Arctic ice melts less this year

[Puggit]

http://news.bbc.co.uk/1/hi/sci/tech/8261953.stm

Global warming not so lethal this year

[HarryW]

But its still 24% less than the 1979-2000 average.......does anyone know why this period was chosen.
[rant]
It must be at least 1million percent less than the 3000-1000BC average too. The ice has been retreating for thousands of years, why will mankind reverting to a pre industrial revolution age help it , just get over it and move on ffs.
[/rant]

[The Ben]

Winky as managed to cool the earth down. Enviromental tax is working then

[HarryW]

The Ben said:

Winky as managed to cool the earth down. Enviromental tax is working then

So if I pay even more tax after a while the ice will cover Scotland and the north again the plan has merit

[Spiritual_Beggar]

I heard that the more Tax you pay, the more Carbon Diovxides are taken out of the atmosphere.

True Story.

[chris watton]

Spiritual_Beggar said:

I heard that the more Tax you pay, the more Carbon Diovxides are taken out of the atmosphere.

True Story.

However – until we come out of this recession (that started in America...), and until tax receipts start to pick up again, MMGW is ‘on ice’..

(I hope the government cuts don’t harm our GW statisticians grants too much….)

[ludo]

HarryW said:

But its still 24% less than the 1979-2000 average.......does anyone know why this period was chosen.
[rant]
It must be at least 1million percent less than the 3000-1000BC average too. The ice has been retreating for thousands of years, why will mankind reverting to a pre industrial revolution age help it , just get over it and move on ffs.
[/rant]

I suspect that the start date is due to the launch of the satelite from which the data are obtained. As to the end date, I don't know, but the data are available, so if you wanted to calculate the reduction from the 1979-2009 average it wouldn't be difficult to calculate. The long term trend shows that growth over two year time span is not unusual, but the long term trend is obviously one of a decrease in extent.



This is an example of "regression to the mean", described well in Ben Goldacres book on Bad science - page 39. A record year for anything is rarely followed by another record year (simply because record events are usually the result of a combination of factors coming together at the same time), so following a record low for sea ice extent, you would expect an increase in sea ice extent next year. You can easily see the truth of that in the plot shown above. Everytime a new record low is set, sea ice extent is bigger the following year.

ETA:

National Snow and Ice Data Center said:

Arctic sea ice appears to have reached its minimum extent for the year, the third-lowest extent since the start of satellite measurements in 1979. While this year’s minimum extent is above the record and near-record minimums of the last two years, it further reinforces the strong negative trend in summertime ice extent observed over the past thirty years.

http://nsidc.org/arcticseaicenews/index.html

Edited by ludo on Friday 18th September 09:12

[Bing o]

ludo said:

This is an example of "regression to the mean", described well in Ben Goldacres book on Bad science - page 39. A record year for anything is rarely followed by another record year (simply because record events are usually the result of a combination of factors coming together at the same time), so following a record low for sea ice extent, you would expect an increase in sea ice extent next year. You can easily see the truth of that in the plot shown above. Everytime a new record low is set, sea ice extent is bigger the following year.

How statistically valid are these records over the 30 years when we have had polar ice caps for millions of years?

[ludo]

Bing o said:

ludo said:

This is an example of "regression to the mean", described well in Ben Goldacres book on Bad science - page 39. A record year for anything is rarely followed by another record year (simply because record events are usually the result of a combination of factors coming together at the same time), so following a record low for sea ice extent, you would expect an increase in sea ice extent next year. You can easily see the truth of that in the plot shown above. Everytime a new record low is set, sea ice extent is bigger the following year.

How statistically valid are these records over the 30 years when we have had polar ice caps for millions of years?

While we have had ice caps for millions of years, they have not been static over that time but have grown and shrank at avrying rates. The trend line there is statistically significant (i.e. we can be confident that the (August) sea ice extent is currently shrinking at between 6.4% and 11% per decade). Of course it can't have been shrinking at this rate for very long as otherwise there would have been Summer ice around the U.K. only a thousand years or so ago (I did a rough calculation that shows that extrapolating that rate backwards you would get summer ice at the equator in about 2000 BC!). As someone with actual scepticsm, I wouldn't argue that this is proof of AGW, but it is consistent with AGW, and it certainly isn't evidence of global cooling (and indeed is not consistent with gobal cooling).

