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UAH also recorded another increase in stratospheric temperatures. If history is any guide then that means further troposphere cooling is around the corner. The leading hypothesis for stratospheric warming is still wildfire smoke.

Another day and another sharp decline. The NSIDC did call the top as March 5th.

March 5 with a 5d average of 15.047 on NSIDC might be the max. I'd give greater than 50% odds at this point. We'll see.

RSS was up in February, but not as much. ERA was only up by 0.02C. I keep wondering if UAH is contaminated by what happens in the stratosphere more so than RSS. If so that would partly explain UAH's 0.13C/decade trend which is far lower than what any other dataset shows.

Maybe. I was watching aerosol optical depths closely after that eruption and while there was a lot tephra lofted into the troposphere it didn't appear as if much sulphate aerosols made it into the stratosphere. I think the Australia wildfire smoke is a better hypothesis at this point. In regards to the troposphere...volcanoes typically cool this layer. I don't know of a case where warming resulted from an eruption. And I'm not understanding the link with smoke either. I thought smoke was more effective at blocking incoming shortwave radiation than it was at trapping outgoing longwave radiation.

Hmm...Dr. Spencer is suggesting the smoke warmed both the troposphere and stratosphere. Typically aerosols cool the troposhere and warm the stratosphere. This is an unusual event in that the spike up is observed in both layers. I'm a bit skeptical of his smoke causing radiation induced warming (aka greenhouse effect) claim, but I'm open to hearing what evidence he presents. The thing is that the February troposphere anomaly is primarily the result of warming in the NH. My first thought is that the record +AO may be partly to blame with the spike.

I was not expecting that. The average ONI over the last 3 and 6 months is only 0.5 and 0.3 respectively. Somewhat interesting...the UAH stratosphere temperature spiked up this month. This is only the 3rd time a spike has occurred. The other two were from El Chichon and Pinatubo.

Definitely some export going on there. We are now at that time of year when the max could occur at anytime.

The Arctic Oscillation is once again predicted to top 6 by the Euro.

Good question. This can be found in IPCC AR5 WGI figure 12.28. For the summer minimum not much is expected to change through 2030. In fact, we might even expect a slight increase possibly lasting until mid century until a regime of more consistent declines begin down there. And the detailed breakdown for Arctic summer minimum is in IPCC AR5 WGI TS figure 17. The only scenario that gets to near 100% melt out before 2100 is RCP8.5. But even then a very small patch of ice is predicted to cling the northern tip of Greenland. And, of course, winter ice will likely persistent for a very long time...well past 2100.

I don't equate an ice-free summer regarding Arctic sea ice extents to anything even remotely close to a doomsday scenario though. FWIW the "official" IPCC prediction can be seen in figure TS.17 of the AR5 WGI report. The best guess is about 2045 for RCP8.5, 2065 for RCP6.0, 2080 for RCP4.5, and never for RCP2.6.

Gotcha. Outlier predictions like those from Wedhams are overwhelmingly rejected by mainstream science. The consensus timeline for the first ice free summer in the Arctic region is about 2040-2060 with moderate to high emissions scenarios. Note that "ice-free" means < 1e6 km^2. The disappearance of sea ice altogether would likely take hundreds of years even under an unmitigated emissions scenario. Regarding daily and annual sea ice extents...it's "supposed" to ebb and flow like this. Its best to stick to reputable sources for climate predictions or predictions of any kind in any discipline of science really.

Who is saying that daily or annual sea ice extent would only monotonically decrease?

Sea ice in the SH is doing relatively well too.

Here's a pretty good (and lengthy) article talking about Arctic sea ice and the odds of seeing an ice-free summer. https://interactive.carbonbrief.org/when-will-the-arctic-see-its-first-ice-free-summer/ Bottom line...around 2050 is the 50/50 point especially if carbon emissions take a more middle-of-the-road trajectory being neither abated aggressively or allowed to grow unmitigated...basecially RCP 4.5.

It's interesting what is happening in the SH as well. According to the IPCC the expectation was for mostly flat trends and possibly even an increase through the 2020's. So to see the SH decline and even drop to record lows tells us that at least some sea ice predictions have underestimated the decline down there too. It seems as though there is a long history of sea ice predictions being too conservative; sometimes shockingly so. For example, back in 2001 and inferring from a graphic in AR3 the IPCC predicted that NH sea ice extent wouldn't drop below an annual mean of 10.5e6 until about 2040. It first happened in 2007 and then 6 times after that including the last 4 years in a row. So by taking a more conservative stance and hinting that the declines may moderate in the 2020's I'm doing so fully aware that I could end up getting burned. But I also understand that trendline reversion is a powerful concept and I'm also trying to stay pragmatic and not come across as overly alarmist either.

