[MUSIC] So my name is Professor Julienne Stroeve. I started out doing my early work of Greenland and mostly traveling in the summertime, so quite nice weather for the most part. I started doing sea-ice work more when I was at the National Snow and Ice Data Center. And I did a lot of fieldwork back then too, usually in the springtime, so March and April, usually going out on Ski-Doo's onto the sea-ice or flying onto the ice with aircraft, and then making measurements. But this is my first time going into the Arctic during the polar winter. And so it has a lot of unique challenges for collecting the kind of data that I'm interested in during this expedition. We have our longest climate data record comes from the passive microwave satellite series of sensors that have been monitoring the emission of the Earth at microwave frequencies for basically since the late 1970s. And from this, we can actually reconstruct how much ice is covering the Arctic Ocean. And the reason we can do this is that there's a very big difference in the brightness temperature between sea-ice and open water. And so just taking the difference in the emissions of these two different ice types or I mean open water and ice we can actually monitor how much sea-ice is there. And we can do this regardless if there is darkness, so that's a limitation if you use visible data for example. And we can do this also through clouds, so we can see the surface all the time regardless of cloud cover or whether it's light or dark. So we have a really long data record of how much ice covers the Arctic Ocean but we don't have as long of a data record as to how thick the ice is. There are satellites that are trying to measure sea-ice thickness they're using radar altimetry or using laser altimetry. But neither of these directly measures how thick the ice is. They measure either the ice freeboard in the case of greater altimetry, or they measure the snow freeboard in the case of laser altimetry. So my goal on MOSAiC is to better understand exactly where the radar signature's coming from, so that we can do a better job in exactly defining where that sea-ice freeboard is. Because some of the assumptions that we make at the frequencies that we're using to monitor the sea-ice thickness may not be valid for all times of year. And so key to my MOSAiC project is to better understand how the seasonal evolution of snow pack and how that changes ice characteristics influence where the radar signatures are coming from so that I can do a better job monitoring how thick the ice is. But if I go back to the the 40-year passive microwave satellite data record that data record has really been key to understanding how quickly sea-ice has been changing in the Arctic Ocean. We've been able to observe that in the summer time we've lost about 40 to 50% of a summer ice cover since the late 1970s. And while the summer changes have been really striking and we've been seeing this holding back of the ice cover all along the shores of Siberia and Alaska going more towards the Pole. But also starting to see changes happening in winter, these have been much smaller than we've seen in the summertime. But we've been seeing increase ice loss in the Bering Sea sector for example, which is where we just traveled through on our way to join the polar searchers. We've also been seeing changes in the Chukchi Sea, and these changes are starting to become even more important because what we're seeing is that the melt season is getting longer. So we're starting to melt the ice earlier, we're starting to freeze the ice cover later and in fact in the Bering Sea the last two winters there was no sea-ice. And this winter ice is really key for a lot of ecosystems in that region and for the hunters that use the ice to travel on the ice and hunt. And so they have actually been saying that they have not seen winters before where there was no sea-ice in the Bering Sea. So the Arctic is waking up not just in summer, but also in winter. The other thing that we've been able to do with this data is we've been able to also track how old the ice is and I think that is really key towards our understanding of what's happening to the Arctic sea-ice cover. Because we've seen this reduction in overall age of the ice, how long the ice survives before it melts out completely and typically in the early 1980s. For example, most of the Arctic Ocean consisted of old thick perennial ice, so ice that had been around more than one melt season. But that really started to change in sort of the mid 1990s and and part of this was attributed to just changes atmospheric weather patterns that was flushing some of that old thick ice out of the Arctic Ocean. But now since the 2000s you just see this continued reduction in how old the ice is in the Arctic oceans; so really old thick ice is now melting out every summer and this is one of the reasons why we've seen this large reduction in the summer ice cover that is not recovering. In fact, the basically the ten lowest sea-ice years of all really occurred in the last 10 years or so. So we're not recovering back to conditions that we saw 30, 40 years ago, but regardless of what happens right now in summer in terms of weather patterns and how much warming there is compared to a cooler summer, it doesn't seem to matter so much anymore. So this really tells us that the ice has become quite a bit thinner and more vulnerable to melting out every summer. And that is one of the things that I'm really focused on during my MOSAiC project,which is just better mapping how thick the ice is. Because while the area tells us a lot about how much of the water there is, we really are interested in the total ice volume because that has a lot of implications for when we think about how quickly the Arctic Ocean may become ice-free