Scientists have used satellite observations to study how the distribution of land and water on the Earth’s surface has changed over the last 30 years.
They found that the Earth’s surface has gained 115,000 sq km of water of extra water bodies and 173,000 sq km of water has now become land. The study is published in Nature Climate Change.
The interactive Aqua Monitor was developed by the Deltares Research Institute in the Netherlands. It is the first global-scale tool that shows, with a 30 metre resolution, where water has been transformed into land and vice-versa.
The largest increase in water has been on the Tibetan Plateau, where increased water from melting glaciers are creating huge new lakes.
A rise in the number of dams built over the last 30 years has also increased the number of inland water bodies. Using the satellite data, the team were able to identify previously unreported constructions in Myanmar and North Korea.
The Aral Sea, which lies between Kazakhstan and Uzbekistan, has seen the the greatest conversion of water into land. Formerly one of the four largest lakes in the world, the Aral Sea has been steadily shrinking since the 1960s after the rivers that fed it were diverted by Soviet irrigation projects.
There have also been striking changes along our coastlines. The largest coastal water to land change is the construction of Palm Island and adjacent islands along the coast of Dubai. Many countries have shaped and extended their coastlines by land reclamation, including almost the entire coastline of eastern China from the Yellow Sea all the way down to Hong Kong.
New islands off the coast of Dubai.
Chinese land reclamation projects along it’s entire eastern coast. Green pixels show land reclaimned from the sea.
Big data at everyone’s fingertips
Universally-available analytics for big satellite data may have major implications for monitoring capacity. At the very local scale, members of the general public can now make assessments without expert assistance if their houses are threatened by coastal erosion. At the regional scale, countries can monitor their water body changes and assess flooding impacts and strategy for disaster risk reduction.
Jaap Kwadijk, the Deltares scientific director: “This has never been done before. So it is difficult to imagine all the new applications that will be made using this tool. But the tool can be used by everybody and so I am sure multiple applications will emerge in the next few years”.
The enthusiastic skiers or snow hikers among you may have already experienced the red snow phenomenon, which is caused by tiny microorganisms – the snow algae. Often termed ‘watermelon snow’ because of its colour and scent, I would not recommend eating it though. All the algae need to thrive is sunlight and liquid water. That’s why they form massive blooms in the warm months in spring and summer. But too much sun is not good for them either. They produce their own ‘sunscreen’ in the form of red pigments (the so called carotenoids), that gives them their red colouration.
Red snow looks very pretty, but why should we care about these tiny organisms? Well, even the smallest organisms can have a large impact. The red coloration darkens snow and glacial surfaces. This decreases their so called albedo. The albedo determines how much sunlight is reflected back from a surface. White snow reflects more sunlight, whereas the darker red snow reflects less. Therefore more heat is retained, which causes more melting. It is the same effect that makes people choose white clothing in places with high sun exposure such as deserts. Black clothing would make the sun even more unbearable.
I was really lucky to work on this topic during my PhD at the University of Leeds. Together with my supervisor Liane G. Benning, we collected 40 samples from various places in the Arctic, ranging from Greenland to Iceland, Svalbard and Northern Sweden. We found that these algal communities are very similar in all studied places and over one melt season they reduce the albedo by an additional 13%. Calculating how much this equates in additional melting is not easy and will be addressed in our ongoing work.
Our findings have been published in Nature Communications. Since the paper was published I have been approached by a many worried journalists who aske me what we should do against these dreadful algae. Well, we cannot and should not do anything against them. Snow algae are actually very important members of the natural food chain. Like plants, they do photosynthesis, and in doing so they fix atmospheric CO2 and transform it into organic carbon that can be used by other organisms. However, there is one thing that is worrying – and that is global warming, which may cause a ‘runaway effect’. Snow algae need liquid water to bloom, with rising temperatures more melting will increase the extent of the snow algae, which will further darken the glacial surfaces, causing more melting, and so on. So the only thing we can and should do is to reduce human-induced climate change.
We’ve just come back from gathering samples from the Greenland Ice Sheet, where a record-breaking ice melting enderway. As part of a big international, UK led team, we will further investigate the extent of these algae and their contribution to melting. At the moment climate models don’t consider the effect of algae on snow and ice melt, it is time to change that!
Dr Stefanie Lutz is a postdoctoral research associate at the GFZ Helholtz centre in Potsdam, Germany.
Recently a video has been circulating of Paul Beckwith from the University of Ottawa explaining how the northern and southern polar jet streams linked briefly across the equator this week.
Climate scientist Dr Caroline Holmes, who specialises in atmospheric dynamics, provides her independent view on this event below:
The essence of this video is the claim that the northern and southern hemisphere jet streams have connected via air crossing the equator, for a brief period of time; that this is ‘unprecedented’; and that it heralds dangerous consequences. To give my thoughts, I’ll address some of the concepts that come up in the video and some issues of language or terminology that are crucial for understanding it, and try to give an answer on whether I think this is a worrying development or not.
