The Earth Story

The forest is getting hotter This is a Mixed Forest, also called a Temperate-Broadleaf Forest, found in West Virginia. These are some of the classic forest types on Earth outside of jungles – they contain both conifers and broadleaf trees, the only continents without them are Africa and Antarctica, and they cover broad areas in North America, Europe and Asia. They occur in relatively warm, balanced climates – cold but not too cold in the winter, dry and warm but not too dry and worm in the summer. Scientists have characterized these forests worldwide, and a new study has found that they are seeing the fastest changes in the type of plants present out of any global ecoregion due to warming conditions.

Warming Earth, Warming Atmosphere This image is one you might see commonly during the winter, showing the difference between types of freezing and wet precipitation. If there is warm air near the surface, generally precipitation hits the ground as rain, while cold air near the surface allows it to snow or sleet. Even outside of winter storms, the same phenomenon occurs; high in the atmosphere, water is frozen as ice particles, but closer to the surface everything melts to become rain. Over the time where there are solid weather records, the surface of the Earth has warmed by just over 1°C. 

Siberian Heat Wave This is a plot of average global surface temperatures for the first 5 months of 2020 – over 75% of the Earth’s surface was above its long-term average temperature, and this time period has been the warmest January-May that humans have recorded. Notice the gigantic red spot over Siberia? Right now, Siberia is experiencing some of the warmest conditions that area has seen since records began, building on the temperature extremes from earlier this year.

Local Sea Level Rise- one of the trickiest predictions, part 4: Distribution delay and freshwater forcing

This is the final post of my 4 part series on why sea level rise is not distributed equally throughout the world’s oceans. If you missed the first posts, here are the links; (http://on.fb.me/1C2B9Lx , http://on.fb.me/1JsFhdw andhttp://on.fb.me/1CL9HST.

In this final post, I’ll explain the distribution delay and freshwater forcing mechanisms that can influence different sea levels worldwide.

Ice melting from glaciers and ice sheets contributes immediately to the global mean sea level rise but is not instantaneously uniform throughout the globe. It takes time for water to become distributed globally. For example, melt water from Greenland contributes to sea level rise in the North Atlantic within months, but can be on the decadal time scale to have a worldwide effect due to boundary, Kelvin and Rossby waves (these explain some of the physics behind water movement in the worlds oceans). A similar process can be observed with melt water from the Antarctic. It isn’t that simple though – for example, changes in atmospheric patterns due to the melting of the Greenland Ice Sheet could result in sea level changes in the Pacific within months.

Another aspect of freshwater forcing that should be of concern, particularly those on the North American Coast is the weakening of the overturning process that drives ocean currents. In North America, the warm Gulf Stream flows north until it reaches an area between the UK and Greenland where it cools (becoming denser) and sinks. This deep, cold water then flows south-west until it eventually rises and heads back north as warm water once again. Increased freshwater input from the melting of Greenland's Ice Sheet is diluting the dense salty water which impedes the waters ability to sink. A warmer North Atlantic region may also slow the cooling of the Gulf Stream, further inhibiting its ability to sink and flow. But what does all of that mean? Simply put, if less cool water is sinking, the out flow of Gulf Stream will slow. The slowing of that oceanic current will cause a build-up of water behind it, which is one reason why the North American coast is vulnerable to the fastest and largest sea level rise this century.

Increased freshwater input from Antarctic Ice Sheet melt water could also have severe global implications, as the Antarctic Circumpolar Current is the ‘engine room’ of global ocean circulation. I have touched on this in a previous post (although not with respect to sea level rise), see:http://on.fb.me/1MRhJo7

This series of posts was simply an overview of the complications in local sea level rise predictions. Other factors such as land depression from oil extraction and thermal expansion estimates further complicate the predictions. But hopefully now you have an idea of how difficult sea level rise is to predict, especially for a particular region!

-MJA

Image Credit: James Balog , illustrating melt water on the Greenland Ice Sheet. Further reading/references:

IPCC on sea level rise: http://bit.ly/1CrvtOk

General Article on Local SLR: http://bit.ly/1nddrec(http://on.fb.me/1C2B9Lx

and http://on.fb.me/1JsFhdw

The Greenhouse Effect and how humans are driving it in one measurement

We would not be here without the greenhouse effect. Without the atmosphere, the Earth’s climate would be a lot like the moon – over a hundred degrees C during the day, hundreds of degrees C below zero during the night. Sunlight is absorbed by the atmosphere and converted to heat, the atmosphere takes a while to let that heat out, acting like a greenhouse that keeps the dark side of the planet from freezing and enabling life as we know it to exist.

