Climate Wars - Arctic vs Antarctic Ice Melt

Arctic sea ice is melting. This is one of the most common points made whenever climate change is discussed (in addition to the obvious point that the climate is heating up). But Antarctic sea ice is growing, so it's a wash, right?

No. No. No.

This time of year climate scientists (and the informed public) spend a lot of time tracking the annual melting of sea ice in the Arctic. Climate deniers counter by exclaiming: "but the ice is growing in Antarctica." Deniers cry that the overall global sea ice total is the most important number and that Antarctica makes up for the ice lost in the Arctic.

Again. Emphatically. No. No. No.

This idea is akin to saying that a person making a billion dollars a year and a person making minimum wage (about $15,000/year) are equitable because the average income between the two is over $500 million.

In other words, it's silly.

To begin with, over the last 40 years the Arctic has lost about 21,000 square miles of sea ice per year. During that same time the Antarctic has gained only about 7,300 square miles per year. So even if "total global sea ice" was a valid measurement (which it isn't), it would show a net loss of nearly 14,000 square miles per year. That's hardly a winning argument.

The fact is that the Arctic and Antarctic are completely different systems and not directly comparable in any way. To help people understand the difference between the two poles, let's take a look at the main processes of both. 


The most obvious difference is that the Arctic is an ocean surrounded by land and the Antarctic is continental land surrounded by ocean. This difference has a profound affect on how and when ice is formed, not to mention what happens when it melts.

Arctic

Every summer sea ice shrinks in the Arctic, and every winter it grows. To track these patterns we rely on several measurements, one of which is sea ice extent (others are ice volume and ice age). Sea ice extent is defined as an area of ocean covered by at least 15% sea ice.* Two key numbers are the maximum ice extent (the greatest ice extent of any given year, usually in February) and the minimum ice extent (the least ice extent of any given year, usually in September). Generally the melting in the summer is not complete, that is, there is still sea ice even at the minimum. This, however, could change as various feedback effects tend to increase melting (e.g,. more open water means more warming, which means faster and greater melting). It is expected that at some point we'll see an ice free Arctic for some period of time during the summer. For a variety of reasons, that's not a good thing at all.

Both the minimum and maximum indicators have been showing an overall decrease in sea ice extent in the Arctic. For example, the following chart shows ice extent for March 1979-2016. As can be seen, some years are worse than others, but the general trend is clearly loss of ice over time. The same pattern applies to every single month. Feel free to look at other examples on the National Snow & Ice Data Center website.

Because of short-term variations in weather, the year to year values vary, but the trend is clear - the Arctic is losing ice. [See here for a video explanation of trend and variation] By the way, when deniers claim "Arctic ice has recovered," they are falsely cherry picking one of those little peaks and dishonestly ignoring the clear overall trend to fabricate their entirely - and obviously - false conclusions. [This intentional deception is why we know that deniers are being dishonest, not merely ignorant]

Antarctic

While the Arctic is frozen ocean, the Antarctic is frozen land. While the sea ice in the Arctic grows out into the ocean and is constrained by the land, the sea ice in the Antarctic grows out from the land, basically surrounding the continent and expanding without much resistance as far as the cold water and winds can take it. Remember that sea ice extent is defined as "at least 15% coverage of a unit area," so it doesn't necessarily mean the entire area is covered with ice, but with that much unhindered space to grow, it can go a long way.

Scientists have a very good understanding of the processes driving ice gain and loss in the Arctic; for the Antarctic there is greater uncertainty. What we do know from measurements is that, like the Arctic, the sea ice in the Antarctic grows in the winter and shrinks in the summer. Unlike the Arctic, the sea ice shrinks almost completely away each year in the Antarctic. In recent years there has been a pattern of increasing sea ice extent in the Antarctic, the opposite pattern of what we're seeing in the Arctic. The reasons for this are still a point of discussion, but new data have helped clarify the reasons for the trend.


One important factor is that greater melting of land-based glaciers and ice sheets has put more freshwater into the ocean surrounding Antarctica. Since the water is so cold, and because the freshwater tends to float on top of the denser saltwater of the ocean, you see rapid freezing of this new surface water. Another factor is the wind. Unlike the land-constrained Arctic, the winds have virtually limitless ability to push any forming sea ice floes further out to sea, where the cold temperatures tend to fill in the spaces and increase sea ice extent. Studies have also shown greater and faster movement of Antarctic glaciers toward the coasts, which helps push more ice offshore. In addition, the west Antarctic ice shelf** has been collapsing, and will continue to do so irreversibly.

