Humans' 10,000-Year Warming Habit

BBC ^ | 12-10-2003 | Richard Black

[blam]

Humans' 10,000-year warming habit

By Richard Black
BBC science correspondent, in San Francisco

Human influence on climate is hotly debated

Humans have been warming the Earth's climate for the last 10,000 years, US scientist William Ruddiman claims. The University of Virginia professor says agriculture has put greenhouse gases in the atmosphere, pushing up temperatures by about one Celsius.

This, he claims, has broadly balanced the cooling that should have come from a natural reduction in the Sun's heat reaching Earth over the same period.

The professor has presented his ideas to the American Geophysical Union.

The AGU is holding its annual autumn meeting here in San Francisco.

Natural cooling

Over timescales of thousands of years, the Earth goes through a natural cycle of warmer and colder periods, driven by changes in heat coming from the Sun.

Professor Ruddiman has now calculated that if the Earth had followed its natural cycle over the last 10,000 years, it should have got steadily colder.

It has not because, he believes, human activities have been keeping the temperature steady.

"What should have happened with the natural climate is it should have cooled substantially," he told BBC News Online.

"And instead humans just started adding greenhouse gases at a rate which cancelled most, but not all, of that natural cooling; and so it's a combination of a natural cooling mostly cancelled by a human warming."

Fast warming

The birth and development of agriculture is the key, and it substantially changed the nature of the land and its interaction with the atmosphere.

Our ancestors started adding the greenhouse gas carbon dioxide principally by cutting down trees for farming. Methane concentrations - another potent greenhouse contributor - started to rise with wet farming of rice.

Professor Ruddiman, of the Department of Environmental Sciences at Virginia, believes this 10,000-year warming added almost a degree Celsius to the global average temperature.

This though is a radical departure from existing theories about climate change and will inevitably be debated by other researchers.

But there is supporting evidence, and it is consistent with what we know about deforestation and farming today.

And it does not alter the assertion that almost a further degree Celsius has been added over the last century alone, mainly through our dependence on fossil fuels.

The broad body of scientific opinion is of the view that the world is now warming faster than at any time in recorded history.

Sophisticated ways

Other research here at the AGU meeting suggests changes in climate brought into existence the civilisations of southern Mesopotamia, widely regarded as the birthplace of modern western society.

In northern Mesopotamia, rain-fed agriculture had been practised with success for 1,000 years when it was brought to a shuddering halt by a sudden reduction in rains 8,200 years ago, according to Professor Harvey Weiss from Yale University.

Professor Weiss told the AGU that this sudden drying out necessitated a change to irrigated fields.

But that was impossible in northern Mesopotamia where the Tigris and Euphrates rivers, which bordered Mesopotamia, ran in channels below the level of the agricultural land.

It was possible, however, in southern Mesopotamia, which is why - so the argument goes - great societies emerged there characterised by art, literature and sophisticated social structures.

Professor Weiss said it was something of an irony that natural changes in climate made modern society possible, whereas society was now changing the climate in ways which threatened its existence.

[blam]

Global warming ping.

[samtheman]

Hmmm. Sounds like this subject needs more study. Which is what Bush has been saying all along. Duh!

[GungaLaGunga]

6-8" of global warming expected here in Cleveland tonight.

[discostu]

We know from Roman documentation of farming in Europe that is has gotten colder in at least the last 2000 years. Once again the global warmers are just nutty.

[Bikers4Bush]

I knew it was the faults of the damn farmers. (Sarcasm of course)

[ClearCase_guy]

We definitely need to return to hunting and gathering. Well, gathering anyway. Then the world will be a better place. This agricultural crap is killing the planet!

[farmfriend]

Rights, farms, environment ping.

Let me know if you wish to be added or removed from this list.
I don't get offended if you want to be removed.

[LiteKeeper]

Agriculture often replaces natural vegetation. How can there be a significant shift in the balance then?

[LiteKeeper]

Please add me to your ping list

LiteKeeper
Batchelor of Science, K-State, 1966

[polemikos]

this 10,000-year warming added almost a degree Celsius to the global average temperature.

Run for the hills! The sky is falling. The sky is falling!

[AppyPappy]

The Earth is always getting warmer except when it is getting cooler.

