New Findings Hint at The True Reasons For The Decline of This Ancient Civilisation

[geovalin]

 

ALISON KYRA CARTER, THE CONVERSATION

 

It was built in the early 12th century by King Suryavarman II, one of the most famous kings of the Angkorian civilization that lasted from approximately the ninth to 15th centuries. The structure is so strongly associated with Cambodian identity even today that it appears on the nation's flag.

 

For many years, historians placed the collapse of the Angkor civilization in 1431, when Angkor's capital city was sacked by the Thai Kingdom of Ayutthaya and abandoned.

 

The idea that the Angkorian capital was abandoned also played a part in the 19th-century colonial interpretation of Angkor as a civilization forgotten by the Cambodians and left to decay in the jungle.

 

read more https://www.sciencealert.com/archaeologist-find-hints-to-why-ancient-civilisation-at-angkor-wat-cambodia-declined

[inThailand]

New Findings Hint at The True Reasons For The Decline of This Ancient Civilisation. 

 

I thought this was about the declining LOS that hasn't made it past the stone age? 

[cmarshall]

Good article.  Similarly, the Peruvians never entirely forgot about Machu Picchu.  They told Hiram Bingham where it was after which he became famous for "discovering" it.

[VincentRJ]

"A series of decades-long droughts, interspersed with heavy monsoons, disrupted Angkor's water management network meant to capture and disburse water.

 

One study of the moats around the walled urban precinct of Angkor Thom suggest the city's elite were already departing by 14th century, almost 100 years before the supposed sack of the capital by Ayutthaya."

 

I read about this rapid change in climate many years ago, which was also confirmed by a study of tree rings in the area, by a group of Australian scientists. A rapid cooling in the Himalayas could also have reduced the amount of water flowing down the Mekong, leaving the dams dry and resulting in large numbers of the population abandoning the area.

 

It's interesting to note that these decades-long droughts occurred around the same time that the climate in Europe was changing from the Medieval Warm Period to the Little Ice Age, suggesting that the MWP and the LIA were in fact global events, which Climate Change alarmists seem to deny.

[phycokiller]

3 hours ago, VincentRJ said:

"A series of decades-long droughts, interspersed with heavy monsoons, disrupted Angkor's water management network meant to capture and disburse water.

 

One study of the moats around the walled urban precinct of Angkor Thom suggest the city's elite were already departing by 14th century, almost 100 years before the supposed sack of the capital by Ayutthaya."

 

I read about this rapid change in climate many years ago, which was also confirmed by a study of tree rings in the area, by a group of Australian scientists. A rapid cooling in the Himalayas could also have reduced the amount of water flowing down the Mekong, leaving the dams dry and resulting in large numbers of the population abandoning the area.

 

It's interesting to note that these decades-long droughts occurred around the same time that the climate in Europe was changing from the Medieval Warm Period to the Little Ice Age, suggesting that the MWP and the LIA were in fact global events, which Climate Change alarmists seem to deny.

you better send them a letter, hey climate change alarmists, there was an alarming climate change so therefore there cant be alarming climate changes

[gk10002000]

This is not new news.  I have watched documentaries about this at least a decade ago.

[VincentRJ]

7 hours ago, phycokiller said:

you better send them a letter, hey climate change alarmists, there was an alarming climate change so therefore there cant be alarming climate changes

No. The message is, alarming climate change has happened frequently before when CO2 levels were low, so don't fall into the trap of thinking you can stop it happening again by spending trillions of dollars reducing CO2 levels. 

 

Instead, build more dams, long water pipes, and desalination plants, so nobody ends up like the ancient Khmers did, and other ancient civilizations, as a result of natural changes in climate.

[phycokiller]

20 hours ago, VincentRJ said:

No. The message is, alarming climate change has happened frequently before when CO2 levels were low, so don't fall into the trap of thinking you can stop it happening again by spending trillions of dollars reducing CO2 levels. 

 

Instead, build more dams, long water pipes, and desalination plants, so nobody ends up like the ancient Khmers did, and other ancient civilizations, as a result of natural changes in climate.

I dont think anyone is claiming co2 is the only cause of climate change

[VincentRJ]

6 hours ago, phycokiller said:

I dont think anyone is claiming co2 is the only cause of climate change

Of course not. That would be very silly. ????

