Do you agree that the debate is over...

[blizzard1024]

It really depends on how much "faith" you put into the science behind climate sensitivity and CO2. If you are a climate scientist or atmosphereic scientist you must be willing to accept that whatever warm cycle was occuring is now amplified by the expanding CO2 concentrations. The real debate is mostly how long it will take to reach that 3-4C+ above baseline.

 

This is why I am constantly rehashing paleoclimate along with others, the extreme warming scenarios will be inevitable if we keep pumping out CO2....it's quite simple. The aspect that trips most skeptics up is the fact that CO2 follows temperature in the climate record. However, unlike in the past, CO2 is now being released very quickly. Fast enough to act as a primary driver and the lag time between temperature and CO2 will be substantial because the oceans are currently in a state that reflects mid 20th century CO2 levels.

 

However the global state change will most likely take place on century-based timescales instead of millenniums due to the CO2 processes breaking out of the background/historic state and rising towards around 800 ppm by 2100 as a result of continued emissions and positive feedbacks.

 

 

These graphs as you state show that CO2 concentration passively follows the temperature based on the proxy data.

This is because oceans are colder during glaciations and absorb more CO2. Also due to lower sea levels there was more

land and vegetation.

 

CO2 did not initiate the warming or cooling of the past. That is what is so hard for me to believe.  CO2 concentrations never

drove the past climates so why do they today??  In fact there are periods where CO2 is rising and the temperatures are falling in these proxy records and vice-versa. That makes no sense if you believe CO2 drives climate. CO2 varied by 100-120 ppm between glacials and interglacials which is roughly the same order of magnitude that we have seen CO2 rise recently. These ancient rises and falls didn't drive the climate back then.   So I find it hard to believe that the climate is now driven by CO2 when it never was in the past. This is further emphasized by the fact that CO2 is a minor GHG with H20 vapor and clouds the primary GHGs.  So we have a trace gas that in the last 100 years now drives the climate when it didn't before?? In a hundred years or so, people will look back and think we were fools to believe this stuff. I don't deny there will be some warming...like maybe 1C from a doubling over a couple hundred years...but I really doubt the feedbacks are positive. If they were then CO2 would have driven climate in the past and it never did.  This is all common sense that has been so twisted by the mainstream field of climate science mainly from computer model simulations. Nothing is unusual about today's weather and climate. The climate warms and cools all the time. It always did and always will. 

[StudentOfClimatology]

Yes this is well known paleoclimatology stuff. But the isotopes are a marker for temperature and that is the point. I don't care if it is Greenland temperature or the SSTs of the midlatitudes/sub-tropics.  The point is that is shows temperature variations from this ice core data.  Clearly there are swings in temperature for centuries...both warming and cooling. I am not as concerned about the actual temperature...it is the trend that matters. Maybe it is warmer now than it was earlier in this graph. The point is that if the past showed periods of warming and cooling on the order of centuries than what makes this warm period so special? We could be in the middle of a 200 year warm cycle for all we know. This also has nothing to do with skeptics or "deniers" which is the way you like to insult people.

The fact that the Holocene climate was so unstable without significant triggers tells us that climate sensitivity must be very high. The radiative forcing increase we've applied to the system today dwarfs any natural trigger(s) over the past 12,000 years at least..we're playing with fire, and if we don't recognize that, we're going to get burned.

Also, as the Younger Dryas and 8200kyr events prove, the climate can turn on a dime..as in, warm/cool several degrees centigrade within 1-10 years. Evidence suggests that significant climate change occurs in "jumps" rather than a gradual, sloping response. We will have no time to adapt to that.

At the end of the younger dryas, global temperatures warmed 3-4C in about 5 years...that's legitimately terrifying.

[skierinvermont]

These graphs as you state show that CO2 concentration passively follows the temperature based on the proxy data.

This is because oceans are colder during glaciations and absorb more CO2. Also due to lower sea levels there was more

land and vegetation.

 

You can't say just by looking at a graph that it is passive. According to radiative physics (which you claim to understand), it necessarily acted as a positive forcing. Moreover, it is difficult to explain those variations in climate without CO2 as a positive feedback. In addition Shakun et al 2012 found that CO2 increase preceded northern hemisphere temperature increase. Milankovitch began melting of the ice sheets, the fresh water disrupted the Antlantic Meridional Overturning Current, this caused the southern ocean and southern hemisphere to warm and release CO2, and the CO2 caused warming of the northern hemisphere (lagging CO2). 

 

 

 

 

 That is what is so hard for me to believe.  CO2 concentrations never

drove the past climates so why do they today?? 

 

Because there has never been a natural phenomenon that could suddenly dredge up and burn trillions of tons of fossil fuels. 

 

 

In fact there are periods where CO2 is rising and the temperatures are falling in these proxy records and vice-versa.

 

Not really. There's no period where CO2 goes up or down by more than 20ppm and temperature was not also higher or lower. It doesn't prove causation, but your statement and the conclusions based on it are false.

 

 

These graphs as you state show that CO2 concentration passively follows the temperature based on the proxy data.

This is because oceans are colder during glaciations and absorb more CO2. Also due to lower sea levels there was more

land and vegetation.

 

 CO2 varied by 100-120 ppm between glacials and interglacials which is roughly the same order of magnitude that we have seen CO2 rise recently. These ancient rises and falls didn't drive the climate back then.   So I find it hard to believe that the climate is now driven by CO2 when it never was in the past. 

 

These statements are unsupported. You have not proven that CO2 did not act as the primary positive feedback. Nothing you've presented demonstrates that. Radiative physics proves strong positive radiative forcing, and paleoclimate data I presented above shows that temperature rise in the NH lagged CO2 increase. CO2 was a major positive feedback. The Milankovich cycles which melted ice sheets at the end of the last ice age caused 3.5W/m2 of forcing, but GHGs added a 3W/m2 positive feedback according. Total forcing was 6.5W/m2, and temperature change was 4C, implying a climate sensitivity of 2.5C/doubling.

 

 

 

This is further emphasized by the fact that CO2 is a minor GHG with H20 vapor and clouds the primary GHGs.  

 

 

False. If all other GHGs were removed from the atmosphere, 34% of the GHE would remain due to CO2. See any basic radiative transfer code going as far back as Ramathan and Coakley 1978. 

 

There is no proof co2 enhanced past warming, its all speculation, co2 always trailed warm periods. Its very possible a shift in climate caused a massive die-off and co2 release. It would have taken a while for newly adapted foliage to begin to keep up with the natural rate of co2 emission.

 

It is not all 'speculation.' It's basic radiative physics that has been around for over one hundred years. 

 

 The point is that if the past showed periods of warming and cooling on the order of centuries than what makes this warm period so special? We could be in the middle of a 200 year warm cycle for all we know. 

 

This is the only warming period being driven by CO2 because it is the only warming period where CO2 levels have been artificially raised by burning of fossil fuels. Also, no other warming period has occurred anywhere near as quickly. It is impossible to see with the scales provided, but the 1C of temperature increase thus far, has occurred 3X faster than any time in the last 400,000 years. 

