Quick Arctic Update - 15 Sept 2014

We are near the traditional end of the Arctic sea ice melt season, so I thought I'd check in and post a quick update.  Two years ago, 2012 set the the all-time recorded sea ice melt record (so far) with a minimum sea ice extent over 3 million square kilometers below the 1981-2010 average.  By comparison the 2014 Arctic sea ice melt season looks fairly tame, but don't be fooled, the current sea ice extend is creeping up on 1.5 million square kilometers below the long-term average, and it's still declining.  

This year's minimum sea ice extend will almost certainly not reach the record set in 2012, but it was a significant melt all the same.  This melt qualifies 2014 to be the 6th largest Arctic sea ice melt year on record, exceeded only by 2007, 2008, 2010, 2011, and 2012.  The other years, 2009 and 2013 were just shy of this year's mark.  This also means that the eight years with the greatest Arctic se ice melt were the past 8 years.  It looks like a trend is forming....the bottom line, the sea ice melt is becoming more extensive as time goes on. 

(Graphs courtesy of the National Snow and Ice Data Center, Univ of Colorado at Boulder, NSIDC.org)

The 2014 Arctic Sea Ice Melt is ON!

Every summer some of the sea ice in the Arctic Ocean melts.  And, it's once again that time of year.  The Arctic sea ice melt is on! 

There is no way to know how much sea ice will be left at the end of any melt season, but there's one thing we can be pretty sure of, and that's that there will be less sea ice up there at the end of this melt season than the 1981-2010 average of 6.3 million square kilometers.  

2001 was the last year the sea ice minimum was greater than long-term average.  

The data below show the annual minimum sea ice extent for the Arctic Ocean between 1979 and 2013 (data courtesy of the NSIDC.org).  There is a lot of variability in the data (which is normal for any natural system), but the interesting and worrisome thing is that on average the amount of sea ice remaining at the end of the summer melt season is dropping at an increasing rate (see the trend line through the data).   

The increasing steepness of the slope is what worries me.  These data indicate that not only do we have a trend of increasing sea ice melt in the Arctic, but that the rate ice is melting is accelerating.

Climatologists have long projected that the effects of global climate change will be observed earliest and most clearly in the Arctic.  The rate of melting sea ice is just one of those indicators, but it's a powerful one!

Global warming is not just some wild-eyed idea; the reality of global warming is a scientific conclusion based on decades of multiple lines of evidence.

Will we see a new record Arctic sea ice minimal this summer?  No one can know this, but science can with a high degree of confidence predict that there will be less ice on average this summer than we've seen in the past.

The data below show the current sea ice extent and recent extent history comparing 2014 and 2012, the year with the current minimum sea ice extent) so far.

So what!?

The answer to the so what question is this.  Global warming is real, and unless we get busy doing what we can to mitigate the effects of climate change we are in for some serious trouble.

America...the alarm clock is ringing.  Are you waking up?

Spring in the west, and deep freeze in the east

The Arctic Ocean usually reaches its maximum sea ice extent about this time of year, and we as start observing the annual spring/summer sea ice melt up north the sea ice extent is about 1,000,000 square kilometers below the 1981-2010 average.  Wow!   

This has also been a wild winter ride, and it's not over for people in the midwest.  As I type this entry schools including universities across that region are closed or running on a weather-impacted schedule.  Out here in the mountain west though it looks and feels like spring has already sprung.  We did have a dose of snow over the weekend...I had to shovel twice on Saturday and once on Sunday, but later on Sunday temperatures shot back up to 40+oF and it's headed back there today.

Normally where I live in SE Idaho is only starting the annual spring snow melt by now, but this year the snow is already all gone, except for small patches along the north sides of homes and buildings.  Wild!

Other signs of spring around here include daffodils and crocuses pushing up through the soil, motorcycles appearing in parking lots, and students walking wearing sweatshirts and even short-sleeved shirts.