 

The message that is being promoted by the politicians and the scientists whose jobs rely upon government funding, is that human caused CO2 emissions are the primary driver of the current warming, and that we can stop the warming, and the predicted increase in the severity of extreme weather events, by halting our emissions of CO2.

 

For some strange reason it is thought that warming is 'bad', yet the ancient Khmer civilization began around the time of the beginning of the Medieval Warm Period in Europe, and flourished during the course of that warm period, just as the Vikings flourished in Greenland.

 

When the climate began changing from warm to cool, during the 14th century, the Vikings deserted Greenland and the Khmers deserted their civilization around Angkor Wat.

 

If it's true that rising CO2 levels are the primary cause of the current warming, which I doubt, as do lots of very qualified scientists whose research is marginalized, then maintaining the current levels of CO2 could protect us from the devastation of the next 'cool' period which, in the past, appears to have at least contributed to the destruction of the Khmer civilization.

 

We might be shooting ourselves in the foot by reducing CO2 levels. We should try harder to learn from history.

[soalbundy]

On 6/5/2019 at 3:11 PM, inThailand said:

New Findings Hint at The True Reasons For The Decline of This Ancient Civilisation. 

 

I thought this was about the declining LOS that hasn't made it past the stone age? 

I thought it was about brexit

[soalbundy]

4 minutes ago, VincentRJ said:

Of course not. That would be very silly. ????

 

The message that is being promoted by the politicians and the scientists whose jobs rely upon government funding, is that human caused CO2 emissions are the primary driver of the current warming, and that we can stop the warming, and the predicted increase in the severity of extreme weather events, by halting our emissions of CO2.

 

For some strange reason it is thought that warming is 'bad', yet the ancient Khmer civilization began around the time of the beginning of the Medieval Warm Period in Europe, and flourished during the course of that warm period, just as the Vikings flourished in Greenland.

 

When the climate began changing from warm to cool, during the 14th century, the Vikings deserted Greenland and the Khmers deserted their civilization around Angkor Wat.

 

If it's true that rising CO2 levels are the primary cause of the current warming, which I doubt, as do lots of very qualified scientists whose research is marginalized, then maintaining the current levels of CO2 could protect us from the devastation of the next 'cool' period which, in the past, appears to have at least contributed to the destruction of the Khmer civilization.

 

We might be shooting ourselves in the foot by reducing CO2 levels. We should try harder to learn from history.

Yes, not only CO2 we have methane to worry about now as the permanent frost ground heats up and the oceans warm releasing the far more dangerous methane gas a far bigger greenhouse gas than CO2.

[VincentRJ]

2 hours ago, soalbundy said:

Yes, not only CO2 we have methane to worry about now as the permanent frost ground heats up and the oceans warm releasing the far more dangerous methane gas a far bigger greenhouse gas than CO2.

Methane might be a more significant greenhouse gas than CO2 per molecule, but the total quantity in the atmosphere is even tinier than the quantity of CO2. Currently there is around 404 'parts per million' of CO2 in the atmosphere. In recent years the amount of Methane has risen from 0.7 ppm to 1.8 ppm. The amounts are so tiny they are usually described in 'parts per billion'.

Ooh! I'm getting really nervous. I'm trembling with anxiety. ????

 

Water vapor is by far the most significant greenhouse gas, accounting for perhaps as much as 85% of the total greenhouse effect. However, the amount of water vapor in the atmosphere at any particular location and time, varies considerably. It can be as high as 4% (a thousand times greater than the amount of CO2) in hot, humid conditions, and close to zero in the dry deserts. Perhaps on average, it comprises about 2-3% of the lower atmosphere or troposphere.
 

[phycokiller]

4 hours ago, VincentRJ said:

Of course not. That would be very silly. ????

 

The message that is being promoted by the politicians and the scientists whose jobs rely upon government funding, is that human caused CO2 emissions are the primary driver of the current warming, and that we can stop the warming, and the predicted increase in the severity of extreme weather events, by halting our emissions of CO2.

 

For some strange reason it is thought that warming is 'bad', yet the ancient Khmer civilization began around the time of the beginning of the Medieval Warm Period in Europe, and flourished during the course of that warm period, just as the Vikings flourished in Greenland.

 

When the climate began changing from warm to cool, during the 14th century, the Vikings deserted Greenland and the Khmers deserted their civilization around Angkor Wat.