 

There should be debate on how much man has contributed to the recent warming. That's the problem.  How come these scientists ignore the ocean cycles like the PDO and AMO and their contributions to the global temperature?  

 

They aren't ignored. Climate models include simulations of the AMO and PDO and many models are tuned to the present state of the PDO and AMO and forecast subdued temperature increase in the near future because of it. 

 

 

 If you superimpose these two cycles, you can describe most of the warming since 1950 without invoking external forcing from CO2 increases.

 

Superimposing two or three lines on a graph isn't science. Plus, there's really no correlation in long-term temperature to the PDO+AMO. The PDO is negative, and the AMO is not as positive as it once was. The PDO and AMO are in a pretty similar state to the 1950s right now. And yet temperatures are .6C higher and the oceans have gained an incomprehensible amount of heat since then (enough to raise the level of the entire ocean 6"). 

 

 

 In addition, there were periods in the Medieval Warm Period and even during the Little Ice Age based on paleoclimate proxy data that saw periods of warming on the order of 100 years and periods of cooling at the same intervals. How do we know that the last 60 years is unusual? We have much finer resolution data now that we did then as inferred from the proxy data. How do these scientists explain these multi-century variations in the proxy data which did not have the influence of increasing CO2? 

 

This graph below shows the variations in the Greenland temperatures based on ice core data and you can see periods of warming and cooling locally. It warmed over Greenland about 1-2C over a couple hundreds years leading up to several warm periods including the Minonian....Roman and Medieval warm periods. The resolution of ice core data is much lower than today's high res data so I bet during these warm periods, arctic sea ice was decreasing, glaciers were retreating etc.  How do we know that the last 60 years were unprecedented??  These previous warm periods no doubt saw tremendous changes in the Arctic which globally sees the wildest swings in temperature.

 

 greenland-ice-core-temperature-and-co2-11000-bp.jpg

 

The only thing that climate scientists can hang their hat on are computer model simulations which lead to this conclusion that anthropogenic CO2 increases are dominating the climate system now. Models are not reality, especially atmospheric models.

 

 

What's ironic, is that you (and most other fake skeptics) love to talk about and even at times exaggerate past climate changes. These past climate changes were caused by quite small changes in radiative forcing. This implies a large climate sensitivity. 

 

You also accept (or so you say) that doubling CO2 causes 3.7W/m2 of radiative forcing. This is a much larger forcing than initiated most ice ages or deglaciations. Thus the temperature response to this massive forcing will be even larger.

[blizzard1024]

The fact that the Holocene climate was so unstable without significant triggers tells us that climate sensitivity must be very high. The radiative forcing increase we've applied to the system today dwarfs any natural trigger(s) over the past 12,000 years at least..we're playing with fire, and if we don't recognize that, we're going to get burned.

Also, as the Younger Dryas and 8200kyr events prove, the climate can turn on a dime..as in, warm/cool several degrees centigrade within 1-10 years. Evidence suggests that significant climate change occurs in "jumps" rather than a gradual, sloping response. We will have no time to adapt to that.

At the end of the younger dryas, global temperatures warmed 3-4C in about 5 years...that's legitimately terrifying.

 

 

You are correct about Younger Dryas as it was postulated to be related to a massive influx of fresh meltwater into the North Atlantic Ocean which halted the North Atlantic Ocean Current (which encompassed the Gulf Stream) and pushed the climate back to ice age levels. The climate was very volatile when there was a lot of land ice back then in the late Pleistocene. If you look at the paleoclimate records you will see rapid climate changes which halted once the continental ice sheets melted. The 8.2 KYR event has unknown origins as far as I know. Most of the land ice was gone by then. But, except for this event, the Holocene actually has seen a much more stable climate vs when there were large continental glaciers.  Fluctuations in the North Atlantic Current had and still has huge implications for the global climate. Even today it continues to vary but not nearly as much as it did when it was shut down at times from rapid freshwater intrusions from meltwater. This current is critical for the entire climate system and is why I strongly believe that the AMO is a real oscillation.

The paleo records suggest that when it warms in the North Atlantic Ocean from thermohaline oceanic circulation variations, heat is drawn away from the southern oceans and hence the two hemispheres are out of phase in the temperature proxy data. This can be seen today to a much smaller extent. It is presently warm in the north Atlantic BUT it is cold in the southern oceans. Hence Arctic sea ice is low BUT Antarctic sea ice is at record levels!! The two hemispheres are continuing this out of phase relationship as seen in the proxy data. When the North Atlantic cools again in the next couple decades or so, the Arctic sea ice will recover and we will see the Antarctic sea ice decline. This is consistent with the paleo climate data but inconvenient to the current theories of climate change. 

[blizzard1024]

You can't say just by looking at a graph that it is passive. According to radiative physics (which you claim to understand), it necessarily acted as a positive forcing. Moreover, it is difficult to explain those variations in climate without CO2 as a positive feedback. In addition Shakun et al 2012 found that CO2 increase preceded northern hemisphere temperature increase. Milankovitch began melting of the ice sheets, the fresh water disrupted the Antlantic Meridional Overturning Current, this caused the southern ocean and southern hemisphere to warm and release CO2, and the CO2 caused warming of the northern hemisphere (lagging CO2). 

 

 

 

 

 

Because there has never been a natural phenomenon that could suddenly dredge up and burn trillions of tons of fossil fuels. 

 

 

 

 

Not really. There's no period where CO2 goes up or down by more than 20ppm and temperature was not also higher or lower. It doesn't prove causation, but your statement and the conclusions based on it are false.

 

 

 

 

These statements are unsupported. You have not proven that CO2 did not act as the primary positive feedback. Nothing you've presented demonstrates that. Radiative physics proves strong positive radiative forcing, and paleoclimate data I presented above shows that temperature rise in the NH lagged CO2 increase. CO2 was a major positive feedback. The Milankovich cycles which melted ice sheets at the end of the last ice age caused 3.5W/m2 of forcing, but GHGs added a 3W/m2 positive feedback according. Total forcing was 6.5W/m2, and temperature change was 4C, implying a climate sensitivity of 2.5C/doubling.

 

 

 

 

False. If all other GHGs were removed from the atmosphere, 34% of the GHE would remain due to CO2. See any basic radiative transfer code going as far back as Ramathan and Coakley 1978. 

 

 

It is not all 'speculation.' It's basic radiative physics that has been around for over one hundred years. 

 

 

This is the only warming period being driven by CO2 because it is the only warming period where CO2 levels have been artificially raised by burning of fossil fuels. Also, no other warming period has occurred anywhere near as quickly. It is impossible to see with the scales provided, but the 1C of temperature increase thus far, has occurred 3X faster than any time in the last 400,000 years. 

 

 

They aren't ignored. Climate models include simulations of the AMO and PDO and many models are tuned to the present state of the PDO and AMO and forecast subdued temperature increase in the near future because of it. 