 Why the early Spring-like conditions?  Well, the radical swing of the jet stream this winter has stayed north of us while it's swung far to the south over the Great Plains and Midwest.

The map below shows the current jet stream track.  Idaho is south of it, and the entire eastern part of the USA, except for the Everglades and Miami are north of it and still freezing.  Yikes!

Will this madness never end?

Cheers!

What's going on in the Arctic? The winter sea ice freeze is on, but Arctic sea ice cover still 1 million km2 below historical averages

 It's been quite a while since I gave you an update on what's happening in the Arctic.

First of all, the Arctic Oscillation shifted recently from its Positive Phase to its Negative Phase; it has been mostly in the Positive Phase since the 1970s .  During the Positive Phase there is a large low pressure region dominating the Arctic, but during the Negative Phase there is a large high pressure system there.  This switch means that masses of cold Arctic air are more likely to push south and perhaps stay longer than they used to.  This is especially true for western North American.  This also helps explain the ice-box conditions we have been experiencing lately in the mountain west.

In other news, the Arctic Ocean sea ice freeze is well under way.  After the record ice melt of the summer of 2013, climatologists are keeping an interested eye on 2013's freeze up.  As the map below from the NSIDC.org shows, sea ice extent is at or sightly above normal in the Bering Sea and beyond the Kamchat peninsula.  At the same time, it is well below historical averages east of Scandinavia and south of Greenland.

If you recall, the Bering Sea produced above average sea ice coverage last year, and the lower than average sea ice in east of Greenland also lagged behind historical averages.

Though sea ice production and sea ice extent are still rising - as is to be expected this time of year - current sea ice extent is about 1 million km2 below historic averages (see the graph below from the NSIDC.org) 

FYI - The last time sea ice cover reached or exceeded the historic average for this time of year was in 1998 - yep, 15 years ago.  Every year since then, mid-January sea ice extent has been below average.  The take home message is that the Arctic continues to warm, and that sea ice extent continues to decline (on average) as the years go by.

2012 Arctic Sea Ice Melt Shatters 2007 Record

Arctic sea ice extent -  A NEW RECORD MINIMUM

On 19 September the National Snow and Ice Data Center (NSIDC) released a preliminary report stating that the 2012 minimum sea ice extent in the Arctic was probably reached on 16 September 2012.  On that date the sea ice extent was 3.41 million km2.  That sea ice extent smashed the previous record minimum sea ice extent from 2007 by 760,000 km2.

The map below shows the sea ice extent on 9/16/2012 when it was at its minimum (white area).  The orange lines show the 1979-2000 average for sea ice extent.

What percent of sea ice cover remained of the historical 1979-2000 average at the end of this year's melt season?  Just over 51%.  That's right, the Arctic sea ice was nearly half gone at the end of the melt season.

Again, some people might argue that the sea ice extent minimum might have been a fluke random event, but that is looking less and less likely.  When we look at the past several years' sea ice minimum data they ALL fall below the 1979-2000 average.  The graph below shows the sea ice minimum extents for all the years 2007-2012.  The likelihood of this many years of sea ice minima below the average by random chance alone is just 1.56%.

And this table shows the actual sea ice extent data:

To wrap things up, "Is the climate change house on fire?" Should we be alarmed?  Look at the data and reach your own conclusion - and these data are just the tip of the iceberg.

Record sea ice melt season reduces sea ice extent to only about 50% of its historical average

It's nearly the middle of September, the traditional end of the sea ice melt season in the Arctic Ocean.  The rate of sea ice melt has slowed over the past few days, perhaps signaling the beginning of the end of the Arctic Ocean sea ice melt season for 2012, but it's not completely done yet, and it's been a crazy summer in the Arctic!

Do you see what I see?  The extent of sea ice cover in the Arctic Ocean is WAY smaller now than the 1979-2000 average (orange lines) with only ~51% of the 1979-2000 average sea ice cover remaining today.

Consider this...

