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Home https://server7.kproxy.com/servlet/redirect.srv/sruj/smyrwpoii/p2/ Science https://server7.kproxy.com/servlet/redirect.srv/sruj/smyrwpoii/p2/ An impressive study finds a point of reversing the cloud

An impressive study finds a point of reversing the cloud



  Clouded clouds like the two-thirds of this image are common to the oceans.
Enlarge / Slush clouds, like those in the two thirds of this image,

The word "hysteresis" does not immediately look threatening; he hints in the "history" and "thesis" portraits ̵

1; perhaps heavily read, but they never killed anyone. But the word does not mean that. Hysteresis is a deep behavior that some systems can show by crossing some point of return. Dial things in just one step, and you can push the system through a radical change. To return to normal, you may need to dial it to five or six levels.

Earth's climate system can give examples. Take the water circulation in the conveyor belt in the Atlantic Ocean. Looking back on the past, you can see times that the circulation seems to have turned an alternative model to the climatic consequences around the North Atlantic. Moving from one model to another makes a significant boost, but it's hard to reverse – like climbing to the top of the ridge and rolling in the next valley.

A new study, led by Tappi Schneider of Caltech, may have identified a disturbing hysteresis in Earth's climate – a change in the patterns of clouds in response to warming that can rapidly warm the planet. If we continued to emit more and more greenhouse gases, we would finally have done this experiment. (Let's not, please.)

Cloudy Services

The center of this drama is a kind of cloud. Slightly cloudy clouds usually cover about a fifth of low-ocean oceans. Most clouds are formed because the air, heated by the earth (or abused above the mountains), cools when it rises, condensing the water vapor to the droplets of clouds. The convection that raises their moisture is not driven by warming the bottom, but by cooling at the top.

The water in this cloud platform absorbs much of the infrared radiation radiating upward from the warm surface. The class of the cloud re-emits a certain radiance down, while others – in the cosmic space. The air above these clouds is drier and absorbs much less than the outgoing energy passing through it. This means that you can think of these clouds as the cooling fins of the radiator. They throw more heat up than they get from the atmosphere above them, allowing them to cool down from top to bottom. The cold air at the top of the clouds sinks, creating a convection contour that leads the water vapor from the sea surface to the deck of the cloud.

So what happens to this unique process in a warmer world? it was hard to say. The key processes in these cloud clouds happen on a much smaller scale than a cellular network in global climate models, so their physics is not directly simulated. Instead, we have a simplified mathematical position for their overall behavior. There is good reason to believe that this does not allow us to understand the details of how they will react to the ongoing global warming.

Nothing but a blue sky

To deal with this, Schneider and his colleagues turned things around. They use a model that can simulate these clouds in a small part of the atmosphere – considering a simplified version of the world around them. In particular, they simulated a stretch of subtropical ocean with straw-cloud clouds and a neighboring stretch of tropical ocean responding to global warming. They have done this for different greenhouse gas concentrations equivalent to 400 parts per million CO 2 (similar to today's) to 1600 parts per million.

Up to about 1,000 parts per million, there were no big surprises. Things got warmer about 4 ° C and numbers change for things like water vapor and cloud height. But the cloud deck seemed familiar.

At about 1,200 parts per million, however, the simulated clouds suddenly dissipated. And without this shadow reflecting sunlight, the world warmed up another 8 ° C .

  Processes responsible for breaking the cloud, destroying about 1200 ppm of CO2 in the model. Temperatures shown in kelvin units. "Src =" https://cdn.arstechnica.net/wp-content/uploads/2019/02/schenider_fig-640x424.jpg "width =" 640 "height =" 424 "srcset =" https: //cdn.arstechnica </span> Click to enlarge </span> Processes responsible for breaking the cloud of about 1200 ppm CO2 in the Model. </div>
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<p>  How does <sub> 2 </sub> scroll the switch of these clouds? Researchers have discovered two simple processes that work together in their simulation. First, warmer air transfers more water vapor from the sea surface and, when this water vapor condenses, it produces very latent heat. This additional latent heat gives the air a little buoyancy boosting, increasing the turbulent motion that can mix the dry air from above into the cloud layer. This drains the cloud platform and makes cloud formation less likely. Second, the increased CO <sub> 2 (and water vapor) in the air over the cloud means it absorbs more than the output infrared radiation. Instead of staying away from the road and allowing the cloud layer to release heat into space, the upper layer captures more and radiates some back to the clouds. </p>
<p>  Both processes weaken the cloud, either by slowing the convection of the cooling device or by mixing in the dry air. In the model the cloud deck suddenly can no longer support. </p>
<p>  From there, hysteresis is impressive. Warming, which results from the loss of these clouds, strengthens the processes that first break the clouds. Dropping less than 1,200 parts per million CO <sub> 2 </sub> again <em> does not </em> switch clouds back. Instead, the researchers had to bring it up to 300 parts per million to see the cloud reform and stabilize. </p>
<h2>  What does all this mean </h2>
<p>  Are we doomed to see this game soon? It has to be a good case, if not optimism, at least to neglect pessimism. This will take about a century of continued emission growth to reach the equivalent of 1200 parts per million CO <sub> 2 </sub>. Even the promises already made to reduce emissions can hinder this. </p>
<p>  But along with this data, researchers noted that other changes in the warming atmosphere could raise this threshold. Some other expected circulatory trends would increase the stability of the cloud platform, which will allow to maintain higher concentrations of CO <sub> </sub>. The model used in this study, which simplifies the global picture to increase the scale of an aspect, can not represent these processes. This means that the exact numbers here are not important. The main conclusion is that this sudden change in cloud behavior is possible. Researchers will now focus on understanding it better. </p>
<p>  It is tempting to think that this can help solve another scientific puzzle. Climate patterns are often tested against past periods of climate change and to study the causes of these climate changes. Efforts to simulate some very warm climates (such as the ecuana 50 million years ago) usually fail to get enough warmth. To match the heat indicated by the geological records, the models required a higher CO <sub> 2 </sub> than it looks then. There may be no models – a great temperature boost caused by the loss of sea clouds. </p>
<p>  Fortunately, astonishing studies attract many follow-up activities. So we need to have more answers to these questions long before we feel the need to look up and check that these clouds are still there. </p>
<p>  <em> Nature Geoscience </em> 2019. DOI: 10.1038 / s41561-019-0310 -1 (for DOI). </p>
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