 

 

 

 

Superimposing two or three lines on a graph isn't science. Plus, there's really no correlation in long-term temperature to the PDO+AMO. The PDO is negative, and the AMO is not as positive as it once was. The PDO and AMO are in a pretty similar state to the 1950s right now. And yet temperatures are .6C higher and the oceans have gained an incomprehensible amount of heat since then (enough to raise the level of the entire ocean 6"). 

 

 

 

 

What's ironic, is that you (and most other fake skeptics) love to talk about and even at times exaggerate past climate changes. These past climate changes were caused by quite small changes in radiative forcing. This implies a large climate sensitivity. 

 

You also accept (or so you say) that doubling CO2 causes 3.7W/m2 of radiative forcing. This is a much larger forcing than initiated most ice ages or deglaciations. Thus the temperature response to this massive forcing will be even larger.

 

All this stuff you present is based on computer model simulations that are overly sensitive to CO2 forcing and imply a positive water vapor feedback.The water vapor feedback is not necessarily positive. It is very uncertain and according to some lines of data it is actually negative. But this study is all in the computer model simulations which have to have accurate boundary conditions too. We don't know exactly what the boundary conditions were back then. It is a huge assumption to assume CO2 caused the warming out of the last glaciation. I highly doubt a trace gas is the primary driver of the climate system. It does contribute but I doubt it is the driver. 3.7 w/m2 is not that much forcing when you look at the big picture. The Earth's greenhouse effect radiates anywhere from 330 to 340 w/m2 back to the Earth(depends on the source). In Trenberth et al 2009 the error bars of the net radiative imbalance at the surface of + .6 w/m2 is 17 w/m2!!!! So 3.7 w/m2 isn't much but does have some effect of course. Basically 3.7 w/m2 equals about 1.2K with all things being equal which we know won't be the case. The feedbacks are likely neutral to negative based on how we are seeing the present climate respond to the CO2 increase to 400 ppm. In fact, both methane and CO2 forcing is close to 3 w/m2 now and the climate has only warmed .8C since pre industrial times. This assumes that ALL of the warming since 1850 is from increased GHGs which we know is not true since the LIA peaked in the 1700s and early 1800s. Some of this warming is most likely a recovery from the LIA. Glaciers began to retreat around 1850 which hints at this. If we have warming in the pipeline as some say, then it shows that the oceans will buffer this extra radiative forcing and keep the Earth's climate stable enough that the GHG induced forcings will be spread out over long periods of time...probably a few centuries. The present "hiatus" in global warming is being explained by the deep oceans absorbing heat which indicates the buffering power of the oceans (if you believe the OHC data). So even if we do see 3-4C from a doubling of CO2...it will occur over a long enough period of time as to not cause any problems for humans to adapt.  I still believe the climate is not that sensitive to CO2 forcing. But that's my own opinion.  

 

For those who don't know me. I do advocate alternate renewable energy. I would love to see solar panels affordable and used by all. I would love to see us stop burning fossil fuels but only if we don't decimate the global economy. I do believe that oil companies do not want to see a conversion to renewables and clean energy for profits sake. I don't like this either. Pollution is pollution and it is bad. So if the outcome of all this is to get us moving toward renewable and clean energy sources than, in the long run, it would be worth it. As a scientist though, I just think the CO2 problem is overstated.  

 

Look...I also appreciate your comments and the debate and if I have ever crossed the line I apologize. The debate is fun and I do learn stuff. You challenge me to dig deeper.  No hard feelings here. If you can convince me  that CO2 does drive climate that would be an accomplishment. I do have an open mind on this stuff. thanks. 

[Jonger]

These radiative figures are so ridiculous.There are so many more factors, that can't be produced in a lab... Most likely that's why we end up with poor climate model verification.

[AvantHiatus]

 

You also accept (or so you say) that doubling CO2 causes 3.7W/m2 of radiative forcing. This is a much larger forcing than initiated most ice ages or deglaciations. Thus the temperature response to this massive forcing will be even larger.

 

Good point, I think people lose sight of the spatial dimensions of global climate and the various intricacies that lead to warm and cold periods. Milankovich cycles are sufficient enough to cause ice ages simply by altering the obliquity of the Earth by a few degrees.

 

Finally, the past glacial periods required 20,000k+ years to fully evolve, observing 1 C temperature increase globally within about a century is significant and says alot about how much we are affecting Earth Climate Sensitivity just by pumping out 250 ppm CO2 from our dirty carbon-based society. There should really be no debate about whether this current warm period is significant.

 

The 8.2 kiloyear event featured temperature increases and decreases similar to the amount predicted by IPCC (3-4 C), yet they occurred over 150 years with just a very small forcing (relative to recent CO2 increases) caused by a meltwater pulse. This is one of the most severe abrupt climate change events and yet it does not come close to matching the potential of the recent anthropogenic warming.

 

Additionally, this event would be more comparable if a secondary methane feedback occurred, as this would have the same effect as a meltwater pulse on the global ocean and climate, but instead raising global temperatures.

 

[StudentOfClimatology]

You are correct about Younger Dryas as it was postulated to be related to a massive influx of fresh meltwater into the North Atlantic Ocean which halted the North Atlantic Ocean Current (which encompassed the Gulf Stream) and pushed the climate back to ice age levels. The climate was very volatile when there was a lot of land ice back then in the late Pleistocene. If you look at the paleoclimate records you will see rapid climate changes which halted once the continental ice sheets melted. The 8.2 KYR event has unknown origins as far as I know. Most of the land ice was gone by then. But, except for this event, the Holocene actually has seen a much more stable climate vs when there were large continental glaciers. Fluctuations in the North Atlantic Current had and still has huge implications for the global climate. Even today it continues to vary but not nearly as much as it did when it was shut down at times from rapid freshwater intrusions from meltwater. This current is critical for the entire climate system and is why I strongly believe that the AMO is a real oscillation.

The paleo records suggest that when it warms in the North Atlantic Ocean from thermohaline oceanic circulation variations, heat is drawn away from the southern oceans and hence the two hemispheres are out of phase in the temperature proxy data. This can be seen today to a much smaller extent. It is presently warm in the north Atlantic BUT it is cold in the southern oceans. Hence Arctic sea ice is low BUT Antarctic sea ice is at record levels!! The two hemispheres are continuing this out of phase relationship as seen in the proxy data. When the North Atlantic cools again in the next couple decades or so, the Arctic sea ice will recover and we will see the Antarctic sea ice decline. This is consistent with the paleo climate data but inconvenient to the current theories of climate change.

Latest evidence suggests the Younger Dryas was not caused by freshwater release...the tropics and Southern Hemisphere cooled dramatically and simultaneously with the rest of the globe upon entrance, and warmed simultaneously as it ended.

If anything, a collapse of the THC would warm the tropics. A global, radiative forcing change was likely responsible.

[StudentOfClimatology]

Here's a fascinating read on rapid climate changes of the recent past: http://www.esd.ornl.gov/projects/qen/transit.html

Notice how significant climate change tends to occur in explosive jumps. This is very worrisome given the geologically incredible increase in radiative forcing due to our emissions.

All the evidence indicates that most long-term climate change occurs in sudden jumps rather than incremental changes.

