By: Dr. Ricky Rood , 2:30 AM GMT on March 16, 2007


From the previous blog: Yes - 1993 was the year of the flooded Midwest. If you go back and look at that wavelet analysis figure once again, you will see the northward moisture flux in the long period scale. It builds up over the course of the summer.

A couple of weeks ago I gave my climate science 101 lecture to a class. At the end of the class I was asked a question--what did I think were the most credible arguments that the current warming we are seeing is not caused by the carbon dioxide greenhouse effect? At the top of my list is the question of whether or not we have properly accounted for natural variability.

So far we have looked at, perhaps, two extremes. We have seen and discussed the record of carbon dioxide and temperature cycles associated with the ice ages and temperate periods. We are currently in a temperate period, and there is no doubt that if human commerce is a measure of success, we have done well when it is temperate--dare I say warm? These oscillations are on periods of tens to hundreds of thousands of years. At the other end of the scale, I introduced the idea that weather-scale events are the mechanisms that make up the climate, and that the low level, diurnal jet stream was a climate feature because it was so important to the seasonal water cycles for the North American continent. There is a whole array stuff in between these two extremes.

Two of the most important flavors of natural variability are the El Nino-La Nina cycles and the North Atlantic Oscillation. The observations and analysis of the IPCC 2001 report came to closure at about the time of 1997-1998 El Nino; hence, the Earth was in a warm cycle. That raised doubt that the warm temperatures at the end of the 1990s were part of a trend. This was reflected in the wording of that report. Since that time, the warming trend has continued irrespective of the El Nino-La Nina cycle. There is little debate today about whether or not the planet is warming.

The North Atlantic Oscillation (NAO) is familiar to many people reading this blog. The NAO is associated with a change in the surface pressure pattern, which is easily observed in the position of the Icelandic Low. The figures below show the surface pressure field in the two modes of the North Atlantic Oscillation. These are from the Lamont Doherty Earth Observatory's NAO web page. The first figure shows positive phase with the Icelandic Low being deeper and Azores High higher than normal. The second figure shows the opposite phase.

Figure 1: Positive Phase of the North Atlantic Oscillation. from LDEO

Figure 1: Negative Phase of the North Atlantic Oscillation. from LDEO

In a general sense, this type of oscillation, which is observed in both the northern and southern hemisphere, is associated with a redistribution of mass between the middle and high latitudes. (more info from the Climate Prediction Center) Remember, pressure at the Earth's surface is a measure of the weight of air above the surface. The oscillation, therefore, is also seen as up and down variations of pressure at the poles. When there is a pressure change on this spatial scale, the storm tracks change. They move north and south. Hence, we can also expect to see some large scale changes in temperature and wind--warming and cooling at the poles. This is a source of natural variability, which like El Nino-La Nina, has significant global signals. I will come back to how researchers have tried to "remove" these sources of natural variability in order to isolate trends.

While the North Atlantic Oscillation and El Nino-La Nina are natural, this does not mean that they are independent of climate change. Climate models show that as the Earth warms there will be changes in variability; the period might change, or the Earth may spend more time in one phase than the other. In recent years the mode with low pressure over the North Pole and higher pressure in middle latitudes has been observed. The question arises is this natural, or is the more common appearance of this mode a consequence of forcing by increasing greenhouse gases, changes in stratospheric ozone, or some other process?


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17. desertdisaster
4:30 PM GMT on March 19, 2007
Here:-Link you can see some of the data taken in consideration for the CCSR/NIES model that is predecting a warming of 7°C for Land & 3.8°C for Ocean in 100 years.

The model includes the following...
Gravity-wave Drag - Solar Constant/Cycles - Radiation - Convection - Surface Fluxes - Surface Characteristics - Cloud Formation and more...
16. desertdisaster
3:54 PM GMT on March 19, 2007
Oups.. here is the Link
15. desertdisaster
3:45 PM GMT on March 19, 2007
What the models are reveling for now is:
14. desertdisaster
3:23 PM GMT on March 19, 2007
A computer model is only as reliable as the physics that are built into the program. The physics that are currently in these computer programs are still insufficient to have much confidence in the predicted magnitude of global warming, because we currently don't understand the detailed physical processes of clouds that will determine the extent and nature of water vapor's feedback into the Earth's temperature!

More intersting reading here: Link
10. LowerCal
12:28 AM GMT on March 19, 2007
ricky, the previous three blog entries with the " Wavelet analysis of north-south moisture flux at San Antonio, Texas" did require some extra study, lol.

I'm very interested in the ways that "... researchers have tried to “remove” these sources of natural variability in order to isolate trends."
Member Since: July 26, 2006 Posts: 59 Comments: 10335
9. Patrap
12:53 PM GMT on March 18, 2007
If the info is digested as I seem to have done..the temperate zones..although in a less variable zone..sees the swings in a more pronounced way than the Artic regions..with more people affected by the waxing and waning of the NAO..
Member Since: July 3, 2005 Posts: 452 Comments: 144123
8. SatBeachFL
3:05 PM GMT on March 17, 2007
not too complex, keep em coming
7. Trouper415
9:46 PM GMT on March 16, 2007
Wow, Rickey, a phenomenal breakdown of these trends. Very interesting and fascinating as you described then with great detail as well as putting them in readable lamen terms for me.

Great work! Thanks for the blogs!

Member Since: September 22, 2005 Posts: 5 Comments: 725
6. PuntaGordaPete
8:31 PM GMT on March 16, 2007
Blog is right on target. There are zillions of pages of full-complexity scientific papers, and endless popular accounts in newspapers. This is right in the middle.
Member Since: September 5, 2006 Posts: 0 Comments: 48
4. Dr. Ricky Rood , Professor
5:03 PM GMT on March 16, 2007
I think that the link to ozone in the Antarctic is pretty easy to make. It's harder to make in the Arctic because there is a lot more variability in the north. I think it is safe to say that the models that resolve the stratosphere do a better job of explaining the observations than those that do not. That does not mean that it is ozone; there are dynamical feedbacks as well. r
Member Since: January 31, 2007 Posts: 374 Comments: 391
3. desertdisaster
2:53 PM GMT on March 16, 2007
Thanks Ricky

Very interesting & well explained.
and I am only trying to learn...

We know that Surface warming must be balanced by upper-atmosphere cooling...

My question is:
Knowing that The Arctic stratosphere has cooled 3°C in the past 20 years due the combined effects of ozone loss, greenhouse gas accumulation, and natural variability.Is it possible that the Arctic stratosphere cooling has an effect on the pressure that influence the N.A.O.?
2. nsrainshine42
3:45 AM GMT on March 16, 2007
Check one for not too complex. The view from the sky of the "inland sea" of early summer '93 will be one not forgotten. We flew from Boston to San Diego, no clouds below -- and a window seat.
Climate Change and tempreture highs v lows what impact? Higher highs deeper lows?
Member Since: October 26, 2006 Posts: 0 Comments: 0
1. Dr. Ricky Rood , Professor
2:58 AM GMT on March 16, 2007
On this blog ... Am I getting too complex for a blog. Let me know. Old blogs should be at the right. "Entries for 2007."
Member Since: January 31, 2007 Posts: 374 Comments: 391

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Dr. Ricky Rood's Climate Change Blog

About RickyRood

I'm a professor at U Michigan and lead a course on climate change problem solving. These articles often come from and contribute to the course.

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Clouds in the lee of the Rockies at sunset.
Clouds in the lee of the Rockies at sunset.
Clouds in the lee of the Rockies at sunset.
Clouds in the lee of the Rockies at sunset.