1)What’s so special about the equator?
Crash course covering two aspects: one is thermal, i.e., its to do with heat. As we know, the equator receives more heat from the sun than the poles do. Therefore it’s warmer. The atmosphere ‘tries’ to redistribute this heat from the equator to the poles, which is the reason for a lot of the circulation (i.e. large-scale movement of air and water) that we see in the ocean and atmosphere. Note, that in the northern hemisphere (I’ll call it NH from now on!) summer, the maximum heat from the sun is actually felt slightly north of the equator, and in southern hemisphere (…SH…) summer, slightly to the south of the equator. So, actually the ‘heat redistribution’ in the atmosphere is really from about 10°N to both poles in NH summer (SH winter) and from 10°S to both poles in SH summer. The other special thing about the equator is to do with the fact that the earth is a rotating sphere. So every point on the earth’s surface is rotating, once a day, around an axis that runs from the north to south pole. At the equator, this rotation requires covering a lot more distance (a circle of bigger circumference) than it does near the poles. So as air moves away from the equator (and indeed anywhere) it’s subject to forces linked to this rotation. (I’ll stop there because that’s a whole ‘nother blog post!)
2)What is a jet stream? The term ‘jet stream’ typically refers to a tight (i.e. short north-south extent) band of very fast winds, high in the atmosphere. We usually use the wind speed at 250 hPa (i.e. the level in the atmosphere where pressure is 250 hPa; about 16 km, very roughly speaking) to describe it, although in some jet streams winds are fast near the Earth’s surface too. At the simple level, each hemisphere has one, or two, jet streams. One is on the edge of the tropics, and one is in mid-latitudes (broadly about 30-60°N). Sometimes, or indeed often, the two combine. The jet streams fundamentally exist because of the two things I already mentioned above; the rotation of the earth, and the fact that the atmosphere tries to distribute heat from equator to pole. In the time-average picture, they are nice and smooth, and largely west to east, although not entirely so, and in the NH especially they are not a continuous band around the world; they are split up by, in particular, the Rocky mountains and the Eurasia continent. As time varies, however, the jets have big waves in them; they break up; they shift from north to south; they pulse in strength. They are hugely variable.
3) Is the climate system normally ‘stable and predictable’ and now becoming ‘chaotic’?
The atmosphere certainly isn’t. One of the most fundamental things about the atmosphere is that it is a chaotic system. You’ve probably heard the ‘butterfly flapping its wings causes a hurricane around the world’ saying. It’s that. Or, less dramatically; tiny changes in the atmosphere in one place can push it into a different state from the one it was heading to. It’s why we can’t do weather forecasts perfectly; because without knowing the state (by which I mean its temperature, how much water it contains, how fast it is moving and in what direction) of every point in the atmosphere, perfectly, we can’t be sure we are on the right path. The climate system on the other hand is a much trickier issue. I’m not even sure what the video is trying to explain regarding this. There are aspects of the climate system that are certainly predictable (seasons, for example. And they aren’t going to be eroding in a hurry, because they rely on changes of the earth’s orbit around the sun and the angle of its axis, which happen slowly. I.e. 10s to 100s of thousands of years slowly.) The stability of the climate system is a genuine question. Imagine a ball on a slope.
If I shove it gently, it returns to where it was. This is a ‘stable’ condition. If I shove it hard, however, it might go over the ‘hill’ to the right; it will not return to where it was. This is what is meant by unstable. A related concept is ‘tipping points’; if it goes over that hill, it might end up in another ‘bowl’; but it has been tipped into another type of behaviour (in this case, a different area to roll around in).
4)What is climatology?
Climatology is a very broad field. It’s the study of climate. For example, it’s a term that could probably cover people who study the output from climate models about what will happen in the next century; look at observational data gathered over the past 100 years; examine tree rings to try and work out what has happened to climate over the last several millennia; use mathematical techniques to explore what will happen to earth’s climate, and so on. There are better, or more detailed description for all these jobs, but climatologist is not wrong. The key thing is that a professor of climatology need not be (and in fact, probably is not) an expert on atmospheric dynamics, i.e., the movements in the atmosphere and what causes them, which is what this is all about.
5)What is this graphic?
