See Ice Today, Sea Ice Tomorrow?

"Human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations in the atmosphere, positive radiative forcing, observed warming, and understanding of the climate system." (IPCC Fifth Assessment Report (AR5), 2013).

We all know about climate change, right? It's an issue that has spread beyond the realm of the scientific community, and found its way into the public consciousness. Furthermore, I'm sure I'm not alone in feeling - as a member of the human race - more than a little guilty about it. In their Fifth Assessment Report (AR5), the Intergovernmental Panel on Climate Change (IPCC) deemed it "extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century", finding it "unequivocal that anthropogenic increases in the well-mixed greenhouse gases (WMGHGs) have substantially enhanced the greenhouse effect". If climate change is 1) anthropogenic in origin and 2) impacting upon the polar regions, then it's definitely something we need to address here. So, how are the polar systems responding to climate change, and are the observed consequences similar in the Arctic and Antarctic?

Ask a child why they should turn off the lights, and they might reply "to save the polar bears". On the face of it, that seems a pretty big leap of logic...but we all understand what they mean. The fact that the polar bear has become the archetype of species under threat from climate change suggests that there's something not too good happening up there in the north...The map below begins to explain why:

Global map showing trends in mean surface air temperature between 1960 and 2011. The inset graph shows the relationship between temperature change and latitude. Source: https://nsidc.org. Credit: NASA GISS.

As can be seen here, large areas of the Arctic have been warming at a rate greater than 2°C over the last half century (NSIDC, 2014). This means that over recent decades the Arctic has been the most rapidly warming area on Earth. As a consequence of this, significant negative trends in sea ice extent have been recorded. The following statistics were published in the IPCC Fifth Assessment Report (AR5), 2013:

• Between 1979 and 2012 sea ice extent (defined by the IPCC as "the sum of the ice covered areas with concentrations of at least 15%") declined by ~3.1 - 4.1% per decade, which is equivalent to 0.45 - 0.51 million square kilometres per decade.

• Perennial ice (ice which has lasted for at least one summer, and found by measuring the summer minimum extent) decreased from 7.9 million square kilometres in 1980 to 3.5 million square kilometres in 2012, with an 11.5±2.1% decline per decade. Furthermore, multi-year ice (ice which has lasted for at least two summers) decreased even more rapidly, by 13.5±2.5% per decade. 

• Owing to the decline in older ice types (see previous bullet point), average ice thickness decreased by 1.2 metres between 1980 and 2000. 

• As a result of thinner ice, the drift speed of sea ice has increased. Transport of multi-year ice into the southern Beaufort Sea accounted for over a third of older sea ice loss between 2005 and 2008.

That's probably enough numbers for now - you get the idea. If you're interested in sea ice decline, the National Snow and Ice Data Center website posts a daily image of current Arctic sea ice extent. Also, this video shows the decline of sea ice in 2012, when its extent hit a record low: 

These statistics are all very well, but what really matters is what they mean. I've set out to gain a balanced scientific understanding of how mankind is impacting upon the polar regions, rather than wishing to sound too sensationalist. But I must admit, most of what I've read is pretty gloomy. Reduced sea ice has a number of consequences, not least, loss of habitat. In other words (or rather, a picture) this:

As promised, a polar bear picture. Here showing how sea ice reduction will alter the Arctic habitat. Source: www.polarbearsinternational.org

Other repercussions are rising sea levels, greater variation in ocean salinity throughout the year, changing species distributions, and increased risk for indigenous populations (Rodger, 2009). We'll take a more detailed look at some of these later on. Before I finish, however, one more important point must be made. Sea ice has a high albedo; this simply means that it is highly reflective, and therefore capable of returning large amounts of radiation to space. Water has a significantly lower albedo, absorbing heat rather than reflecting it. Therefore, as sea ice declines (and melt period lengthens), the albedo of the Arctic decreases, leading to a positive feedback loop of warming. The Arctic currently acts to cool the rest of the planet, meaning changes to this region will have far-reaching consequences (NSIDC, 2014). Indeed, one study suggests that a scenario where the Arctic is ice free for one month in the summer (with a reduced amount of ice throughout the year), would lead to a global radiative forcing of 0.3 Wm-2 (Hudson, 2011).

I wanted to begin by taking a look at Arctic sea ice decline, because this in itself has facilitated many of the other ways in which humanity is impacting upon this region. Next we'll take a look at the Antarctic, because surely climate change is causing loss of sea ice here too?