[E.G.C.]

BTTT!!!!

[Bernard Marx]

Agriculture often replaces natural vegetation. How can there be a significant shift in the balance then?

My question exactly. Of course the replacement of natural or agricultural vegetation with asphalt and concrete might have some long term effect (mainly on the global warmers' temperature gauges), but cities really represent a tiny percentage of the world's total area.

[farmfriend]

Consider yourself added. If you ever change your mind, or I get you on the wrong list, just let me know.

[ClearCase_guy]

Well, I think the whole GW thing is crap, but I think I can explain part of this thinking. Let me cover animals first. In a state of nature there are X number of cattle on the planet. They pass methane, which is a greenhouse gas. Now, with humans and modern farming methods, the number of cattle on the planet is probably "X times 10,000" and the amount of methane is increased "beyond what is natural".

Just so, with agriculture. If you clear an acre of forest, and plant an acre of corn and harvest and re-grow it annually, I would think that the impact on CO2 levels would be "beyond what is natural".

Let me be clear: I don't think any of this matters. The sun warms the plant. End of discussion. But I think it is still OK to say that human agriculture can have a greater impact than natural vegetation.

[talleyman]

See? Global warming good! Heat makes things expand - that's why the days get longer in the summer!

[ClearCase_guy]

Although the sun does "warm the plant" I meant to say the sun "warms the Planet".

[elli1]

ah ha! Hear this vegetarians? Vegetables are the cause of global warming.

[Always Right]

Glaciers covered much of what is now the midwestern section of the US 20,000 years ago. 10,000 years ago these glaciers were gone. Did man do that too????

[-YYZ-]

Which keeps a larger amount of carbon locked up: an acre of forest or an acre of vegetable farm? Obviously the trees lock up more carbon than the plants that replaced them do. As long as the wood from those trees is kept intact, you're actually slightly ahead of the game. As soon as that wood decomposes, or is burned, you've released that carbon into the atmosphere. So yes, replacing woodlands with farms does put some carbon into the atmosphere, eventually. If you do slash and burn like in the Amazon, you immediately release the carbon into the atmosphere, and the land may be so poor when you're done farming it that it won't grow much of anything for a long, long time.

Of course, none of that really matters if global warming exists and is not caused by so-called greenhouse gasses.

[4mycountry]

Sounds like hot air to me.

[Bernard Marx]

I think it is still OK to say that human agriculture can have a greater impact than natural vegetation.

Possibly. The thing is, we don't really know. Ever-increasing human populations contribute humungous amounts of methane as well. How many "cattle" were there in a state of nature? Last I heard there are more trees in the U.S. now than when Columbus arrived in the New World, and forests are extending their ranges northward.

My criticism is based on the fact there are no hard data in the study. If you can quantify and actually compare Mammoth Herd X to Black Angus Herd Y, and so many million acres of Tempskya Fern in the Jurassic to an actual amount of present day sorghum (plus crop rotation cycles) then I might pay attention. But it's all Blue Sky academic posturing.

[F.J. Mitchell]

All speculation beyond the scope of one's knowledge, is pure BS, regardless of the number of diplomas that decorate the walls of the genius.

[from occupied ga]

this 10,000-year warming added almost a degree Celsius to the global average temperature.

It is all of the diesel tractors that were used in the paeolithic that started the problems. Once these tractors were converted to run on ethanol in the neolithic then global warming slowed

[Pan_Yans Wife]

Did you hear that in Australia, the farmers are now charged a methane tax, because of environmental impact? :)

[ancient_geezer]

Humans have been warming the Earth's climate for the last 10,000 years, US scientist William Ruddiman claims.

 

Figure 1-2 Climate of the last 2400 years

Hmmm! strange definition of warming trend by humans there. Looks like overall down to me.

Figure 1-3 Climate of the last 12,000 years

Ohh! I see, It must-a-been that jump in temperature just before agriculture set in from all them caveman hunter/gatherer campfires.

[Calvin Locke]

Don't forget Mars. Mars is warming too. Must be all those failed spacecraft that keep crashing (if they're lucky
enough to even reach the planet) on Mars. No other reason for it.