The average sea ice cover (extent) in the Arctic from 1979-2000 was about 6.7 million square kilometers.  Right now there is only about 3.45 million square kilometers of sea ice in the Arctic (as shown above).  The area of ice that is MISSING is shown on the map below.  Sea ice extent has NEVER been this low.

How does this compare to the previous sea ice melt record?  The previous sea ice melt record was in 2007.  The dark gray line on the graph below shows the 1979-2000 average sea ice cover.  The dashed green line shows the sea ice cover during 2007, and the blue line shows sea ice cover during 2012.  The 2012 ice melt smashed the 2007 record, with over 750,000 km2 more sea ice melting than in 2007.

Interestingly, the high amount of sea ice melt in 2007 was largely the result of an unusual Arctic weather year.  It had huge high pressure regions over large areas of the polar north, and lots and lots of sunshine, which meant lots of sea ice melting.  In 2012 however weather conditions did not appear to be set up to produce lots of sea ice melt.  There was a major cyclonic low pressure system that produced lots of cloud cover.  And that combined with associated winds normally slows sea ice melt.  But not this year.  It has just apparently gotten too warm overall in the Arctic for that kind of weather system to slow sea ice melt as much as it used to.

Maybe the sea ice melt in 2007 and 2012 were just statistical outliers.  I would have considered that as a possibility...until I saw the data for sea ice in the Arctic for the years between 2007 and 2012.

The graph below shows the sea ice cover data for the years 2007-2012 plus the 1979-2000 average.  An outlier is an observation that falls well outside of the observed long term trend.  What we see when we look at the data is that every year since 2007, and others not shown here, all fall well outside the 1979-2000 average.  But because there are getting to be so many years outside that average they collectively no longer can really be considered outliers.  Instead, they are possibly representing a new trend.

I just read an extremely interesting paper on what is and has been going on in the Arctic with respect to sea ice.  I recommend it highly if you are seriously interested in this topic.

• Stroeve, J. C., et al. 2012. The Arctic's rapidly shrinking sea ice cover: a research synthesis. Climate Change 110:1005-1027 DOI 10:1007/s10585-011-0101-1

Here is a link to a PDF file containing that paper: 

https://arcus.org/files/projects/supplemental/674/stroeve_etal_seaice_synthesis_2011.pdf

One of the things I found most compelling in Stroeve's article was the analysis of sea ice extent over the last 30+ years.  The conclusion is that the rate of sea ice loss is no longer linear.  Annual sea ice extents are dropping faster over the past decade than during previous decades.  The upper graph shows the rate of sea ice loss 1979-1998 in blue, and the rate of sea ice loss 1999-2010 in red.  The significant difference in these rates of sea ice loss is worth noting.  Stroeve's paper refers to models that suggest that the Arctic could become ice free in the summer as soon as 30 years from now.    

On the heels of this year's record sea ice melt, however, some climatologists are starting to suggest the possibility of a summer free of ice in the Arctic as soon as 10 years from now.  Yow!

2012 Arctic sea ice melt sets new record with no signs of slowing down

This is amazing...it's like watching a slow motion train wreck.  You want to look away, but you just can't do it!

The former record Arctic Ocean sea ice melt was set five years ago, in 2007, and though a couple of other years since then looked like they might flirt with setting a new record, none of them really came close.  In October 2007 The National Snow and Ice Data Center reported that the Arctic sea ice had shattered the pre-exisitng record from 2005.  You can read that full report by clicking the link below.

http://nsidc.org/news/press/2007_seaiceminimum/20071001_pressrelease.html

This graph from the NSIDC October 2007 report shows the difference between the sea ice melt in 2005 and 2007.

The dark gray line shows the 1979-2000 satellite data showing the average sea ice extent during those 20 years.  The dashed green line shows the record set in 2005, and the blue line shows the new record that was set in 2007.