It’s a beautiful visualisation of atmospheric conditions. It’s always worth being aware that first, the data that went into this is not as gorgeous as the end product! You can toggle the ‘grid’ button to show a point at every location where there is real data from the forecast model; the rest is interpolation between these points. And second, our eyes aren’t that good at interpreting information like this (sorry!) and are naturally drawn to colour boundaries. So, it’s easy to over-interpret patches of a different colour as indicating something very different. Now, as for some specific questions from the video, I’ll first address the idea that the jet stream should get, and is getting, ‘wavier’ as the atmosphere gets warmer. This argument is still, as far as I know, really controversial. I discussed this issue extensively during my PhD. The theory relies on a chain of about five causal relationships (i.e., A causes B, B causes C, and so on) in a chaotic system. Some of these are fairly convincing and some are not. The data providing evidence of this use information from a fairly short time series (30 years, which for finding robust results about anything other than time-average is too short). The original paper can be found here: http://onlinelibrary.wiley.com/doi/10.1029/2012GL051000/full. However, later papers examining the claim across different datasets, and for various measures of ‘waviness’, don’t find strong evidence for such a pattern (e.g. http://onlinelibrary.wiley.com/…/10…/grl.50880/abstract). Therefore, citing it as fact is very misleading. The second question is whether something remarkable just happened, and whether it can be described as ‘the jet crossing the equator’. Flow crossing the equator is not surprising; as I’ve mentioned above, the atmospheric flow is very variable. A colleague at Monash University kindly quickly checked a month of reanalysis data (essentially, this blends observations- from the surface, satellites, and upper air measurements from weather balloons- with the best available weather forecast models, to produce a historical ‘best guess’ of what the atmosphere has looked like over recent decades). She found that the wind speeds with flow across the equator of the speed seen here (about 20 metres per second) aren’t that rare. So as above; flow across the equator isn’t astonishing. Can this be described as the jet crossing the equator? Tricky; not all fast upper level winds are jet streams, and in addition the jet streams are generally a lot faster than this (about 100 metres per second). So then, is this behaviour where there appears to be some linkage between the NH and SH jet surprising (even ‘unprecedented’)? Unfortunately I can’t answer that right now! Links like this are easy to see by eye, but harder to define when you look for it in real data, so it wouldn’t be a totally trivial job to find out. However, I think that there is no reason why it would be surprising; given that the jets move around, and airflow crosses the equator. For the same reason I don’t think it’s a particularly meaningful event. Finally, it’s worth saying, the jet streams have been exhibiting weird behaviour recently. The winter of 2013/14 was really remarkable in the NH, for example, and the UK met office produced a great report about the storms and floods that occurred in the UK as a result as well as what was happening in Canada at the time. So I think it’s important to understand what the jets are doing, and why, and whether it’s new. The changing temperature of our atmosphere due to climate change is hugely worrying, and how this might impact the jet streams, particularly in the northern hemisphere, is still poorly understood. However, in conclusion, I don’t think this particular instance is panic worthy.
————————————————————————– Dr Caroline Holmes gained her PhD in climate science from the University of Reading, where her thesis investigated the effects of Arctic change (warming and sea ice loss) on mid-latitude climate, in particular the jet streams. She now works on understanding the impacts of climate change in Scotland at the University of Edinburgh.
Unabated greenhouse gas emissions could lead to sea level rise twice as high as we had anticipated, according to a recent study published in Nature.
By the end of this century, scientists predict that sea levels could rise by over 2 meters on average. Note that this is a global average, meaning that some areas could see much higher local rises in sea level. For Small Island Developing States, this could mean the end of their existence altogether. The research has been welcomed by the scientific community, who had already raised reservations with regards to what was called “very conservative” estimates of sea level rise caused by a changing climate.
So what has changed, how could we suddenly double sea level rise? The answer lies in complex processes involved in the melting of ice in Antarctica. Previous estimates had failed to take into account accelerated melting caused by disintegrating ice sheets. In fact, scientists had only been able to consider the melting ice shelves due to increased air and water temperatures, and had ignored the impact of surface melt-water and rainfall which can help fracture large chunks of ice.
Climate change adaptation has been hailed as the ultimate recourse to prevent negative impacts of sea level rise. For instance, in a number of coastal regions, ecosystem-based adaptation helped by mangroves has been underway for some years already. Mangroves play a significant role in protecting coastal regions from intense storms including typhoons, expected to increase in frequency with climate change. Combined with sea level rise, such storm could be catastrophic, especially in densely populated areas.
In previous adaptation planning, the unique property of mangroves to “grow soil” had been counted on to mitigate the impacts of rising sea levels. The rate of growth of mangroves was very much in line with previous climate change projections, yet this new data would suggest that these fragile ecosystems would no longer be able to keep up with the increased rate of sea level rise. Hence, millions of the most vulnerable coastal communities will likely have to rethink their adaptation strategies, a very costly endeavour.
So what is the silver lining? If we achieve the targets set in the 2015 Paris Agreement, sea levels will continue to rise, but never to the rate which would occur if Antarctica’s melting was to start accelerating. Coastal communities will still need to adapt, but costs will be reduced and lives will be saved.
