The Biggest Control Knob: CO2 in Earth's Climate History

By: Dr. Jeff Masters , 9:05 PM GMT on March 24, 2010

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It's been a busy past two months of weather and climate change news, and I haven't found time to blog about the research presented at December's American Geophysical (AGU) meeting in San Francisco. That is the world's largest scientific conference on climate change, and the place to be if you want to get the pulse of the planet. The keynote speech at the AGU meeting was given by Dr. Richard Alley of Penn State University. Dr. Alley is the Evan Pugh Professor of Geosciences at the Pennsylvania State University, and one of the most respected and widely published world experts on climate change. Dr. Alley has testified before Congress on climate change issues, served as lead author of "Chapter 4: Observations: Changes in Snow, Ice and Frozen Ground" for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), and is author of more than 170 peer-reviewed scientific articles on Earth's climate. He is also the author of a book I highly recommend--The Two Mile Time Machine, a superb account of Earth's climate history as deduced from the 2-mile long Greenland ice cores. A standing-room only audience of over 2,000 scientists packed the lecture hall Dr. Alley spoke at, and it was easy to see why--Alley is an excellent and engaging speaker. I highly recommend listening to his 45-minute talk via a very watchable recording showing his slides as he speaks in one corner of the video. If you want to understand why scientists are so certain of the link between CO2 and Earth's climate, this is a must-see lecture.


Figure 1. Dr. Richard Alley of Penn State University, delivering the keynote speech at the 2009 AGU conference on climate change.

The Biggest Control Knob: CO2 in Earth's Climate History
Earth's past climate has been shaped by a number of key "control knobs"--solar energy, greenhouse gas levels, and dust from volcanic eruptions, to name the three main ones. The main thrust of Dr. Alley's speech is that we have solid evidence now--some of it very new--that CO2 has dominated Earth's climate over the past 400 million years, making it the climate's "biggest control knob". Dr. Alley opens his talk by humorously discussing a letter from an irate Penn State alumnus. The alumnus complains that data of temperatures and CO2 levels from ice cores in Antarctica don't match:

"CO2 lags Earth's temperature...This one scientific fact which proves that CO2 is not the cause of recent warming, yet...Dr. Alley continues to mislead the scientific community and the general public about 'global warming'. His crimes against the scientific community, PSU, the citizens of this great country, and the citizens of the world are significant and must be dealt with severely to stop such shameful activities in the future".

Dr. Alley explains that the irate alumnus is talking about the Antarctic ice core record, which shows that as we emerged from each ice age, the temperature began increasing before the CO2 did, so increased CO2 was not responsible for the warmings that brought us out of these ice ages. Climate change scientists and skeptics alike agree that Earth's ice ages are caused by periodic variations in Earth's orbit called Milankovich Cycles. "There's no doubt that the ice ages are paced by the orbits", says Dr. Alley. "No way that the orbit knows to dial up CO2, and say 'change'. So it shouldn't be terribly surprising if the CO2 lags the temperature change. The temperature never goes very far without the CO2. The CO2 adds to the warming. How do we know that the CO2 adds to the warming? It's physics!"

Dr. Alley then discusses that the physics that govern how CO2 absorbs and re-emits heat energy, when plugged into state-of-the-art climate models, show that about half of the observed 5 - 6°C natural warming that occurred since the last ice age ended was due to extra CO2 added to the atmosphere. At the peak of the Ice Age, CO2 was about 190 ppm. By the end, it was about 280 ppm (Figure 1). Earth's orbital variations "forced" a warming, which caused more CO2 to escape from swamps and oceans, with a time lag of several centuries. The increased CO2 reinforced the warming, to double what it would have been otherwise--a positive feedback loop. "Higher CO2 may be forcing or feedback--a CO2 molecule is radiatively active regardless of how it got there", says Dr. Alley. "A CO2 molecule does not remember why it is there--it only remembers that it is there". In other words, the fact that higher CO2 levels did not trigger an end to the Ice Age does not mean that the CO2 had no warming effect. Half of the the observed 5 - 6°C natural warming that occurred since the last ice age ended was due to the extra CO2 added to the atmosphere. So, the irate PSU alumnus was half right. The CO2 does lag temperature. However, we can only explain approximately half of the warming since the last ice age ended if we leave out the increase in CO2 that has occurred. "If higher CO2 warms, Earth's climate history makes sense, with CO2 having caused or amplified the main changes. If CO2 doesn't warm, we have to explain why the physicists are so stupid, and we also have no way to explain how a lot of really inexplicable climate events happened over Earth's history. It's really that simple. We don't have any plausible alternative to that at this point".


