Dr. Konrad Steffen, Director of CIRES
In September of 2008, CA-CP had the opportunity to speak with Dr. Konrad Steffen, Director of the Cooperative Institute for Research in Environmental Sciences (CIRES), at the University of Colorado. He described his extensive research on the Greenland Ice Sheet since his Swiss Camp was built in 1990 which he has corroborated with satellite observations collected since 1979. He explained how the ice mass of Greenland is decreasing, especially around the edges. In addition to melt water flowing directly to the ocean, melt water collects on the top of the sheet and works its way down through tunnels to the base of the ice sheet accelerating ice flow to the oceans causing icebergs to break off. Dr. Steffen anticipates sea levels to rise by 1-1.5 meters by 2100 given current conditions. The interview below delves into his important work.
CA-CP: Can you tell us about your current research efforts and how long you have been working in Greenland?
Dr. Steffen: I started working on the Greenland Ice Sheet in 1990 when we put up a camp, now called Swiss Camp, about 70°C north on the western slope of ice sheet. It was a pure science camp in 1990. The idea was originally to study interaction of the climate and the ice sheet itself. We built a 30-meter tower to study the boundary layer of the atmosphere and worked locally around the camp to study the processes of energy transfer from the atmosphere into the ice. We also studied precipitation and the turnover of the energy involved in melt and evaporation. We did not anticipate the climate change study. Then after two years, there was a big volcanic explosion in Mt. Pinatubo that cooled the climate in the northern hemisphere by 1.5°C - mainly in the Arctic. That was the year without summer. We had no melt at that station which is 1100 meters above sea-level and we continuously had snow. Since the station was under so much snow, it could not be moved out and the opportunity arrived to buy the station with NASA for $1. Since this purchase, I have gotten continual research funding from NASA to use this station and other stations built later to continue basic research for climate, using satellites to collaborate.
CA-CP: Can you explain more about this work with NASA?
Dr. Steffen: After 1990, we worked about three years, and then we started the big program in NASA, called the Program for Arctic Regional Climate Assessment– PARCA. NSF joined in the later years and we started to put up climate stations on the ice sheet to find out if the Greenland ice sheet is balanced, which means if the precipitation that falls on the ice sheet is equal to the surface melt that runs off and the icebergs that break off. It’s hard to believe, but in 1990 we did not know yet if Greenland was gaining mass or losing mass. And the stations we put up – we have 22 –record the precipitation, melt, and surface height change; that was one part of the PARCA program. We collected ice cores funded by NSF, which looked at the past history of the ice sheet. The shallow ice cores of 100 meters in depth provide a climate history of up to 800 years By 2000, eight different universities collaborated under the PARCA umbrella to do climate research on the ice sheet. That’s how it started. We just received more funding from NASA that continues research for next 3-4 years to use the climate stations and satellites and process studies on ice sheets to understand the mass exchange of the ice sheet. A good example is a new Ice, Cloud, and land Elevation Satellite, also called ICESat. This is the first satellite built for crysopheric research to measure the change of the global cryospheric ice. ICESat has a laser that measures surface height very accurately and changes can be derived from one orbit to the next over the same region. Changes in height are not only caused by changes in precipitation or melt but also by the variability of the temperature within the surface snow. To understand the effects of a warming climate, we need to have a good combination of field measurements and small-scale in-situ process studies that we then use to correlate with satellite geophysical data. The stations have become very valuable because we didn’t have any long-term record of the ice sheet. By now, we have 17 years of data for most stations. This data shows us that the climate is changing. With a long-term record, you realize that the temperature in the summer months has increased since 1990 by about 2°C, which is a really large signal. Because most of the time, here in mid-latitude, temperature change is only a fraction of a degree centigrade over that time period. That’s why the Arctic becomes important. The temperature changes further north are enhanced which means we see a much bigger signal that has to do the albedo feedback. Albedo is the reflection of the sun on the earth’s surface. When you have snow cover, about 90% of the solar energy that goes through the atmosphere is reflected back into space. If you have portions of the snow cover getting wet, which is now occurring at higher elevations of the ice sheet, only about 70% is reflected back into space, and if you go further, and more water is added, which is occurring with the increase in temperature, and you expose some blue ice in the lower regions of the ice sheet, then only 50% of the sun’s energy is reflected back into space. That positive feedback increases the temperature and the melt. That occurred from 1990 to present. Actually we do have data from 1979 to the present from NASA satellites that use passive microwaves to measure the Earth surface at least twice daily. We use that satellite data to calculate the melt extent of the ice sheet. We now have an image that shows how many square kilometers of ice are melting on the ice from 1979 to present.