The graphic above comes from NASA's GRACE satellite. It shows that despite the annual winter increase (and annual summer loss) of sea ice in the Antarctic, the overall ice mass of the continent itself has been dropping. Ice mass on Greenland shows the same pattern, only worse.

All of this information tells us that while we may see short-term increases in the Antarctic annual sea ice extent, continued warming of the climate will inevitably result in a much rapider overall ice loss as the glaciers continue to move to the coast and the west Antarctic ice shelves disappear.

So we can see that the two poles are completely different in every aspect, which makes any adding of their ice masses meaningless. All the factors in the Arctic point to continued and rapid ice losses by every measurement (sea ice extent, ice mass, ice age, ice thickness, ice volume). The increased open water results in even faster warming and melting, with these effects getting worse as additional feedback mechanisms kick in. Antarctica is showing a very different pattern but one no less of concern. Sure, the sea ice extent is increasing, but the reasons for it all point to major long term problems in Antarctica that will eventually have global ramifications even coming from such a remote continent. Continued overall ice loss from the land will contribute, along with ice melting on Greenland, to rapid sea level rise. Some recent studies have suggested that we could reach a  threshold that would cause a catastrophic melting of the two ice sheets, thus resulting in huge increases in sea level in a matter of decades rather than centuries. That may not happen, but then again, it might.

As mentioned earlier, climate deniers like to talk about the Antarctic whenever the discussion is about the Arctic (especially given it is the winter growth period in the south while we're watching the summer melting in the north). But adding the two together to get some sort of "total sea ice" value is both meaningless and dishonest. The two areas work independently, both in how they are impacted by man-made climate change and how they contribute to it.

By no honest analysis can anyone say the trends are good.


Notes from text:

*The 15% threshold is a bit confusing because it doesn't mean the entire area is covered with ice or that any given area is exactly 15% - the area could have anywhere from 15% to 100% sea ice. Obviously, an area that is 100% packed with ice would have more ice than an area only 15% covered by ice, yet they would both be counted as being the same sea ice extent. This is why we also look at ice volume, ice age, and thickness.

** Ice shelves are floating ice still connected to the land. Sea ice is that which has broken off and is floating. Ice sheets are the massive layers of ice that cover huge areas of land - Greenland and Antarctica carry the two remaining large ice sheets. Glaciers can be thought of as mini ice sheets flowing down mountains.

Arctic Sea Ice Continues to Decline at Record Pace

The decline of Arctic sea ice extent continues to decline at a record pace. As noted here two weeks ago, January sea ice extent was the lowest in the modern satellite record. Well guess what - February 2016 sea ice extent was the lowest February on record.

Larger here.

As the graph above shows, sea ice extent in February has been declining for many years, with the linear rate of decline at 3% per decade. [The previous post explains how to read the graphs] NASA and NOAA also note that February continued the trend of ten straight months of record-breaking high global surface temperatures, with the Arctic being especially hot (more than 4 degrees Celsius above the baseline).

It could have been even worse. Most of the month had almost no ice growth, in a time of year where it should be growing substantially (sea ice extent grows in winter, falls in summer). Only a late month burst of growth got it to where it was - and it was still a record low for the month. That's how bad it is.

Let's take a closer look:

The chart above is kind of busy even though I've only selected the most recent years. You can go here and use the interactive chart to include whatever years you want.  I highly encourage looking at all the years going back. The previous post explains what the lines and shading mean.

As you can see, sea ice extent grows in winter and shrinks in summer. This happens every year, so what you want to look for is how much it grows and shrinks compared to previous years. Keep in mind that the baseline mean (the black line and gray shaded area) was lowered recently to reflect the continuing declines. [This means if we had kept the old baseline the current sea ice extent would be even worse]

The current year is the burnt red line in the upper left corner, right at the bottom of the other lines shown. Right now it's about the same as where last year was at this time (darkish blue), but only because of that late-February bump up. We're right about the maximum now, though we won't know officially until we get a little further along. That doesn't bode well as last year was only barely above the second worst minimum extent years (see where the lines reach their most downward loop around September).

Starting the melt season in such a bad maximum doesn't mean we'll set a new record minimum. You can see that at this time in 2012 the maximum in late March (dashed green line) was higher than it was in ensuing years, yet 2012 smashed the previous record minimum year of 2007 (light blue line). Because sea ice extent is highly sensitive to local weather conditions (especially wind), we simply won't know how bad the minimum will be this year until we reach it in September. But we do know that it will be a bad year because every recent year has been a bad year. All you have to do is look at where all the lines fall compared to the baseline mean - they are all below. That means the baseline mean will again have to be lowered at some point, once again tracking the race to the bottom. At some point we're likely to see an ice-free Arctic for part of the summer.