Lying on the floodplains of the mighty Ganges, Brahmaputra and Meghna rivers Bangladesh is a rich, fertile land. These giant river systems meet in the centre of the country and flow together into the Bay of Bengal which, at over 1600km wide, is the largest delta in the world.
Rising Sea Level
Bangladesh is often cited as one of the countries that will be most negatively affected by rising sea levels from human induced climate change. Two thirds of the country lies less than 5m above of sea level. With vast regions to the south much less than a 1m above sea level. The Intergovernmental Panel on Climate Change (IPCC) claims that just 1m rise in sea level could directly expose nearly 14 million people and result in potentially 17% land loss in southern Bangladesh.
Most of the country receives on average more than 2.5m of rainfall a year, 80% of which falls in about 4 months during the peak monsoon season, resulting in large annual floods. The flood waters bring nutrient rich clays and silts from the high Himalayas and deposit them on the river floodplains. These rich soils produce bountiful harvests of rice and other crops. Unsurprisingly, farming is the most common profession.
However floods, once welcomed by farmers and their families are now harbingers of disaster. Human induced climate change has resulted in more erratic monsoon weather patterns with often larger than normal volumes of water being delivered in shorter time intervals. The resulting floods have had devastating effects on the Bangladeshi people. In 2012 three large floods hit the country in swift succession between the months of July and September directly affecting more than 5 million people. These are now a common annual occurrence.
Bangladesh is also subject to annual tropical cyclones, storm surges and tornadoes. Some of the worst natural disasters in recorded history were results of cyclonic storms in the Bengal region. Among them, the 1970 Bhola cyclone which claimed over 500,000lives! Worryingly new research into the impacts of climate change has shown that large cyclonic storms will become a more common occurrence in the years and decades to come.
The foothills of the great Himalayan mountain belt has historically been the location of many large earthquakes. Earthquakes in the continent tend to be more infrequent compared to regions such as Japan and California. However this makes them more unpredictable and often unexpected. But when one does occur it can result in significant ground shaking. The 1897 magnitude 8.1 and 1950 magnitude8.7 Assam earthquakes were two of the biggest to hit the region in recent times. The current building stock in Bangladesh is poorly built and most are not built to withstand ground shaking in an earthquake. The collapse of poorly built buildings is the greatest hazard during an earthquake.
So what can we as earth scientists do?
Bangladesh has a population of over 160 million and among the highest population density of any country in the world. With the majority of the country built on river floodplains combined with widespread corruption and ignorance a large earthquake could quite possibly result in the greatest natural calamity to have ever hit the country!
Bangladesh needs to increase its resilience if its people are to survive the multitude of natural hazards they face. Earth scientists are well placed to understand the risks involved from these hazards and can play a key role in all aspects of building a resilient infrastructure.
Climate science research is ongoing and needs to continue to better understand the affect human induced climate is having and will have on the annual monsoon. This knowledge needs to be translated into rainfall variation and flooding potentials and communicated with the people who need this information. The socio-economic issues of a rising sea level needs to be addressed and plans put in place to allow big cities to efficiently absorb and cater for migrants moving away from hazard prone coastal regions. Hydro-geologists and geochemists are helping to find sustainable clean, arsenic free water sources for drinking and farming. Seismologists and earthquake scientists are working to better understand the seismic risk in the Himalayan foothills; produce more accurate hazard maps and importantly identify the active faults within the region.
These are to name but a few of the ways earth scientists can get involved. I believe it is our moral duty to translate the practical aspects of our science into real benefits for people.
A historic agreement to tackle climate change and pave the way towards a low carbon, greener and cleaner future has been adopted by 195 nations in Paris.
This was a truly monumental political achievement that was only possible because of the deep urge felt unanimously by all member nations to act on one of the greatest challenges humanity has ever faced; that the climate is changing with disastrous consequences for people all over the world.
The Paris Agreement’s main aim is to limit global warming to well below 2 degrees Celsius by the end of the century and to drive efforts to limit temperature increase to 1.5 degrees.
The 1.5 degree Celsius limit is a significantly safer defence line against the worst impacts of a changing climate.
To reach these ambitious goals will require collaboration in a global scale, with richer nations providing much of the financial and technological means to implement low carbon, green initiatives throughout the world.
French President Francois Hollande told the assembled delegates: “You’ve done it, reached an ambitious agreement, a binding agreement, a universal agreement. Never will I be able to express more gratitude to a conference. You can be proud to stand before your children and grandchildren.”
Over the next few weeks I will be posting about the key implications of this agreement.
You might have heard reports recently that El Niño is expected to strengthen in the coming months to potentially become one of the strongest events since 1950. Here’s a great Met Office video explaining how they work.