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Human-induced climate change reversed 6,500-year global cooling trend

Human-induced climate change r...
A new study spanning 12,000 years shows that human-induced climate change has disrupted a long-term global cooling trend
A new study spanning 12,000 years shows that human-induced climate change has disrupted a long-term global cooling trend
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A chart demonstrating temperature changes over the past 12,000 years, relative to the 19th century average
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A chart demonstrating temperature changes over the past 12,000 years, relative to the 19th century average
A new study spanning 12,000 years shows that human-induced climate change has disrupted a long-term global cooling trend
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A new study spanning 12,000 years shows that human-induced climate change has disrupted a long-term global cooling trend

What would Earth’s climate naturally be doing if it weren’t for human intervention? Researchers at Northern Arizona University have now analyzed over 12,000 years of climate data, and found that human-induced warming interrupted and reversed a long-term natural global cooling period.

It’s no secret that the Earth is heating up at an incredible speed, with recent months, years and decades all breaking temperature records. But this data only goes back to the 1880s, when observations began being routinely recorded. So how does the current trend compare in the longer term?

To find out, researchers have been compiling data from various sources that stretch back many millennia. A few months ago, a team of 93 scientists published a particularly comprehensive record of paleoclimate data, spanning the past 12,000 years. It includes 1,319 data records from samples like lake deposits, marine sediments, peat, cave deposits, coral, and glacier ice cores, collected from 679 sites around the world.

From that, the researchers were able to chart changes in the surface air temperature over the last 12,000 years – a time when the world was coming out of the last Ice Age. This was then compared to the average for the century between 1800 and 1900, to track how the Industrial Revolution might have changed things.

A chart demonstrating temperature changes over the past 12,000 years, relative to the 19th century average
A chart demonstrating temperature changes over the past 12,000 years, relative to the 19th century average

As expected, at the beginning of that period temperatures were much colder than the 19th century baseline. But they steadily warmed up over the next several millennia, eventually surpassing the baseline. Temperatures peaked around 6,500 years ago, and since then the planet has been slowly but surely cooling down.

“The rate of cooling that followed the peak warmth was subtle, only around 0.1 °C (0.2 °F) per 1,000 years,” says Michael Erb, co-author of the study. “This cooling seems to be driven by slow cycles in the Earth’s orbit, which reduced the amount of summer sunlight in the Northern Hemisphere, culminating in the ‘Little Ice Age’ of recent centuries.”

Of course, the world is no longer cooling – human activity saw to that. Instead, we’ve raised average temperatures by as much as 1 °C (1.8 ° F) since the mid-19th century. That’s a huge spike in a relatively short time, rising even higher than that peak 6,500 years ago.

“It’s possible that the last time the sustained average global temperature was 1°C above the 19th century was prior to the last Ice Age, back around 125,000 years ago when sea level was around 20 feet higher than today,” says Darrell Kaufman, lead author of the study.

Although we’re heading into largely uncharted territory, in terms of climate change, investigating these historic patterns can help us better understand what might lie ahead, under different scenarios.

The research was published in the journal Scientific Data.

Source: Northern Arizona University

19 comments
Rumata
"we’ve raised average temperatures by as much as 1 °C (1.8 ° F) since the mid-19th century"

Totally wrong. The recent global warming phase had started in the 17. century, when human CO2 emission was neglible, and the increase in CO2 level had started only in the 19. century.
Hence, it is clear, that not "we", but natural forces caused the global warming.
Worzel
The planet did not exit an 'Ice Age' some 12,000 years ago, it exited a glacial period. Glacial periods are tied to the Malenkovitch cycle, and have a period of about 100,000 years, as confirmed by deep sea, and lake bed cores covering the last 10 cycles, or approximately 1 million years. The planet has been in an Ice age, that started more than 40 million years ago, is still in that ice age, and has many more millions of years before this ice age is over. Therefore any ''global warming'' is merely a momentary hiccup in that process. The alleged cause of this present ''global warming'' of human produced CO2, is a total political myth. CO2 has had zero effect on climate in the last 600 million years, even when CO2 was 7000 ppm, 17 times present. At the end of a glacial age, as the glaciers retreat, they leave behind huge amounts of ground up rock dust, which contains many nutrients, and is an ideal fertiliser for plants, especially trees. However, during the 10,000 year warmer period following the retreat, rain gradually washes these nutrients down through the soils until they are out of reach of tree roots. The trees then suffer malnutrition, and therefore transpire less water. One mature tree can transpire 150,000 litres of water per year. Transpiration by trees cools, multiply this by trillions of trees, and you have a significant climate cooling effect, world wide. As the trees suffer, and die, towards the end of the glacial period, the climate gradually heats up. It is the loss of tree cover that causes climate warming, not CO2. Humans are accelerating this process by mass forest destruction, also world wide. Hence the coincidental warming with the industrial revolution, when tree felling for wood and charcoal fuel was extensive. However, when wood and charcoal was replaced, by other fuels, felling increased for timber use in construction and domestic use. The present warming is temporary, and as the Malenkovitch cycle progresses, it can be expected to change to a very rapid cooling. This change has occurred in as little as 20-50 years during the last 10 cycles. As the change occurs, the permanent snow line, begins to advance, snow reflects sunlight, prevents the ground from absorbing sunlight and causes additional cooling, which causes more snow to accumulate. This is a positive feedback exponential/asymptotic process, which will lead to many of the main food producing areas like the Prairies and Steppes becoming too cold for crops to reach maturation and be harvested. World population will consequently then decrease, rapidly.