 

If it's true that rising CO2 levels are the primary cause of the current warming, which I doubt, as do lots of very qualified scientists whose research is marginalized, then maintaining the current levels of CO2 could protect us from the devastation of the next 'cool' period which, in the past, appears to have at least contributed to the destruction of the Khmer civilization.

 

We might be shooting ourselves in the foot by reducing CO2 levels. We should try harder to learn from history.

 while I agree that humans likely have accidentally prevented ourselves from going into the next ice age I think scientists probably have a good idea as when we are overdoing it

[VincentRJ]

5 hours ago, phycokiller said:

 while I agree that humans likely have accidentally prevented ourselves from going into the next ice age I think scientists probably have a good idea as when we are overdoing it

The next 'true' Ice Age might be a long way off. During the last Ice Age, glaciers have advanced and retreated over 20 times, often blanketing North America with ice. Our climate today is actually a warm interval between these many periods of glaciation, known as an interglacials. The most recent period of glaciation, which many people think of as the "Ice Age," was at its height approximately 20,000 years ago. This is more correctly termed the 'Last Glacial Maximum'. The last Ice Age began about 2.6 million years ago.

 

Within these many cycles of 'glacials and interglacials', there are smaller cycles such as the flourishing 'Roman Warm Period', the cold and miserable 'Dark Ages', the bounce-back to the warm Middle Ages, the troublesome Little Ice Age causing the extinction of the Khmer empire, and now the magnificent Anthropocene, the current warm period during which our civilization has flourished.

 

History tells us that warm periods are good. At the end of the Medieval Warm Period, around 1300 AD, temperatures dropped dramatically and the cold periods that followed were devastating. The population of Europe had become dependent on cereal grains as a food supply during the Medieval Warm Period, and with the colder climate, early snows, violent storms, and recurrent flooding that swept Europe, massive crop failures occurred, resulting in widespread famine and disease (Fagan, 2000; Grove, 2004). Glaciers in Greenland and elsewhere began advancing and pack ice extended southward in the North Atlantic, blocking ports and affecting fishing. Three years of torrential rains that began in 1315 led to the Great Famine of 1315–1317, and of course, extensive droughts followed by massive floods destroyed the Khmer civilization.

 

I think scientists probably have a good idea as when we are overdoing it.

 

What do you mean by 'it'? CO2 emissions? There's a lot of pollution resulting from human activities, such as plastic and industrial waste, and pesticide and fertilizer run-off affecting the Great barrier Reef, but CO2 is a clean and odorless gas which is essential for all life. Plants just love it.

 

There are many scientists who think that human emissions of CO2, at the current rates, have a relatively insignificant effect on the current warming. The temperature in the desert can change drastically from day to night because the air is so dry, lacking water vapor, that heat escapes rapidly at night. The daytime temperature averages 38°C while in some deserts it can get down to -4°C at night. The 0.04% of CO2 in the desert atmosphere doesn't seem to help much in preventing the extreme cooling at night, although it does help the Cacti, small bushes and short grasses grow better in the extremely dry conditions.

 

[phycokiller]

2 hours ago, VincentRJ said:

The next 'true' Ice Age might be a long way off. During the last Ice Age, glaciers have advanced and retreated over 20 times, often blanketing North America with ice. Our climate today is actually a warm interval between these many periods of glaciation, known as an interglacials. The most recent period of glaciation, which many people think of as the "Ice Age," was at its height approximately 20,000 years ago. This is more correctly termed the 'Last Glacial Maximum'. The last Ice Age began about 2.6 million years ago.

 

Within these many cycles of 'glacials and interglacials', there are smaller cycles such as the flourishing 'Roman Warm Period', the cold and miserable 'Dark Ages', the bounce-back to the warm Middle Ages, the troublesome Little Ice Age causing the extinction of the Khmer empire, and now the magnificent Anthropocene, the current warm period during which our civilization has flourished.

 

History tells us that warm periods are good. At the end of the Medieval Warm Period, around 1300 AD, temperatures dropped dramatically and the cold periods that followed were devastating. The population of Europe had become dependent on cereal grains as a food supply during the Medieval Warm Period, and with the colder climate, early snows, violent storms, and recurrent flooding that swept Europe, massive crop failures occurred, resulting in widespread famine and disease (Fagan, 2000; Grove, 2004). Glaciers in Greenland and elsewhere began advancing and pack ice extended southward in the North Atlantic, blocking ports and affecting fishing. Three years of torrential rains that began in 1315 led to the Great Famine of 1315–1317, and of course, extensive droughts followed by massive floods destroyed the Khmer civilization.

