4 ms·

The earth was actually cooling starting about 5000 years ago until whenever carbon emissions started having their effect ~100 years ago. Between 5,000 and 11,0

The earth was actually cooling starting about 5000 years ago until whenever carbon emissions started having their effect ~100 years ago. Between 5,000 and 11,000 years ago the Sahara was green. I wonder if this is a little taste of what's to come.

irthomasthomas 2y ago
There where warm periods, called intra-glacials in the bronze age, the late Roman, and the middle-ages.
TacticalCoder 2y ago
[dead]
culi 2y ago
The Sahara is on a regular-ish cycle going from green to desert about every 30k years. It's had multiple green eras. The last one is called the African humid period
- fuzztester 2y ago
  any idea why so?
  - thworp 2y ago
    Briefly: earth‘s rotational axis had a different tilt, leading to completely different climate and weather systems behavior. Incidentally, before the green sahara period, the sahara was much larger than today.
    - jjtheblunt 2y ago
      i've read the axis precesses completing a cycle every 24,000 years, so the fraction of ocean vs land in direct sun gradually and continually changes accordingly.
  - colechristensen 2y ago
    There are many higher order gravitational effects which alter earths orbit and axial tilt and therefore both yearlong and seasonal solar radiation patterns. One of these is a cyclical pattern of tens of thousands of years that caused warming and cooling somewhat less that a degree. For about six thousand years earth was half a degree warmer and weather patterns in the Sahara were different. Then there was some cooling until modern CO2 issues. In the early twentieth century there were some very real concerns about long term climate cooling as climate science was being developed but instead greenhouse gases have blasted us very far and very fast in the other direction.
- Dennip 2y ago
  Any idea, how does the dirt/each return over time to sustain plant life? Or is it just a gradual grow inwards with plant matter slowly forming topsoil?
  - culi 2y ago
    The Amazon rainforest's soil is extremely poor in nutrients and very shallow due to all the rain. In addition, at least 50% of the rain it gets comes from the trees themselves. The division between abiotic and biotic factors is a lot more fuzzy than people realize The Sahara's sand is actually full of a lot of nutrients. In fact the massive Saharan sandstorms that traverse the Atlantic Ocean are a significant source of fertilizer for the Amazon rainforest All the elements are there. You just need the right weather and plant life to get things going. Of course we can't ignore the human element. Archeological evidence suggests humans played a massive role in transitioning the Amazon Rainforest from the grassland it once was to the jungle it now is. Reforestation projects, Great Green Wall, half-moon berm projects, etc are all way way more effective than they were just a few years ago. We're learning a lot about how much humans can do to revitalize soils
  - colechristensen 2y ago
    Pioneer species that can grow on basically nothing are slowly replaced by other species as the ground builds up organic matter. Fungi play a very large part in building soil as well as big and small animals.
permo-w 2y ago
you have it backwards. the sahara was green because the world in general was cooler back then, so the equator had weather more appropriate for the tropics. the world has gotten hotter since then, turning the region into a desert.
- prmph 2y ago
  It's probably not so much that the world was cooler, but that it had more equable temperature. Remember Greenland was green once.
  - mtlmtlmtlmtl 2y ago
    Greenland was probably once green, but we're talking several 100000 years ago, well before any humans(that we know of) appeared there. The origin of the name is actually that Eric the Red called it that to attract settlers there. Just marketing, really.
- colechristensen 2y ago
  This is just not correct. There’s a 10,000 year period from the exit of the last ice age to about the year 0 where global temperatures were at least as warm as the 1960-1990 average. For a maybe 6000 year period within that global temperatures were about a half a degree or a little less warmer than that 1960-1990 average. You’re just wrong. Before greenhouse gas emissions took control there’s a well recognized pattern of slow global cooling over a few thousand years. Look at the graph https://www.climate.gov/news-features/climate-qa/what’s-hottest-earth-has-been-“lately” https://www.climate.gov/news-features/climate-qa/what’s-hott...

irthomasthomas 2y ago

There where warm periods, called intra-glacials in the bronze age, the late Roman, and the middle-ages.

TacticalCoder 2y ago

[dead]

culi 2y ago

The Sahara is on a regular-ish cycle going from green to desert about every 30k years. It's had multiple green eras. The last one is called the African humid period

fuzztester 2y ago
any idea why so?
- thworp 2y ago
  Briefly: earth‘s rotational axis had a different tilt, leading to completely different climate and weather systems behavior. Incidentally, before the green sahara period, the sahara was much larger than today.
  - jjtheblunt 2y ago
    i've read the axis precesses completing a cycle every 24,000 years, so the fraction of ocean vs land in direct sun gradually and continually changes accordingly.
- colechristensen 2y ago
  There are many higher order gravitational effects which alter earths orbit and axial tilt and therefore both yearlong and seasonal solar radiation patterns. One of these is a cyclical pattern of tens of thousands of years that caused warming and cooling somewhat less that a degree. For about six thousand years earth was half a degree warmer and weather patterns in the Sahara were different. Then there was some cooling until modern CO2 issues. In the early twentieth century there were some very real concerns about long term climate cooling as climate science was being developed but instead greenhouse gases have blasted us very far and very fast in the other direction.
Dennip 2y ago
Any idea, how does the dirt/each return over time to sustain plant life? Or is it just a gradual grow inwards with plant matter slowly forming topsoil?
- culi 2y ago
  The Amazon rainforest's soil is extremely poor in nutrients and very shallow due to all the rain. In addition, at least 50% of the rain it gets comes from the trees themselves. The division between abiotic and biotic factors is a lot more fuzzy than people realize The Sahara's sand is actually full of a lot of nutrients. In fact the massive Saharan sandstorms that traverse the Atlantic Ocean are a significant source of fertilizer for the Amazon rainforest All the elements are there. You just need the right weather and plant life to get things going. Of course we can't ignore the human element. Archeological evidence suggests humans played a massive role in transitioning the Amazon Rainforest from the grassland it once was to the jungle it now is. Reforestation projects, Great Green Wall, half-moon berm projects, etc are all way way more effective than they were just a few years ago. We're learning a lot about how much humans can do to revitalize soils
- colechristensen 2y ago
  Pioneer species that can grow on basically nothing are slowly replaced by other species as the ground builds up organic matter. Fungi play a very large part in building soil as well as big and small animals.

permo-w 2y ago

you have it backwards. the sahara was green because the world in general was cooler back then, so the equator had weather more appropriate for the tropics. the world has gotten hotter since then, turning the region into a desert.

prmph 2y ago
It's probably not so much that the world was cooler, but that it had more equable temperature. Remember Greenland was green once.
- mtlmtlmtlmtl 2y ago
  Greenland was probably once green, but we're talking several 100000 years ago, well before any humans(that we know of) appeared there. The origin of the name is actually that Eric the Red called it that to attract settlers there. Just marketing, really.
colechristensen 2y ago
This is just not correct. There’s a 10,000 year period from the exit of the last ice age to about the year 0 where global temperatures were at least as warm as the 1960-1990 average. For a maybe 6000 year period within that global temperatures were about a half a degree or a little less warmer than that 1960-1990 average. You’re just wrong. Before greenhouse gas emissions took control there’s a well recognized pattern of slow global cooling over a few thousand years. Look at the graph https://www.climate.gov/news-features/climate-qa/what’s-hottest-earth-has-been-“lately” https://www.climate.gov/news-features/climate-qa/what’s-hott...