Learning Global Warming facts and fiction

[snowlover91]

"Based on this graph posted on the previous page, the two circled regions are remarkably similar in magnitude. Only 3 of the datasets here go back to the 1940 period. It's hard to tell where exactly the GIS, ERA20C and Berkeley temps are in the late 90s to early 2000s but the Berkeley dataset is similar, ERA20C appears to be a little warmer for 1 year but similar the other years and GIS appears similar as well. The IPCC and several other sources I cited also mentioned the warmth as comparable so I think there is enough data there to make this claim while also realizing that due to uncertainty with dataset bias and limited records/coverage in the 1930s and 40s the numbers could have been either higher or lower. We might just have to agree to disagree on this one"

I didn't want to have to do this because I thought you could see this for yourself in the link I sent, so here comes a ton of maps. Here's what those datasets show for the period centered on the peak of the warming spike in 1940 (give or take 5 years) vs 1998-2004.

You should get my point now, 1998-2004 is warmer than 1935-1944 in the arctic in virtually all of these datasets. Could 1935-1944 be warmer though? Possibly, it's within the margin of error, but it's more likely to have been cooler than the late 1990s & early 2000s.

This graph you posted previously shows 3 data sets with similar temperature anomalies at both periods in history when compared with the 1981-2010 baseline and would seem to conflict with the series of maps you posted above. I'm not sure what your source for the graph was and would be interested in reading the methodology behind it to see why there appears to be a discrepancy between it and the maps. Furthermore, I would be interested in your thoughts on all the graphs and data posted below.

This graph uses GHCN data and again shows temperature anomalies in the 90s and early 2000s were similar to the 1930s and 40s.

The IPCC had this to say in AR5 chapter 10.
“A question as recently as 6 years ago was whether the recent Arctic warming and sea ice loss was unique in the instrumental record and whether the observed trend would continue (Serreze et al., 2007). Arctic temperature anomalies in the 1930s were apparently as large as those in the 1990s and 2000s. There is still considerable discussion of the ultimate causes of the warm temperature anomalies that occurred in the Arctic in the 1920s and 1930s (Ahlmann, 1948; Veryard, 1963; Hegerl et al., 2007a, 2007b). The early 20th century warm period, while reflected in the hemispheric average air temperature record (Brohan et al., 2006), did not appear consistently in the mid-latitudes nor on the Pacific side of the Arctic (Johannessen et al., 2004; Wood and Overland, 2010). Polyakov et al. (2003) argued that the Arctic air temperature records reflected a natural cycle of about 50 to 80 years. However, many authors (Bengtsson et al., 2004; Grant et al., 2009; Wood and Overland, 2010; Brönnimann et al., 2012) instead link the 1930s temperatures to internal variability in the North Atlantic atmospheric and ocean circulation as a single episode that was sustained by ocean and sea ice processes in the Arctic and north Atlantic. The Arctic-wide increases of temperature in the last decade contrast with the episodic regional increases in the early 20th century, suggesting that it is unlikely that recent increases are due to the same primary climate process as the early 20th century.”

Polyakov et al. includes this in their abstract:

“In contrast to the global and hemispheric temperature, the maritime Arctic temperature was higher in the late 1930s through the early 1940s than in the 1990s.” http://www.personal.kent.edu/~jortiz/paleoceanography/warm_apr02.pdf

Yamanouchi had this to say and also referenced the Polyakov study
“It is known that a large warming event occurring from the 1920s to the 1940s in the Arctic, comparable to the recent 30-year warming, as observed in Fig. 3 by Polyakov et al., 2002, Polyakov et al., 2003a. The original objective of the former study was to confirm that the long-term surface air temperature (SAT) trends did not support the hypothesized polar amplification of global warming due to a large multidecadal variability; however, the authors did show that Arctic warming in the 1930s to the 1940s was exceptionally strong, reaching 1.7 °C, compared with the year 2000 maximum of 1.5 °C. Even though there was a global mean surface temperature rise from the 1920s to the 1940s, the actual increase was dominant mostly in the higher latitude.”

