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As our orbital geometry changes, a new ice age is virtual certainty. In fact I'm surprised it hasn't happened already. This present interglacial is, by a significant margin, the longest one of at least the last six or so and by some accounts, the second warmest. The most recent ice age's last gasp was an event scientists like to call the "Younger Dryas" named for a low lying shrub that is common in arctic and alpine tundra regiemes today, and once ranged as far south as southern France in Europe and the mid-South here in the U.S.
That all ended abruptly about 12000 years BCE so we have been relatively ice free for nearly 14000 years already. No other interglacial has lasted longer than 11500 or 12000. The present orbital configuration and our axial tilt screams "Ice Age" as loudly as a four year old with a tantrum but there's no hint of one even starting up. We are a minimum of 2000 years and maybe as much as 4000 years over due for the next crash.
And yet there are some climatologists who believe mankind's activities has put the kabosh on any future glaciations and that gasses known to have a heat retention effect have already effectively cancelled the next ice age. Dr. James Hansen and Dr. David Archer claim that as long as humans remain on earth (by no means a foregone conclusion) and retain even a vestige of an industrial capacity, we will never again see another.
Personally, I don't believe that. Orbital forcing factors will eventually overwhelm anything we do to our atmosphere and, eventually the glaciers will come again. The onset may be delayed - I think it already has been - but sooner or later the ice will return.
But because there are so many experts (and they can't all be wrong) who believe we are inexorably warming up and at a pace that can not be explained by any natural phenomen we know about, I think it only fair to present this one little tidbit. The presenter is not a climate expert and the sound quality is horrible but everything in it has either been demonstated to be true or is plausible so the video shouldn't be dismissed as so much alarmist rot, either:
As our orbital geometry changes, a new ice age is virtual certainty. In fact I'm surprised it hasn't happened already. This present interglacial is, by a significant margin, the longest one of at least the last six or so and by some accounts, the second warmest. The most recent ice age's last gasp was an event scientists like to call the "Younger Dryas" named for a low lying shrub that is common in arctic and alpine tundra regiemes today, and once ranged as far south as southern France in Europe and the mid-South here in the U.S.
That all ended abruptly about 12000 years BCE so we have been relatively ice free for nearly 14000 years already. No other interglacial has lasted longer than 11500 or 12000. The present orbital configuration and our axial tilt screams "Ice Age" as loudly as a four year old with a tantrum but there's no hint of one even starting up. We are a minimum of 2000 years and maybe as much as 4000 years over due for the next crash.
It does not scream ice age. Maybe mini-ice age, but not full blown ice age. See the graph on the first page of this paper:
from the paper: The small amplitude of future insolation variations is exceptional. One of the few past analogs (13) occurred at about 400,000 years before the present, overlapping part of MIS- 11.
Unlike the end of the last interglacial (around 115,000 years ago), solar insolation isn't projected to go to as low levels. With the really low levels, ice and snow can form in North Hemisphere that may be able to survive high solar insolation levels as ice reflects sunlight.
Quote:
And yet there are some climatologists who believe mankind's activities has put the kabosh on any future glaciations and that gasses known to have a heat retention effect have already effectively cancelled the next ice age. Dr. James Hansen and Dr. David Archer claim that as long as humans remain on earth (by no means a foregone conclusion) and retain even a vestige of an industrial capacity, we will never again see another.
Personally, I don't believe that. Orbital forcing factors will eventually overwhelm anything we do to our atmosphere and, eventually the glaciers will come again. The onset may be delayed - I think it already has been - but sooner or later the ice will return.
Orbital forcing is weaker than greenhouse gases because orbital forcing does not change the total incoming radiation on Earth — it just redistributes geographically and time-wise. Greenhouse gases changes the earthwide total.
Still, regional differences can be pretty powerful. Just look at what's happened with the Arctic versus the Antarctic. A new glacial at some point is inevitable, and will probably occur in a timeframe in between next month and 50 000 years from now. Greenhouse gases are but one of many factors that drive climate, and their relative power has been greatly overestimated. History over the past 50 years has demonstrated that much; temperatures have followed sunspot cycles and PDO cycles as much as they've followed CO2 (if they only followed CO2 it would've been homogenous warming for 100 years, but the climate cooled from 1945-1980). However, even if CO2 is the primary driver of climate, it won't make any difference in the end. Within the next few centuries, even if we continue to guzzle fossil fuels, the fossil fuels will run out, and Earth's atmosphere will cycle back to more normal conditions once emissions drop to zero, as they inevitably will. Since the arrangement of the continents guarantees conditions conducive for ice ages for at least the next few million years, the recurrence of a glacial period in this current ice age cycle is assured.
As for more recent climate, I think the climate will cool in the next few decades to centuries, and a mini-ice age such as what occurred in 1315-1850 will occur. A full glacial looks unlikely at this point, but I suppose it is possible. Something more similar to the Younger Dryas (a partial return to glacial conditions) is also possible. If we do get a mini-Ice Age in the next few centuries it could transition over to a full ice age later, though I won't make any predictions on what it could transition into after the year 2500 or so.
It should also be noted that if you compare the climate record to the orbital forcing, it doesn't precisely match up. Some scientists have noted that, as well as a change in the glacial cycle to 50 000 to 100 000 years. Other processes are at work besides orbital forcing that are not completely understood.