[Jackson Brown]

If you do slash and burn like in the Amazon, you immediately release the carbon into the atmosphere, and the land may be so poor when you're done farming it that it won't grow much of anything for a long, long time.

This is true if you just consider the "burn" part. However, it is also true that the rotting "material" on the Amazon's floor produces more CO2 than the Amazon's trees take in. This is more or less true for most old growth forests...and, NO, I'm not suggesting any actions here, including cutting down of old growth forests...just adding to the mix.

[Consort]

Weather is caused by stray lingering thoughts of dead humans. Everybody knows that.

[Jackson Brown]

And it does not alter the assertion that almost a further degree Celsius has been added over the last century alone, mainly through our dependence on fossil fuels.

This theory might not alter this conclusion, but the facts do. The short AND long term records show that warming came first and then the atmospheric CO2 build up FOLLOWED! Since warmer soil and water can retain less CO2, it is more logical to view warming as the cause of atmospheric CO2 and not visa versa...especially since that is what the most recent studies that address the cause and effects now show...but are ignored by the GW entrepreneurs!

[-YYZ-]

"This is true if you just consider the "burn" part. However, it is also true that the rotting "material" on the Amazon's floor produces more CO2 than the Amazon's trees take in."

I can't see how that is possible over the long term if the forest is fairly stable over a long term. Where does the rotting material come from, if not from the trees? If a tree dies and falls, it ends up rotting on the forest floor, but another tree will eventually fill that space and consume an equivalent amount of carbon from the air. Otherwise all the rotting material on the forest floor would eventually disappear.

However, that does mean that once mature, a forest like that is essentially neutral in terms of carbon inputs and outputs. The carbon is not being locked away, like in fossil fuels or the carbonates from sea creatures of all sizes that eventually become limestone. But it does keep a certain amount of carbon tied up, and that amount is larger than fields under cultivation would tie up.

[Old Professer]

This is typical of "scientists": when your argument proves unmarketable, change arguments.

[Mad Dawgg]

"6-8" of global warming expected here in Cleveland tonight."

I predict no matter what frigged-up science the global warming nuts use to try and prove their point the will ultimately fail because of Buffalo New York and Cleveland Ohio.

Anyone who has spent a winter in either place will never believe there is anything at all to the phenomenon known as Global Warming!!!

[Jackson Brown]

I writing this quickly, so if it not completely clear, or comprehensive...I apologize in advance.

There are a lot of recent studies that show this (the dead material emitting more CO2 than the trees take in). I can't lay my hands on them right now, but the explanation -- for rain forests like the Amazon -- is that 50% of the dry trunk of tree (these are often 100+ feet tall and quite big around) is carbon. However, in dense old growth forests, 90% of the CO2 breathing part of the tree (where photosynthesis takes place and it gives off Oxygen) is in the first 15-20 feet of the canopy -- when you get 50 feet down from the canopy, only 2% exists.

When those trees falls, they more likely to cause the trees near it spread out and not be replaced by a new one of the same type...What sun does reach the floor usually just supports small plants that use less CO2 and emit less O2.

That 100+ foot tree -- and ALL the debris that the trees sluff off -- then emits it's stored carbon as it rots -- especially in very wet rain forests during rainy weather.

The dead material that flows into the streams and rivers gives off CO2 at an even more rapid pace. (see BBC report below on the Amazon that gives a small bit of the details regarding this)

---

'No solution' found in more trees

Planting trees to curb the effects of global warming is unlikely to work.
A US-Brazilian team has found that some parts of the Amazon rain forest emit more carbon dioxide (CO2) than they absorb in very wet conditions.

Their report, published in the journal Science, says previous studies have almost certainly overestimated how much CO2 the Amazon can take in.

And their study is backed by other work which shows newly planted trees will not grow fast enough to mop up CO2.

The Science papers are pertinent because the idea of using forests to curb global warming forms a central plank of the Kyoto Protocol, which world governments will discuss next week in Milan.

The protocol allows countries to plant new trees and conserve old forests rather than cut the amount of greenhouse gases they produce.

[SNIP]

Saleska's study of old-growth Amazonian rainforest shows clearly that drought or other disturbances that kill trees can lead to higher levels of carbon dioxide release.

These increases in carbon loss occur during wet seasons when the dead wood breaks down, not during the dry season as has been generally found.