“The situation that a large temperature increase was mostly confined to high latitudes is most clearly indicated in Fig. 5 by Serreze and Francis (2006).” https://www.sciencedirect.com/science/article/pii/S1873965211000053#fig4

Given that all these analysis have similar conclusions and the IPCC agreed that anomalies in the 1930-40s were similar to the late 90s and early 2000s, I don't think my conclusion is a stretch by any means of the imagination. Sure, with the limited data available in the 1930-40 period this presents unique challenges and it's entirely possible that it was cooler than the 1990-2004 period but it's also quite possible it was just as warm as the above data indicates.

 

[GaWx]

@snowlover91 and @Webberweather53,
We're all confident that the 2010s are warmer than 1990-2009 in the Arctic, correct? So, why is there so much discussion now of comparing the 1930s/40s to 1990-2009? Shouldn't the focus be on comparing 1930/40s to the 2010s?

 

[snowlover91]

@snowlover91 and @Webberweather53,
We're all confident that the 2010s are warmer than 1990-2009 in the Arctic, correct? So, why is there so much discussion now of comparing the 1930s/40s to 1990-2009? Shouldn't the focus be on comparing 1930/40s to the 2010s?

Larry, I’ll add my 2 cents in here. My original assertion was that the warming experienced in the 1920-45 period was similar to what we’ve seen recently, but I didn’t clarify that I was thinking more of pre-2005 which I believe caused some confusion. I’ll let Webber clarify his thoughts on it but for me personally I believe there is sufficient evidence to say the warming pre-2005 is similar to that seen in the 30s and 40s.

However, after 2005 it seems as if the Arctic has had a shift warmer. What’s interesting to me is that some of the data I’ve seen indicates the shift warmer has been primarily in the winter and spring whereas the summer is closer to average. I haven’t done a lot of research as to the reasons why this would be or to confirm if that is indeed the case, though, but it would be an interesting area to examine.

One of the graphs I did post goes to 2017 and uses GHCN stations north of 60N. That graph is below.

 

[Webberweather53]

The graph and the maps are saying the same thing and the methodologies aren’t any different, your eyes can deceive you unless you’re digging deep into the data. I also included other datasets like NOAAs 20th Century Reanalysis and CERA-20C that weren’t explicitly shown on that other graph. Now I will say that the 1930s-40s aren’t too far off from the late 1990s-2000s in general but it seems the latter period esp after 1998 is warmer, if I were to include data before 1998, the two periods would be closer temperature wise. I think you would have a very solid case claiming the period from after the El Chichon eruption in 1983 thru 1998 were virtually the same as the 30s/40s because the amount of global warming relative to the cooler period in the 1960s and 70s is comparable. Yes, I think some of the debate stemmed over the period of question because the late 2000s and 2010s were warmer than the late 90s and early 2000s in the Arctic. The case for 1998-2004 being warmer is weaker than the late 2000s and 2010s. Other than isolated areas of Eurasia where fall and winter temps have been cool and we’ve seen many years with large snowfall advance over Siberia (indicative of and reinforcing the cold anomalies there), you’d have a hard time convincing most that the Arctic hasn’t warmed between the 1930s and now because it definitely has particularly on the North American side of the arctic. Recent years, since 2013 really have flipped this around though with a stronger Greenland and Baffin Bay vortex, I think this is a consequence of both natural variation in the AMO and Hadley cell expansion from global warming in addition to solar activity perhaps that have amplified this persistent vortex here. A modoki El Niño like we’re expecting this winter is a good way to break down that Baffin vortex but like 2014-15 shows us, it doesn’t guarantee its demise. Something to chew on both at seasonal and interannual timescales.

 

[GaWx]

However, after 2005 it seems as if the Arctic has had a shift warmer. What’s interesting to me is that some of the data I’ve seen indicates the shift warmer has been primarily in the winter and spring whereas the summer is closer to average. I haven’t done a lot of research as to the reasons why this would be or to confirm if that is indeed the case, though, but it would be an interesting area to examine.

I found the same thing using this site:
http://ocean.dmi.dk/arctic/meant80n.uk.php

Click on the years 2005-18. The met. autumns and winters were pretty consistently warmer than normal but the springs must less so and the summers not at all and if anything a hair colder than normal!
So, @Webberweather53, do you know why that would be the case? Why the seasonal patterns?