If the past is a predictor of the future, this is how the climate will respond in the coming decades. We will not be able to adapt.

Sudden stepwise instability is also a disturbing scenario to be borne in mind when considering the effects that humans might have on the climate system through adding greenhouse gases. Judging by what we see from the past, conditions might gradually be building up to a 'break point' at which a dramatic change in the climate system will occur over just a decade or two, as a result of a seemingly innocuous trigger. It is the evidence for dramatic past changes on the timescale of centuries to decades which will be the subject of this review.

[sokolow]

The problem with his explanation is that you cannot accurately attribute "The tombstones" so to speak with AGW.

The uncertainties are well documented in the peer reviewed science. You make policy decisions based on money and risk. There's probably an awful lot of different opinions on just how much risk is worth the price of different actions levels. However, none of this gives any excuse for poor science or to let these political biases get in the way of the scientific method.

Hopefully the science is what dominates these discussions and not politics.

Its what Stephen Schneider and his predecessors in the STS crowd called "post-normal" or an intractable policy/science problem that collapses boundaries.

This is from 1997

AFAIK he thought the same in 2010 and certainly Christy did as of 2011. Public opinion otoh is way more polarized. Makes me kind of sad considering Schneider's focus on developing ways to do decisionmakig and policy formation under irreducible uncertainty :/

[skierinvermont]

These radiative figures are so ridiculous.There are so many more factors, that can't be produced in a lab... Most likely that's why we end up with poor climate model verification.

 

Even Blizzard1024, denier head-honcho, understands radiative forcing and the associated temperature response. Pretty much every other regular poster on this board besides you understands this. Even most public deniers don't even dispute this like Lindzen and Spencer (they mostly postulate implausible net negative feedbaacks).

 

And of course you're going up against the entire field of atmospheric physics and thousands of researchers far more intelligent and knowledgeable than you for the last 50 years.

 

Oh and let's not forget, these figures have been validated empirically. 

[skierinvermont]

All this stuff you present is based on computer model simulations that are overly sensitive to CO2 forcing and imply a positive water vapor feedback.The water vapor feedback is not necessarily positive. It is very uncertain and according to some lines of data it is actually negative. But this study is all in the computer model simulations which have to have accurate boundary conditions too. 

 

You'll note I did not mention computer models once. And nothing I stated had anything to do or relies upon computer models at all. You've simply ignored what I said and changed the topic.

 

 

The feedbacks are likely neutral to negative based on how we are seeing the present climate respond to the CO2 increase to 400 ppm. In fact, both methane and CO2 forcing is close to 3 w/m2 now and the climate has only warmed .8C since pre industrial times. 

 

You've ignored the massive global dimming of the sun by aerosol pollution and the large negative forcing. Negative forcing from aerosols and land use changes is estimated at -.97W/m2. 

 

Total RF since 1750 is estimated at 2.29W/m2.

 

The large majority of that is since 1950. Total RF since 1950 is estimated at 1.72W/m2. 

 

So the appropriate # is not 3W/m2. It is 2.3W/m2. And there remains a .6-.8W/m2 imbalance. So we've experienced about 1.6W/m2. .9C over 1.6W/m2 is a sensitivity of 2.1C. Plus some slow feedbacks like ice sheet loss could make it a little bigger than that. 

 

This fits into my thinking of a climate sensitivity on the lower end of the AR5 range of 1.5-4.5C (I'd guess 2-3C).

 

If aerosol forcing has been on the more negative side of the confidence interval (closer to -2W/m2) then ECS could be on the higher end of the AR5 range. 

[sokolow]

blizzard idk if its the one Terry was talking about but when I was reading about giant arctic camels and other Ellesmere island oddities this is the one I filed:

A millennial-scale record of Arctic Ocean sea ice variability and the demise of the Ellesmere Island ice shelves

JH England, TR Lakeman, DS Lemmen… - Geophysical Research …, 2008

Durham hosts a public access copy:

http://dro.dur.ac.uk/6877/1/6877.pdf

[AvantHiatus]

You'll note I did not mention computer models once. And nothing I stated had anything to do or relies upon computer models at all. You've simply ignored what I said and changed the topic.

 

 

 

 

You've ignored the massive global dimming of the sun by aerosol pollution and the large negative forcing. Negative forcing from aerosols and land use changes is estimated at -.97W/m2. 

 

Total RF since 1750 is estimated at 2.29W/m2.

 

The large majority of that is since 1950. Total RF since 1950 is estimated at 1.72W/m2. 

 

So the appropriate # is not 3W/m2. It is 2.3W/m2. And there remains a .6-.8W/m2 imbalance. So we've experienced about 1.6W/m2. .9C over 1.6W/m2 is a sensitivity of 2.1C. Plus some slow feedbacks like ice sheet loss could make it a little bigger than that. 

 

This fits into my thinking of a climate sensitivity on the lower end of the AR5 range of 1.5-4.5C (I'd guess 2-3C).

 

If aerosol forcing has been on the more negative side of the confidence interval (closer to -2W/m2) then ECS could be on the higher end of the AR5 range. 

Just for the record, 2-3C would be equivalent to the radiative forcing of 400ppm CO2 at 100% equilibrium...correct? Also I suppose without the negative aerosol forcing.

[TerryM]

blizzard idk if its the one Terry was talking about but when I was reading about giant arctic camels and other Ellesmere island oddities this is the one I filed:

A millennial-scale record of Arctic Ocean sea ice variability and the demise of the Ellesmere Island ice shelves

JH England, TR Lakeman, DS Lemmen… - Geophysical Research …, 2008

Durham hosts a public access copy:

http://dro.dur.ac.uk/6877/1/6877.pdf

Thanks

Out of town for the evening and couldn't respond.

Anything by English is authoritative and most is not paywalled.

The findings simply point out that no cycle that occurred within the last ~5k yr was sufficient to break up the fast ice that had been in place during that period & therefore can't be used as an argument against AGW which demonstrably has opened the coastline of Ellesmere for the first time since long before the pyramids were built. 

The only way to dispute the evidence would be to dispute carbon dating & that might be enough to get you a debate with Bill Nye.

Terry

[blizzard1024]

Thanks

Out of town for the evening and couldn't respond.

Anything by English is authoritative and most is not paywalled.

The findings simply point out that no cycle that occurred within the last ~5k yr was sufficient to break up the fast ice that had been in place during that period & therefore can't be used as an argument against AGW which demonstrably has opened the coastline of Ellesmere for the first time since long before the pyramids were built. 

The only way to dispute the evidence would be to dispute carbon dating & that might be enough to get you a debate with Bill Nye.

Terry

 

stop. I believe in carbon dating and that the Earth is round and that the Earth revolves around the sun and that the Earth is billions of years old...not 6000 years old. anyway Thanks! 

[bluewave]

Latest evidence suggests the Younger Dryas was not caused by freshwater release...the tropics and Southern Hemisphere cooled dramatically and simultaneously with the rest of the globe upon entrance, and warmed simultaneously as it ended.

If anything, a collapse of the THC would warm the tropics. A global, radiative forcing change was likely responsible.