And that is not a good thing. Not a good thing at all.

What is Happening to the Arctic? How to Read the Graphs

As 2016 starts off even hotter than the record-breaking heat of 2015 because of man-made climate change, one of the fastest warming areas of the planet is the Arctic. This year one of the key measures of Arctic "health" - sea ice extent - is showing signs of even more severe impact than normal. This fact has scientists fearful of a major speed up in climate change effects. It also has fossil fuel lobbyists scrambling to find new ways to deny the science.

So how do normal people (that is, us) know what's going on in the Arctic and elsewhere? This post gives a basic primer on how to read the graphs put out by the National Snow & Ice Data Center (NSIDC). The NSIDC collects data from a variety of sources and provides a monthly update. For this post I'll focus on Arctic sea ice extent as reported in NSIDC's Arctic Sea Ice News and Analysis page. As I write this the last update was in early February covering the status through the end of January. The next update will be in early March covering up through February.

One of the first things visitors to the see will be the "Daily Image Update" in the top right corner. As of today it shows:

See it larger here.

The graphic is fairly simple but shows a lot of important information. The bottom scale shows the months from November to March, so this represents the winter period where Arctic sea ice extent is expected to grow, which it does every year. [In the summer months it shrinks every year] The left scale shows extent in millions of square kilometers, but for now you don't need to worry about that; focus on the graph lines themselves.

See that thick black line running through the gray area? That represents the baseline sea ice extent from 1981 to 2010. It's essentially an average. One important point - that average was recently recalculated because all of the years after the end of the old averaging period were much lower than average. Therefore, the baseline has been lowered. What that means is that we should roughly see as many years over the average line as below. That hasn't been happening, even after lowering the bar. That's a bad thin. But let's not forget the gray area. That represents a range around the average. It gives you some idea of where the current year levels stand compared to the baseline years.

Which gets us to the solid blue (2015-2016) and dashed green (2011-2012), which represent the current year and the year with the record low ice extent. As you can see, the current year (blue line) is tracking well below the record low year. That's not a good thing, but we need more information so NSIDC also gives us the following graph, a bigger version of which can be seen here:

As you can see, this graph is the same as the previous one but shows several more recent years to provide context (note they changed the color of the 2011-2012 record year to purple instead of green, but it's still the only dashed line). You can see that the ice extent lines wiggle along; that's because short-term weather systems can either increase or decrease sea ice extent for any given time period, while man-made climate change is the reason for the longer trends. More on that shortly.

Want even more data? You can pick the years you want to plot on the graph with this handy Chartic Interactive Sea Ice Graph, which is also on the NSIDC page in the right hand column.

The graphs for 2015-2016 (the current winter) show that sea ice extent is dramatically lower than any other year. January was a record low and it looks like February will be too. Scientists are worried that we may have already seen the yearly maximum, which would be very early and dramatically lower than normal. It's from this point that the sea ice extent decreases until it reaches its yearly minimum (usually in September).

That doesn't necessarily mean we'll see a record low sea ice extent minimum this year. If you look at the Charctic Interactive graph you'll see that even though last year started out much lower in winter, it managed to reach only the fourth lowest minimum on record. That's not good at all, but it could have been worse. We won't know how bad this year will be until we reach the minimum, but based on where we're starting and the historic trend, we're pretty much assured it will be bad.

That gets us to the last graph I'll talk about today (larger):

This graph is for January but you can pick any other month and it will reflect exactly the same trend.
What the graph shows is the trend for that month over the years, that is, what the sea ice extent is in January each year from 1978 to 2016. Because of those short-term factors that make the lines in the first graphs wiggle, you see some years where the January extent is higher and some years lower. But look at the trend. The blue line shows how the sea ice extent has been decreasing for decades. The end of the black (and blue) line to the right of the graph is this year, the lowest ever recorded. You can see that this isn't a one-off problem, it's the continuation of a long-term decline in sea ice extent. Again, this graph shows January but every other month shows the same downward trend.

Bottom line: We're losing ice. Big time.

There are more graphics and information on the Arctic Sea Ice and Analysis page, plus information on Antarctica, Greenland, glaciers, and other snow and ice-related topics on the National Snow & Ice Data Center website. These are accurate, scientific sources of information that readers should save for future reference.