Tuesday, 5 July 2016

Water vapour in troposphere as a positive feedback

Keeping an eye on the Arctic and many other things has meant that I have ignored some other very important positive feedbacks

Catastrophic Water Vapor Feedback is Kicking in * 1°C - Warming is as Much as 3°C * Climate Change

See Guy McPherson's list of self-reinforcing positIve feedbacks HERE

Global warming amplifier: Rising water vapor in upper troposphere tointensify climate change

13 August, 2014

A new study from scientists at the University of Miami Rosenstiel School of Marine and Atmospheric Science and colleagues confirms rising levels of water vapor in the upper troposphere -- a key amplifier of global warming -- will intensify climate change impacts over the next decades. The new study is the first to show that increased water vapor concentrations in the atmosphere are a direct result of human activities.

Each 1 Degree C We Warm the Planet adds 7% increase in Moisture

Kevin Hester

For every 1 degree C we increase the temperature on the planet we see 7% more moisture in the atmosphere. We are heading to and beyond the IPCC worst case scenario of  6C minimum which will generate another 40% of moisture in the air. This will lead to a greater number of flooding events and increased number of lightning strikes and Tornadoes.

This is an enormous amount of energy and associated warming as water vapour is in itself a green house gas.

The impact of climate change may be worse than previously thought, a new study suggests”:  As world leaders hold climate talks in Paris, research shows that land surface temperatures may rise by an average of almost 8C by 2100, if significant efforts are not made to counteract climate change.”

Personally I disagree with the suggestion that it will take until the magic 2100 for our locked in 8C temperature rise. Factor in the myriad of feedback loops and we could be there in a few decades,not that humans will survive that long to bare witness.

Such a rise would have a devastating impact on life on Earth:  ‘Climate Outlook May be Worse than Feared.’

The amount of water vapor in the atmosphere exists in direct relation to the temperature. If you increase the temperature, more water evaporates and becomes vapor, and vice versa. So when something else causes a temperature increase (such as extra CO2 from fossil fuels), more water evaporates. Then, since water vapor is a green house gas, this additional water vapor causes the temperature to go up even further—a positive feedback.”

How much does water vapor amplify CO2 warming? Studies show that water vapor feed backroughly doubles the amount of warming caused by CO2. So if there is a 1°C change caused byCO2, the water vapor will cause the temperature to go up another 1°C. When other feedbackloops are included, the total warming from a potential 1°C change caused by CO2 is, in reality, as much as 3°C.

A warmer atmosphere can hold more moisture, and globally water vapour increases by 7% for every degree centigrade of warming.”

Excellent article and Q & A from The Guardian below:  ‘How Will Climate Change Affect Rainfall?

Human-caused global warming is causing the upper troposphere to become wetter

We have long suspected that greenhouse gases which cause the Earth to warm would lead to a wetter atmosphere. The latest research published by Eul-Seok Chung, Brian Soden, and colleagues provides new insight into what was thought to be an old problem. In doing so, they experimentally verified what climate models have been predicting. The models got it right… again.

To be clear, this paper does not prove that water vapor is a greenhouse gas. We have known that for years. Nevertheless, the paper make a very nice contribution. The authors show that the long-term increase in water vapor in the upper troposphere cannot have resulted from natural causes – it is clearly human caused. This conclusion is stated in the abstract,

Our analysis demonstrates that the upper-tropospheric moistening observed over the period 1979–2005 cannot be explained by natural causes and results principally from an anthropogenic warming of the climate. By attributing the observed increase directly to human activities, this study verifies the presence of the largest known feedback mechanism for amplifying anthropogenic climate change.

As stated earlier, climate models have predicted this moistening – before observations were available. In fact, the models predicted that the upper troposphere would moisten more than the lower atmospheric layers. As the authors state,

Given the importance of upper-tropospheric water vapor, a direct verification of its feedback is critical to establishing the credibility of model projections of anthropogenic climate change.

To complete the experiments, the authors used satellite measurements of radiant heat. The emissions have changed but it wasn’t clear why they have changed. Changes could be caused by increases in temperature or from increased water vapor. To separate the potential effects, the authors compared the first set of experiments with others made at a different wavelength. That comparison provided a direct measure of the separate effect of moistening.

Next, the authors used the world’s best climate models to test whether the observed trends could be caused by natural changes in the Earth’s climate or whether they require a human influence. Sure enough, only the calculations that included human-emitted greenhouse gases matched the observations. The authors conclude that,

Concerning the satellite-derived moistening trend in recent decades, the relations of trend and associated range among three experiments lead to the conclusion that an increase in anthropogenic greenhouse gases is the main cause of increased moistening in the upper troposphere.

The authors then went further by showing that their computed results encompass third-party measurements only when the impacts of human-emitted greenhouse gases are included.

I chuckled when I asked Dr. Andrew Dessler about this study, and he told me,

Because of water vapor’s importance as a greenhouse gas, the water vapor feedback occupies a central role in the climate system. Over the years, our understanding of this process has increased steadily, and this paper is a very useful contribution. It nicely demonstrates that the observations of upper tropospheric moistening are unlikely to have arisen without the increase in carbon dioxide from human activities. At this point, I think it would be fair to say, “stick a fork in it, the water vapor feedback’s done.”

So once again, observations have confirmed the models and the scientists can check another item off their “to do” box.

No comments:

Post a Comment