 

[Webberweather53]

I found the same thing using this site:
http://ocean.dmi.dk/arctic/meant80n.uk.php

Click on the years 2005-18. The met. autumns and winters were pretty consistently warmer than normal but the springs must less so and the summers not at all and if anything a hair colder than normal!
So, @Webberweather53, do you know why that would be the case? Why the seasonal patterns?

There may be several reasons for this. An earlier point/quote snowlover91 brought up touches on this, wherein during the winter because the temperatures are so cold in the arctic, the saturation vapor pressure is low (thus even fully saturated air at -20C is still dry relative to the rest of the globe), and this lack of integrated vapor during the winter over the arctic also means the temperature can fluctuate wildly. Also, the mid-latitude storm track is more active during the winter and thus Rossby Waves impinging on major mountain ranges like the Rockies and the Himalayas will deposit their momentum onto the polar night jet that encapsulates the polar vortex, mixing warm, ozone rich low-mid latitude air into the polar vortex, sometimes these mixing events can be so profound they trigger stratospheric warming events (which we all should be well aware of) that lead to large-scale and very significant warming over the polar cap region in the winter.

In the summer, things are different, the warmer temperatures mean saturation vapor pressures rise, and because water has a high heat capacity, raising the water content in the air also means it's generally more difficult for large-scale temperature changes to occur. Also, since the mid-latitude rossby waves are weaker in the summer, this isolates the polar vortex from the surrounding mid-latitude air that's laden with ozone (which warms the stratosphere), the lack of ozone being entrained into the polar vortex during the summer also favors stratospheric cooling. Akin to what I mentioned earlier regarding why I think the Antarctic is responding differently to climate change than other areas of the globe, I think some of this manifests in the northern hemisphere summer too, when like the Antarctic vortex year round, the northern polar vortex becomes more "isolated". Why does this matter? Ozone loss from the release of CFCs that were prevalent several decades ago destroys ozone in the stratosphere as Chlorine molecules are released by UV radiation in the stratosphere, and its these Chlorine molecules contained within these CFCs that catalyze hundreds of thousands of times over with free oxygen radicals (i.e. unpaired, singular oxygen atoms) before dissipating or mixing into the troposphere again. In the process one CFC molecule ends up destroying ~100,000 ozone molecules. This has a dramatic effect on the stratosphere's temperature distribution, because with less ozone available, the stratosphere cools, especially over the polar regions, and these cooler temperatures over the polar cap create circulation anomalies that descend into the troposphere, creating what essentially amounts to the positive phase of the Arctic or North Atlantic Oscillation (+AO) & (+NAO) respectively, and this tropospheric pattern is more conducive to retaining sea ice as well as keeping temperatures cooler over the polar cap and the arctic.

Based on what I've gleaned thru my own experiences, professional talks, literature, and interaction with actual climate scientists, I think it's a combination of both saturation vapor pressure changes (linked to moist static energy budget changes) & contributions from anthropogenic CFC release that occurred decades ago in addition to greenhouse gases which trap more radiation in the troposphere, allowing less to escape and warm the stratosphere, thereby cooling it. This is the most viable and reasonable explanation for what you're observing imo.

 

[BHS1975]

So once the ozone builds back up the melting should accelerate?


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[Webberweather53]

So once the ozone builds back up the melting should accelerate?


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Well if nothing else changed that would certainly be the case, unfortunately there are competing factors here too. The previously mentioned influence from GHGs on cooling the stratosphere by blocking more radiation from escaping the troposphere, Hadley Cell expansion which causes the jet to move poleward and favors stronger polar vortices (due to angular momentum conservation), and on shorter scales (somewhat unrelated to the long-term climate we're concerned about but they're nonetheless worth mentioning) via energetic particle forcings from solar proton events that occur in major solar storms and coronal mass ejections are all capable of offsetting the impacts from ozone recovery in the stratosphere. Contrary to common misconceptions about solar activity, these solar proton events can still occur during solar minimum, and the Ap index (a measure of global geomagnetic activity) usually lags sunspots s.t. it peaks a few years or so after solar max.