CA-CP: What is the trend that you see when you go back to 1979?
Dr. Steffen: We discovered, already in late 1990s, that there had been a strong increase in ice sheet melt extent. The increase is not linear; we had a variability of 2-3 years with a new maximum in melt extent. Over the time period 1979 to present, the area that melted on the ice - when you add up the summer melt – has increased by 30%. This indicates that the summer air temperatures are rising. Increased warmth enables the snow to melt at higher elevation - the Greenland ice sheet ranges from sea level to 10,000 feet (3300 meters). Only the margins of the ice sheet are actually melting, but this melt region is moving uphill towards the center and the total area has increased by 30% - not as a steady increase, but every 2-3 years, a larger area. The year 2007 was our last maximum and that was a 10% larger melt area than any year from 1979 until that time. It’s interesting to see that it’s not only the summer temperatures that increase – the biggest increase is actually in the winter months. But winter is still very cold so the temperature is below freezing. For the time period 1990 to present we had about a 4.5°C temperature increase at the one station we call Swiss Camp, which is 70° north, western slope, 1,100 meters above sea level, close to the town Ilulissat, also known as Jakobshavn in the old days.
CA-CP: How important is Greenland to the world’s climate? What are the risks to the expected continuing warming?
Dr. Steffen: Greenland is like a big barrier. It is about 3300 meters high; it runs north-south - 65° north to 80° north. We know that the weather machine for Europe starts in the US – the cyclones that spin off the northern parts of the US cross the Atlantic and cyclones moving across the Atlantic are a driver for the weather in Europe. In the winter Greenland is very cold and it’s so cold that these cyclones can’t cross the ice sheet. Cold air is heavier so cyclones bounce off at the southern tip of Greenland and cross over Iceland. They are usually called Icelandic lows in Europe. If the climate is altered over the ice sheet in Greenland, this will affect the weather pattern in the northern hemisphere. More important, however, is when you consider how much ice is stored in Greenland. If we were to take all the ice on Greenland and dump it in the ocean one way or the other – melt or ice dynamics – (this will not happen for decades) it would raise the sea level globally by 7 meters. This is one of the bigger issues – to understand better how quickly Greenland will melt in a warmer climate. The IPCC, the International Panel on Climate Change, came out with a report last year and it indicated that by 2100, sea level will rise by up to 53 cm. This is based on the current melt rate of the glaciers, of the ice sheet (mainly Greenland), and of the thermal expansion of the ocean. If you warm the ocean, the ocean has a bigger volume, so 50% of the sea level rise is from the ocean expansion. The IPCC analysis does not include what we call the dynamic response of the ice. In 1995 we realized that the ice sheets are moving faster towards the ocean during the summer months with additional melt. We used instrumental evidence to verify this process. We found that melt water runs by gravity towards the coast and then into the ocean. The melt water runs not on the surface but finds its way into the ice through cracks or through moulins. A Moulin is a large vertical tunnel where the melt water cascades down. That water finds its way to the bottom of the ice sheet, since water is heavier than ice, it can act as lubrication underneath the ice sheet. During the recent summers we measured more surface runoff from melt and also ice that is moving faster towards the coast, indicating that the melt water reaches underneath the ice sheet acts as a lubricant or reduces the friction and advances the ice motion. It flows faster towards the coast and causes more icebergs to break off. It’s our current understanding that 50% of ice loss in Greenland is due to melt and the other 50% is due to icebergs that break off from large floating ice tongues into the ocean. A gravity experiment satellite called GRACE measures the total ice loss. Results from the GRACE satellite reveal that Greenland ice is currently losing on the order of 150 – 200 cubic kilometers of ice annually. That is about 1 - 1.5 times all the ice we have in the European Alps. Since the satellite was launched in 2002, there exists a good record about of mass change. The mass loss of the ice sheet has increased every year, and in 2007 it was 200 cubic kilometer or 200 gigatonnes of ice loss, which is an imbalance. This means we lose more ice into the ocean than falls by precipitation. And that is the big question – how can we model that? IPCC did not have this number in their prediction by 2100. We actually were able to put some remarks into the IPCC report which states that the 50 cm sea level rise by 2100 is due to the melt, but if you take into consideration the dynamic response of the ice, sea level rise might be much higher. The big question now is how much higher would it be? It’s very hard to give a prediction because we are currently working to model this faster ice flow but it actually takes years - 3-4 years - to get a model working which can predict the future based on the ice flow. We do know that we have a considerable loss of ice mass right now and we believe the 50 cm sea level increase by 2100 is too low because we already see now that the ice is moving faster. There is ice loss in Antarctica as well that was not considered in the IPCC report, that is of similar order, 100-150 cubic kilometers ice loss annually. It could well be possible that we have one meter or more of sea level rise by 2100 and even larger sea level rises in the years after 2100. Most of the model prediction go only to 2100 but sea level will continue to rise for centuries The temperature will continue to increase even if you reduce greenhouse gases today, and the ice loss will continue, too. I don’t think we can lose the Greenland ice sheet in a short time. Seven meter sea level rise is not something we will experience in next several 100 to 1000 years. But it’s well possible we’ll have up to one meter of sea level rise due to the thermal expansion, due the ice mass in Greenland and Antarctica and we shouldn’t forget all the glaciers – mid-latitude glaciers are actually melting the fastest right now. If all the glaciers of the earth would melt - except the ice sheet – sea level would rise only by half a meter. So this means the big uncertainties are coming from the Greenland ice sheet and from Antarctica.