The NSIDC analysts concluded that the 2007 record ice melt was the result of a series of weather and other factors including the following:

• Lower than average sea ice extent at the beginning of the ice melt season
• Thinner ice than average at the beginning of the ice melt season
• A persistent high pressure cell over the central Arctic Ocean through much of the melt season.  That high pressure cell meant clearer skies, and increased amount of solar radiation that struck the ice and ocean surface, accelerating melting.
• Low pressure cells over northern Siberia that produced strong offshore winds that pushed sea ice offshore faster and earlier than normal, plus these winds were warm and promoted further sea ice melt

OK, so what!?

Well, this year, 2012, the Arctic Ocean sea ice melt season still has anywhere from 2 weeks to a month to go, and there is already a new sea ice melt record that from all current indications has the potential to not only exceed, but smash the old record!

This is what the 2012 sea ice melt season looks like so far.

The dark gray line shows the 1979-2000 average, and the dashed green line shows pattern of sea ice melt in 2007, the year of the previous record sea ice melt.  The blue line in this graph shows the sea ice melt pattern for 2012.  If you look at the vertical axis on the left of the graph you can eyeball it and see that the sea ice extent for 29 Aug is probably between 500,000 and 1,000,000 km2 less in 2012 than it was in 2007.  All right, so what were the conditions this year?

The map below shows the maximum sea ice cover of the Arctic Ocean in spring 2012 (18 March 2012). If you look, the sea ice extent is greater than average in the Bering Sea and off Kamchatka.  It reached historical average extents off of the east coast of Greenland and exceeded them off the west coast of Greenland.  At the same time Arctic sea ice cover was below average in the Barents Sea north of Scandinavia and Russia's Kola Peninsula, but not really many other places.

OK, so what conditions existed over the Arctic that led to the current sea ice melt record?

Well, for one thing, there was a strong, cyclonic Arctic low pressure cell that appeared near the end of the first week of August.  Analysts at the NSIDC reported that this type of storm normally spreads sea ice out and slows the rate of sea ice melt, but if you look at the graph of 29 Aug 2009 for the first part of August 2012 the rate of sea ice melt actually increased instead of decreasing!  This is completely counterintuitive when compared to the effects of similar conditions in the past.

This map shows the high and low pressure cells that produced that Arctic storm.  The low pressure cell in the middle of the map should have been a place where cloud cover formed, blocked solar radiation, and produced winds that slowed the compacting of sea ice and sea ice melt...but that didn't happen.

So, to sum up, there was a lot of ice when the melt season began, conditions conducive to rapid sea ice melt were not particularly evident in this year's weather patterns, but a record-setting sea ice melt has already occurred and there are still at least two weeks and perhaps as many as four weeks to go in the ice melt season.

This is what the sea ice cover looked like as of 29 August 2012.  Remember that the orange lines represent the average area of sea ice cover from 1979-2000.  The map speaks for itself.

The only thing we can do now is sit back and see how long the sea ice melt will continue, and by how much the old sea ice melt record will be broken.  Sigh...

Global Climate Update - summer 2012

I know that you're probably miffed at me because I've been slacking off for the past couple of weeks, and I haven't given you any Arctic sea ice or national or global climate updates.  Well, everyone deserves a break, but now that we managed to survive July, and some of the agencies and labs that track climate trends have reported in, it's time to take a look at what's going on out there.

First of all...IT'S HOT OUT THERE!

This map shows the global temperature anomalies for June 2012 compared to a long-term average of temperature data from 1971-2000.  The bigger the red circle, the hotter it is compared to the historical average, and the bigger the blue dot the cooler.

Yep, almost everywhere, especially almost everywhere on land, is hot!  And in most of the high north latitudes as much as 4-5oC hotter than the historic average.  Localized weather conditions are keeping a few places, like Australia, central Africa. and the North Pacific cooler than usual, but everywhere else it's hot, dang hot!

Yeah, like you needed a map from NOAA (The National Oceanographic and Atmospheric Administration) to tell you that.

Next let's take a look at the United States drought index.  This map is provided courtesy of the USDA (Dept of Agriculture and other govt. agencies that track weather, climate, and their effects on agriculture.