Figure 2. Ice core record from Vostok, Antarctica, showing the near-simultaneous rise and fall of Antarctic temperature and CO2 levels through the last 350,00 years, spanning three ice age cycles. However, there is a lag of several centuries between the time the temperature increases and when the CO2 starts to increase. Image credit: Marian Koshland Science Museum of the National Academy of Sciences: Global Warming Facts and Our Futures, originally provided to that site by Kurt Cuffey, University of California, Berkely.

CO2 and temperatures rise and fall in synch
Dr. Alley continues with a discussion of how CO2 and temperature levels have risen and fallen in synch over most of geologic time. But for many years there was still a mystery: occasionally there were eras when temperature changes did not match CO2 changes. But new paleoclimate research, much of it just in the past two years, has shown that nearly all of these mis-matches were probably due to suspect data. For example, the mismatch in the Miocene Era has significantly improved, thanks to a new study published this year by Tripati et al. Another example occurs during the Ordovician Era 444 million years ago, as discussed in a recent post at the excellent skepticalscience.com blog.


Figure 3. Atmospheric CO2 and continental glaciation, 400 million years ago to the present. The vertical blue bars mark where ice ages have occurred. The length of the blue bars corresponds to how close to the Equator the ice sheets got (palaeolatitude, scale on the right side of the plot). The left scale shows atmospheric CO2 over the past 400 million years, as inferred from a model (green area) and from four different "proxy" fossil sources of CO2 information. This is Figure 6.1 of the Palaeoclimate chapter of the 2007 IPCC report.

Is there anything else we should be worried about?
Dr. Alley continues with a discussion of other influences that may be able to explain global warming, such as volcanos, changes in solar output, and cosmic rays. A whole bunch of the competing hypotheses don't work", says Dr. Alley. "When there's a bunch of big volcanos, they make it cool. If volcanos could get organized, they'd rule the world. There might be a tiny bit of organization due to flexing of the crust, but they're not controlling the world".

Regarding solar changes: "When the sun changes, it does seem to show up in the temperature record. As far back as we can see well, the sun is friendly, it doesn't change much. If the sun changed a lot, it would control things hugely. But it only changes really slowly--as far as we can tell. The record doesn't go back as far as we'd like, and there's work to be done here--but it just doesn't seem to be doing much".


Figure 4. Greenland ice core proxy measurements of temperature (top curve) and cosmic ray flux (bottom curve) for the past 60,000 years. The Earth's magnetic field weakened by 90% 40,000 years ago, for a period of about 1,000 years, but there was no change seen in the temperatures in Greenland.

Regarding cosmic rays: "The sun doesn't change much, but the sun modulates the cosmic rays, the cosmic rays modulate the clouds, the clouds modulate the temperature, and so the sun is amplified hugely. It's really interesting hypothesis, there's really good science to be done on this, but there's reason to think its a fine-tuning knob". He goes on to show an ice core example from a period 40,000 years ago (Figure 4) where the Earth magnetic field had near-zero strength for hundreds of years. This allowed a massive flux of cosmic rays to penetrate to the Earth's surface, creating a huge spike in ice core Beryllium-10, a radionuclide made by cosmic rays. If cosmic rays were important to climate, we would expect to see a corresponding major swing in temperature, but the ice core shows no change during the period of enhanced cosmic ray bombardment 40,000 years ago. "We had a big cosmic ray signal, and the climate ignores it", Dr. Alley comments.

How sensitive is climate to a doubling of CO2?
The IPCC report talks extensively about computer climate models' calculations of "climate sensitivity"--how much Earth's climate would warm if CO2 doubled from pre-industrial levels of 280 ppm, to 560 ppm (we're currently at 390 ppm). A mid-range number from the 2007 IPCC report often used by climatologists is that the climate sensitivity is 3°C for a doubling of CO2. Dr. Alley takes a look at what paleoclimate has to say about the climate sensitivity to CO2. "The models actually do pretty well when you compare them to the past. The best fit is 2.8°C.

Dr. Alley concludes, "Where we really stand now, is, we're not quite at the pound on the table, this story is very clearly not done. But an increasing body of science indicates that CO2 has been the most important controller of global average climate of the Earth."

I'll have a new post Sunday or Monday.

Jeff Masters

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Read it and weep.
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Levi,is that very blue area south of Alaska and west of North America the cold PDO?

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Figure 4. Greenland ice core proxy measurements of temperature (top curve) and cosmic ray flux (bottom curve) for the past 60,000 years. The Earth's magnetic field weakened by 90% 40,000 years ago, for a period of about 1,000 years, but there was no change seen in the temperatures in Greenland.

