Andrew Shepherd

Andrew Shepherd

Director of the UK Centre for Polar Observation and Modelling and Principal Scientific Advisor to the European Space Agency's CryoSat satellite mission
@AndyShep_CPOM

Location Leeds and London

Activity

  • Hi That's right, plug not plig. In fast flowing glaciers and ice streams basal water is created via friction, and exists all year round. Geothermal heating can help too!

  • Hi You are right, if ice thins this does reduce the amount of discharge into the oceans, but in both Greenland and Antarctica this is compensated by increases in flow speed (glacier discharge = thickness x width x speed). In some cases the glacier terminus also simply retreats inland as a consquence of the thinning, to a place where the ice is thicker.

  • Hi Many of the advances in satellite and sensor technology are driven by the need or desire to innovate capability, for example to reduce costs, and not just as to meet science measurement requirements. The sensors on some of the oldest satellites - especially the radars - are good enough to meet many of todays science requirements.

  • Hi When water gets to the base of ice (alpine or ice sheet) it can lead to reduced friction and the ice slips along the bedrock. At the very small scale this is probably in jerks, and causes stretching or fracturing of the ice, but at the larger scale (which is I think your question) the vertical profile of speed is pretty flat, with similar rates at the top...

  • Hi Tide gauge stations are really helpful as they started recording sea levels a long time ago, but satellites are much more reliable as they sample far more of the global oceans. As far as we can tell, the tide guages and satellites are in agreement

  • Hi This could be answered in different ways, but for example the ice sheet receives about 750 Gt of ice each year through snowfall, and loses about 350 Gt of ice each year through melting and about 700 Gt each year through glacier discharge. So it is losing abour 300 Gt of ice each year, so about 40% out of balance

  • Hi Waming of newly exposed rock and land will definitely have local effects, but I dont think it is expected to impact signinicantly on the ice sheet as a whole

  • Hi The state of sea ice is very closely linked to ocean tempeartures; as the ocean warms it creates leads which then absorb much more of the suns heat and get warmer to melt more ice.

  • Hi We tend to use GIS mostly for making visuals of the satellite data we produce, which mostly are processed using software such as Matlab, IDL, etc

  • Hi Iceland's ice caps are losing about 5 gigatons of ice per year in total. There are complex interactions between climate and the volcanism, but generally most of the ice caps are thinning at their edges where air temperatures have warmed

  • Hi I am not a fan of the term tipping point as it's quite subjective. But your last question can be answered for sure - the rate of ice melt from Greenland has increased by a factor 5 since 1990

  • Yes, the current generation of climate models do couple the ocean with the ice sheets and so the effects of ice melting are taken into account.

  • Hi Greenland is usually considered vulnerable because air temperatures there are a lot warmer than in Antarctica and the ice sheet experiences summer melting. Warming air temperatures are responsible for most of Greenland's recent ice loss. In Antarctica, only a few places experience summer melting and we don't expect air temperature rises to cause substantial...

  • Although Greenland is losing ice due to the effects of climate change, its not bad news to learn about this!

  • Hi. there are no major ice shelves around Greenland as the water is generally too warm and there are few sheletered ambayments where shelves typically grow. Petermann Glacier in the far north west has the best example.

  • Glad to hear you are enjoying the course. There are plans for an Antarctica version so watch this space

  • Hello Oluwole. I am very happy for you to use any of the content from this course in your teaching. Andy

  • I'd like to see a successor to CryoSat commissioned; the mission was an ESA Earth Explorer, which means it was designed to demonstrate new technology and new science. The programme which funded it can't pay for its successor, so we have to persuade somebody else to foot the bill. We think the mission data are critical for climate and maritime services, and so...

  • Hello Penny. Depending on the complexity of the satellite sensor design, missions tend to cost between 100 million euros and 1 billion euros to build and launch. With 2000 units in space, that's probably pushing 1 trillion euros of hardware up there. The operating costs tend to be much lower, around 1 to 10 million euros per year, so the cost of keeping them...

  • In the past, we have had to rely on altimeter missions that were tailored to surveying the global oceans, , but fortunately we have right now a satellite - CryoSat - which has an orbit that was especially desinged to monitor the polar ice sheets. This has transformed our capability to monitor changes in land and sea ice, and we have shown that ice losses from...

  • Hello Guido. For this I asked Richard Francis, CryoSat's original project manager. He tells me that the mission choice was a compromise between dense coverage of sea ice, which in the Arctic streches all the way to the pole, and land ice, which needs measurements at crossing points of the orbit ground track for stability, and these are more dense if the orbit...

  • Yes, lots. We are very often suprised by what missions can be used for. SMOS, which was designed to monitor soil moisture and ocean salinity, is now measuring sea ice thickness. CryoSat, which is an ice mission, is now mapping the sea floor depth and inland rivers. GOCE, which was designed to map Earth's geoid, has helped provide an improved view of ice losses...

  • Hello Anne. I'm afraid that past climate is a long way from my expertise. It's really hard to be certain about ancient environments because we have to rely on either computer models (which often don't even do a good job of simulating today's events) or sparse geological records. About a decade ago there was a lot of interest in the idea that therrmohaline...