CA-CP: You said the melt rates are higher than anticipated when you wrote the IPCC report?
Dr. Steffen: It’s not the melt rate; it’s actually the ice loss by ice motion that is not in any model. Satellite measurement from GRACE shows that we are losing 100-150 Gtons of ice yearly. We cannot explain that by melt because that would use way more energy than we have available right now at these latitudes.
CA-CP: What does the climate history – studies of paleoclimatic history – suggest about what has happened to the Greenland ice sheet in the past?
Dr. Steffen: We have some evidence from the ice cores. A US paleo-climate research group showed that during the last interglacial period (that is the warm period between ice ages) about 140,000 years ago, the climate was about 4°C warmer in Greenland than today. By that time, Greenland actually lost ice to cause about 1-2 meters of sea level rise. It took several centuries then to reach that warmer climate. Today we predict about the same amount of warming in less than 100 years in that region due to greenhouse gas feedbacks. However, I would not expect a two meter sea level rise from Greenland that by 2100 because it takes centuries to remove that much ice just by melt. The scientific community needs to understand ice sheet dynamics better to predict sea level rise accurately. We believe that half a meter is the guaranteed low end and it is possible we could have 1.5 meters of sea level rise. It took several hundred to thousand years to get a 4°C increase in warming during the last interglacial period and it is likely we will do this in only 100 years now.
CA-CP: You mentioned that in 2007 the melt rate around the edges reached the highest level ever?
Dr. Steffen: Since we only have satellite measurements from 1979-present, we don’t know what it was like in the 1930s. In the 1920s and 30s, we had temperatures similar to today, but it took several decades and then got cooler again, which was one of the normal climate variabilities. We are past that point already – warmer now than in the 1930’s but we have no data from the ice sheet from the 1930s or 20s.
CA-CP: 2007 was also the year of the greatest extent of sea ice loss in the Arctic and 2008 is close. Is there something to be said that both of these things are happening at the same time?
Dr. Steffen: There is a connection. We have looked into that question for several years now; the cryosphere of the Arctic is all connected together. As a good example, if sea ice coverage in the Arctic Ocean is reduced then more of the dark ocean surface is exposed absorbing more energy and warming the surface water layer. . The ocean has a long-term memory, and if you warm up the ocean temperature, that has an effect on the ice sheet. Ocean water travels as currents under the floating ice and melts the ice from underneath, reducing ice mass. It is not the major part of the ice melt yet it will have an effect. For example – if we lose all that summer Arctic ice in the Arctic Ocean in 10-30 years, that will give us a very large area of dark surface, evaporation of ocean water into the atmosphere, bringing different circulation and that affects precipitation and melt region. It is interesting to note that during the time we had the very low sea-ice extent, we had increased melt areas in the north of Greenland. So there is a direct link – less sea ice, warmer air temperature, more melt of the ice sheet. It takes a while to warm a large portion of the ocean because there are ocean currents that transport energy away – so in the longer term, yes, there will be an ocean warming. It was the ocean that reduced ice thickness, made ice weaker, and that’s why it was breaking in part and reduced the area. We still don’t know the ice thickness in the Arctic very well. None of the satellites can estimate how thick the ice flows are. We do know that we lost multi-year ice – ice that survives the winter. That is ice that has very little salinity. Ice loses its salt content over a multi-year period and is much more rigid - meaning it will survive several years. We have less and less of that ice type which gives us the indication ice is getting less thick, but that is actually an estimate; we have not very good data.
CA-CP: Here at CA-CP we believe that you can reduce radiative forcing with the reduction of short lived gases (methane, troposhperic ozone, and black carbon) that could produce a quick result and you also need to work hard on the longer-term carbon dioxide reductions. There is a school of thought that at this point you have to consider geo-engineering schemes like reflectors on the Arctic Ocean or sulfates in the stratosphere. Do you have an opinion?