Dan
Rumata, who has commented below, is incorrect.

The 17th century was far from negligible in terms of climate change and CO2.

The 17th century Agricultural Revolution transformed forests and previously undisturbed land into farmland, destroyed habitats, decreased biodiversity and released a significant amount of carbon dioxide into the atmosphere.
SendSauce
Human activity has had an effect over the last century, but not only is it relatively negligible in combination with natural forces, but the idea that warming will just continue to go on unchecked without natural damping, or that a bit warmer planet will be catastrophic is just more politically and financially driven hysteria.
SteveBarry
Or, it had no effect at all.
Ste Vae
It would be doing the EXACT SAME THING!!!!! Man does NOT make global warming. And anyone with a working brain should know this by now. The earth has been heating up and cooling down for billions of years BEFORE man or industry came along. This is just a money grabbing ploy, as most things the liberal left bitch and complain about...
Cryptonoetic
Wow. This is only the second time I have encountered a hypothesized positive effect of AGW (i.e., delaying the next ice age).
clay
I have to say, regarding almost every BIG societally impacting scientific topic: politics and dogma rule the day, and I get tired of it. Global Warming is obviously no exception.

There is so much politically correct bigotry orbiting this topic that I simply do not believe what is being published...the is ESPECIALLY TRUE of the UN/IPCC.

The problem with Global Warming is simply politics, money and religion. It has become a religion, and if one dares question the dogma or politics, or falsification of numbers (from heat islands to quotients applied to arrive at expect outcomes... Well, then one is just an ignorant "Denier".

The economic convenience (to the scientific community) of having this topic as a political issue cannot be understated.

it is so bad within the area of this topic that anyone who makes their living in the space MUST toe the line “or else”. Dare to challenge the collective, go ahead, see what happens. Your career is over... you become a pariah... even if you are actually applying the Scientific method AND questioning everything…in order to find out what is really going on.

These shenanigans are deplorable and are THE key drivers of my great hesitation to accept the opinions of the current "Scientific Consensus" on the topic.

This is worse (by far) than the ~75 year old Clovis First doctrine that ensured ANY scientist, who dared to dig even an INCH below the Clovis Line, was OSTRACIZED and de-monetized by the community.

This topic is even worse than the intolerant blacklisting of Wegener in the early 1920's for daring to propose the Continental Drift theory in his book "The Origins of Continents and Oceans".


The sad truth is: The scientific community has long applied closed minded, protectionist (to one's own publishings), ignorant, belligerent, and outright hostile tactics toward any who dare question the norm. This terrible and long standing behavior mode is justified in the name of Extraordinary Claims Require Extraordinary Evidence, but this is just the sword and shield, not the actual reason. I say bull, this is all just normal human behavior (with fancier tools):
No scientist wants some up-and-comer to arrive with a new model that challenges (and paints ignorant) the prior model.
No Scientist wants to have their published compendium to be made irrelevant; for ego and economic reasons
- Ego: Loads of famous scientists have egos as lofty as their status (again, not blaming them, it is just human nature)
- Economics: Given most of scientists in academia do not actually produce product, they rely upon the monetary structure of their patron university, if their knowledge is deemed ...wrong.. then they feel they will lose relevance or prominence with respect to funding of additional studies.

The truth is prior models inform subsequent evolutions and revolutions.

I therefore MUST question the validity and purpose of the entire area of "study"
drBill
Based on my research into the matter, Rumata has a good take on it. New Atlas would do well to be just a bit more skeptical of the "gee-whiz" kind of stuff that passes peer review these days.
Catweazle
Apart from the long Malenkovich cycles there are two important cycles that govern the Earth's surface, the first has a period of ~1,100 years and is responsible for the Minoan, Roman and Medieval Warm periods, all of which were warmer that the current temperature and the cold periods such as the Dark Ages and the Little Ice Age, we are currently in the positive phase of this cycle. The second has a period of ~60 years and is responsible for the warm period that peaked in the 1930s and the cold period that was responsible for the Ice Age scare of the 1960s and 1970s, we are currently in the negative phase of this cycle as is steadily becoming apparent. Mankind has not had and cannot have any significant effect on these cycles, all are moderated by the Sun and by oceanic cycles as warmer and colder layers of water are interchanged as a result of convection and the same Coriolis forces that drive the cyclones and anticyclones that are responsible for the World's weather.