This map shows that state of drought conditions across the United States as of 31 July 2012.  Yep, the darker red the color, the more intense the drought.  Scarily, the most intensive drought conditions stretch across the country's bread basket of the Great Plains states.

I just talked with my folks who live in Wichita, KS, and they say that the corn around there is in REALLY bad shape.  They told me that the leaves are dry and brittle, just hanging down on the stalks.  They also told me that while traveling to Oklahoma City recently that they saw a thermometer that said 118oF!  Yow!  

Only the Pacific NW and isolated parts of other states seem to be spared this year's summer drought.

All right, let's see what's brewing up north - our "canary in a coal mine" for global climate.

First stop - Greenland.  This graph from the National Snow and Ice Data Center (NSIDC.org) shows a disturbing development.  The puple-ish area at the bottom of the graph shows the historical average including data from 1980-1999 of ice melt area on Greenland.  The other colors show observed ice melt in 2010 (blue), 2011 (green), and 2012 (red) through the middle of July.  This year the ice melt area has shot off the charts, uncovering between 4-5x the normal amount of land area uncovered by melting ice.  Other data (not shown here) show that Greenland's ice cap is getting thinner around the edges and thicker in the middle, but that all in all ice is melting faster than it is being added.  The bottom line?  The Greenland ice cap is starting to shrink.

OK, what about the Arctic Ocean 2012 spring and summer sea ice melt?  The graph below shows the historical average amount of ice melt from the years 1979-2000, and the ice melt trends for 2007-2012.  The ice melt in 2007 was the most extreme recorded so far, but if you look at the graph again you will see that the sea ice melt trend for 2012 is nearly identical to that seen in 2007 at this point in the year (8-5-2012).  There is no way to know if this rapid rate if ice melt will continue, but if it does we may well be looking at a new record sea ice melt.  It is, at least, but not by much, the record for Arctic sea ice melt for this date.

The amount of sea ice remaining in the Arctic ocean is currently about 2 MILLION square kilometers less than the 1979-2000 historical average.  Now that's worth noting.

This map shows the current extent of sea ice cover (at least 15% cover) in the Arctic Ocean.  The NW Passage has opened up again west of Baffin Island, and sea ice melt is greatly ahead of historical trends (the orange lines) north of most of both Alaska and Siberia.  OK...so what?

  

This graph shows what has become a predictable trend of decreasing sea ice cover.  July 2012 is a close second to 2011 as the all-time lowest sea ice cover for this month.  The downward trend of sea ice cover, i.e., increasing trend of sea ice melt continues...

Climatologists who study the patterns and processes of climate and climate change developed a set of scenarios regarding Arctic sea ice melt.  This graph shows two scenarios starting in 1900 and running through 2100.  The blue line indicates a scenario of "business as usual" greenhouse gas emissions, and the red line represents an updated scenario based on an improved model, but the black line, that represents observed sea ice extent data for the month of September 1952-2011 shows sea ice cover declining at an even faster rate than even the latest model scenario.

How different are the observed data and the model scenarios?  The original "business as usual" model scenario indicates that the sea ice melt over the past few years is happening 40-50 years sooner than the original scenario showed.  And the observed sea ice melt is still proceeding 10-20 years faster than the newer model suggests should be happening.

No matter how you slice it, it's warmer out there now than it used to be.  It's warmer on land, ice is melting faster on Greenland, and sea ice is melting faster in the Artctic than it used to.  The bottom line is that, believe it or not, like it not, the global climate is changing - warming.

One last thing...what about the Antarctic?  Sea ice formation and melting appears to be proceeding normally there, but this is south polar pattern is maintained due to unique currents and oceanographic factors around the Antarctic continent that keep it colder than anyplace else on the planet.  In short, the Antarctic East Wind Drift Current and Antarctic West Wind Drift Current create the Antarctic Divergence that keeps supercooled water inshore AND moves supercooled water north away from Antarctica.  This supercooled water is denser and will not readily mix with the warmer, less dense water masses found in the southern Indian, Atlantic, and Pacific Oceans.  So the Antarctic is the exception to what is happening globally.  But to explain this more fully would require another complete posting.  

