Predicting warming effect of human-induced greenhouse gases

Jan 27, 2014

The warming effect of human-induced greenhouse gases is a given, but to what extent can we predict its future influence? That is an issue on which science is making progress, but the answers are still far from exact, say researchers from the Hebrew University of Jerusalem, the US and Australia who have studied the issue and whose work which has just appeared in the journal Science

Indeed, one could say that the picture is a "cloudy" one, since the determination of the greenhouse gas effect involves multifaceted interactions with .

To some extent, aerosols –- particles that float in the air caused by dust or pollution, including – counteract part of the harming effects of warming by increasing the amount of sunlight reflected from clouds back into space. However, the ways in which these aerosols affect climate through their interaction with clouds are complex and incompletely captured by climate models, say the researchers. As a result, the radiative forcing (that is, the disturbance to the earth's "energy budget" from the sun) caused by human activities is highly uncertain, making it difficult to predict the extent of global warming.

And while advances have led to a more detailed understanding of aerosol-cloud interactions and their effects on climate, further progress is hampered by limited observational capabilities and coarse climate models, says Prof. Daniel Rosenfeld of  the Fredy and Nadine Herrmann Institute of Earth Sciences at the Hebrew University of Jerusalem, author of the article in Science. Rosenfeld wrote this article in cooperation with Dr. Steven Sherwood of the University of New South Wales, Sydney, Dr. Robert Wood of the University of Washington, Seattle, and Dr. Leo Donner of the US National Oceanic and Atmospheric Administration. .

Their recent studies have revealed a much more complicated picture of aerosol-cloud interactions than considered previously. Depending on the meteorological circumstances, aerosols can have dramatic effects of either increasing or decreasing the cloud sun-deflecting effect, the researchers say. Furthermore, little is known about the unperturbed aerosol level that existed in the preindustrial era. This reference level is very important for estimating the radiative forcing from aerosols.

Also needing further clarification is the response of the cloud cover and organization to the loss of water by rainfall. Understanding of the formation of ice and its interactions with liquid droplets is even more limited, mainly due to poor ability to measure the ice-nucleating activity of aerosols and the subsequent ice-forming processes in clouds.

Explicit computer simulations of these processes even at the scale of a whole cloud or multi-cloud system, let alone that of the planet, require hundreds of hours on the most powerful computers available. Therefore, a sufficiently accurate simulation of these processes at a global scale is still impractical.

Recently, however, researchers have been able to create groundbreaking simulations in which models were formulated presenting simplified schemes of cloud-aerosol interactions, This approach offers the potential for model runs that resolve clouds on a global scale for time scales up to several years, but climate simulations on a scale of a century are still not feasible. The model is also too coarse to resolve many of the fundamental aerosol-cloud processes at the scales on which they actually occur. Improved observational tests are essential for validating the results of simulations and ensuring that modeling developments are on the right track, say the researchers.

While it is unfortunate that further progress on understanding aerosol-cloud and their effects on climate is limited by inadequate observational tools and models, achieving the required improvement in observations and simulations is within technological reach, the researchers emphasize, provided that the financial resources are invested. The level of effort, they say, should match the socioeconomic importance of what the results could provide: lower uncertainty in measuring man-made climate forcing and better understanding and predictions of future impacts of on our weather and climate.

Explore further: The importance of aerosol research: A Q&A with Alex Guenther

More information: "Climate Effects of Aerosols-Cloud Interactions." Daniel Rosenfeld, Steven Sherwood, Robert Wood, Leo Donner. Science VOL 343 24 JANUARY 2014

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jackjump
2.3 / 5 (12) Jan 27, 2014
And if you discover that clouds create a net negative feedback to the warming effect of human-induced greenhouse gases, what will that do to the catastrophic global warming hypothesis? Efforts to find that out might consume the last dregs in the 'save the planet from the impending catastrophic global warming' government funding honey bucket. Naahhh! What am I thinking? That'll just fill up the 'convince everyone impending catastrophic global warming exists' government funding honey bucket but it will change the honey bears.
Maggnus
3.7 / 5 (12) Jan 27, 2014
Wow way to publicly display your ignorance. This "catastrophic global warming hypothesis" of which you speak includes several ongoing studies regarding the off-setting effect of clouds. Unfortunately, it appears they will have very little over all effect (Harmon 009, Walsh 2009).

But lets not rain all over your little "government conspiracy" tantrum! Maybe if you stomp your little foot harder, someone will pretend to notice you're ranting.
runrig
3.7 / 5 (12) Jan 27, 2014
jackjump:
All studies show that clouds have an overall cooling effect and none have shown a negative feed-back due to warming.
So you are arguing that no matter how much GHG effect we create whilst polluting the one planet we have easy access too, then somehow, miraculously clouds will come to our rescue and reflect more solar irradiation away to mitigate it all. What a sad denialist person you are. Go away a read up the science for a few years than come back and make some intelligent statement. Thank you.
Maggnus
2.5 / 5 (8) Jan 27, 2014
Hey runrig, check this out: http://www.report...ion.html

So maybe not an overall cooling effect after all?
thermodynamics
3.3 / 5 (9) Jan 27, 2014
And if you discover that clouds create a net negative feedback to the warming effect of human-induced greenhouse gases, what will that do to the catastrophic global warming hypothesis? Efforts to find that out might consume the last dregs in the 'save the planet from the impending catastrophic global warming' government funding honey bucket. Naahhh! What am I thinking? That'll just fill up the 'convince everyone impending catastrophic global warming exists' government funding honey bucket but it will change the honey bears.