I'm getting into the long-term here, millions of years after all man-made CO2 will have cycled out of the atmosphere. The graph of Phanerozoic climate change demonstrates that the long-term trend, during the duration of the Cenozoic, is for cooling:
This is on a scale that makes glacials and interglacials into undetectable blips. More recently, glacial periods have gotten longer and colder over the past million years. For the next few million years, the Cenozoic cooling should continue. What happens next depends on continental drift. If "Pangea Ultima" forms, which would be a closing of the Atlantic, then the climate would warm pretty drastically as the ice ages terminate. If "Amasia" forms, which would be a continuation of current trend, merging Asia and Laurentia, then there would be a huge continent over the North Pole and extending into the midlatitudes. This configuration is quite similar to the arrangement during Snowball Earth, and under this scenario the ultimate cooling will occur in about 100 million years - a descent back into Snowball Earth conditions. This may persist for as long as Amasia remains over the pole, or if it remains in a Snowball Earth or Ice Age state the climate will start to warm quite a lot around 1 billion years from now, as the Sun continues on its march to red giant status.
Still, regional differences can be pretty powerful. Just look at what's happened with the Arctic versus the Antarctic. A new glacial at some point is inevitable, and will probably occur in a timeframe in between next month and 50 000 years from now. Greenhouse gases are but one of many factors that drive climate, and their relative power has been greatly overestimated. History over the past 50 years has demonstrated that much; temperatures have followed sunspot cycles and PDO cycles as much as they've followed CO2 (if they only followed CO2 it would've been homogenous warming for 100 years, but the climate cooled from 1945-1980). However, even if CO2 is the primary driver of climate, it won't make any difference in the end. Within the next few centuries, even if we continue to guzzle fossil fuels, the fossil fuels will run out, and Earth's atmosphere will cycle back to more normal conditions once emissions drop to zero, as they inevitably will. Since the arrangement of the continents guarantees conditions conducive for ice ages for at least the next few million years, the recurrence of a glacial period in this current ice age cycle is assured.
The paper I linked to suggested that the next glacial won't happen until at least 50,000 years naturally.
The 20th century was also partially affected by sun reflecting aersols; a quantity that's harder to measure than CO2 and rather to quantify effects. Solar radiation hasn't really changed much (see here). I think CO2 will become more clearly dominate as it increases.
If every fossil fuel available is burnt, CO2 levels would reach 2000 ppm, roughly 9x the pre-industrial level (280 ppm, about 393 ppm currently). Skimming the wikipedia page, 50% of added CO2 would be removed within a century, but 20% will last for thousands of years.
Quote:
It should also be noted that if you compare the climate record to the orbital forcing, it doesn't precisely match up. Some scientists have noted that, as well as a change in the glacial cycle to 50 000 to 100 000 years. Other processes are at work besides orbital forcing that are not completely understood.
Agreed. Orbital forcing does seem like the biggest explanation, but it's rather incomplete
Quote:
I'm getting into the long-term here, millions of years after all man-made CO2 will have cycled out of the atmosphere. The graph of Phanerozoic climate change demonstrates that the long-term trend, during the duration of the Cenozoic, is for cooling:
that's a bit of a separate topic. Two comments.
Quote:
This is on a scale that makes glacials and interglacials into undetectable blips. More recently, glacial periods have gotten longer and colder over the past million years. For the next few million years, the Cenozoic cooling should continue. What happens next depends on continental drift. If "Pangea Ultima" forms, which would be a closing of the Atlantic, then the climate would warm pretty drastically as the ice ages terminate. If "Amasia" forms, which would be a continuation of current trend, merging Asia and Laurentia, then there would be a huge continent over the North Pole and extending into the midlatitudes. This configuration is quite similar to the arrangement during Snowball Earth, and under this scenario the ultimate cooling will occur in about 100 million years - a descent back into Snowball Earth conditions. This may persist for as long as Amasia remains over the pole, or if it remains in a Snowball Earth or Ice Age state the climate will start to warm quite a lot around 1 billion years from now, as the Sun continues on its march to red giant status.
The continental configuration that would encourage a snowball earth configuration would not be continents concentrated at the poles but rather near the tropics. Continents reflect more sunlight than ocean, and so continents in the locations of the most intense solar radiation is a situation that creates a colder planet. The sun has steadily increased in strength; it would be harder to have a snowball earth now than it was 500 million years ago.
The paper I linked to suggested that the next glacial won't happen until at least 50,000 years naturally.
The 20th century was also partially affected by sun reflecting aersols; a quantity that's harder to measure than CO2 and rather to quantify effects. Solar radiation hasn't really changed much (see here). I think CO2 will become more clearly dominate as it increases.
If every fossil fuel available is burnt, CO2 levels would reach 2000 ppm, roughly 9x the pre-industrial level (280 ppm, about 393 ppm currently). Skimming the wikipedia page, 50% of added CO2 would be removed within a century, but 20% will last for thousands of years.
Agreed. Orbital forcing does seem like the biggest explanation, but it's rather incomplete
that's a bit of a separate topic. Two comments.
The continental configuration that would encourage a snowball earth configuration would not be continents concentrated at the poles but rather near the tropics. Continents reflect more sunlight than ocean, and so continents in the locations of the most intense solar radiation is a situation that creates a colder planet. The sun has steadily increased in strength; it would be harder to have a snowball earth now than it was 500 million years ago.
Can you explain this in more depth.. I find that fascinating..
I remember one of the of the articles I read having to do with wind power. She believed there was enough wind to take care of most of our uses. I'll see if I can find the article.
Well, when Rodinia caused Snowball Earth it was positioned at mid to high latitudes. It's all about blocking the transport of water from the equators to the poles, and that hypothetical future configuration would do that methinks.
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