Could Cirrus Clouds Have Warmed Early Mars?

Could Cirrus Clouds Have Warmed Early Mars?

Authors:

Rameriz et al

Abstract:

The presence of the ancient valley networks on Mars indicates that the climate at 3.8 Ga was warm enough to allow substantial liquid water to flow on the martian surface for extended periods of time. However, the mechanism for producing this warming continues to be debated. One hypothesis is that Mars could have been kept warm by global cirrus cloud decks in a CO2-H2O atmosphere containing at least 0.25 bar of CO2 (Urata and Toon, 2013). Initial warming from some other process, e.g., impacts, would be required to make this model work. Those results were generated using the CAM 3-D global climate model. Here, we use a single-column radiative-convective climate model to further investigate the cirrus cloud warming hypothesis. Our calculations indicate that cirrus cloud decks could have produced global mean surface temperatures above freezing, but only if cirrus cloud cover approaches ~75 - 100% and if other cloud properties (e.g., height, optical depth, particle size) are chosen favorably. However, at more realistic cirrus cloud fractions, or if cloud parameters are not optimal, cirrus clouds do not provide the necessary warming, suggesting that other greenhouse mechanisms are needed.

How Volcanic Eruptions & Sulfur can Effect Clouds

It has long been suspected that sulfur emissions can brighten clouds. Water droplets tend to clump around particles of sulfuric acid, causing smaller droplets that form brighter, more reflective clouds.

But while humans have pumped sulfur into Earth's atmosphere since the Industrial Revolution, it's been hard to measure how this affects the clouds above. New University of Washington research uses a huge volcanic eruption in Iceland to measure the change.

The new study, to be published in Geophysical Research Letters, a journal of the American Geophysical Union, shows that sulfur emissions do indeed result in smaller cloud droplet size, leading to brighter clouds that reflect significantly more sunlight.

"This eruption is a chance to nail down one of the big uncertainties in climate models," said first author Daniel McCoy, a UW doctoral student in atmospheric sciences.

The study takes advantage of a unique geologic event. During six months from summer 2014 until early 2015, a crack in the Bardarbunga volcano seeped lava and sulfur gas. This was not one of Iceland's huge explosive eruptions that fill the skies with ash and shut down airplane routes. Instead it was a long, slow, low-elevation seep of sulfur emissions that produced an amount of lava second only to Laki in the recent history of Iceland eruptions.

The UW researchers looked at data for that region recorded by NASA's MODIS, or Moderate Resolution Imaging Spectroradiometer, instrument to measure the size of droplets in the marine cloud layer. While the volcano was spewing sulfur, the droplets were the smallest in the 14-year record of observations.

"You can see the effect over an entire ocean for a two-month period," McCoy said. "It was a pretty unique geophysical event within the satellite record."

link.

Impact of Antarctic Clouds on Climate

Impact of Antarctic mixed-phase clouds on climate

Authors:

Lawson et al

Abstract:

Precious little is known about the composition of low-level clouds over the Antarctic Plateau and their effect on climate. In situ measurements at the South Pole using a unique tethered balloon system and ground-based lidar reveal a much higher than anticipated incidence of low-level, mixed-phase clouds (i.e., consisting of supercooled liquid water drops and ice crystals). The high incidence of mixed-phase clouds is currently poorly represented in global climate models (GCMs). As a result, the effects that mixed-phase clouds have on climate predictions are highly uncertain. We modify the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM) GCM to align with the new observations and evaluate the radiative effects on a continental scale. The net cloud radiative effects (CREs) over Antarctica are increased by +7.4 Wm−2, and although this is a significant change, a much larger effect occurs when the modified model physics are extended beyond the Antarctic continent. The simulations show significant net CRE over the Southern Ocean storm tracks, where recent measurements also indicate substantial regions of supercooled liquid. These sensitivity tests confirm that Southern Ocean CREs are strongly sensitive to mixed-phase clouds colder than −20 °C.

Robo Brain: the Cloud Machine Learning for the Robopocalypse

Robo Brain – a large-scale computational system that learns from publicly available Internet resources – is currently downloading and processing about 1 billion images, 120,000 YouTube videos, and 100 million how-to documents and appliance manuals. The information is being translated and stored in a robot-friendly format that robots will be able to draw on when they need it.

To serve as helpers in our homes, offices and factories, robots will need to understand how the world works and how the humans around them behave. Robotics researchers have been teaching them these things one at a time: How to find your keys, pour a drink, put away dishes, and when not to interrupt two people having a conversation. This will all come in one package with Robo Brain.

