Arctic Temperatures Since the mid-90s – Climate Sanity
Posted by The Diatribe Guy on September 15, 2009
To summarize my post: one can plainly see that since 2001, the RSS anomalies have declined on an overall basis, with the rate of decline being steeper the shorter the time frame. Beyond that, the linear best-fit on all longer periods is increasing. My analysis was done on the RSS data from latitude 70-85, which should cover things pretty well (though there is that pesky 5 degrees that isn’t covered). It is based on a best-fit of the anomalies on a month-by-month basis through July 2009. The satellite data goes back to 1979.
Our friends at Climate Sanity have looked at the DMI data by going through a process of extracting data from graphs.
The overall conclusions seem pretty similar if you read the post (linked above in the first line – or click on the link under my blogroll. I have not asked permission to duplicate the post here, so I’ll provide reference links instead.) Fitting linear trends yields overall warming on longer periods, but the highest slope occurs from the mid-90s to current.
The interesting part of the post that really helps put a picture to the discussion, though, is his analysis on a day-by-day basis. I will link to two charts (click on the blue text).
1 – Chart #1 shows the trend by day over time from 1958 through 2009.
2 – Chart #2 shows the trend by day over time split between the periods from 1958 – 1995, and from 1995 – 2009.
This is an interesting perspective in that you see almost no seasonality in the trend through 1995, but since 1995 you see a very distinct seasonality. Part of this may be noise (fewer data points), part of this may be accuracy in measurement (one presumes we’ve gotten better), but even considering for those elements the differential is striking.
One argument against this being “noise” is that the difference in seasons trends fairly smoothly. The January portion of the graph shows the highest trend, and this drops off fairly smoothly until the summer months, where – interestingly enough – we see almost no trend at all (and if there is one, it’s actually slightly negative). We then see the fall – winter months increase towards the right of the graph. There is a weird, anomalous drop at the end of December which makes one question the data there, but again with only 15 data points for each day, things like that will occur.
There are some interesting questions that come of this. First, why the change? Someone referred to the AMO cycle, which I have looked at considerably (most recently in June). The AMO cycle crossed into the positive territory around that same time (mid-90s), though it has actually been increasing from its trough since the 1970s. Further, I’m not sure why a positive AMO would cause a seasonal trend while a negative AMO would not – perhaps in an opposite fashion. But this is just me musing.
Another point that was made in the comments at the original post was that the increased trend seems to be weighted precisely during the seasons when it would seem to have the least impact on ice melt. Indeed, if one looks at the historical ice extent, the winter months don’t seem to deviate all that much, even though this study might imply otherwise.
While that may be true, it would also be true that colder temperatures in the winter probably thicken the ice more, and still makes the ice colder. Colder ice will require more energy input to get it up to the melting point, so it seems quite reasonable to me that warmer winter temperatures will still have an impact on overall ice melt during the summer months. It’s simple Physics.
It’s important for us to recognize ALL the trends and data with these issues. We all know that conclusions can be drawn that are entirely opposite from one another depending on which data is cherry-picked. Just tell the truth in the matter.
And here’s the truth, as I see it: The Arctic, over time, has most definitely warmed. In fact, it has warmed at times quite steeply over some short periods of time, and overall it has warmed over long time frames. This warming, however, has definitely stalled since 2001 and we’ve seen the anomalies cooling off in the most recent years. The slope in the short-term is quite negative.
We have seen ice extent in the Arctic go through a decline, with the minimum ice level occurring in 2007. The warmer temperatures continued into the early part of this decade, and even after they started to decline, it was from such a high level that – while a bit lower – the temps still encouraged more melting. It wasn’t until 2007 that the temperature decline seemed to finally reach the point where it would now encourage a rebound in ice level. And so we saw in late 2007 a significant rebound in the winter ice, leading to a higher minimum level in the summer of 2008. Again, winter ice rebounded in 2008, and I think we can now definitively say that we will see the 2009 minimum ice level come in at a higher level than 2008. Below is today’s chart from IJIS:
I’m still curious about the seasonality, and I thank the poster at Climate Sanity for presenting that interesting analysis. But I think, all in all, the conclusions on my end remain unaffected.