in the future. So while we have about 40 years of satellite observations of changes in the sea-ice area, this record is still a relatively short when we're trying to understand what is driving sea-ice lost, it's really good to have as long as the data record as possible. But there have been attempts with earlier satellite data as well as aircraft ship observations whaling log reports, early ice charting, efforts by the Danish or the Russians to reconstruct. For example, how was the ice like even 150 years ago? And when we do that we can see that today's changes in the sea-ice cover are unique and unprecedented compared to the last 150 years at least. And right now we're seeing declines and sea-ice everywhere in the Arctic Ocean during all kinds year. So the Arctic is really waking up and is transforming rapidly to at one point covered by sea-ice year-round in the Arctic Ocean to one that's going to transition towards an Arctic Ocean that is ice-free in summers. And one of the ways that we understand this is we also look at climate model output and when we do climate model simulations and we put in historical observations of CO2 in greenhouse gases, we can simulate that all of the climate models are showing the sea-ice should be declining over the period of observations that we have. The problem is that a lot of these models are underestimating how fast is the ice has been declining. And part of this could be that they don't have a strong enough sensitivity for example to increase in greenhouse gases or the warming that we're experiencing from increasing atmospheric greenhouse gases. So the sensitivity seems to be less than were observing in our climate system today. One of the things I'm hoping with MOSAiC is by better understanding the processes in the couple ice ocean atmosphere system. We might be able to improve some of our parameterizations to improve our climate models and our future forecast of what's going to happen in the Arctic Ocean. But even if we don't use climate models, we can see a very strong linear relationship between sea-ice loss and increases in greenhouse gases in the atmosphere. Or at the same time we can see this is a really strong linear relationship between sea-ice loss and global mean temperatures. And by doing that and looking at our current emission rates, which is about 35 to 40 gigatons of carbon per year and the fact that we lose about 3 square meters of sea-ice for every metric ton of CO2 we add to the atmosphere. We can pretty much say that before the middle of this century we will likely start to see Arctic Ocean that's ice-free in the summertime on a regular basis and less we start to really reduce our greenhouse gas emissions. So because the melt season is starting earlier in the Arctic than it used to, that means that you're starting to melt the snow off the ice earlier, which actually starts lowering the Albedo. So the Albedo basically is a measure of how much of the sun's incoming energy is reflected back out to space. Snow is very bright, it has a very high Albedo, usually around 85% for new snow. But as we melt snow and we expose the bare ice beneath the Albedo kinds of drop to around 60%. And this then allows the ice to absorb more of the incoming solar radiation from the sun. So if we start melting the ice earlier, we also start breaking it up earlier and then we expose even the darker ocean surface below which has a very low Albedo and absorbs most of the sun's energy. So what we've been seeing is because the melt season is been starting a bit earlier than it used to we're enhancing this ice Albedo feedback, whereby you're allowing more of the sun's energy to be absorbed either in the ice or in the open ocean or once melt ponds develop that also gets absorbed in the melt ponds, which further accelerates ice melt during the summertime. This enhanced ice Albedo feedback has been a key driver in why we're not freezing up the Arctic Ocean as early as we used to to. So the freeze up is happening much later, and in fact much later than the melt onset is happening earlier and this this is because the ocean is now absorbing a lot of the heat that normally would have been reflected back out to space by the sea-ice keeping it covered. And so before the ice can form again in wintertime, the ocean has to release all that heat back out to space. And so we've been seeing this huge delays in freeze up, and even right now kind of in early December that we're in almost middle December basically there's still no sea-ice in the Chukchi Sea. And typically by now and December the Chukchi Sea would have already been frozen over. And this has been really a lot to do with the fact that the ocean is absorbing so much more heat than it used to. This also has implications, we think now for how much ice maybe grows over the winter season because while typically there's this negative feedback that can compensate a little bit for the positive ice Albedo feedback, whereby the more open water you have you'll quickly start forming thin ice, once the sun dips below the horizon and the air temperatures fall again below freezing, but we've also been seeing these winters that have been unusually warm the last few years. And so we're starting to see that thermodynamic ice growth is reducing over time, which resulting is thinner over all sea-ice. And in fact, there's some suggestions right now, just looking at comparisons between two different satellites' radar altimetry and laser altimetry. That perhaps we have been overestimating how thick the ice is using radar altimetry. And that the ice might have been a lot thinner than we suspected. And if this is the case that would also help explain why we just can't recover any more in the summer time and why we just keep seeing record low sea-ice years one after another.