 

A new paper focuses on Greenland melt.

 

http://sciencenordic.com/greenland-icebergs-may-have-triggered-younger-dryas

 

 

Just as the last Ice Age was drawing to a close, Greenland icebergs changed the temperature in the Atlantic and triggered a 1,000-year-long extension of the Ice Age.

 

 

Now the latest research indicates that it was not meltwater from Canada that triggered the  Younger Dryas cooling (see Factbox). According to a new study, this was caused by icebergs and meltwater from Greenland.

”Even though the Greenland ice sheet is a dwarf compared to the gigantic North American ice sheet of the last Ice Age, our studies of the seabed in the Labrador Sea, located between the two ice caps, show that the sediments deposited just prior to the Young Dryas originated from Greenland, not Canada. This sheds new light on the Greenland Ice Sheet’s role in the global climate,” says Paul Knutz, a senior researcher at the Geological Survey of Denmark and Greenland (GEUS).

The scientific results show that last glacial-interglacial transition was associated with interactions between ice sheets, ocean and climate,” says the researcher. “Up to now, our knowledge on how the Greenland ice sheet affects this system was limited, but our study shows that it probably had a significant effect on the climate towards the end of the last Ice Age some 10,000 - 14,000 years ago.”

Should we worry about global cooling?

Since melting ice masses and icebergs from Greenland played a role in the climate at the end of the last Ice Age, one could perhaps rightfully ask if this could lead to a global cooling if large amounts of inland ice disappear from Greenland.

“Of course, it’s a different situation because back then we were in an Ice Age, and today we’re in an interglacial period with different conditions. You could say that the link between ice sheets and ocean currents is very sensitive, and we know that especially the deep water masses in the Labrador Sea are closely linked to the rest of the world’s oceans, so if meltwater from Greenlandic glaciers are to have an impact, they’re in the right region,” says Knutz.

“But further studies are required to determine whether icebergs from Greenland only caused a cooling during the Younger Dryas, or whether this link is a more general phenomenon that could also occur today.”

 

The new findings are published in the journal Earth and Planetary Science Letters.

[blizzard1024]

A new paper focuses on Greenland melt.

 

http://sciencenordic.com/greenland-icebergs-may-have-triggered-younger-dryas

 

 

Just as the last Ice Age was drawing to a close, Greenland icebergs changed the temperature in the Atlantic and triggered a 1,000-year-long extension of the Ice Age.

 

 

Now the latest research indicates that it was not meltwater from Canada that triggered the  Younger Dryas cooling (see Factbox). According to a new study, this was caused by icebergs and meltwater from Greenland.

”Even though the Greenland ice sheet is a dwarf compared to the gigantic North American ice sheet of the last Ice Age, our studies of the seabed in the Labrador Sea, located between the two ice caps, show that the sediments deposited just prior to the Young Dryas originated from Greenland, not Canada. This sheds new light on the Greenland Ice Sheet’s role in the global climate,” says Paul Knutz, a senior researcher at the Geological Survey of Denmark and Greenland (GEUS).

The scientific results show that last glacial-interglacial transition was associated with interactions between ice sheets, ocean and climate,” says the researcher. “Up to now, our knowledge on how the Greenland ice sheet affects this system was limited, but our study shows that it probably had a significant effect on the climate towards the end of the last Ice Age some 10,000 - 14,000 years ago.”

Should we worry about global cooling?

Since melting ice masses and icebergs from Greenland played a role in the climate at the end of the last Ice Age, one could perhaps rightfully ask if this could lead to a global cooling if large amounts of inland ice disappear from Greenland.

“Of course, it’s a different situation because back then we were in an Ice Age, and today we’re in an interglacial period with different conditions. You could say that the link between ice sheets and ocean currents is very sensitive, and we know that especially the deep water masses in the Labrador Sea are closely linked to the rest of the world’s oceans, so if meltwater from Greenlandic glaciers are to have an impact, they’re in the right region,” says Knutz.

“But further studies are required to determine whether icebergs from Greenland only caused a cooling during the Younger Dryas, or whether this link is a more general phenomenon that could also occur today.”

 

The new findings are published in the journal Earth and Planetary Science Letters.

 

I have heard about this. There is uncertainty related to what caused Younger Dryas. But remember Younger Dryas occurred as the end of the Pleistocene not the Holocene. The 8.2 KYR cooling event was in the early Holocene and really is unknown as to what caused this.  It could have been a localized event? Most if not all the large continental NH glaciers were gone by this time. For some reason, after this cooling event, the Holocene world-wide has been pretty stable climate-wise. Locally, there have been measured variations but overall the Holocene has been pretty benign in its climate changes. Below is a graph of the calcium concentration in the GISP2 ice core and it shows that during colder times, there is much more dust in the atmospheric circulation because it is drier. You can see Younger Dryas and other rapid changes in climate in the Pleistocene in this data. But these variations completely end in the Holocene suggesting a very stable climate. Since this is a measure of dustiness in the atmosphere and related to large scale circulation it serves as a proxy for large scale moisture and temperature not just a local effect in Greenland. 

 

[bluewave]

I have heard about this. There is uncertainty related to what caused Younger Dryas. But remember Younger Dryas occurred as the end of the Pleistocene not the Holocene. The 8.2 KYR cooling event was in the early Holocene and really is unknown as to what caused this.  It could have been a localized event? Most if not all the large continental NH glaciers were gone by this time. For some reason, after this cooling event, the Holocene world-wide has been pretty stable climate-wise. Locally, there have been measured variations but overall the Holocene has been pretty benign in its climate changes. Below is a graph of the calcium concentration in the GISP2 ice core and it shows that during colder times, there is much more dust in the atmospheric circulation because it is drier. You can see Younger Dryas and other rapid changes in climate in the Pleistocene in this data. But these variations completely end in the Holocene suggesting a very stable climate. Since this is a measure of dustiness in the atmosphere and related to large scale circulation it serves as a proxy for large scale moisture and temperature not just a local effect in Greenland. 

 

Picture1.png

 

While this paper doesn't go that far back in time, the temperature changes in Greenland over the last 4000 years 

are documented pretty well.