Gases in the atmosphere drive the greenhouse effect. Sunlight absorbed by the rocks on the surface converts to heat and that heat is radiated away as infrared light. The atmosphere is transparent to visible light (that’s why we can see the sun), but certain molecules absorb some wavelengths of light in the infrared. When that light is re-absorbed in the atmosphere, it is converted back to heat, holding onto the energy for longer and keeping things warm. That’s the essence of how the greenhouse effect works. When you have a cloudy sky, or a humid day at night - it tends to keep the surface warmer because the heat cannot escape out to space, same effect.

As the abundance of molecules in the atmosphere that absorb infrared light increases, more light should be absorbed and converted back into heat. That’s the basic logic that leads to the concept of climate change as a function of CO2 – add extra CO2 to the atmosphere and basic physics says it has to hold in more heat.

Because the earth’s atmosphere is a complicated place, full of clouds, water vapor, and other species, even though we know this physics, measuring the exact behavior of CO2 in the atmosphere has been a bit more difficult until now. This plot shows the exact behavior of CO2 measured in the atmosphere by satellites over a 10 year period and how additional energy is being absorbed as humans release more CO2. 

A group of researchers led by scientists from Lawrence-Berkeley National Laboratory collected these 2 data sets in areas that commonly have clear skies - Southern Great Plains and the North Slope of Alaska. They measured specifically the emission of light at the wavelengths released by CO2 on those days – how much light goes out to space versus how much light is re-absorbed and converted back into heat. The higher the “radiative forcing”, the more energy CO2 is holding in the atmosphere and and the more is being sent back down to Earth.

Every year, CO2 goes down during northern hemisphere summer because there is more land area and more plants in the northern hemisphere, but it goes up again the next winter. On top of those yearly oscillations, there are short-term changes from events like wildfires and weather.  Finally there is a long-term trend where every year more energy is absorbed - that’s the part humans are doing. Pump more CO2 into the atmosphere by burning fossil fuels, the CO2 absorbs more energy, converts it to heat, and the Earth’s atmosphere has to figure out what to do with all that new energy. Note how the grey curves for measured CO2 in the atmosphere at the sites and the red curves for the atmospheric spectra themselves are highly correlated, as they should be. 

This is the greenhouse effect and the way CO2 contributes to climate change captured in one single plot.

-JBB

Image credit and original paper: http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14240.html

The PETM – Why It Feels Like Deja Vu

The Palaeocene Eocene Thermal Maximum was an event that took place 56 million years ago at the end of the Palaeocene and lasted for 150,000 – 200,000 years. The average global temperature rose by 5-9°C (9-16°F) leading to mass migrations and extinctions of flora and fauna.

The event was discovered when marine sediment cores from Antarctica showed a large and sudden excursion ( a sharp spike in the values) in carbon isotopes, indicating that a large amount of CO2 had been rapidly expelled into the atmosphere. Sounds familiar doesn’t it?

Further evidence of a large expulsion of CO2 is shown within marine sediment cores. As you can see, there is an abrupt change from white to red, indicating a rapid dissolution of calcium carbonate (white mud) that only recovers after the event (the red clay). (Increases in CO2 dissolved within seawater lead to calcium carbonate dissolving and eroded terrestrial clays (red) are deposited instead).

Today global temperatures are increasing at rate that far exceeds that of the PETM; a warming of 1°C per 100 years compared to 0.025°C in the Palaeocene.

While current global temperatures are far lower than those during the PETM it is the speed of the change that matters. All life forms take time to adapt and evolve, and it is the rapidity with which the world is warming that is threatening life as we know it. Humans are not immune to this change, and it is very likely that the current warming could lead to the next mass extinction if it is not curtailed.

Climate change is still a topic of hot debate but the most important fact to remember is this: No matter what happens the Earth will still exist and life will find a way to go on. The Earth has survived global glacials as well as global deserts and has feedback cycles that always return it to a habitable state. However, these climate shifts always incur casualties, and if there is another mass extinction, there is no guarantee that the human race will survive to tell the tale. There is no doubt that humans are expelling large volumes of CO2 into the atmosphere and therefore control over the future really does lie in our hands.

