Despite the rapid retreat of Arctic sea ice in recent years, the ice may temporarily stabilize or somewhat expand at times over the next few decades, new research indicates.Why is this finding just showing up now? (I haven't read the paper yet).
A new computer modeling study reinforces previous findings by other research teams that the level of Arctic sea ice loss observed in recent decades cannot be explained by natural causes alone, and that the ice will eventually melt away during summer if the climate continues to warm.
But in an unexpected new result, the research team found that Arctic ice under current climate conditions is as likely to expand as it is to contract for periods of up to about a decade.
“One of the results that surprised us all was the number of computer simulations that indicated a temporary halt to the loss of the ice,” says Jennifer Kay, the lead author and a scientist at the National Center for Atmospheric Research (NCAR). “The computer simulations suggest that we could see a 10-year period of stable ice or even an increase in the extent of the ice. Even though the observed ice loss has accelerated over the last decade, the fate of sea ice over the next decade depends not only on human activity but also on climate variability that cannot be predicted.”
The entire release is here, and the paper here.
Actually I think this is very reasonable and doesn't discount AGW at all. It can be argued that it is an out for those scientists who have made what I think are wild claims about the loss of the Arctic ice sheet but that's about all.
ReplyDeleteThe earth has been heating for 20,000 years although the heating has been anything but steady.
Probably the best long term indication of the earth's temperature is historic sea levels but I suspect that at best they are an indication of multi-decade or more likely century estimates.
This link provides a Wikipedia chart showing sea level estimates for the last 24,000 years or so.
http://upload.wikimedia.org/wikipedia/commons/1/1d/Post-Glacial_Sea_Level.png
The thing that impresses me most are the differing estimates by different sources. Some are off by 20 meters from one site to another. That is why I call this an estimate but think about the error bars not shown. That doesn't make the chart useless but it does mean that the data should be taken as an estimate.
From my reading of the chart sea level started rising steadily about 20,000 years ago, accelerated about 15,000 years ago but with at least 2 slower periods in them before slowing down about 8,000 years ago. I'm guessing that sea level has risen about 2.5 meters in the last 8,000 years or about 31 mm per century or about one-tenth what the satellite data is showing (300 mm per century) we are increasing currently but the increase was anything but steady. You can see that although the trend is steady there were periods of increase and decrease in it. Additionally in the last 20,000 years sea level has risen about 130 meters or 650 mm per century. That’s less then half the 20,000 average. I love how averaging half of the 20,000 years can be called “unprecedented”.
My whole point in this is that there is a boatload of natural variability out there. To try and predict over a period of years is absurd. I think a decade is risky. Apparently so does NCAR.
Trouble is, the NCAR model is missing some physics.
ReplyDeleteSteve Bloom,
ReplyDeletePerhaps, perhaps not. The overall trend of the Arctic has certainly been negative but the Antarctic has been flat to slightly positive.
Globally the trend is slightly negative but the data only exists for 31 - 32 years (I'm too lazy to look it up).
Even if the trend continues that doesn't mean that it will be consistent each and every year.
The Antarctic is very different from the Arctic--most of it lies on land, not ocean. In a warming world that is also a wetter world, an area that is still below freezing would be expected to gain snow/ice.
ReplyDeleteDavid,
ReplyDeleteWe're talking sea ice not land ice.
Antarctic sea ice has increased by about 1.33 per decade since 1979.
http://nsidc.org/cgi-bin/bist/bist.pl?annot=1&legend=1&scale=100&tab_cols=1&tab_rows=12&config=seaice_extent_trends&submit=Refresh&hemis0=S&img0=plot&mo0=01&year0=2011&mo1=02&year1=2011&mo2=03&year2=2011&mo3=04&year3=2011&mo4=05&year4=2011&mo5=06&year5=2011&mo6=07&year6=2011&mo7=08&year7=2011&mo8=09&year8=2011&mo9=10&year9=2011&mo10=11&year10=2011&mo11=12&year11=2011