 

http://icebubbles.ucsd.edu/Publications/Kobashi_2011_GRL.pdf

 

 

Greenland recently incurred record high temperatures and ice loss by melting, adding to concerns that anthropo- genic warming is impacting the Greenland ice sheet and in turn accelerating global sea‐level rise. Yet, it remains imprecisely known for Greenland how much warming is caused by increasing atmospheric greenhouse gases versus natural variability. To address this need, we reconstruct Greenland surface snow temperature variability over the past 4000 years at the GISP2 site (near the Summit of the Greenland ice sheet; hereafter referred to as Greenland tem- perature) with a new method that utilises argon and nitrogen isotopic ratios from occluded air bubbles. The estimated aver- age Greenland snow temperature over the past 4000 years was −30.7°C with a standard deviation of 1.0°C and exhibited a long‐term decrease of roughly 1.5°C, which is consistent with earlier studies. The current decadal average surface tem- perature (2001–2010) at the GISP2 site is −29.9°C. The record indicates that warmer temperatures were the norm in the earlier part of the past 4000 years, including century‐long intervals nearly 1°C warmer than the present decade (2001– 2010). Therefore, we conclude that the current decadal mean temperature in Greenland has not exceeded the envelope of natural variability over the past 4000 years, a period that seems to include part of the Holocene Thermal Maximum. Notwithstanding this conclusion, climate models project that if anthropogenic greenhouse gas emissions continue, the Greenland temperature would exceed the natural variability of the past 4000 years sometime before the year 2100. Citation: Kobashi, T., K. Kawamura, J. P. Severinghaus, J.‐M. Barnola, T. Nakaegawa, B. M. Vinther, S. J. Johnsen, and J. E. Box (2011), High variability of Greenland surface temperature over the past 4000 years estimated from trapped air in an ice core, Geophys. Res. Lett., 38, L21501, doi:10.1029/2011GL049444.

[skierinvermont]

Just for the record, 2-3C would be equivalent to the radiative forcing of 400ppm CO2 at 100% equilibrium...correct? Also I suppose without the negative aerosol forcing.

 

No 2-3C would be the sensitivity in response to doubling (560ppm). 2.5C is the # referred to in the Hansen study I referenced in the post based on climate variation that ended the last ice age. 2.1C is the # I come up with based on climate variation for the last 260 years using IPCC forcing and temperature change estimates (.9C/(2.3W/m2 minus .7W/m2 imbalance remaining =2.1C per doubling). Some recent studies come up with lower numbers than that but I believe they ignore some of the uncertainty in aerosols and the -PDO). The problem with using just the last 250 years is it doesn't include slow feedbacks (esp. since most of the forcing occurred in the last 50 years). The Hansen study is based on a much longer time period (the end of the last ice age).

 

2-3C/doubling is well within the AR5s range of 1.5-4.5C.

 

I believe there is also likely a big difference between the fast and slow ECS. The TCR after 20 years might be 1.8C, the ECS after 100 years might be 2.2C, while ECS 1000 years later might be closer to 3C or higher. This would be due to very slow processes like melting of the greenland ice sheet. 

[StudentOfClimatology]

A new paper focuses on Greenland melt.

http://sciencenordic.com/greenland-icebergs-may-have-triggered-younger-dryas

Just as the last Ice Age was drawing to a close, Greenland icebergs changed the temperature in the Atlantic and triggered a 1,000-year-long extension of the Ice Age.

Now the latest research indicates that it was not meltwater from Canada that triggered the Younger Dryas cooling (see Factbox). According to a new study, this was caused by icebergs and meltwater from Greenland.

”Even though the Greenland ice sheet is a dwarf compared to the gigantic North American ice sheet of the last Ice Age, our studies of the seabed in the Labrador Sea, located between the two ice caps, show that the sediments deposited just prior to the Young Dryas originated from Greenland, not Canada. This sheds new light on the Greenland Ice Sheet’s role in the global climate,” says Paul Knutz, a senior researcher at the Geological Survey of Denmark and Greenland (GEUS).

The scientific results show that last glacial-interglacial transition was associated with interactions between ice sheets, ocean and climate,” says the researcher. “Up to now, our knowledge on how the Greenland ice sheet affects this system was limited, but our study shows that it probably had a significant effect on the climate towards the end of the last Ice Age some 10,000 - 14,000 years ago.”

Should we worry about global cooling?

Since melting ice masses and icebergs from Greenland played a role in the climate at the end of the last Ice Age, one could perhaps rightfully ask if this could lead to a global cooling if large amounts of inland ice disappear from Greenland.

“Of course, it’s a different situation because back then we were in an Ice Age, and today we’re in an interglacial period with different conditions. You could say that the link between ice sheets and ocean currents is very sensitive, and we know that especially the deep water masses in the Labrador Sea are closely linked to the rest of the world’s oceans, so if meltwater from Greenlandic glaciers are to have an impact, they’re in the right region,” says Knutz.

“But further studies are required to determine whether icebergs from Greenland only caused a cooling during the Younger Dryas, or whether this link is a more general phenomenon that could also occur today.”

The new findings are published in the journal Earth and Planetary Science Letters.

I do not buy the notion that the collapse of the Atlantic THC can force a global cooling regime..that sounds like climate denier pseudoscience to me.

The Younger Dryas was observed from South Africa, to South America, which should have warmed following a reduction in meridional pumping.

There are hundreds of peer reviewed studies indicating both the Younger Dryas and 8200kyr event were global in nature:

https://itia.ntua.gr/hsj/redbooks/208/hysj_208_01_0269.pdf

Huesser & Rabassa (1987) established the correspondence between the late-glacial cooling recorded in southernmost South America and the Younger Dryas. In a recent study, Labracherie et al. (1989) also showed that the last déglaciation in the southern ocean was interrupted by a cooling phase similar to the Younger Dryas.

http://www.sciencedirect.com/science/article/pii/S0921818100000424

The Pleistocene/Holocene transition in South Africa: evidence for the Younger Dryas event

There are indications from a number of studies, however, that it was indeed a worldwide event. Seeking evidence to define the Pleistocene/Holocene transition in southern Africa, the oxygen isotope ratios in shell fragments of the giant land snail, Achatina sp. (as derived from dated strata in the archaeological excavations of the Bushman Rock Shelter in the Transvaal region of South Africa), were measured. A sequence of colder episodes, including what we believe to be the YD event, is indicated, and there is evidence as for an earlier (Older Dryas?) event as well. We also measured the oxygen isotope ratios of modern land snail shells from South Africa and showed that they exhibit a good correlation with latitude, enabling us to make some deductions as to the general climatic conditions during the Pleistocene/Holocene transition compared to today.

[blizzard1024]

I do not buy the notion that the collapse of the Atlantic THC can force a global cooling regime..that sounds like climate denier pseudoscience to me.

The Younger Dryas was observed from South Africa, to South America, which should have warmed following a reduction in meridional pumping.

There are hundreds of peer reviewed studies indicating both the Younger Dryas and 8200kyr event were global in nature:

https://itia.ntua.gr/hsj/redbooks/208/hysj_208_01_0269.pdf

Huesser & Rabassa (1987) established the correspondence between the late-glacial cooling recorded in southernmost South America and the Younger Dryas. In a recent study, Labracherie et al. (1989) also showed that the last déglaciation in the southern ocean was interrupted by a cooling phase similar to the Younger Dryas.

http://www.sciencedirect.com/science/article/pii/S0921818100000424

The Pleistocene/Holocene transition in South Africa: evidence for the Younger Dryas event

There are indications from a number of studies, however, that it was indeed a worldwide event. Seeking evidence to define the Pleistocene/Holocene transition in southern Africa, the oxygen isotope ratios in shell fragments of the giant land snail, Achatina sp. (as derived from dated strata in the archaeological excavations of the Bushman Rock Shelter in the Transvaal region of South Africa), were measured. A sequence of colder episodes, including what we believe to be the YD event, is indicated, and there is evidence as for an earlier (Older Dryas?) event as well. We also measured the oxygen isotope ratios of modern land snail shells from South Africa and showed that they exhibit a good correlation with latitude, enabling us to make some deductions as to the general climatic conditions during the Pleistocene/Holocene transition compared to today.