Climate Status: Warming

As you probably know by now, I have a tendency to blog ad nauseum about global warming and the Arctic Ocean - I admit it, I find that to be an intriguing topic.  I'll bet, though, that many of you may be wondering what's been happening with Earth's climate in a broader sense.

In a word: warming!  In lots of words?  Hang on....

First of all, Robert A. Heinlein probably said it best when he said, "Climate is what you expect, weather is what you get."

Here's a glimpse of recent weather in the USA...

• 2.1 million acres burned in wildfires
• 113 million people under extreme heat advisories
• 2/3 of the country experiencing droughts
• Regional flooding in MN and FL
• A derecho (a straight-line storm that was 5x more power than a normal thunderstorm) blowing from Chicago to Washington DC
• 3,215 new daily high temperature records

...and that was just in the month of June!

When we look back a bit farther, that is, since January 2012, we have experienced over 40,000 new daily high temperature records across the USA.  Yow!  Historically both high and low temperature records were set at about a one to one ratio.  But Borenstein (see the source below) reports that between 2000-2010 we observed two new high temp records for each low temp record, and that so far during 2012 we are seeing seven new high temp records for every new low temp record.  And, scientific climate models also indicate that by the middle of the century we may see a ration of twenty to one!!! 

(Source: "Climate Change: US Heat Waves, Wildfires, and Flooding Are 'What Global Warming Looks Like', by Seth Borenstein, AP 03:04am 07/03/12).

As this article mentions, it is extremely difficult to tie a particular weather event directly to climate change, because weather is twitchy...it's all over the place.  One thing that can safely be said, however, is that scientists have predicted these kinds of events to become more likely to occur as climate change proceeds in its warming trend.

In order to see what's going on with climate we need larger sets of observations, ideally at least 30 years' worth in order to see whether any observable trends are emerging.

The following data are from the National Oceanographic and Atmospheric Administration (NOAA) and the National Climactic Data Center (NCDC) 21st Annual State of the Climate Report.  (FYI, this report is peer-reviewed and includes work from scientists from 45 countries.)

• The first important finding is that the Earth is still getting warmer.
• The second important finding is that CO2, an important greenhouse gas, is still on the rise in Earth's atmosphere.
• About now some people ask, if CO2 levels are rising, why isn't the Earth heating faster?  One of the main reasons is because much of the excess energy is being absorbed by the ocean.  This can happen because water has to absorb a LOT of energy before its temperature increases.  If it wasn't for the ocean's huge heat capacity, we'd probably already be experiencing runaway warming, not just the gradual warming we see today.

• Some people are convinced that the current, observed warming trend is the result of increasing solar output.  This is not the case.  If you look at the graph below you'll see solar output fluctuating slightly up and down, but there is no long-term trend increasing solar output, so that just doesn't match up with warming we see.
• Glaciers are melting
• Total greenhouse gas concentrations are increasing

• Next, sea level is continuing its slow, but steady rise
• Arctic sea ice is melting...its actually melting at about 2x the historical average at the moment.
• And there is less spring snow cover than in years past.

In addition, northern latitudes are getting warmer and having longer growing seasons.

When you add all of these things together, what do you get?  All of the data together support only one main conclusion...global warming.

It's real, and it's happening.  Now what are we going to do about it?

"The Heat is On" - Arctic Sea Ice Melt 2012 Is Now Underway

Winter 2012 wasn't that severe for most parts of the country, but don't you still love signs of spring?

One sure sign of Spring is the start of the annual sea ice melt in the Arctic Ocean.

The National Snow and Ice Data Center (NSIDC; http://nsidc.org/arcticseaicenews/) reported this week that the Arctic Ocean Sea Ice melt is now underway.  Or, at least, that it looks like we've reached maximum sea ice extent.  Next stop? Summer!

