation depth around 46–34 million years ago could be explained, in part, by changes in weathering and in the type of organic carbon supplied to the sea floor.

Plumes of mineral dust in East Asia deleteriously impact the health and livelihoods of hundreds of millions of people in Mongolia, China, Korea, and Japan and perturb Earth’s energy balance and climate. However, the sources of this dust are not well-documented, limiting understanding of dust emissions. Here, we systematically quantify dust source activation frequency (DSAF) across East Asia (80–130° E; 27–52° N) between January 2016 and December 2023. Our data reveal a vast dust-active area extending from the Tibetan Plateau (TP) in the southwest to the Huin Bair Sandy Land in the northeast, but two regions dominate: southern sources centered on the margins of the Taklimakan Desert and northern ones centered on the valleys of the Gobi Desert. East Asia is most dust-active in boreal spring (46% of all recorded events). This seasonal peak is pronounced in northern sources where snow cover, vegetation and orographic/topographic influence on winds are clear controls on DSAF. The main southern sources are active year-round with DSAF hotspots attributable to desiccated lakes and riverbeds. The TP, commonly considered a sink for in-bound windblown dust, is also a dust source, particularly in winter, with emissions controlled by precipitation patterns, snow cover and wind funneling through deep river gorges. Contrary to suggestions, our data show that the Loess Plateau is not a major dust source. We document a marked increase in dust source activation during the 2020 extreme heat wave on the overgrazed Mongolian Plateau grasslands. Our data provide a framework to study past variability in the two-way climate interactions that control dust emissions on historical and geological timescales and a baseline from which to measure future change.

Earth’s obliquity and eccentricity cycles are strongly imprinted on Earth’s climate and widely used to measure geological time. However, the record of these imprints on the oxygen isotope record in deep-sea benthic foraminifera (δ18Ob) shows contradictory signals that violate isotopic principles and cause controversy over climate-ice sheet interactions. Here, we present a δ18Ob record of high fidelity from International Ocean Drilling Program (IODP) Site U1406 in the northwest Atlantic Ocean. We compare our record to other records for the time interval between 28 and 20 million years ago, when Earth was warmer than today, and only Antarctic ice sheets existed. The imprint of eccentricity on δ18Ob is remarkably consistent globally whereas the obliquity signal is inconsistent between sites, indicating that eccentricity was the primary pacemaker of land ice volume. The larger eccentricity-paced early Antarctic ice ages were vulnerable to rapid termination. These findings imply that the self-stabilizing hysteresis effects of large land-based early Antarctic ice sheets were strong enough to maintain ice growth despite consecutive insolation-induced polar warming episodes. However, rapid ice age terminations indicate that resistance to melting was weaker than simulated by numerical models and regularly overpowered, sometimes abruptly.

Anthropogenic carbon dioxide emissions are forcing rapid ocean chemistry changes and causing ocean acidification (OA), which is of particular significance for calcifying organisms, including planktonic coccolithophores. Detailed analysis of coccolithophore skeletons enables comparison of calcite production in modern and fossil cells in order to investigate biomineralization response of ancient coccolithophores to climate change. Here we show that the two dominant coccolithophore taxa across the Paleocene–Eocene Thermal Maximum (PETM) OA global warming event (~56 million years ago) exhibited morphological response to environmental change and both showed reduced calcification rates. However, only Coccolithus pelagicus exhibits a transient thinning of coccoliths, immediately before the PETM, that may have been OA-induced. Changing coccolith thickness may affect calcite production more significantly in the dominant modern species Emiliania huxleyi , but, overall, these PETM records indicate that the environmental factors that govern taxonomic composition and growth rate will most strongly influence coccolithophore calcification response to anthropogenic change. Calcifying organisms such as planktonic coccolithophores may be particularly vulnerable to increased ocean acidification. Here, O’Dea et al. show that two fossil coccolithophore species exhibited reduced calcification rates during a global warming acidification event 56 million years ago.

The ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth. At present, this depth is ∼4,500 m, with some variation between and within ocean basins. The calcite compensation depth is linked to ocean acidity, which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate 1 . Geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the Eocene/Oligocene boundary (∼ 34 million years ago) 2 when significant permanent ice sheets first appeared on Antarctica 3 , 4 , 5 , 6 , but the relationship between these two events is poorly understood. Here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical Pacific Ocean that cover the Eocene/Oligocene boundary. We find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40,000 years each, synchronous with the stepwise onset of Antarctic ice-sheet growth. The glaciation was initiated, after climatic preconditioning 7 , by an interval when the Earth's orbit of the Sun favoured cool summers. The changes in oxygen-isotope composition across the Eocene/Oligocene boundary are too large to be explained by Antarctic ice-sheet growth alone and must therefore also indicate contemporaneous global cooling and/or Northern Hemisphere glaciation.