 

"I do not buy the notion that the collapse of the Atlantic THC can force a global cooling regime..that sounds like climate denier pseudoscience to me."   (my emphasis added)

 

Mainstream climate science has taught that the disruption of the Atlantic THC could plunge the Earth into a cold period.  

But there are a lot of unknowns regarding this so it is fair to disagree with this. But to call people names because they don't agree with you???? why do you do this? 

 

Also I never said Younger Dryas was not global in nature. It was and so was the 8.2 kyr event. 

[blizzard1024]

While this paper doesn't go that far back in time, the temperature changes in Greenland over the last 4000 years 

are documented pretty well.

 

http://icebubbles.ucsd.edu/Publications/Kobashi_2011_GRL.pdf

 

 

Greenland recently incurred record high temperatures and ice loss by melting, adding to concerns that anthropo- genic warming is impacting the Greenland ice sheet and in turn accelerating global sea‐level rise. Yet, it remains imprecisely known for Greenland how much warming is caused by increasing atmospheric greenhouse gases versus natural variability. To address this need, we reconstruct Greenland surface snow temperature variability over the past 4000 years at the GISP2 site (near the Summit of the Greenland ice sheet; hereafter referred to as Greenland tem- perature) with a new method that utilises argon and nitrogen isotopic ratios from occluded air bubbles. The estimated aver- age Greenland snow temperature over the past 4000 years was −30.7°C with a standard deviation of 1.0°C and exhibited a long‐term decrease of roughly 1.5°C, which is consistent with earlier studies. The current decadal average surface tem- perature (2001–2010) at the GISP2 site is −29.9°C. The record indicates that warmer temperatures were the norm in the earlier part of the past 4000 years, including century‐long intervals nearly 1°C warmer than the present decade (2001– 2010). Therefore, we conclude that the current decadal mean temperature in Greenland has not exceeded the envelope of natural variability over the past 4000 years, a period that seems to include part of the Holocene Thermal Maximum. Notwithstanding this conclusion, climate models project that if anthropogenic greenhouse gas emissions continue, the Greenland temperature would exceed the natural variability of the past 4000 years sometime before the year 2100. Citation: Kobashi, T., K. Kawamura, J. P. Severinghaus, J.‐M. Barnola, T. Nakaegawa, B. M. Vinther, S. J. Johnsen, and J. E. Box (2011), High variability of Greenland surface temperature over the past 4000 years estimated from trapped air in an ice core, Geophys. Res. Lett., 38, L21501, doi:10.1029/2011GL049444.

 

This paper actually shows nothing unusual about present day Greenland temperatures. The LIA was very cool and this simply shows a recovery to present temperatures. It was warmer in Greenland before man-made CO2 and CH4 etc were pumped into the atmosphere. It does show a lot of local variability in climate on decadal and century scales.   

[bluewave]

This paper actually shows nothing unusual about present day Greenland temperatures. The LIA was very cool and this simply shows a recovery to present temperatures. It was warmer in Greenland before man-made CO2 and CH4 etc were pumped into the atmosphere. It does show a lot of local variability in climate on decadal and century scales.   

 

I think the speed of the decline in the sea ice over the last century coupled with the faster Greenland warming made it

noteworthy . But the sea ice has been lower in the Arctic and temperatures  were warmer in Greenland in the past.

Maybe the rate of warming in the distant was more gradual compared to the last century.

 

 

http://www.sciencemag.org/content/333/6043/747.full

 

Excerpt: In general, our sea-ice record for North Greenland follows the Holocene climate development, with an early warm period followed by declining temperatures, which were punctuated by relatively warmer and colder intervals (17, 25). The reduction of the HTM sea ice in northern Greenland fits with the simulated ice distribution and surface temperature in orbitally forced ECHAM5/JSBACH/MPI-OM (EJM) and LOVECLIM general circulation climate model simulations (3, 4, 10). A tentative first approximation of the large-scale changes associated with the observed ice retreat north of Greenland can be obtained by selecting among the numerical experiments performed with the LOVECLIM model those that are the most similar to our observations [experiments E3 to E5 (3) and fig. S3]. In this exercise, our records would correspond in the model to an Arctic Ocean sea-ice cover in summer at 8 ky B.P. that was less than half of the record low 2007 level. The general buildup of sea ice from ~6 ky B.P. agrees with the LOVECLIM model, showing that summer sea-ice cover, which reached its Holocene maximum during the LIA, attained its present (~2000) extent at ~4 ky B.P. (fig. S3)

[StudentOfClimatology]

Mainstream climate science has taught that the disruption of the Atlantic THC could plunge the Earth into a cold period.

Mainstream climate science has never "taught" me this. How exactly can a reduction in Atlantic meridional pumping *cool* the tropics and Southern Hemisphere? I honestly would love to know.

The tropical waters are already significantly warmer than the cold North Atlantic, and weakening meridional circulation will reduce the rate of heat transport from the tropics to the poles..this should warm the tropical regions, not cool them. To me it sounds like someone is desperate for a non-radiative mechanism.

But there are a lot of unknowns regarding this so it is fair to disagree with this. But to call people names because they don't agree with you???? why do you do this?

Please provide a quote, I didn't call anyone names.

Also I never said Younger Dryas was not global in nature. It was and so was the 8.2 kyr event.

I agree, but you initially claimed changes in North Atlantic circulation were responsible. You're essentially saying that the tiny, cold North Atlantic forced the globe back into Ice Age conditions in 10 years, dropped sea levels rapidly, etc. In my opinion, that is a pseudoscientific fairytale.

[blizzard1024]

Mainstream climate science has never "taught" me this. How exactly can a reduction in Atlantic meridional pumping *cool* the tropics and Southern Hemisphere? I honestly would love to know.

The tropical waters are already significantly warmer than the cold North Atlantic, and weakening meridional circulation will reduce the rate of heat transport from the tropics to the poles..this should warm the tropical regions, not cool them. To me it sounds like someone is desperate for a non-radiative mechanism.

Please provide a quote, I didn't call anyone names.

I agree, but you initially claimed changes in North Atlantic circulation were responsible. You're essentially saying that the tiny, cold North Atlantic forced the globe back into Ice Age conditions in 10 years, dropped sea levels rapidly, etc. In my opinion, that is a pseudoscientific fairytale.

 

Actually the North Atlantic Meridional Overturning Current is critical for the global climate. Glaciations began in cycles about 2.6 million years ago when the isthmus of Panama closed off and the Atlantic and Pacific Oceans were separated. This led to the NAMOC which transported heat and moisture way to the north into the Arctic. This led to much more snowfall at high latitudes which initiated NH glaciations. Changes in albedo from more snowcover also profoundly impacted the climate system.   It is postulated that if this current shut down much colder conditions would be experienced in Europe at least and one wonders how this would impact the general circulation of the NH...especially in the winter.  It might only be a local impact as the tropics and SH would warm up as the ocean currents there would not be able to dump all their heat to the high latitudes. Arctic sea ice would increase dramatically also and this would feedback to colder NH conditions. But there are very likely many scenarios that could happen as our climate system adjusts.  