Reference: https://www.e-education.psu.edu/earth103/node/639

Further Reading: http://www.wunderground.com/climate/PETM.asp?MR=1 http://www.skepticalscience.com/co2-rising-ten-times-faster-than-petm-extinction.html http://www.geol.umd.edu/~jmerck/geol100/lectures/36b.html Image Credit: University of California Santa Cruz - Earth and Planetary Sciences

Montana’s “Glacier” National Park

Glacier National Park, located in North Western Montana, is one of the ‘must-see’ locations in the North American West. It encompasses over 16,000 square miles of beautiful valleys, mountains and lakes. Unfortunately, time is running out for the park’s most stunning and crucial wonders – the glaciers.

Over 100 years ago, Glacier National Park housed over 150 thick sheets of ice that wedged themselves in mountain valleys across the region. Since then, these ice sheets have been melting at an astonishing rate due to an increase in temperature: and as of 2015, only 26 glaciers remain. In the next 15 years, the United States Geological Survey projects that all glaciers within the park will be completely melted, drastically shifting an incredible mountainous ecosystem.

In the western states, about 80 percent of all water comes from snow and ice melt in the mountains. During the spring, as temperatures rise, rivers and streams generously flow with water, but within the past few decades, snow and ice sheets have been melting up to two weeks earlier, causing meager summer flows because of a warming climate.

The amount of snow fall in the region is also decreasing steadily. Mountains and glaciers are not receiving enough snow to replenish what has been lost earlier in the year. The water from the melting snow and ice are crucial to the wildlife within and outside of the park, but people who live in the area also depend on the glaciers and snow for drinking water. Once these glaciers disappear, water will become much scarcer, depriving the ecosystem of Earth’s most precious natural commodity.

The disappearance of Montana’s glaciers and snow fields are already having detrimental effects on the region, but one can only imagine the vast transformation the park, and even the state itself, will go through. Because of the lack sufficient snow fall and dwindling streams, many plant populations could decrease, especially those that are reliant on snow melt.

Animal populations could also decline, such as the fragile wolverine population, due to the ongoing transformation of their habitat. Many of the transformations can vary, but Glacier National Park’s current implications could reveal how other mountainous ecosystems, such as the Rocky Mountain region in Colorado, could be affected by rising temperatures.

*Photo Credit to Mark Wagner: http://commons.wikimedia.org/ /wiki/File:Glacier_National_Park_Hidden_Lake_overview_20060703.jpg Check out previous TES articles: http://on.fb.me/1AXzZnJ http://on.fb.me/1vC74A9

Read more here: New York Times Article: http://www.nytimes.com/2014/11/23/us/climate-change-threatens-to-strip-the-identity-of-glacier-national-park.html?_r=0 USGS Glacial Retreats: http://nrmsc.usgs.gov/research/glacier_retreat.htm USGS G.N.P. Glacier Photography Project:http://nrmsc.usgs.gov/repeatphoto/

Original caption:

For Icelanders their glaciers are a living embodiment of Iceland’s national identity. ‘Meltdown' explores the bond between this iconic landscape and a group of local glacier guides, who are now fighting to save these natural wonders from climate change extinction.

Glacial retreat The pair of photos show the Pedersen glacier in the Kenai mountains of Alaska in 1917 and 2005, revealing how much is has retreated in that time. A century ago the glacier calved into a lake near the sea, which has now filled with glacial sediment deposited by melt water and ice and turned into a grassland. They were released as promotion for a new NASA app that allows you to track some of the changes we are wreaking around the globe using juxtaposed images. Most glaciers worldwide are in retreat due to global warming, depriving us of much mountain beauty and endangering future water resources for hundreds of millions worldwide. Being a child of the Alps I have seen it myself in several places, sometimes to a shocking extent within a mere half decade. Loz Image credit: Louis H. Pedersen (1917) and Bruce F. Molina (2005)/ National Snow and Ice Data Center/World Data Center for Glaciology http://climate.nasa.gov/blog/1096 A link to the app: 1.usa.gov/SfNZ9L http://www.climate.gov/news-features/understanding-climate/2012-state-climate-glaciers

Of mist and nuts...

California remains one of the main source of fruit, vegetables and nuts for both the US market (95%) and worldwide export. Much of this is grown in the Central Valley, watered by irrigation, pollinated by bees, and dependent on a particular kind of winter fog to convince these originally colder clime plants that a winter has occurred. New research suggests that these vital fogs are becoming rarer with climate change, endangering a substantial chunk of the state's economy.

The mists are known as Tule fogs after the grassy wetlands that once covered the valley. They form between November and April, and are caused by cold air sinking into the valley at night from the surrounding mountains, condensing the moisture in the warmer valley air (a process known as radiation fog). They can linger for days along the whole 650km length of the valley, since winds cannot budge the dense air and temperature inversions can often keep them confined in the valley.