Dr. Steffen: I’m not a very big supporter of geo-engineering. By putting too much CO2 into the atmosphere, we have made a geo-engineering experiment that went wrong. It is very hard to get CO2 out of the atmosphere. There are a lot of mechanisms we don’t fully understand. Geo-engineering at that scale, like increasing cloud cover over the ocean, could reduce the incoming short radiation but how well do we know the side-effects? Do we increase precipitation? Flooding in other areas? If you have mirrors in space that reflect energy out into space – what happens if there were several volcanic eruptions cooling the climate by several degrees? The volcanic eruptions are very powerful by reducing the amount of solar energy coming to the earth. If we put reflectors into space, you cannot remove them over night. They come down by gravity and it might take a decade, so we might actually enter a cold phase on earth by having a geo-engineering and a natural cooling. Therefore I think it’s quite dangerous to go for these big programs for a short-term fix. The long-term fix is to reduce greenhouse gases and start now because as it takes up to 400 years for the CO2 to be absorbed in the ocean, to be taken out of the system. Whatever we do now, we should start working at the base of the problem. We should discuss geo-engineering, but additional and careful studies are needed first before we enter such a large project of reducing solar energy reaching earth because if it goes wrong, it can go badly wrong.
CA-CP: Are there any tipping points we should be worrying about? Are there any things associated with Greenland that once we go beyond a certain point, if we cool the atmosphere back down, we don’t get back to where we are now?
Dr. Steffen: We try to learn from the past history, but the data is usually not that accurate. Tipping point is a good example. Tipping point would mean that we understand the process so well that we can predict when it is going into a different phase. I personally don’t think we know when a tipping point would occur. Some researchers mention a tipping point – if you add 500 parts per million (ppm) carbon dioxide into the atmosphere, there is no returning back to the current system. I personally think we don’t know the system that well that we can discuss tipping points because there are all the feedback mechanisms we don’t understand right now. If you have 450 or 550 ppm in the atmosphere, I would be cautious to use it as a point of no return because most of the climate responses are not linear. There are so many feedback mechanisms, we don’t even understand the ocean systems that well. We already have indication that part of the ocean is saturated with carbon. If this is the case, the tipping point is very close. If there is no equilibrium at 550, the tipping point is further away. That’s why I am hesitant to give you a direct answer – whether it will be in twenty or five years.
CA-CP: Based on where Greenland is going and the loss of ice mass, what is your best estimate on how much sea level rise we’ll have by 2100?
Dr. Steffen: Estimates for conditions in 2100 have different components. Thermal expansion will increase. Greenland’s ice sheet is certainly reacting now. The biggest sea level rise currently from the cryosphere is coming form the glaciers - about 50% of the crysopheric contribution. But we actually know how much ice is left in the mid-latitude glaciers –enough to raise sea level by half a meter. Before and by 2100 maybe 2/3 of glaciers on earth will have melted away. Greenland is hard to predict. It’s not only melt (we can model that with temperature increase). The dynamic part is not well understood. Will it continue at its current rate with the ice flowing faster, or will there be an upper velocity with no additional increase? I would predict an upper limit of sea level in the order of 1 - 1.5 meters by 2100 due to thermal expansion, and ice loss from Antarctic, Greenland and the glaciers.
CA-CP: We’ve read that the rate of the ice flow was slower than we’d thought a year ago.
Dr. Steffen: There was a study that looked at radar data and rightly they assessed the increase in velocity is only during the summer months. This is correct and if you take the amount of ice that increases the velocity and add as sea level rise, this is not the major part – I agree with that assessment. But, what we observe is that a lot of outlet glaciers start to accelerate into the ocean. It is not the lubricated ice sheet that makes the big change. The outlet glaciers are flowing faster. For example, Jakobshavn Isbrae, the fastest flowing glacier on earth, was flowing in 2000 at 7.5 km/year into the ocean. Right now it is flowing 14 km/year into the ocean. We think it is triggered by the lubrication at higher elevations which pushes the ice towards the fjord areas and they accelerate down. Outlet glaciers contribute more to ice loss, and if you double the speed you lose much more ice than this 10-30% increase in velocity over a few weeks in the summer. In conclusion, most climate issues are long-term and we need to make changes now to get future sea level rise under control. Most predictions end at 2100 which is two generations down the road, and we do hope we have an earth that is livable by 2300 or 2500. Given the current rate of increase in carbon dioxide output, I’m afraid it will be hard to curb that sea level rise in the near future, which has a marked impact on generations to come. We know that about 150 million people are living within one meter of sea level rise, currently. By 2100 to move that many people away from the coastline will be difficult. We know that 1/3 of the population on earth lives close to the coast and that is the area that grows the fastest - the whole economics there has to change in the decades to come to have a secure life on earth.