 

[setxwx]

Damn good discussion today... the little feisty back and forth was fine by me. This is a very important and complex topic and a few heated moments are going to occur. The referee needs to keep things from getting out of hand of course(can't have these guys sucker punching below the belt, or trying to bite each other's ears off), but clamping down on some good honest aggressive chat doesn't make the conversation better. JMO. (I know, not worth spit).

 

[MichaelJ]

Found this neat graph where you can compare Ice melt in Greenland all the way back to 1979. Fun to play with and shows that the concern about melt in Greenland is overblown http://nsidc.org/greenland-today/greenland-surface-melt-extent-interactive-chart/

 

[BHS1975]

Looks like the climate switch has been flipped with these “1000” year storms every year now which probably was pretty common during warm epochs in earths history.


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[ForsythSnow]

Looks like the climate switch has been flipped with these “1000” year storms every year now which probably was pretty common during warm epochs in earths history.


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The whole thousand year thing can only be attributed to Harvey for what I can remember, and all of it is all statistical anyway. Florence may get that classification but 2 years at best is barely a way to call events of this magnitude "common". Get the same storms the next 10 years sure, but I can't recall a major event other than heat records attaining a thousand year storm label. I don't count media claims as evidence unless it' backed by a reputable source.

 

[WeatherLC]

Seems like a lot more storms stall and cause massive floods.

2015-SC
2016: Baton Rouge and West Virginia
2017:Harvey

 

[GaWx]

Looks like the climate switch has been flipped with these “1000” year storms every year now which probably was pretty common during warm epochs in earths history.

The extremely heavy rain from Harvey and Flo is largely due to them both slowing to a literal crawl for long periods. Are you trying to say that slower moving storms are more common due to global warming? If so, why? Where’s the beef?

 

[BHS1975]

The extremely heavy rain from Harvey and Flo is largely due to them both slowing to a literal crawl for long periods. Are you trying to say that slower moving storms are more common due to global warming? If so, why? Where’s the beef?

The arctic is warming faster than the tropics so the jet stream is slowing down which allows it to meander. You end up with a more amplified pattern that can get stuck for days with strong ridges in places that weaken the steering. During the warmer periods when the arctic had little to no permanent ice the jet stream was probably much weaker than today with stagnant weather patterns.


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[GaWx]

The arctic is warming faster than the tropics so the jet stream is slowing down which allows it to meander. You end up with a more amplified pattern that can get stuck for days with strong ridges in places that weaken the steering. During the warmer periods when the arctic had little to no permanent ice the jet stream was probably much weaker than today with stagnant weather patterns.

Interesting theory for sure! The good news is that there’s plenty of data (i.e., tracks of storms back to 1851) that conceivably could be analyzed to see if average forward speed has slowed. This is the kind of analysis I love doing. However, it would seemingly be such a mammoth undertaking that I doubt I’d even try unless I could think of a shortcut that wouldn’t sacrifice much accuracy.

Edit: OTOH, wouldn't you think that's something the NHC could provide relatively easily, say, the average forward motion by decade? Come to think of it, the 1960s was quite a cool decade globally speaking. What if the average forward speed for TCs of the 1960s was compared to that of the 2010s? That should tell us something right there. IF the average forward speed for those two decades were similar, then that would probably mean your theory isn't valid.

 

[GaWx]

The arctic is warming faster than the tropics so the jet stream is slowing down which allows it to meander. You end up with a more amplified pattern that can get stuck for days with strong ridges in places that weaken the steering. During the warmer periods when the arctic had little to no permanent ice the jet stream was probably much weaker than today with stagnant weather patterns.

Well, lookie here! A study has already been done that showed average forward speeds:

https://www.nature.com/articles/s41586-018-0158-3

"The magnitude of the slowdown varies substantially by region and by latitude, but is generally consistent with expected changes in atmospheric circulation forced by anthropogenic emissions. Of particular importance is the slowdown of 30 per cent and 20 per cent over land areas affected by western North Pacific and North Atlantic tropical cyclones, respectively, and the slowdown of 19 per cent over land areas in the Australian region."

So, that combined with heavier rain rates caused by warmer air holding more moisture would mean GW does, indeed, mean more and more extreme heavy rain events from landfalling TCs.