Regarding cosmic rays: "The sun doesn't change much, but the sun modulates the cosmic rays, the cosmic rays modulate the clouds, the clouds modulate the temperature, and so the sun is amplified hugely. It's really interesting hypothesis, there's really good science to be done on this, but there's reason to think its a fine-tuning knob". He goes on to show an ice core example from a period 40,000 years ago (Figure 4) where the Earth magnetic field had near-zero strength for hundreds of years. This allowed a massive flux of cosmic rays to penetrate to the Earth's surface, creating a huge spike in ice core Beryllium-10, a radionuclide made by cosmic rays. If cosmic rays were important to climate, we would expect to see a corresponding major swing in temperature, but the ice core shows no change during the period of enhanced cosmic ray bombardment 40,000 years ago. "We had a big cosmic ray signal, and the climate ignores it", Dr. Alley comments.

How sensitive is climate to a doubling of CO2?
The IPCC report talks extensively about computer climate models' calculations of "climate sensitivity"--how much Earth's climate would warm if CO2 doubled from pre-industrial levels of 280 ppm, to 560 ppm (we're currently at 390 ppm). A mid-range number from the 2007 IPCC report often used by climatologists is that the climate sensitivity is 3°C for a doubling of CO2. Dr. Alley takes a look at what paleoclimate has to say about the climate sensitivity to CO2. "The models actually do pretty well when you compare them to the past. The best fit is 2.8°C.

Dr. Alley concludes, "Where we really stand now, is, we're not quite at the pound on the table, this story is very clearly not done. But an increasing body of science indicates that CO2 has been the most important controller of global average climate of the Earth."

I'll have a new post Sunday or Monday.

Jeff Masters
Member Since: July 3, 2005 Posts: 426 Comments: 128749
Quoting bappit:
The people who come on here and post how some recent weather event is the tell tale of impending disaster are not any better. They are like wishcasters. They contribute to the obfuscation, misdirection and time-wasting. There is no real scientific question about the effects of CO2. The only real questions are economic, i.e., so what do we do about it? But this is a weather blog. The people on here are even less prepared to discuss that issue.

So why don't you go to a football blog and discuss it all with some intelligent folks, then?

Hey everyone, we are morons because we visit a weather blog. (If only it were really just about weather...)
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863

Yep. Nice day. It's a great day in fact. Now back to whining ...
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Quoting bappit:
The people who come on here and post how some recent weather event is the tell tale of impending disaster are not any better. They are like wishcasters. They contribute to the obfuscation, misdirection and time-wasting. There is no real scientific question about the effects of CO2. The only real questions are economic, i.e., so what do we do about it? But this is a weather blog. The people on here are even less prepared to discuss that issue.

wrong and wrong. There is no fact that determines what CO2 will do to our atmosphere. There is evidence on both sides and it's your argument and others who say "Well let's treat it like it's real so that just in case it is, we'll be okay and if it's not then we will have done good!" That line of thinking has happened in history. It didn't end well.
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Quoting altesticstorm10:

Can't fish with the water temps <20C.

Do a lot of fishing in the Atlantic from Dallas? I think we all know why you are cheering for higher SSTs.
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Quoting Levi32:


What do you think happened the last time there was no ice in the northern hemisphere? We all died, that's why we're still here.


Might want to research what happened and give an informed answer.
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@Bappit.
You make no sense. You are only serving to diminish your side's argument and I'll tell you what I tell the over zealous skeptics as well: .... Do yourself a favor and post a valid point rather than "lalalala you're no expert can't hear you lalala." Get over yourself.
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Quoting altesticstorm10:


Today



Last week...



.....Colding.


I do not see where you are talking about. I see some areas are warmer like in the Atlantic and near the Islands and a few areas maybe that are cooler, but not to the emphasis that you are showing
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Quoting bappit:
The thing is, y'all come on this blog and totally ignore what the blog's host has said and given you. You totally ignore the evidence given to you.