Learn more about Dr. Steffen's work at the Steffen Research Group web page of CIRES
CA-CP: Can you tell us about your current research efforts and how long you have been working in Greenland?
Dr. Steffen: I started working on the Greenland Ice Sheet in 1990 when we put up a camp, now called Swiss Camp, about 70°C north on the western slope of ice sheet. It was a pure science camp in 1990. The idea was originally to study interaction of the climate and the ice sheet itself. We built a 30-meter tower to study the boundary layer of the atmosphere and worked locally around the camp to study the processes of energy transfer from the atmosphere into the ice. We also studied precipitation and the turnover of the energy involved in melt and evaporation. We did not anticipate the climate change study. Then after two years, there was a big volcanic explosion in Mt. Pinatubo that cooled the climate in the northern hemisphere by 1.5°C - mainly in the Arctic. That was the year without summer. We had no melt at that station which is 1100 meters above sea-level and we continuously had snow. Since the station was under so much snow, it could not be moved out and the opportunity arrived to buy the station with NASA for $1. Since this purchase, I have gotten continual research funding from NASA to use this station and other stations built later to continue basic research for climate, using satellites to collaborate.
CA-CP: Can you explain more about this work with NASA?
Dr. Steffen: After 1990, we worked about three years, and then we started the big program in NASA, called the Program for Arctic Regional Climate Assessment– PARCA. NSF joined in the later years and we started to put up climate stations on the ice sheet to find out if the Greenland ice sheet is balanced, which means if the precipitation that falls on the ice sheet is equal to the surface melt that runs off and the icebergs that break off. It’s hard to believe, but in 1990 we did not know yet if Greenland was gaining mass or losing mass. And the stations we put up – we have 22 –record the precipitation, melt, and surface height change; that was one part of the PARCA program. We collected ice cores funded by NSF, which looked at the past history of the ice sheet. The shallow ice cores of 100 meters in depth provide a climate history of up to 800 years By 2000, eight different universities collaborated under the PARCA umbrella to do climate research on the ice sheet. That’s how it started. We just received more funding from NASA that continues research for next 3-4 years to use the climate stations and satellites and process studies on ice sheets to understand the mass exchange of the ice sheet. A good example is a new Ice, Cloud, and land Elevation Satellite, also called ICESat. This is the first satellite built for crysopheric research to measure the change of the global cryospheric ice. ICESat has a laser that measures surface height very accurately and changes can be derived from one orbit to the next over the same region. Changes in height are not only caused by changes in precipitation or melt but also by the variability of the temperature within the surface snow. To understand the effects of a warming climate, we need to have a good combination of field measurements and small-scale in-situ process studies that we then use to correlate with satellite geophysical data. The stations have become very valuable because we didn’t have any long-term record of the ice sheet. By now, we have 17 years of data for most stations. This data shows us that the climate is changing. With a long-term record, you realize that the temperature in the summer months has increased since 1990 by about 2°C, which is a really large signal. Because most of the time, here in mid-latitude, temperature change is only a fraction of a degree centigrade over that time period. That’s why the Arctic becomes important. The temperature changes further north are enhanced which means we see a much bigger signal that has to do the albedo feedback. Albedo is the reflection of the sun on the earth’s surface. When you have snow cover, about 90% of the solar energy that goes through the atmosphere is reflected back into space. If you have portions of the snow cover getting wet, which is now occurring at higher elevations of the ice sheet, only about 70% is reflected back into space, and if you go further, and more water is added, which is occurring with the increase in temperature, and you expose some blue ice in the lower regions of the ice sheet, then only 50% of the sun’s energy is reflected back into space. That positive feedback increases the temperature and the melt. That occurred from 1990 to present. Actually we do have data from 1979 to the present from NASA satellites that use passive microwaves to measure the Earth surface at least twice daily. We use that satellite data to calculate the melt extent of the ice sheet. We now have an image that shows how many square kilometers of ice are melting on the ice from 1979 to present.
CA-CP: What is the trend that you see when you go back to 1979?