"Our laptops and cell phones have access to all the information we want. If a robot encounters a situation it hasn't seen before it can query Robo Brain in the cloud," said Ashutosh Saxena, assistant professor of computer science at Cornell University. Saxena and colleagues at Cornell, Stanford and Brown universities and the University of California, Berkeley, say Robo Brain will process images to pick out the objects in them, and by connecting images and video with text, it will learn to recognize objects and how they are used, along with human language and behavior.

If a robot sees a coffee mug, it can learn from Robo Brain not only that it's a coffee mug, but also that liquids can be poured into or out of it, that it can be grasped by the handle, and that it must be carried upright when it is full, as opposed to when it is being carried from the dishwasher to the cupboard.

Saxena described the project at the 2014 Robotics: Science and Systems Conference, July 12-16 in Berkeley, and has launched a website for the project at http://robobrain.me

link.

Humans Greatly Impact Cloud Formation

Understanding how clouds affect the climate has been a difficult proposition. What controls the makeup of the low clouds that cool the atmosphere or the high ones that trap heat underneath? How does human activity change patterns of cloud formation? The research of the Weizmann Institute's Prof. Ilan Koren suggests we may be nudging cloud formation in the direction of added area and height. He and his team have analyzed a unique type of cloud formation; their findings, which appeared recently in Science indicate that in pre-industrial times, there was less cloud cover over areas of pristine ocean than is found there today.

Clouds need tiny particles called aerosols that rise in the atmosphere, in order to form. These aerosols – natural ones like sea salt or dust, or such human-made ones as soot – form nuclei around which the cloud droplets condense. In relatively clean environments, clouds can only grow as large as the amount of aerosols in the atmosphere allows: They will be the limiting factor in cloud formation.

The question is: Does the current load of aerosols in the atmosphere already exceed that limit, in which case adding extra particles should not greatly affect cloud formation; or do they continue to be a limiting factor as pollution rises, so that added aerosols would continue to influence the clouds? A model developed by Koren and his team showed that an increase in aerosols, even in relatively polluted conditions, should result in taller, larger clouds that rain more aggressively. But proving the model was another story: Experimenting on clouds, or even finding ways to isolate the various factors that go into their formation in real time, is a highly difficult undertaking.

Koren, research student Guy Dagan and Dr. Orit Altaratz in the Earth and Planetary Sciences Department looked to an unlikely place to test their model: near the horse latitudes. These are subtropical regions far out in the oceans that were reviled in the past by sailors because the winds that carried their sails would die out there for weeks on end. Here was a lab for them to test the basic physics of their model: an atmospheric region controlled by well-defined meteorological conditions, which was sometimes pristine, sometimes containing low levels of aerosols. If the model was correct, transitions from one to the other should be dramatic. And they wanted to test their theory on the clouds that do form in this region – warm convective clouds that are fuelled by the ocean's moisture.

With other potential factors – wind, large temperature swings or land formations – out of the way, the team could concentrate on the aerosols, comparing daily satellite images of cloud cover and measurements of the aerosol load to the predictions of the model. Using many different types of analysis, they found that their model closely matched the satellite observations.

They then looked at another source of data: that of the Clouds' and the Earth's Radiant Energy System (CERES) satellite instruments which measure fluxes of reflected and emitted radiation from the Earth to space, to help scientists understand how the climate varies over time. When analyzed together with the aerosol loading over the same area at the same time, the outcome, says Koren, was a "textbook demonstration of the invigoration effect" of added aerosols on clouds. In other words, the radiation data fit the unique signature of clouds that were growing higher and larger. Such clouds show a strong increase in cooling due to the reflected short waves, but that effect is partly cancelled out by the enhanced, trapped, long-wave radiation coming from underneath.

At least over the oceans, the pre-industrial cloud conditions would have been considerably different from those of today; this implies that the aerosols we have been adding to the atmosphere may have had a significant effect on global patterns of cloud formation and rain.

Koren: "We showed that convective clouds do not necessarily stop being aerosol-limited; under relatively polluted conditions the increase in aerosol loading will make the clouds taller, larger and their rain-rate stronger. As the area of this cloud cover grows, it reflects more of the shortwave radiation; but as the clouds get taller, their greenhouse effect becomes more significant, counteracting about half of their total cooling effect."

link.