WTH do you mean? I am sure *alomst* every has at least read it and at least carefully considered what was posted.
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quitcher whining.
perfect day in ECFl today.
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The thing is, y'all come on this blog and totally ignore what the blog's host has said and given you. You totally ignore the evidence given to you. Then you turn around and complain about people not paying attention to your evidence when you are not an expert. It would seem that the starting point of any debating should be the evidence provided by the acknowledged experts. They have devoted far more effort to the issue than any of the posters on this blog ever will, but the posters on this blog largely ignore what they have to say. How is that a setting for any reasonable debate? The skeptics do not want to deny. They want to obstruct. They have no scientific agenda. They are not interested in scientific debate. Why should I waste my time pretending to debate them over only what they want to talk about?
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Quoting altesticstorm10:
Why is the Atlantic colding when the NAO is actually becoming negative again after the 2-week positive burst?


where are the SSTs "colding" in the Atlantic?
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Quoting altesticstorm10:
Why is the Atlantic colding when the NAO is actually becoming negative again after the 2-week positive burst?
huh? Is "Atlantic colding" a real phrase?
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849

There just ain't no point in debating.
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Looks like Kansas City is about to get wet.
Link
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854. Skyepony (Mod)
Atmo~ I was refuring to that 9/11 paper..which is both widely excepted & somewhat disputed. Here's a 3rd opinion..

Others agree. ”Aircraft are likely to be a significant factor in future climate, but probably not via their contrails,” NASA’s James Hansen told NOVA . “I think our main concern about aircraft will be their CO2 emissions, not contrails, which are a pretty small climate force.”


Growing food here..I've had a near month here & there where suddenly it's near daily dimmed sun from so many contrails turned to clouds. That plus SAL & it can be a weird blown haze, not a regular dust event. It delays harvet, even without the SAL. Not that I have any clue what's exactly going on but I'm observant, it's certainly a change from what would have been.

Other countries boast about their climate control attempts for like Olympics & stuff. Our country has an agency for it, there is some info out there that admits frequent cloudseeding & companies that advertise their services. I don't really see enough evidence to think we are being sprayed like rats with birth control or some other harmful substance..
Member Since: August 10, 2005 Posts: 175 Comments: 38212
TROPICAL CYCLONE WARNING

TROPICAL CYCLONE ADVICE NUMBER 9
Issued by the BUREAU OF METEOROLOGY, DARWIN
at 5:00 am CST Sunday 28 March 2010

A Cyclone WARNING continues for coastal and island communities from Milingimbi
to Numbulwar, including Nhulunbuy and Groote Eylandt.

A Cyclone WATCH continues for coastal and island communities from Maningrida to
Milingimbi and Numbulwar to Port McArthur.

At 3:30 am CST a Tropical Low was estimated to be 75 kilometres south southwest
of Nhulunbuy and 125 kilometres north of Alyangula and moving southwest at 12
kilometres per hour.
The low is currently located near the coast and is expected to develop into a
tropical cyclone in the next 6 to 12 hours.

GALES with gusts to 110 kilometres per hour are expected to develop between and
MILINGIMBI AND NUMBULWAR, including GROOTE EYLANDT, today.

Tides will be HIGHER THAN NORMAL between ELCHO ISLAND and NUMBULWAR, including
GROOTE EYLANDT, today. Large waves may produce MINOR FLOODING of low-lying
coastal areas.

HEAVY RAIN may lead to localised flooding and significant stream rises in the
Arnhem and Roper-McArthur Districts during Sunday.

Details of Tropical Low at 3:30 am CST:
.Centre located near...... 12.8 degrees South 136.5 degrees East
.Location accuracy........ within 55 kilometres
.Recent movement.......... towards the southwest at 12 kilometres per hour
.Wind gusts near centre... 85 kilometres per hour
.Severity category........ below cyclone intensity
.Central pressure......... 999 hectoPascals

The next advice will be issued by 8:00 am CST Sunday 28 March.
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Radar Image of Tropical Low 1
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There's a climate bill coming before Congress. Why shouldn't people against economic change parade on a weather blog?
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I ain't no expert. You ain't no expert.
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Quoting bappit:
Maybe I should repeat the graph from the Good Doctor's post everytime someone posts some junk on the blog.


Cant debate with someone who refuses to even acknowledge a differing view

In your mind what you see is right and any evidence to the contrary is garbage

You seem to not be able to debate someone without getting snippy with them.

I could be wrong though, just an observation
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Quoting bappit:


Who cares about your list?


Your right, no other scientific "peer reviewed" evidence is any good if it does not agree with you. Gheeze....
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Maybe I should repeat the graph from the Good Doctor's post everytime someone posts some junk on the blog.
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Quoting bappit:
809

The funny thing about your post is that you know we are in a solar minimum.

Possible that there is a significant lag between sunspots and surface temps.
This one says 10 years (cannot say if it is right or not, personally...guess we will know soon):
http://www.mps.mpg.de/dokumente/publikationen/solanki/c153.pdf

Makes some sense considering how heat is distributed and moved around the oceans.
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Quoting nrtiwlnvragn:


LOL at the LOL, better check the link, which takes you to the same place, they just updated the list. They refuse to take out of the list authors who request it.