Dr. Steffen: We discovered, already in late 1990s, that there had been a strong increase in ice sheet melt extent. The increase is not linear; we had a variability of 2-3 years with a new maximum in melt extent. Over the time period 1979 to present, the area that melted on the ice - when you add up the summer melt – has increased by 30%. This indicates that the summer air temperatures are rising. Increased warmth enables the snow to melt at higher elevation - the Greenland ice sheet ranges from sea level to 10,000 feet (3300 meters). Only the margins of the ice sheet are actually melting, but this melt region is moving uphill towards the center and the total area has increased by 30% - not as a steady increase, but every 2-3 years, a larger area. The year 2007 was our last maximum and that was a 10% larger melt area than any year from 1979 until that time. It’s interesting to see that it’s not only the summer temperatures that increase – the biggest increase is actually in the winter months. But winter is still very cold so the temperature is below freezing. For the time period 1990 to present we had about a 4.5°C temperature increase at the one station we call Swiss Camp, which is 70° north, western slope, 1,100 meters above sea level, close to the town Ilulissat, also known as Jakobshavn in the old days.
CA-CP: How important is Greenland to the world’s climate? What are the risks to the expected continuing warming?
Dr. Steffen: Greenland is like a big barrier. It is about 3300 meters high; it runs north-south - 65° north to 80° north. We know that the weather machine for Europe starts in the US – the cyclones that spin off the northern parts of the US cross the Atlantic and cyclones moving across the Atlantic are a driver for the weather in Europe. In the winter Greenland is very cold and it’s so cold that these cyclones can’t cross the ice sheet. Cold air is heavier so cyclones bounce off at the southern tip of Greenland and cross over Iceland. They are usually called Icelandic lows in Europe. If the climate is altered over the ice sheet in Greenland, this will affect the weather pattern in the northern hemisphere. More important, however, is when you consider how much ice is stored in Greenland. If we were to take all the ice on Greenland and dump it in the ocean one way or the other – melt or ice dynamics – (this will not happen for decades) it would raise the sea level globally by 7 meters. This is one of the bigger issues – to understand better how quickly Greenland will melt in a warmer climate. The IPCC, the International Panel on Climate Change, came out with a report last year and it indicated that by 2100, sea level will rise by up to 53 cm. This is based on the current melt rate of the glaciers, of the ice sheet (mainly Greenland), and of the thermal expansion of the ocean. If you warm the ocean, the ocean has a bigger volume, so 50% of the sea level rise is from the ocean expansion. The IPCC analysis does not include what we call the dynamic response of the ice. In 1995 we realized that the ice sheets are moving faster towards the ocean during the summer months with additional melt. We used instrumental evidence to verify this process. We found that melt water runs by gravity towards the coast and then into the ocean. The melt water runs not on the surface but finds its way into the ice through cracks or through moulins. A Moulin is a large vertical tunnel where the melt water cascades down. That water finds its way to the bottom of the ice sheet, since water is heavier than ice, it can act as lubrication underneath the ice sheet. During the recent summers we measured more surface runoff from melt and also ice that is moving faster towards the coast, indicating that the melt water reaches underneath the ice sheet acts as a lubricant or reduces the friction and advances the ice motion. It flows faster towards the coast and causes more icebergs to break off. It’s our current understanding that 50% of ice loss in Greenland is due to melt and the other 50% is due to icebergs that break off from large floating ice tongues into the ocean. A gravity experiment satellite called GRACE measures the total ice loss. Results from the GRACE satellite reveal that Greenland ice is currently losing on the order of 150 – 200 cubic kilometers of ice annually. That is about 1 - 1.5 times all the ice we have in the European Alps. Since the satellite was launched in 2002, there exists a good record about of mass change. The mass loss of the ice sheet has increased every year, and in 2007 it was 200 cubic kilometer or 200 gigatonnes of ice loss, which is an imbalance. This means we lose more ice into the ocean than falls by precipitation. And that is the big question – how can we model that? IPCC did not have this number in their prediction by 2100. We actually were able to put some remarks into the IPCC report which states that the 50 cm sea level rise by 2100 is due to the melt, but if you take into consideration the dynamic response of the ice, sea level rise might be much higher. The big question now is how much higher would it be? It’s very hard to give a prediction because we are currently working to model this faster ice flow but it actually takes years - 3-4 years - to get a model working which can predict the future based on the ice flow. We do know that we have a considerable loss of ice mass right now and we believe the 50 cm sea level increase by 2100 is too low because we already see now that the ice is moving faster. There is ice loss in Antarctica as well that was not considered in the IPCC report, that is of similar order, 100-150 cubic kilometers ice loss annually. It could well be possible that we have one meter or more of sea level rise by 2100 and even larger sea level rises in the years after 2100. Most of the model prediction go only to 2100 but sea level will continue to rise for centuries The temperature will continue to increase even if you reduce greenhouse gases today, and the ice loss will continue, too. I don’t think we can lose the Greenland ice sheet in a short time. Seven meter sea level rise is not something we will experience in next several 100 to 1000 years. But it’s well possible we’ll have up to one meter of sea level rise due to the thermal expansion, due the ice mass in Greenland and Antarctica and we shouldn’t forget all the glaciers – mid-latitude glaciers are actually melting the fastest right now. If all the glaciers of the earth would melt - except the ice sheet – sea level would rise only by half a meter. So this means the big uncertainties are coming from the Greenland ice sheet and from Antarctica.