 

 

 

 

What do you mean by 'it'? CO2 emissions? There's a lot of pollution resulting from human activities, such as plastic and industrial waste, and pesticide and fertilizer run-off affecting the Great barrier Reef, but CO2 is a clean and odorless gas which is essential for all life. Plants just love it.

 

There are many scientists who think that human emissions of CO2, at the current rates, have a relatively insignificant effect on the current warming. The temperature in the desert can change drastically from day to night because the air is so dry, lacking water vapor, that heat escapes rapidly at night. The daytime temperature averages 38°C while in some deserts it can get down to -4°C at night. The 0.04% of CO2 in the desert atmosphere doesn't seem to help much in preventing the extreme cooling at night, although it does help the Cacti, small bushes and short grasses grow better in the extremely dry conditions.

 

Im with you up until "There are many scientists who think that human emissions of CO2, at the current rates, have a relatively insignificant effect on the current warming." unless by many you mean about half a dozen

[VincentRJ]

7 hours ago, phycokiller said:

Im with you up until "There are many scientists who think that human emissions of CO2, at the current rates, have a relatively insignificant effect on the current warming." unless by many you mean about half a dozen

Looks like you've been duped by the common mantra, repeated ad nauseam, that 97% of all scientists (in the field of climatology) believe that the current warming is unprecedented, is driven mainly by human emissions of CO2 and will be catastrophic if the emissions are not stopped.

 

If you dig into the background of how this figure was derived you'll find that this figure of 97% applies only to those scientists who are willing to express an opinion of certainty on the issue, which is a minority of them. Most scientists who are genuinely unbiased realize that the issue is too complex and chaotic for any certainty to be expressed.

 

One of the founders of this 97% myth is John Cook, creator of the blog Skeptical Science. In an analysis of 12,000 abstracts, he found “a 97% consensus among papers taking a position on the cause of global warming in the peer-reviewed literature, that humans are responsible.” “Among papers taking a position” is a significant qualifier: Only 34 percent of the papers Cook examined expressed any opinion about anthropogenic climate change at all. Since 33 percent appeared to endorse anthropogenic climate change, he divided 33 by 34 and — voilà — 97 percent! 
 

[phycokiller]

18 hours ago, VincentRJ said:

Looks like you've been duped by the common mantra, repeated ad nauseam, that 97% of all scientists (in the field of climatology) believe that the current warming is unprecedented, is driven mainly by human emissions of CO2 and will be catastrophic if the emissions are not stopped.

 

If you dig into the background of how this figure was derived you'll find that this figure of 97% applies only to those scientists who are willing to express an opinion of certainty on the issue, which is a minority of them. Most scientists who are genuinely unbiased realize that the issue is too complex and chaotic for any certainty to be expressed.

 

One of the founders of this 97% myth is John Cook, creator of the blog Skeptical Science. In an analysis of 12,000 abstracts, he found “a 97% consensus among papers taking a position on the cause of global warming in the peer-reviewed literature, that humans are responsible.” “Among papers taking a position” is a significant qualifier: Only 34 percent of the papers Cook examined expressed any opinion about anthropogenic climate change at all. Since 33 percent appeared to endorse anthropogenic climate change, he divided 33 by 34 and — voilà — 97 percent! 
 

there's plenty if evidence humans pumping greenhouse gasses into the atmosphere is the main cause of the current change, and nobody has come up with an alternative explanation, altho Im sure the oil companies would pay them handsomely if they could

[Enki]

On 6/5/2019 at 2:59 PM, VincentRJ said:

which Climate Change alarmists seem to deny.

Why would anyone deny that, especially if he is a climate researchers? Climate change deniers are denying everything, though.

[Enki]

On 6/7/2019 at 5:14 AM, VincentRJ said:

Of course not. That would be very silly. ????

 

The message that is being promoted by the politicians and the scientists whose jobs rely upon government funding, is that human caused CO2 emissions are the primary driver of the current warming, and that we can stop the warming, and the predicted increase in the severity of extreme weather events, by halting our emissions of CO2.