I learned something new. All I had heard from JB and others about Harvey was that GW had nothing to do with it...just that it happened to move very slowly. Well, if GW causes slower moving TCs on average, then GW INDIRECTLY causes an increase in the number of and severity of cat. rain events from TCs.

 

[BHS1975]

Heavy rain events definitely seem more intense. When that heavy rain band was training over Durham the other day I was seeing reflectivities in the mid 70s dbz briefly which is probably over 5 in per hour rates.


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[snowlover91]

Well, lookie here! A study has already been done that showed average forward speeds:

https://www.nature.com/articles/s41586-018-0158-3

"The magnitude of the slowdown varies substantially by region and by latitude, but is generally consistent with expected changes in atmospheric circulation forced by anthropogenic emissions. Of particular importance is the slowdown of 30 per cent and 20 per cent over land areas affected by western North Pacific and North Atlantic tropical cyclones, respectively, and the slowdown of 19 per cent over land areas in the Australian region."

So, that combined with heavier rain rates caused by warmer air holding more moisture would mean GW does, indeed, mean more and more extreme heavy rain events from landfalling TCs.

I learned something new. All I had heard from JB and others about Harvey was that GW had nothing to do with it...just that it happened to move very slowly. Well, if GW causes slower moving TCs on average, then GW INDIRECTLY causes an increase in the number of and severity of cat. rain events from TCs.

I think the bolded section above is important to examine. The author of the paper assumes these changes in atmospheric circulation are forced by AGW entirely and that no other cause/explanation is worth exploring or plausible. Since the entire article is behind a pay wall it's difficult to really tell how the author arrives at that conclusion.

It's also worth noting he uses the years from 1949-2016. Prior to the 1970s when we didn't have satellite data, tropical systems in the Atlantic were tracked through a combination of ship observations, landfall reports and a few other ways. Is it possible the average has been skewed by storms that were missed or the position/speed not accurately tracked due to the low density of observations? We didn't have microwave imagery, high resolution satellites or the hurricane hunters to pinpoint the speed or position of the center so a lot had to be estimated and storms that recurved harmlessly out to sea without ever impacting a ship might be missed entirely or unknown to us in the pre-satellite era. If we had the same technology (hurricane hunters, microwave, GOES satellite, etc) starting in 1949, would the results be the same or significantly different? These are some factors to consider that could skew the average one way or another in a study like this. Since the study is behind a pay wall I can't see if any of those concerns are addressed and if so how but they are worth mentioning in light of the significant technological advances we have seen in the past 20 years.

 

[GaWx]

I think the bolded section above is important to examine. The author of the paper assumes these changes in atmospheric circulation are forced by AGW entirely and that no other cause/explanation is worth exploring or plausible. Since the entire article is behind a pay wall it's difficult to really tell how the author arrives at that conclusion.

It's also worth noting he uses the years from 1949-2016. Prior to the 1970s when we didn't have satellite data, tropical systems in the Atlantic were tracked through a combination of ship observations, landfall reports and a few other ways. Is it possible the average has been skewed by storms that were missed or the position/speed not accurately tracked due to the low density of observations? We didn't have microwave imagery, high resolution satellites or the hurricane hunters to pinpoint the speed or position of the center so a lot had to be estimated and storms that recurved harmlessly out to sea without ever impacting a ship might be missed entirely or unknown to us in the pre-satellite era. If we had the same technology (hurricane hunters, microwave, GOES satellite, etc) starting in 1949, would the results be the same or significantly different? These are some factors to consider that could skew the average one way or another in a study like this. Since the study is behind a pay wall I can't see if any of those concerns are addressed and if so how but they are worth mentioning in light of the significant technological advances we have seen in the past 20 years.

Good points. They are automatically assuming the GW has been mainly due to AGW, which is debatable. But keep in mind "the slowdown of 30 per cent and 20 per cent over land areas affected by western North Pacific and North Atlantic tropical cyclones, respectively, and the slowdown of 19 per cent over land areas in the Australian region." So, there was a large slowdown of those specifically over land per this study.

Does it make sense from a met. view that there'd be a slowdown in average forward speed, especially well away from the tropics, due to GW regardless of the GW main cause?