  • Hello Kathleen. About 2/3 of the ice loss from Greenland is due to increased atmospheric warming which melts the ice at the surface; the remainder is due to ocean warming which melts glaciers as the flow into the sea. Both processes would reverse if the temperatures of the air and ocean were to drop. =Andy

  • Hello Francisco. Its not possible to measure the thickness of ice sheets from space because the radio frequencies we use to penetrate through thick ice (VHF and UHF) are the same as those used for TV, and so a satellite in space would interfere with telecommunications. So we have to rely on airborne measurements which, though helpful, are often very sparse. Andy

  • Hello Catherine. If you are referring to the extent (or area) of Antarctic sea ice, while it has increased this has been at a lower rate than losses in the Arctic and, overall, there is much less sea ice on Earth today than there was 30 years ago. =Andy

  • Hello Andrew. Its not possible to measure the thickness of ice sheets from space because the radio frequencies we use to penetrate through thick ice are the same as those used for TV, and so a satellite in space would interfere with telecommunications. So we have to rely on airborne measurements which, though helpful, are often very sparse. Andy

  • Hello Guido. It becomes increasingly more difficult because the signal has to pass through more atmosphere. For example, SAR sensors are typically inclined at about 20-25 degrees; compared to a nadir looking sensor their signals have to pass through a two-way path length that is 20% longer. =Andy

  • Hello Dana. Its more complicated than thinking about the source of direct heat; the oceans circulate heat around the planet, and any sources of water mass (such as melting ice sheets) get spread out very quickly too. Another thing to bear in mind is that changes in the mass of ice stored on land have an additional effect on the oceans because their...

  • The specification for the hardware was that it must last at least 3.5 years. In the end, the key components were actually built by industry to last 7 years. Last year the mission encountered its first real hiccup when a component that communicates how healthy the satellite is failed. The mission was switched off for 2 weeks to repair the problem, and in the...

  • Hello Joy. IT can sound quite abstract to say we need to improve models, but for ice sheets its really quite simple. The models which are used to make global climate projections have grid resolutions of 50-250 km; this is way too large to represent the ice streams which drain Antarctica and Greenland. The solution is to couple (connect) a separate ice sheet...

  • Stephen - I am with you on this one. CryoSat is a novel class of synthetic aperture radar altimeter; a hybrid of a SAR and altimeter. So you get extra marks from me! =Andy

  • Hello Trevor. All of Greenland's ice is sliding slowly, under its own weight, towards the ocean, even the parts that are deep in the interior.The ice passes through valleys in the mountainous terrain that surrounds the ice sheet, some of which are grounded well below sea level and the ice which flows through these is thought to be at the most risk to future...

  • CryoSat can certainly spot crevasses; even old generation pulse-limited altimeters with large (10 km) Earth footprints could do this because the echoes from sharp features like crevasses can be quite distinct. With its small (<500 metre) Earth footprint, CryoSat does an even better job at detecting small features. For example, to monitor sea ice floes we have...

  • GOCE was designed and launches as part of ESA's Earth Explorer series of satellite missions, alongside others like CryoSat and SMOS. These mission are intended to be demonstrations of new sensors that can detect new information. Once they have done their job, the Earth Explorer programme is not able to pay for a follow-on mission, and so the bill has to be...

  • Good answer Jean-Jacques! Mark, you can read a little more at ESA's mission website http://www.esa.int/Our_Activities/Observing_the_Earth/SMOS/Sensing_salinity but for details on the retrieval I expect you will need to read some scientific papers. I found a readable one herehttp://www.esa.int/esapub/bulletin/bullet111/chapter19_bul111.pdf -Andy

  • Alex is right; microwaves range from 1mm to 1 metre; the shortest do scatter from rain clouds as the are comparable in dimension to water droplots, but the longer wavelengths pass straight through.= Andy

  • Its a nice and often repeated line, but in fact satellites have revealed a great deal about the deep ocean. By measuring tiny changes in the gradient of the sea surface, we can determine perturbations in marine gravity which can be used to map the ocean depth. As the altimeter record has grown, we have built up an increasingly detailed picture of the sea...

  • Hello Ramesh.Quite a few satellite data sets tell us about the composition of the oceans upper layers; for example ESA's SMOS microwave radiometer can detect changes in salinity, and ESA's MERIS optical sensor can detect ocean colour which can be related to sediments or marine nutrients, but all of these only scratch the surface. To detect changes in the...

  • Its not that tricky really; NASA currently list jut over 2000 satellites in space at various orbital altitudes from a few hundred kiometres (spy satellites) upwards. If there were only this many cars on Earth they could drive around forever without even seeing each other let alone colliding! But in reality a collision would be very expensive and so they are...

  • Hello Phumlani. I guess its because the data from 2014 have not been released yet. There are many other data sets (mostly from satellites) which record changes in sea ice extent. Take a look at the US National Snow and Ice Data Center (http://nsidc.org/) as a starting point but there are many others. -Andy

  • Hello Alison. It's really difficult to be sure about past climate (often called palaocliamte) because we have very few pieces of the jigsaw puzzle left behind. I'm not an expert on this, but I think palaeoclimatologists have concluded that there were periods of little or no ice based on their reconstructions of past sea level stand (high relative sea level is...

  • CryoSat's orbit is symmetrical about the equator, and so it covers an identical part of the northern and southern hemisphere. There is an area at both poles of about 215km in radius that is not surveyed. This is needed to allow the ground track to sample lower latitudes adequately, and although we would really like to see all of the polar regions its far...

  • Hello Rocco. Alex is right I'm afraid, there are whole degree level courses on how synthetic aperture radar works (I remember sitting in a great course put on by the engineering department at Leicester University in the UK during my Astrophysics undergraduate degree!). Anyway, the basic principle is that you can take advantage of the movement of a satellite to...

  • Hello Kathleen. Whether or not changes in the amount of ice stored on land will affect patterns of ocean circulation is a big unanswered question right now in climate science. It's proven really tricky to include reliable ice sheet models into the global climate models which are used to make future predictions, and so we are still not sure how big the impact...

  • Hello Catherine. If you are referring to our estimate of the sea level contribution due to the polar ice sheets, its not as tricky to make this measurement as you might think because we are actually computing changes in the amount of ice stored on land and not the change in sea level. Every 350 cubic kilometres of ice lost from land leads to a sea level rise...