 

For some strange reason it is thought that warming is 'bad', yet the ancient Khmer civilization began around the time of the beginning of the Medieval Warm Period in Europe, and flourished during the course of that warm period, just as the Vikings flourished in Greenland.

 

When the climate began changing from warm to cool, during the 14th century, the Vikings deserted Greenland and the Khmers deserted their civilization around Angkor Wat.

 

If it's true that rising CO2 levels are the primary cause of the current warming, which I doubt, as do lots of very qualified scientists whose research is marginalized, then maintaining the current levels of CO2 could protect us from the devastation of the next 'cool' period which, in the past, appears to have at least contributed to the destruction of the Khmer civilization.

 

We might be shooting ourselves in the foot by reducing CO2 levels. We should try harder to learn from history.

Sorry, you have not much clue about the topic.

 

Current climate change is solely caused by human made CO2. If you find another reason interacting and supporting the current climate change, publish it and you get piled over with Nobel Prizes.

 

The Vikings never "flourished" in Greenlands. They had a few settlements, perhaps about 500 people, and they died when the climate changed back to "normal" or "average". Meanwhile we have settlement there again. (With there I mean the south tip of Greenland, with a few farms, they even grow potatoes again. Not the inuit population)

 

There won't be a next "cool period", we have to much CO2 in the atmosphere for that. Or do you mean shifts between El Nino and La Nina causing localized cool periods?

[Enki]

On 6/7/2019 at 3:01 PM, VincentRJ said:

There are many scientists who think that human emissions of CO2, at the current rates, have a relatively insignificant effect on the current warming.

Care to point a few out? I know no one (and I worked for a climate institute).

[phycokiller]

On 6/7/2019 at 1:03 PM, VincentRJ said:

Methane might be a more significant greenhouse gas than CO2 per molecule, but the total quantity in the atmosphere is even tinier than the quantity of CO2. Currently there is around 404 'parts per million' of CO2 in the atmosphere. In recent years the amount of Methane has risen from 0.7 ppm to 1.8 ppm. The amounts are so tiny they are usually described in 'parts per billion'.

Ooh! I'm getting really nervous. I'm trembling with anxiety. ????

 

Water vapor is by far the most significant greenhouse gas, accounting for perhaps as much as 85% of the total greenhouse effect. However, the amount of water vapor in the atmosphere at any particular location and time, varies considerably. It can be as high as 4% (a thousand times greater than the amount of CO2) in hot, humid conditions, and close to zero in the dry deserts. Perhaps on average, it comprises about 2-3% of the lower atmosphere or troposphere.
 

your tiny amount rational is pretty emotional, sort of like saying germs are small so Im not scared of them. green house properties of gasses are testable and have been well known for a long time. nobody is questioning it.  on the subject of water vapor you are correct, but its also testable and is rising with the temperature

[VincentRJ]

2 hours ago, phycokiller said:

your tiny amount rational is pretty emotional, sort of like saying germs are small so Im not scared of them. green house properties of gasses are testable and have been well known for a long time. nobody is questioning it.  on the subject of water vapor you are correct, but its also testable and is rising with the temperature

I think you mean 'nobody who lacks an understanding of the methodology of science is questioning it. True scientists question everything.

 

Emotional? Just the opposite. Alarmism is emotional. Skepticism is rational. Comparing tiny quantities of beneficial inanimate chemicals, such as CO2 and Methane, with lifeforms such as germs, is ridiculous, especially if you are using the usual definition of germ as: 'a microorganism causing disease'. 

 

CO2 is essential for life. Disease-causing germs are not.

 

Methane also plays an essential role in the health of soils. The planet’s ecosystem – made up of many habitats and associated species – both emit and absorb methane. A healthy soil, for instance, contains many microorganisms all playing a complex role in nutrient cycling and regulating the gases of the atmosphere.
Methanotrophs (prokaryotes that metabolize methane as their only source of carbon and energy) are found in aerobic healthy soils, like those of the plains of Africa and America that once supported more wild ruminants than we have domestic livestock today. The first step of the complex but highly effective cycling of methane happens right under the noses of the grazers as they munch.