Rest at --
http://news.bbc.co.uk/1/hi/sci/tech/3246938.stm

[blam]

"This is true if you just consider the "burn" part. However, it is also true that the rotting "material" on the Amazon's floor produces more CO2 than the Amazon's trees take in. "

Read This article.

Rainforest Researchers Hit Paydirt (Farming In South America 11K Years Ago)

[Jackson Brown]

Absolutely --

The bulk soil on the "untouched" Amazon floor is extremely poor -- despite the rotting material that falls since -- for the most part -- it just rots but does not sink into the ground. Most washes into rivers and streams and does not replenish the soil. recent studies show that a GREAT deal of CO2 is given off by the rivers that run through the rain forests that causes the release of the stored CO2. I was aware of what you linked -- but thanks nonetheless!!!!

[Timocrat]

A US-Brazilian team has found that some parts of the Amazon rain forest emit more carbon dioxide (CO2) than they absorb in very wet conditions.

You mean Ronald Reagan was right.

[Jackson Brown]

You mean Ronald Reagan was right.

I'm not aware of what Reagan said, but a WHOLE lot of what people have been screaming about (that has become the basis for a lot of Kyoto) is extremely flawed -- even before Kyoto became THE issue.

OLD GROWTH FORESTS, especially rain forests, are at best CO2 neutral. They are great to have, but don't use them as the basis to prove anything about being the "planets lungs".

FAR More oxygen is given off from the plankton in the oceans than forests...period.

New growth forests -- if managed right (like those planted by lumber/paper companies) -- give off far more O2 than old growth.

[stylin19a]

Professor Ruddiman has now calculated that if the Earth had followed its natural cycle over the last 10,000 years, it should have got steadily colder.

He should have been around my house the time I told my wife "Those slacks make your butt look big"

[3Lean]

Regarding Figure 1-3, it never ceases to amaze me that trained scientists will publish data like the chart you included. Are they really suggesting that they have the ability to measure temperature via tree rings, ice cores, etc. to an accuracy any where close to 1 degree Celsius?
In a past life I had the mind-numbing task of calibrating thermometers (ISO 9000), the only diversion provided was the shock I experienced when I realized how many "scientific" thermometers were not capable of +/-1 degree accuracy.
If Mr. Ruddiman was at all honest he would concede that his 1 degree estimate has a fair amount of inaccuracy associated with it (maybe 5 degrees or more) so in reality his conclusions are meaningless.

[ancient_geezer]

Regarding Figure 1-3, it never ceases to amaze me that trained scientists will publish data like the chart you included. Are they really suggesting that they have the ability to measure temperature via tree rings, ice cores, etc. to an accuracy any where close to 1 degree Celsius?

Absolute temperature is a problem differences are more readily determined, through the study of the proxies used, specifically C¹⁴, Be¹⁰ and O¹⁸ created by the effect of solar activity on cosmic ray intensity.

The concentration of these isotopes and relation to temperature is demonstrated very well in the current era as well as going back in the paleo record. The temperature deviations are derived from correlating a multitude of such measures as well as growth rates of vegetation, sedimentary deposits and many other factors that are temperature related and not on the strenght of any single one of them.

[lepton]

Professor Weiss said it was something of an irony that natural changes in climate made modern society possible, whereas society was now changing the climate in ways which threatened its existence stabilizing climate change.

[lepton]

Let me cover animals first. In a state of nature there are X number of cattle on the planet. They pass methane, which is a greenhouse gas. Now, with humans and modern farming methods, the number of cattle on the planet is probably "X times 10,000"

Let me cover animals first. In a state of nature there are X number of cattle, and Y number of Bison on the planet. They pass methane, which is a greenhouse gas. Now, with humans and modern farming methods, the number of cattle on the planet is probably "X times 10,000", while numbers of Bison have plummetted to an insignificant fraction - though the flatulence of ill-fed cattle is higher than those that are well fed, and the cattle in India are among the most flatulent of all.

[lepton]

If you do slash and burn like in the Amazon [- to support alcohol as a fuel -] you immediately release the carbon into the atmosphere, and the land may be so poor when you're done farming it that it won't grow much of anything for a long, long time.

So it's the environmentalists fault?