Jackjump: What is your idea of "catastrophic?" If it is something like a Hollywood disaster movie with no science in it then you need to clean up your comments because you will not see that from scientists who are making predictions about the next 100 - 200 years. Instead, they predict steady ocean rises that will displace humans from low areas and increased temperatures.
Continued
thermodynamics
3.6 / 5 (8) Jan 27, 2014
Continued: They also discuss the changes in water patterns that could also cause human and animal displacement. These are not predictions like a low budget SiFi disaster movie, they are predictions of serious economic and human impact of a anthropogenic change in the heat balance of the Planet. As Runrig succinctly puts it: "...whilst polluting the one planet we have easy access too..." That is exactly what is happening. This will not be like a comet hitting the Planet, it will be slow and it will progress with most people (I would guess you would fit in this Jackjump) not even being able to notice the change. So, your use of the word "catastrophic" is just a means of diverting attention to the science. Address the real problem of the real change that is taking place and is predicted, not what you can get from your trip to the movies.
runrig
3.7 / 5 (9) Jan 27, 2014
Hey runrig, check this out: http://www.report...ion.html

So maybe not an overall cooling effect after all?


Yes Magnus I am aware of what you linked. I was referring to the overall albedo vs GHE of clouds however, which I do believe to be still more overall cooling than warming. The effect of higher global temperatures as we go forward however can only, at the moment, be studied via model simulation and not by direct measurement.
orti
2.9 / 5 (8) Jan 27, 2014
OMG. Is settled science actually dialing back their hyperbole?
Maggnus
3 / 5 (8) Jan 27, 2014
No orti, it is exactly the same level as it has always been. And its still settled.

runrig, I thought the overall effect was more towards neutral. Your comment on models makes sense though, so I withhold judgment :).
Whydening Gyre
4 / 5 (5) Jan 27, 2014
I was referring to the overall albedo vs GHE of clouds however, which I do believe to be still more overall cooling than warming. The effect of higher global temperatures as we go forward however can only, at the moment, be studied via model simulation and not by direct measurement.

Also agree on the modeling statement.
To address your first sentence - doesn't higher heat equate to more clouds?
discouragedinMI
2.8 / 5 (6) Jan 28, 2014
This is the most truthful climate article I've read in years. There are so many variables and the models are so bad that we really don't know what the effects are going to be.
shavera
4.3 / 5 (6) Jan 28, 2014
This is the most truthful climate article I've read in years. There are so many variables and the models are so bad that we really don't know what the effects are going to be.


Just because the last page of the book isn't written doesn't mean we haven't finished a good few chapters. We may not know exactly, there are still error bars on the reports... but we have pretty good ideas of where it will be. We've included a lot of these variables, and models have significantly improved since the 70s and 90s and 00s.
savroD
4.2 / 5 (5) Jan 28, 2014
@Jackjump...
It amazes me how poor you folks are at economics as well. So some scientists get money to do research; yet, the most profitable corporation in history has no money sloshing around to capture fools like you as customers for life. Also as pointed out, your understanding of science amounts to no more than Hollywood science fiction.
runrig
5 / 5 (4) Jan 28, 2014
I was referring to the overall albedo vs GHE of clouds however, which I do believe to be still more overall cooling than warming. The effect of higher global temperatures as we go forward however can only, at the moment, be studied via model simulation and not by direct measurement.

Also agree on the modeling statement.
To address your first sentence - doesn't higher heat equate to more clouds?


Empirically no, the hydrological cycle should ensure that the RH (rel hum) of the atmosphere remains the same - so same clouds. However as temps rise then so the AH (absolute hum) will rise, thereby creating a greater GHG effect. However as Magnus has linked up thread there are models that predict less cloud and so there would be a +ve feedback in such a scenario (greater warming).
runrig
5 / 5 (4) Jan 28, 2014
runrig, I thought the overall effect was more towards neutral. Your comment on models makes sense though, so I withhold judgment :).


Magnus:
Yes, there are some papers saying that, at least regionally - however...

"Clouds increase the global reflection of solar radiation from 15% to 30%, reducing the amount of solar radiation absorbed by the Earth by about 44 W/m². This cooling is offset somewhat by the greenhouse effect of clouds which reduces the outgoing LW radiation by about 31 W/m². Thus the net cloud forcing of the radiation budget is a loss of about 13 W/m². If the clouds were removed with all else remaining the same, the Earth would gain this last amount in net radiation and begin to warm up. These numbers should not be confused with the usual radiative forcing concept, which is for the change in forcing related to climate change."
http://en.wikiped..._forcing
Ducklet
not rated yet Feb 02, 2014
If the models are so inaccurate, how can the U.N. know that climate change is "drowning Senegal"?