[blizzard1024]

I think the speed of the decline in the sea ice over the last century coupled with the faster Greenland warming made it

noteworthy . But the sea ice has been lower in the Arctic and temperatures  were warmer in Greenland in the past.

Maybe the rate of warming in the distant was more gradual compared to the last century.

 

ScreenShot2884.jpg

 

http://www.sciencemag.org/content/333/6043/747.full

 

Excerpt: In general, our sea-ice record for North Greenland follows the Holocene climate development, with an early warm period followed by declining temperatures, which were punctuated by relatively warmer and colder intervals (17, 25). The reduction of the HTM sea ice in northern Greenland fits with the simulated ice distribution and surface temperature in orbitally forced ECHAM5/JSBACH/MPI-OM (EJM) and LOVECLIM general circulation climate model simulations (3, 4, 10). A tentative first approximation of the large-scale changes associated with the observed ice retreat north of Greenland can be obtained by selecting among the numerical experiments performed with the LOVECLIM model those that are the most similar to our observations [experiments E3 to E5 (3) and fig. S3]. In this exercise, our records would correspond in the model to an Arctic Ocean sea-ice cover in summer at 8 ky B.P. that was less than half of the record low 2007 level. The general buildup of sea ice from ~6 ky B.P. agrees with the LOVECLIM model, showing that summer sea-ice cover, which reached its Holocene maximum during the LIA, attained its present (~2000) extent at ~4 ky B.P. (fig. S3)

 

This is really interesting. It clearly shows the Holocene climatic optimum which was related to different orbital parameters around 8000 years ago. Presently orbital parameters are different so we would not expect warmer conditions presently. 

[StudentOfClimatology]

Glaciations began in cycles about 2.6 million years ago when the isthmus of Panama closed off and the Atlantic and Pacific Oceans were separated. This led to the NAMOC which transported heat and moisture way to the north into the Arctic. This led to much more snowfall at high latitudes which initiated NH glaciations.

Regardless of whether or not that is the case (it is still heavily debated), I'd appreciate a response to my question.

You claimed that the Younger Dryas, an extremely rapid and globally synchronous cooling, followed by an equally rapid, globally synchronous warming, was forced by changes in the North Atlantic THC. Do you stand by this position? If so, how did the tropics and Southern Hemisphere cool synchronously?

It is postulated that if this current shut down much colder conditions would be experienced in Europe at least and one wonders how this would impact the general circulation of the NH...especially in the winter. It might only be a local impact as the tropics and SH would warm up as the ocean currents there would not be able to dump all their heat to the high latitudes. Arctic sea ice would increase dramatically also and this would feedback to colder NH conditions. But there are very likely many scenarios that could happen as our climate system adjusts.

The problem with that theory is the fact that over 70% of merdidional heat transport at a given interval within the tropospheric column is achieved atmospherically, and the warmer tropical/subtropical temperatures that would result from a THC collapse would be pumped poleward by the Hadley Cells, which exist due to differential solar heating by latitude. Strengthen that equator-to-pole gradient, and you strengthen the Hadley Cells.

So frankly, I'm not convinced. There are many yet-to-be-solved paradoxes within the Pleistocene age. An example being the shift from a 41Kyr interglacial cycle seemingly following orbital Obliquity, to a 100kyr cycle seemingly following orbital Eccentricity. Yet I'm sure the Atlantic THC has been blamed for that too..

[blizzard1024]

Regardless of whether or not that is the case (it is still heavily debated), I'd appreciate a response to my question.

You claimed that the Younger Dryas, an extremely rapid and globally synchronous cooling, followed by an equally rapid, globally synchronous warming, was forced by changes in the North Atlantic THC. Do you stand by this position? If so, how did the tropics and Southern Hemisphere cool synchronously?

The problem with that theory is the fact that over 70% of merdidional heat transport at a given interval within the tropospheric column is achieved atmospherically, and the warmer tropical/subtropical temperatures that would result from a THC collapse would be pumped poleward by the Hadley Cells, which exist due to differential solar heating by latitude. Strengthen that equator-to-pole gradient, and you strengthen the Hadley Cells.

So frankly, I'm not convinced. There are many yet-to-be-solved paradoxes within the Pleistocene age. An example being the shift from a 41Kyr interglacial cycle seemingly following orbital Obliquity, to a 100kyr cycle seemingly following orbital Eccentricity. Yet I'm sure the Atlantic THC has been blamed for that too..

 

The change in glaciations from a 40 kyr interval to a 100 kyr interval is another area of uncertainty. In my paleoclimo class of a few years ago, one hypothesis was that initially NH glaciations followed the 40 kyr cycle as they didn't cover as much land or grow enough to reach down into the midlatitudes. So they were of a higher frequency and followed the obliquity cycle. Eventually each glaciation covered more and more land until the ice albedo feedback kicked in to extend the glaciations far enough to the mid latitudes. Maybe a tipping point was reached??  When this eventually occurred, the frequency was longer because of the enormous amount of ice. It took longer to build the ice and also melt it. So the glaciations then followed the 100 kyr cycle. Personally, I was never comfortable with this explanation.  My professor also presented it as one explanation and additionally did indicate that there was a lot of uncertainty and unknowns with this. I never heard of any ocean current related mechanisms. But this is possible too I suppose. It is really an unknown and an area of research.  Not sure if there has been any recent research on this topic. 

[blizzard1024]

The change in glaciations from a 40 kyr interval to a 100 kyr interval is another area of uncertainty. In my paleoclimo class of a few years ago, one hypothesis was that initially NH glaciations followed the 40 kyr cycle as they didn't cover as much land or grow enough to reach down into the midlatitudes. So they were of a higher frequency and followed the obliquity cycle. Eventually each glaciation covered more and more land until the ice albedo feedback kicked in to extend the glaciations far enough to the mid latitudes. Maybe a tipping point was reached??  When this eventually occurred, the frequency was longer because of the enormous amount of ice. It took longer to build the ice and also melt it. So the glaciations then followed the 100 kyr cycle. Personally, I was never comfortable with this explanation.  My professor also presented it as one explanation and additionally did indicate that there was a lot of uncertainty and unknowns with this. I never heard of any ocean current related mechanisms. But this is possible too I suppose. It is really an unknown and an area of research.  Not sure if there has been any recent research on this topic. 

 

If there is more snow and ice in the high latitudes you would change the albedo which could feedback and affect the climate system far away.  Again the climate system has so many variables and is a non-linear/chaotic system. Cooling in the North Atlantic eventually could affect the general circulation and ocean currents and spread it across a large part of the globe. But one thing that is most apparent is that the NH high latitudes see the most dramatic swings in climate for both warming and cooling.  The global average temperature changes are much less than what is observed at high latitudes in the NH.