 

Here are some links showing the importance of methane and its potential uses, in addition to its use as fossil fuel.
https://www.sciencedaily.com/releases/2012/08/120827074226.htm

 

"Methane is taken up by methane oxidizing bacteria, which in turn are eaten by zooplankton and other aquatic organisms. These organisms eventually end up in fish stomachs, meaning that food webs not only feed off organic carbon from plants in the lake or from the surrounding land; but also from deep-lying and oxygen-free, yet carbon-rich, sediment stores where methane is formed.
More studies are being planned to show the potentially vast importance that methane could have on the food chain in different types of lakes and conditions. For example, what happens in Swedish lakes during the winter?"

 

https://www.newscientist.com/article/2112298-food-made-from-natural-gas-will-soon-feed-farm-animals-and-us/

 

"A biotechnology company called Calysta, based in Menlo Park, California, is set to announce the first ever large-scale factory that uses microbes to turn natural gas – methane – into a high-protein food for the animals we eat. The factory, which will be built in the US in collaboration with food-giant Cargill, will produce 200,000 tonnes of feed a year.
The methane-made food has already been approved in the European Union for feeding to farmed fish and livestock such as pigs. Calysta is seeking approval in the US, too – and not just for farm animals. “We want to take it all the way to cats and dogs, and potentially even humans,” says the head of Calysta, Alan Shaw."

 

Germs! Really!! ????????
 

[phycokiller]

On 6/9/2019 at 8:27 PM, VincentRJ said:

I think you mean 'nobody who lacks an understanding of the methodology of science is questioning it. True scientists question everything.

 

Emotional? Just the opposite. Alarmism is emotional. Skepticism is rational. Comparing tiny quantities of beneficial inanimate chemicals, such as CO2 and Methane, with lifeforms such as germs, is ridiculous, especially if you are using the usual definition of germ as: 'a microorganism causing disease'. 

 

CO2 is essential for life. Disease-causing germs are not.

 

Methane also plays an essential role in the health of soils. The planet’s ecosystem – made up of many habitats and associated species – both emit and absorb methane. A healthy soil, for instance, contains many microorganisms all playing a complex role in nutrient cycling and regulating the gases of the atmosphere.
Methanotrophs (prokaryotes that metabolize methane as their only source of carbon and energy) are found in aerobic healthy soils, like those of the plains of Africa and America that once supported more wild ruminants than we have domestic livestock today. The first step of the complex but highly effective cycling of methane happens right under the noses of the grazers as they munch.

 

Here are some links showing the importance of methane and its potential uses, in addition to its use as fossil fuel.
https://www.sciencedaily.com/releases/2012/08/120827074226.htm

 

"Methane is taken up by methane oxidizing bacteria, which in turn are eaten by zooplankton and other aquatic organisms. These organisms eventually end up in fish stomachs, meaning that food webs not only feed off organic carbon from plants in the lake or from the surrounding land; but also from deep-lying and oxygen-free, yet carbon-rich, sediment stores where methane is formed.
More studies are being planned to show the potentially vast importance that methane could have on the food chain in different types of lakes and conditions. For example, what happens in Swedish lakes during the winter?"

 

https://www.newscientist.com/article/2112298-food-made-from-natural-gas-will-soon-feed-farm-animals-and-us/

 

"A biotechnology company called Calysta, based in Menlo Park, California, is set to announce the first ever large-scale factory that uses microbes to turn natural gas – methane – into a high-protein food for the animals we eat. The factory, which will be built in the US in collaboration with food-giant Cargill, will produce 200,000 tonnes of feed a year.
The methane-made food has already been approved in the European Union for feeding to farmed fish and livestock such as pigs. Calysta is seeking approval in the US, too – and not just for farm animals. “We want to take it all the way to cats and dogs, and potentially even humans,” says the head of Calysta, Alan Shaw."

 

Germs! Really!! ????????
 

sure, co2 and methane are great, so is water until you drown in it. point was that big or small is all relative, its the effect that matters, and the effects of greenhouse gasses are well known

[VincentRJ]

6 hours ago, phycokiller said:

sure, co2 and methane are great, so is water until you drown in it. point was that big or small is all relative, its the effect that matters, and the effects of greenhouse gasses are well known

The effects of greenhouse gases and the effects of a million other variable factors which can influence climate to some degree, are definitely not well known. That's the problem. 

 

The other problem is that most people find it difficult live with uncertainty. It's why religions are necessary, and why expressions of certainty about the effects of human emissions of CO2 are considered to be politically useful to control the population.