CA-CP: You said the melt rates are higher than anticipated when you wrote the IPCC report?
Dr. Steffen: It’s not the melt rate; it’s actually the ice loss by ice motion that is not in any model. Satellite measurement from GRACE shows that we are losing 100-150 Gtons of ice yearly. We cannot explain that by melt because that would use way more energy than we have available right now at these latitudes.
CA-CP: What does the climate history – studies of paleoclimatic history – suggest about what has happened to the Greenland ice sheet in the past?
Dr. Steffen: We have some evidence from the ice cores. A US paleo-climate research group showed that during the last interglacial period (that is the warm period between ice ages) about 140,000 years ago, the climate was about 4°C warmer in Greenland than today. By that time, Greenland actually lost ice to cause about 1-2 meters of sea level rise. It took several centuries then to reach that warmer climate. Today we predict about the same amount of warming in less than 100 years in that region due to greenhouse gas feedbacks. However, I would not expect a two meter sea level rise from Greenland that by 2100 because it takes centuries to remove that much ice just by melt. The scientific community needs to understand ice sheet dynamics better to predict sea level rise accurately. We believe that half a meter is the guaranteed low end and it is possible we could have 1.5 meters of sea level rise. It took several hundred to thousand years to get a 4°C increase in warming during the last interglacial period and it is likely we will do this in only 100 years now.
CA-CP: You mentioned that in 2007 the melt rate around the edges reached the highest level ever?
Dr. Steffen: Since we only have satellite measurements from 1979-present, we don’t know what it was like in the 1930s. In the 1920s and 30s, we had temperatures similar to today, but it took several decades and then got cooler again, which was one of the normal climate variabilities. We are past that point already – warmer now than in the 1930’s but we have no data from the ice sheet from the 1930s or 20s.
CA-CP: 2007 was also the year of the greatest extent of sea ice loss in the Arctic and 2008 is close. Is there something to be said that both of these things are happening at the same time?
Dr. Steffen: There is a connection. We have looked into that question for several years now; the cryosphere of the Arctic is all connected together. As a good example, if sea ice coverage in the Arctic Ocean is reduced then more of the dark ocean surface is exposed absorbing more energy and warming the surface water layer. . The ocean has a long-term memory, and if you warm up the ocean temperature, that has an effect on the ice sheet. Ocean water travels as currents under the floating ice and melts the ice from underneath, reducing ice mass. It is not the major part of the ice melt yet it will have an effect. For example – if we lose all that summer Arctic ice in the Arctic Ocean in 10-30 years, that will give us a very large area of dark surface, evaporation of ocean water into the atmosphere, bringing different circulation and that affects precipitation and melt region. It is interesting to note that during the time we had the very low sea-ice extent, we had increased melt areas in the north of Greenland. So there is a direct link – less sea ice, warmer air temperature, more melt of the ice sheet. It takes a while to warm a large portion of the ocean because there are ocean currents that transport energy away – so in the longer term, yes, there will be an ocean warming. It was the ocean that reduced ice thickness, made ice weaker, and that’s why it was breaking in part and reduced the area. We still don’t know the ice thickness in the Arctic very well. None of the satellites can estimate how thick the ice flows are. We do know that we lost multi-year ice – ice that survives the winter. That is ice that has very little salinity. Ice loses its salt content over a multi-year period and is much more rigid - meaning it will survive several years. We have less and less of that ice type which gives us the indication ice is getting less thick, but that is actually an estimate; we have not very good data.
CA-CP: Here at CA-CP we believe that you can reduce radiative forcing with the reduction of short lived gases (methane, troposhperic ozone, and black carbon) that could produce a quick result and you also need to work hard on the longer-term carbon dioxide reductions. There is a school of thought that at this point you have to consider geo-engineering schemes like reflectors on the Arctic Ocean or sulfates in the stratosphere. Do you have an opinion?