[Bing o]

ludo said:

As someone with actual scepticsm, I wouldn't argue that this is proof of AGW, but it is consistent with AGW, and it certainly isn't evidence of global cooling (and indeed is not consistent with gobal cooling).

Arctic ice is regional, so why claim that it isn't evidence of global cooling?

[DSM2]

It seems to me that if you run the trend line through only from 1990 to 2000, the ice actually increased slightly or stayed the same at worst.

What were we doing right in the 90s then?

[Jasandjules]

DSM2 said:

What were we doing right in the 90s then?

Not being taxed on the basis of deceit?

[ludo]

Bing o said:

ludo said:

As someone with actual scepticsm, I wouldn't argue that this is proof of AGW, but it is consistent with AGW, and it certainly isn't evidence of global cooling (and indeed is not consistent with gobal cooling).

Arctic ice is regional, so why claim that it isn't evidence of global cooling?

because the statistically significant trend over the last 30 years is in the wrong direction to be evidence for global cooling, and the trend over the last two years obvioulsy isn't statistically significant and statistically insignificant trends are not evidence of anything.

[ludo]

DSM2 said:

It seems to me that if you run the trend line through only from 1990 to 2000, the ice actually increased slightly or stayed the same at worst.

What were we doing right in the 90s then?

It is more likely just to be an artifact of the year-to-year variability, just like in the temperature datasets, where it is easy to find seven year trends that show cooling over the last thirty years, even though the overall trend shows warming. Man has a great facility for spotting patterns in noise that are not really there, which is why we developed tests of statistical significance.

[Bill]

ludo said:

because the statistically significant trend over the last 30 years is in the wrong direction to be evidence for global cooling, and the trend over the last two years obvioulsy isn't statistically significant and statistically insignificant trends are not evidence of anything.

The obvious problem being that we have no idea whether that 30 year trend is part of a larger cycle.

[rocksteadyeddie]

Bill said:

ludo said:

because the statistically significant trend over the last 30 years is in the wrong direction to be evidence for global cooling, and the trend over the last two years obvioulsy isn't statistically significant and statistically insignificant trends are not evidence of anything.

The obvious problem being that we have no idea whether that 30 year trend is part of a larger cycle.

Climate change is a phenomenon that happens over tens of thousands, if not millions, of years. To extrapolate from the last 30 is simply statistically nonsense.

[ludo]

Bill said:

ludo said:

because the statistically significant trend over the last 30 years is in the wrong direction to be evidence for global cooling, and the trend over the last two years obvioulsy isn't statistically significant and statistically insignificant trends are not evidence of anything.

The obvious problem being that we have no idea whether that 30 year trend is part of a larger cycle.

True, but then what evidence is there that the long term trend is due a larger cycle? They key issue that I am trying to get across is that this particular source of data, like the surface temperature data, provides no reliable support for theories of global cooling and those that want to show that global cooling is happening need to look elsewhere for evidence if they want to influence mainstream scientific opinion.

Anyone can base their opinion on statistically insignificant trends, while ignoring the longer term statistically significant ones, but it isn't science (at least not competent science).

[Diderot]

Check out the BBC front page (quick before they change it) :

http://www.bbc.co.uk/


One of the main stories in Science and Nature is 'Pause in Arctic melting trend'; then look down at the 'more stories' - 'warming arctic halts migration'.

Is their no end to their public funded fkwittery?

[Bill]

ludo said:

True, but then what evidence is there that the long term trend is due a larger cycle?

What evidence is there that it isn't?

[Bing o]

ludo said:

Bing o said:

ludo said:

As someone with actual scepticsm, I wouldn't argue that this is proof of AGW, but it is consistent with AGW, and it certainly isn't evidence of global cooling (and indeed is not consistent with gobal cooling).

Arctic ice is regional, so why claim that it isn't evidence of global cooling?

because the statistically significant trend over the last 30 years is in the wrong direction to be evidence for global cooling, and the trend over the last two years obvioulsy isn't statistically significant and statistically insignificant trends are not evidence of anything.

How on earth is the regional temperature over one of the polar ice caps evidence of global warming.

Why do we not hear about receding ice at the South Pole? (Apart from the break up of the ice shelf that is due to local ocean temperatures IIRC?)