[SevenDaysInMay]

Coincidence has its headlines.

What of other interglacial periods?

What happened 5,000 years ago?

What were the pre-Holocene populations of termites? ( a leading producer of methane)

Could the sublimating methane ice on the ocean floor be a lagging indicator of the ice melt off?

These guys don't know and can't know. so, they just jump to a conclusion like watermellon headline writers.

[lepton]

New growth forests -- if managed right (like those planted by lumber/paper companies) -- give off far more O2 than old growth.

And support more quantiful and diverse life.

[3Lean]

I didn't ask how the temperatures (or differences) were measured. I asked what the accuracy of these measurements were. How does the error compare the the result of 1 degree C?

Your comment about temperature differences intrigues me. You are saying that one cannot determine if the mean global temperature 10,000 years ago was 10 C (for example) but one can determine that the mean global temp was lower by 1 C than it is today? Since we know (fairly accurately) what the mean global temp is today and we know the difference, don't we know the absolute temp then?
Or are you saying that we can't make the comparison between today and 10,000 years ago, but need to proceed in smaller steps (say 1000 years)then the error is compounded at each step.

[ancient_geezer]

We cannot even determing "Global" temperature today with certainty of better than 1/2 degree in absolute measure. Thus we can do no better in determining "absolute" temperature in historical reconstructions.

There are two separate sources of error, accuracy and precision of the measurement. The accuracy relates to errors in offset from true temperature, precision errors deal with the scale factor associated with relative measurements.

It is relatively easy to determine where temperatures must lay between some relative range of values measurable by a proxy quantities such as Be10 or C14 concentrations. It is a more difficult to endow such measurements with an absolute precision.

One can know for example the coldest of temperatures could not exceed a certain value and from that establish a linear relation between temperature and the proxies used. Such a measure yields a values of certain percentage precision of the measurement.

Establishing the absolute value as a fraction of a degree absolute is a separate issue altogether especially in regard to assigning it to a global measurement when one lacks the means of making "global" measures at specific times to weigh and define whatever the average may be. Any local temperatures measured reflect the changes global values assume in relative terms, but the absolute value will remain indeterminate.

[ancient_geezer]

The following is a comparative chart of temperature reconstruction for the last 2,000 years. Helps provide some perspective as reguards the precision of the measurements in relation to the insturmental record for 1850-2000 Northern Hemisphere Land Temperature variation. Note the shaded areas representing the error with respect to instrumental data.

No record can be said to be accurate in an absolute sense. Though they all indicate relative trends in the displayed period.

 

figure 1. Comparison of proxy-based NH temperature reconstructions [Jones et al., 1998; Mann et al., 1999; Crowley and Lowery, 2000] with model simulations of NH mean temperature changes over the past millennium based on estimated radiative forcing histories [Crowley, 2000; Gerber et al., 2002--results shown for both a 1.5°C/2*CO2 and 2.5°C/2*CO2 sensitivity; Bauer et al., 2003). Also shown are two independent reconstructions of warm-season extratropical continental NH temperatures [Briffa et al., 2001; Esper et al., 2002] and an extension back through the past two thousand years based on eight long reconstructions [Mann and Jones, 2003]. All reconstructions have been scaled to the annual, full Northern Hemisphere mean, over an overlapping period (1856-1980), using the NH instrumental record [Jones et al., 1999] for comparison, and have been smoothed on time scales of >40 years to highlight the long-term variations. The smoothed instrumental record (1856-2000) is also shown. The gray/red shading indicates estimated two-standard error uncertainties in the Mann et al. [1999] and Mann and Jones [2003] reconstructions. Also shown are reconstructions of ground surface temperatures (GST) based on appropriately areally-averaged [Briffa and Osborn, 2002; Mann et al., 2003] continental borehole data [Huang et al., 2000], and hemispheric surface air temperature trends, determined by optimal regression [Mann et al., 2003] from the GST estimates. All series are shown with respect to the 1961-90 base period.

 

However, looking at a much longer period using glacial ice core data (e.g. Be10, C14, & O18 proxies) gives a clearer view of Norther Hemisphere climate trends overall.

Figure 1-2 Climate of the last 2400 years

 

Figure 1-3 Climate of the last 12,000 years