Dr. Steffen: I’m not a very big supporter of geo-engineering. By putting too much CO2 into the atmosphere, we have made a geo-engineering experiment that went wrong. It is very hard to get CO2 out of the atmosphere. There are a lot of mechanisms we don’t fully understand. Geo-engineering at that scale, like increasing cloud cover over the ocean, could reduce the incoming short radiation but how well do we know the side-effects? Do we increase precipitation? Flooding in other areas? If you have mirrors in space that reflect energy out into space – what happens if there were several volcanic eruptions cooling the climate by several degrees? The volcanic eruptions are very powerful by reducing the amount of solar energy coming to the earth. If we put reflectors into space, you cannot remove them over night. They come down by gravity and it might take a decade, so we might actually enter a cold phase on earth by having a geo-engineering and a natural cooling. Therefore I think it’s quite dangerous to go for these big programs for a short-term fix. The long-term fix is to reduce greenhouse gases and start now because as it takes up to 400 years for the CO2 to be absorbed in the ocean, to be taken out of the system. Whatever we do now, we should start working at the base of the problem. We should discuss geo-engineering, but additional and careful studies are needed first before we enter such a large project of reducing solar energy reaching earth because if it goes wrong, it can go badly wrong.
CA-CP: Are there any tipping points we should be worrying about? Are there any things associated with Greenland that once we go beyond a certain point, if we cool the atmosphere back down, we don’t get back to where we are now?
Dr. Steffen: We try to learn from the past history, but the data is usually not that accurate. Tipping point is a good example. Tipping point would mean that we understand the process so well that we can predict when it is going into a different phase. I personally don’t think we know when a tipping point would occur. Some researchers mention a tipping point – if you add 500 parts per million (ppm) carbon dioxide into the atmosphere, there is no returning back to the current system. I personally think we don’t know the system that well that we can discuss tipping points because there are all the feedback mechanisms we don’t understand right now. If you have 450 or 550 ppm in the atmosphere, I would be cautious to use it as a point of no return because most of the climate responses are not linear. There are so many feedback mechanisms, we don’t even understand the ocean systems that well. We already have indication that part of the ocean is saturated with carbon. If this is the case, the tipping point is very close. If there is no equilibrium at 550, the tipping point is further away. That’s why I am hesitant to give you a direct answer – whether it will be in twenty or five years.
CA-CP: Based on where Greenland is going and the loss of ice mass, what is your best estimate on how much sea level rise we’ll have by 2100?
Dr. Steffen: Estimates for conditions in 2100 have different components. Thermal expansion will increase. Greenland’s ice sheet is certainly reacting now. The biggest sea level rise currently from the cryosphere is coming form the glaciers - about 50% of the crysopheric contribution. But we actually know how much ice is left in the mid-latitude glaciers –enough to raise sea level by half a meter. Before and by 2100 maybe 2/3 of glaciers on earth will have melted away. Greenland is hard to predict. It’s not only melt (we can model that with temperature increase). The dynamic part is not well understood. Will it continue at its current rate with the ice flowing faster, or will there be an upper velocity with no additional increase? I would predict an upper limit of sea level in the order of 1 - 1.5 meters by 2100 due to thermal expansion, and ice loss from Antarctic, Greenland and the glaciers.
CA-CP: We’ve read that the rate of the ice flow was slower than we’d thought a year ago.
Dr. Steffen: There was a study that looked at radar data and rightly they assessed the increase in velocity is only during the summer months. This is correct and if you take the amount of ice that increases the velocity and add as sea level rise, this is not the major part – I agree with that assessment. But, what we observe is that a lot of outlet glaciers start to accelerate into the ocean. It is not the lubricated ice sheet that makes the big change. The outlet glaciers are flowing faster. For example, Jakobshavn Isbrae, the fastest flowing glacier on earth, was flowing in 2000 at 7.5 km/year into the ocean. Right now it is flowing 14 km/year into the ocean. We think it is triggered by the lubrication at higher elevations which pushes the ice towards the fjord areas and they accelerate down. Outlet glaciers contribute more to ice loss, and if you double the speed you lose much more ice than this 10-30% increase in velocity over a few weeks in the summer. In conclusion, most climate issues are long-term and we need to make changes now to get future sea level rise under control. Most predictions end at 2100 which is two generations down the road, and we do hope we have an earth that is livable by 2300 or 2500. Given the current rate of increase in carbon dioxide output, I’m afraid it will be hard to curb that sea level rise in the near future, which has a marked impact on generations to come. We know that about 150 million people are living within one meter of sea level rise, currently. By 2100 to move that many people away from the coastline will be difficult. We know that 1/3 of the population on earth lives close to the coast and that is the area that grows the fastest - the whole economics there has to change in the decades to come to have a secure life on earth.
Learn more about Dr. Steffen's work at the Steffen Research Group web page of CIRES