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Earth has had oceans for nearly four billion years.sup.1 and Mars had lakes and rivers 3.5-3.8 billion years ago.sup.2. However, it is still unknown whether water has ever condensed on the surface of Venus.sup.3,4 because the planet--now completely dry.sup.5--has undergone global resurfacing events that obscure most of its history.sup.6,7. The conditions required for water to have initially condensed on the surface of Solar System terrestrial planets are highly uncertain, as they have so far only been studied with one-dimensional numerical climate models.sup.3 that cannot account for the effects of atmospheric circulation and clouds, which are key climate stabilizers. Here we show using three-dimensional global climate model simulations of early Venus and Earth that water clouds--which preferentially form on the nightside, owing to the strong subsolar water vapour absorption--have a strong net warming effect that inhibits surface water condensation even at modest insolations (down to 325 watts per square metre, that is, 0.95 times the Earth solar constant). This shows that water never condensed and that, consequently, oceans never formed on the surface of Venus. Furthermore, this shows that the formation of Earth's oceans required much lower insolation than today, which was made possible by the faint young Sun. This also implies the existence of another stability state for present-day Earth: the 'steam Earth', with all the water from the oceans evaporated into the atmosphere. Global climate model simulations of early Venus and Earth show that differences in the cloud regimes prevented ocean formation on Venus but not on Earth., Author(s): Martin Turbet [sup.1] , Emeline Bolmont [sup.1] , Guillaume Chaverot [sup.1] , David Ehrenreich [sup.1] , Jérémy Leconte [sup.2] , Emmanuel Marcq [sup.3] Author Affiliations: (1) Observatoire astronomique de [...]

Australian scientists are rushing to develop new technologies -- such as ways to block sunlight -- to help preserve corals in the face of climate change. Australian scientists are rushing to develop new technologies -- such as ways to block sunlight -- to help preserve corals in the face of climate change., Author(s): Jeff Tollefson Author Affiliations: During a field trial, a turbine generates plumes of seawater droplets that rise into the sky. Credit: Brendan Kelaher/SCU A boat using the sea-spraying cloud [...]

Known sources of formic acid could not explain the observed atmospheric concentrations of this compound. The discovery of a previously unknown pathway that generates formic acid in the atmosphere resolves this discrepancy. Pathway to atmospheric formic acid from formaldehyde in cloud droplets., Author(s): Joost de Gouw, Delphine Farmer Author Affiliations: Cloud droplets aid the production of formic acid in the atmosphere Formic acid is one of the simplest and most abundant organic [...]

Planting forests outside the tropics can sequester carbon and counteract global warming. Planting forests outside the tropics can sequester carbon and counteract global warming., Author Affiliations: Clouds above temperate forests can help to reduce local temperatures. Credit: Johner Images/Alamy Pine trees silhouetted against an evening sky filled with white fluffy clouds. Clouds plus trees [...]

Melting of the world's major ice sheets can affect human and environmental conditions by contributing to sea-level rise. In July 2012, an historically rare period of extended surface melting was [...]

The summer average local-noon ultraviolet radiation (UVR) trends responsible for mammalian skin cancer or plant damage will be considerable in the temperate areas by the end of the 20th century due to insufficient cloud cover. The trends in UVR obtained from estimated trends in total ozone availability are compared with the considerable changes in UVR because of changes in cloud opacity. The total ozone abundance and cloud reflectance are obtained from global satellite measurements.

A study of ozone depletion and its effect on climate showed that ozone depletion can bring out radiative forcing of climate due to its influence on the atmospheric oxidation state. The OH concentration in the atmosphere, which is regulated by the ozone level, directly affects the cloud albedo as it plays a major role in the formation of cloud condensation nuclei. The increase in OH concentration caused due to ozone depletion can result in an increase in droplet number and a decrease in droplet radius, leading to climate forcing.

The extent to which aerosols affect climate is highly uncertain. Observations of clouds interacting with aerosols from a volcanic eruption suggest that the effect is much smaller than was once feared. See Article (https://www.nature.com/articles/nature22974) Volcanic eruption exposes aerosol-cloud interactions Aerosols cast a wide shadow across many aspects of the Earth system. They reflect solar radiation, increase snow and ice melt, and contribute to local air pollution. Aerosols also interact with clouds, but the net effect of these interactions is difficult to disentangle from coinciding meteorological variations. Sulfate aerosols tend to increase reflection, and theoretical principles state that aerosols should lead to more but smaller cloud particles and should increase cloud lifetime and liquid water path. However, firm confirmation of these indirect effects has been hard to come by. Now, Florent Malavelle et al. use observations and modelling to help to understand the effects of a recent volcanic eruption in Iceland. The sulfate aerosols associated with the eruption caused a discernible yet transient brightening effect, but the effects on liquid water path were negligible. This result will help to reduce uncertainties in future climate projections, because results from climate models with excessive liquid-water-path responses can now be rejected., Author(s): Bjorn Stevens [sup.1] Author Affiliations: (1) Max Planck Institute for Meteorology, Hamburg, Germany A difficult question that has preoccupied generations of climate scientists is how strongly the human contribution [...]

Uncertainty in estimates of the effects of aerosols on climate stems from poor knowledge of the past, pristine atmosphere--so getting a better understanding of these effects might not be as [...]