Uh, it's a list. It does not alter their work. I don't see the relevance. Did they ask Google to remove them too? Seems the IPCC has done some similar things when I think of Dr Paul Reiter :)
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35.4 C on my patio.
That's almost 96F.
This is going on for far too long now.
This is a relatively small Island (50X80 miles).
Islands are generally cool places, under the influence of sea breezes that calm the soul and encourage siestas.
But this feels like the middle of a dry continent now. The vegetation is taking a real beating.
Fires have burned many large areas of forest, including the forest on steep hillsides of heavily populated valleys.
The coming rainy season (June) could result in flash-flooding and Horrors in the valleys because there is now very little vegetation to stop the erosion and flooding that may occur.
The forest will survive, but have been set back YEARS by the fires.
Most Tropical Forest grows on relatively poor soil, and the nutrients come from fallen leaves and other Biomass (billions of critters) that break the leaf litter down to useable constituents for plants to feed from.
It is a constant circle of use and re-use. All the nutrient that comes from the soil is recycled by the trees and plants. The trees and plants harvest nutrients from different depths through the root systems.
When you remove the leaf litter (the food), by burning, it takes many years for this balance to be restored.(up to 100 years in some cases). The living organisms are all fried too. Including the fungi, termites, ferns, vines, etc etc. Old trees with dry roots smolder for weeks until they fall down. Young trees are roasted to death.
It is often said that forest needs to burn, from time to time, to maintain its health.
This is absolutely NOT TRUE of Tropical Forest.

Trinidad is 7 miles from Venezuela, and was seperated from Venezuela in recent (geologically speaking) time.
The rain forest here is not unique, but is a very good example of Tropical Rainforest, semi-deciduous forest, mature cloud forest above 2500 feet, wetland forest, salt water swamp (mangrove), and 'savanna' one section of which is called "hard-pan" because it is compressed clay over a bed of silica sand. This last area is very 'boggy' in the rain, and hard as rock in the dry. Unique vegetation grows here.

The northern Range of mountains go up to 3000 ft., and are the end of the Andes Mountains that turn east around Columbia. So the Biology of Trinidad is very rich. ESPECIALLY the Forest and other Vegetation.
Fires here are boo. But no attempt is being made to educate the population. Except for Political Mouthings about "be carefull when you light fires. They can get out of control".
Although private organisations and Non-Governmental Organisations are working on this lack of knowledge, these organisations are not adequately funded. It is a challenge.

It is very sad.
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809

The funny thing about your post is that you know we are in a solar minimum.
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hey Levi we have a developing Cyclone by the northern part of Australia

your thoughts?
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There's a climate bill coming before Congress. Why shouldn't people against economic change parade on a weather blog?
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839. JRRP
Quoting Tazmanian:
did any one see smackdown last night



one part it was too funny LOL

Vickie
“excuse me”
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did any one see smackdown last night



one part it was too funny LOL
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837. DDR
Quoting pottery:


Me too. But early might still be too late for my garden.
Looks like I have lost plenty plants this rounds.

Sorry to hear,but as you know your not the only one and wasa aint making it easy for the farmers.
Pottery im out,peace.
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Quoting DDR:

Hey good to see you.
I'm doing great,just checking the blog before i head out.Yes this heat is terrible!
I'm hoping for an early rainy season.


Me too. But early might still be too late for my garden.
Looks like I have lost plenty plants this rounds.
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835. DDR
Quoting JRRP:

yes

I thought so,back in 2004 i used weather.com to track ivan.
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I am so glad that I did not make a response to post 827, before Presslord did.
I could not have been so spot-on as that.
'Nuff respect!
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833. DDR
Quoting pottery:
Hi DDR.
Hot is an understatement, man.
How you been?

Hey good to see you.
I'm doing great,just checking the blog before i head out.Yes this heat is terrible!
I'm hoping for an early rainy season.
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Quoting whipster:
Wonder how many "research projects" our dear Dr is getting to propound this tripe day after day.


Congratulations!!!! That is, hands down, the greatest display of ignorance I've ever seen here...and that, my friends, is quite a feat...
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831. JRRP
Quoting DDR:
Good afternoon all
JRRP is that Ivan in your pic?
Its another hot day again.35c

yes
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Hi DDR.
Hot is an understatement, man.
How you been?
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828. DDR
Good afternoon all
JRRP is that Ivan in your pic?
Its another hot day again.35c
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Quoting Ossqss:


LoL, better check the dates of the blog post you referenced and then the date on the list. Just sayin :)


LOL at the LOL, better check the link, which takes you to the same place, they just updated the list. They refuse to take out of the list authors who request it.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.