I love maps and graphs - data rock!  Here is a map from the NSIDC showing maximum sea ice cover this winter.

The orange lines show the average extent of sea ice cover for the years 1979-2000.  The white area shows the current sea ice extent with at least 15% sea ice cover.  

This was an interesting sea ice year.  If you look at the map you'll see that we have much more sea ice than average in the Bering Sea, west of Alaska and north of the Aleutians.  At the same time there was not as much ice as usual in the Barents Sea north of Scandinavia and Russia.  Remember the tough time ships had reaching Nome, AK, this year?  That's because of all the sea ice.  

So, how does this winter's maximum extent stack up against recent years?

2011-12 sea ice cover is shown in light blue in the graph above.  

The maximum sea ice extent for this winter didn't reach historical averages...again.  But this year it got within about 600,000 square kilometers of the 1979-2000 average sea ice maximum.  Even so, the NSIDC reports that this year's sea ice extent is the 9th lowest sea ice extent reported since 1979.  You might also be interested to know that all of the past nine years, 2004-2012, are the nine lowest sea ice maximum extents on record.  

So what!?  

Here's what this means.  First, less ice is forming now than it used to.  Second, this means that the edges of the sea ice melts away from coastlines sooner,  This makes it tougher for animals that need the pack ice to get there - like polar bears.  This is especially tough on females and their young cubs.  Mothers and cubs often aren't able to move far from the den and move out onto the ice until the ice melt is well underway.  By this time bears often can't reach the ice pack unless they do a LOT of swimming.  In recent years polar bears have been been seen swimming across huge stretches of open water.  Bears have reportedly been spotted 100s of miles from land or ice...but this takes a toll, especially on cubs.  Sadly, increasing numbers of cubs aren't making it...they fatigue and drown.  It's even getting tougher for adults to make this kind of swim.

Photo - Eric Lefranc Freelance

"DISTRESSED POLAR BEARS"

Polar bear - Ursus maritimus - Olga Strait, Svalbard, Norway - Mother and cub trapped on a little ice floe drifting 12 miles from the nearest coast in Olga Strait. Polar bears are usually good swimmers however the cubs can not swim for so long and will probably not make it. (http://www.poyi.org/67/01/ae01.php)

Polar bears need to pack ice to hunt for their main prey - seals.  The seals live on the ice year round and give birth to their pups in dens under the surface snow.  This is what bears are looking for.  But if the ice is too thin or short-lived both bears and seals have a hard time.  And that's just the effect on these animals.  A bigger effect is the role that sea ice plays in something called the albedo.

The albedo of an object refers to its ability to absorb or reflect light.  

A perfectly black body will absorb all light that strikes it, and we see black.  If it is perfectly white it will reflect all light and it looks brilliant white.  

So what!?

When the Arctic Ocean is covered by sea ice it is closer to white and reflects most of the light that strikes it.  This keeps the Arctic colder than it would otherwise be, but, as the ice melts dark seawater is exposed, and because it is so dark it absorbs most of the light that strikes it.  This can warm the water, melt more ice, and - worse case scenario, eventually warm the Arctic Ocean seafloor.  

Why is this such a bid deal?  Scientists have discovered that some areas of the Arctic Oceans sea floor is actually permafrost - frozen sediment - that contains methane hydrate.  Methane hydrate is methane trapped in ice.  Methane is a greenhouse gas. If the Arctic seafloor warms enough the methane will be released and the Arctic Ocean will "burp" methane into the atmosphere, accelerating warming even more.  

This is a model of methane hydrate.  The methane is the green and gray molecule in the middle, and the red and white molecules are water frozen into ice, trapping the methane inside.  

Methane hydrate is really interesting stuff.  It can, for example, burn...

The white stuff is ice, and the methane is released and burns as the ice melts.  Similarly, methane will be released by sediments in the Arctic Ocean sea floor if the sediment warms enough for the ice to melt.  This photo shows methane being released underwater.  

Bears and ice and methane, oh my!