So if I remember correctly some of the recent computer modeling studies showed that the 2020's might be characterized as period of stalling out on the declines before picking back up again in the 2030's. What do you guys think? Are we going to see the same dramatic declines or will there be a hiatus? I think I'm more in favor of a moderation in the decline rates. But, it's not lost on me that those who have made similar conservative predictions in the past have gotten burned. So I'm prepared to be wrong.

According to NSIDC... For 2019 the NH (Arctic) ended with an annual mean of 10.186e6 km^2 of extent. This is the 2nd lowest after 2016 which ended with 10.163e6. For 2019 the SH (Antarctic) ended with an annual mean of 10.826e6 km^2 of extent. This is the 2nd lowest after 2017 which ended with 10.749e6.

Annual global mean temperatures from most datasets are accompanied with a margin of error. This makes annual rankings probabilistic. Berkeley Earth has a good visualization of this in their 2018 report. You can see how the temperature distribution curve for each year peaks at the reported value and how the tails can overlap with other years. http://berkeleyearth.org/2018-temperatures/ They have an excellent paper describing how the averaging process works and how uncertainties are dealt with and reported. http://berkeleyearth.org/static/papers/Methods-GIGS-1-103.pdf Most other datasets post their uncertainties and make annual rankings in a similar manner.

According to the NSIDC the 5 day average is well outside the interdecile range and just barely inside the 2σ envelope. It is 870,000 sq km below the 1981-2010 mean. Also, I counted 6 other times in which sea ice extent increase from 12/1 to 12/23 was higher.

It's somewhat of an interesting twist isn't it?

NSIDC isn't the source though. Their "NSIDC in the News" section is just links to various articles and blogs that mention NSIDC. They have hundreds of links in this section every year. It's not even clear if these articles (which are dead links now) were in reference to a bona-fide peer reviewed study or some random blogger's opinion. Note the disclaimer in the section. The following items link to media coverage of NSIDC in various news outlets, online magazines, editorial pieces, and blogs. The content of these articles and blog posts does not necessarily reflect the views of NSIDC, our collaborators, or our funding agencies. Like I said, I can't see the articles anymore so I have no idea what the details of these "predictions" are. But based on the timing of when the articles appear I can speculate a bit. There were two fellows during this period that made some very aggressive predictions that got widespread media attention. The first was Maslowski and the second was Wadhams. Neither was characterized by broad acceptance in the academic community. In Wadham's case he was pretty much entirely ignored. Maslowski was a legit researcher but in his defense his work was frequently taken out of context. His 2016±3 date (which was often erroneously cited as 2013) was statistical and appeared in a publication that I believe used many methods to arrive at many different estimates with 2016 being the lowest therefore making a cherry pick and really bad at that. Masklowski even warned against taking his work out of context and specifically chided Al Gore for doing just that. The point...be careful about linking media popularity with the mainstream views of bona-fide scientists. They are often at odds with each other.

Broadly speaking the first "ice-free" year has been getting pushed up. You'll find select studies here and there that have really aggressive predictions, but those are either few in number or not well received enough to influence the consensus much. In the 1990's the prevailing prediction was around 2100 or thereafter. And in the IPCC's AR3 report from 2001 it was stated (via a chart) that the first annual mean extent of 10.5e6 km^2 would not occur until about 2040. In reality it actually occurred in 2007. Even today many sea-ice models continue to struggle with the rapid pace of sea ice declines in both the NH and SH. Today it seems as though the consensus lands somewhere in the 2040-2060 range. So we still have a good wait ahead of us before we see < 1e6 km^2 of extent at the minimum. It's certainly possible that it could occur prior to 2040. Some on this forum and the ASIF believe we'll be lucky to make it to 2040. I'm in the more conservative camp and believe it will be after 2040. I'm prepared to be proven wrong though.

So in an effort to steer this thread back on track...it looks like the refreeze has really ramped up lately. We are still in record territory for this time of year, but it looks like 2019 might jump ahead of 2016 in the next week or so.

CO2 does not add heat. It traps heat. In this context "trap" means to slow the egress transmission of heat without slowing the ingress transmission of heat. The insulation in your home acts as a thermal barrier to trap heat. The furnace adds energy to your home. Because the insulation has changed the rate at which heat is lost your home will achieve a higher equilibrium temperature with the insulation than it would otherwise. But the furnace is still the energy source. ...similarly... The GHGs in Earth's atmosphere act as a thermal barrier to trap heat. The Sun adds energy to the Earth. Because the GHGs have changed the rate at which heat is lost the Earth will achieve a higher equilibrium temperature with the GHGs than it would otherwise. But the Sun is still the energy source.