These fogs are crucial for may fruit and nut trees, giving the plants the impression of a dank, dark and cool European winter. Some trees, such as cherries, almonds and peaches need a dormant period during the winter that needs prolonged coolth to trigger. The rest is vital to their ability to produce buds, flowers and fruit, and its absence results in drastically lowered yields. Recent research at the University of California at Berkeley has shown that these vital fogs have declined dramatically during the last 30 years.

The team used both NASA/NOAA satellite data and weather station records to chart the fogs over the last 32 winters, revealing a 46% drop in fog days during the crucial winter season. Variability between seasons is due to whether the year is wetter or drier, but the lowering trend is unmistakeable. Other work underlines this, showing a drop in several hundred hours of temperatures between 0 and 7 degrees Celsius since the 1950's. The current drought is also preventing their formation, exposing the fruit trees to a variety of mixed stresses.

Climate forecasts imply this situation will worsen, eventually threatening the entire current model for Californian agriculture. Fruit developers are trying to breed varieties that can do without a winter, but without much success for now. Only the future will tell exactly where and how the chips are going to fall, but the best educated guesses suggest that threats to crop yields worldwide from a changing climate are considerable, and may already be affecting world politics, such as the food riots in 2008-9 when a series of unfortunate climate events caused huge rises in the prices of a variety of staple grains. Maybe when climate change hits enough people in the wallet, they may finally awaken and take notice of what is going on around them, lets hope it won't be too late to seek viable solutions to these problems.

Loz

Image credit: CSERC.org

Original paper, paywall access: http://onlinelibrary.wiley.com/doi/10.1002/2014GL060018/abstract

Hurricane Harvey fed off record warm Gulf of Mexico waters

This satellite shot captures Hurricane Harvey at the time it was a category 4 storm, just before it made landfall in Texas. The storm started off as a disturbance crossing the Yucatan Peninsula, but when it made it into the warm waters of the Gulf of Mexico it rapidly strengthened. Harvey became the second costliest disaster ever to hit the United States after it doused the city of Houston with record rainfall totals. A new analysis points squarely at the Gulf of Mexico as the main driving force behind the power of this storm.

Hurricanes feed off of warm temperatures in ocean waters. In the process, they remove heat from the ocean and leave the water behind it cooled off. However, other things can happen that affect ocean temperatures; for example, the winds blowing over the water could mix the shallow layer with deeper water, cooling the surface water by pushing the warm water deeper. As a consequence, it’s not easy for scientists to match up the energy of the storm with the energy of the ocean.

Harvey though represented a unique case. For much of the surrounding month it was the only major weather event in the Gulf of Mexico, and it traveled over areas that are well instrumented so that scientists could see how much heat it removed from the water. On top of that, scientists also have available the Global Precipitation Measurement Satellite system, which enabled estimates of Harvey’s rainfall over wide areas.

A team led by a scientist at the National Center for Atmospheric Research took these two measurements and converted them into total energy. The ocean cooled by a certain amount over a certain volume – that’s an energy measurement. Harvey produced a certain amount of rainfall over a certain area – that’s also an energy measurement. When they compared the number of joules pulled out of the Gulf to the energy released over land by Harvey – they were virtually identical, within 1% of each other. The energy that drove Harvey was the energy in the Gulf; basically every Joule of energy it pulled out of the Gulf, it dumped on Texas.

Harvey became such a disaster because it had an ample supply of energy in the shallow waters of the Gulf of Mexico. Prior to the storm, the waters of the Gulf were at their hottest temperature ever recorded, more than 1.5°C above the long term average. Those temperatures extended downwards, making the Gulf heat content also a record. When Harvey passed over these waters, it cooled them by 2°C. That extra 1.5°C in the Gulf of Mexico in 2017 was enough to almost entirely fuel the storm; had the Gulf not been at record temperatures, Harvey would not have had the energy to produce that rainfall.

Global ocean heat content has been rising steadily since the 1980s as the ocean takes up much of the extra heat kept in the atmosphere by greenhouse gases. The close match between energy taken out of the ocean and energy dumped by the storm verifies that the extra energy trapped in the atmosphere is feeding storms like Harvey. The extra heat in the Gulf of Mexico directly triggered flooding in Houston, and as ocean temperatures continue to increase, it will be able to continue powering devastating storms.

-JBB

Image credit: https://commons.wikimedia.org/wiki/File:Harvey_2017-08-26_0055Z.jpg

Original paper: https://doi.org/10.1029/2018EF000825

Snow melt in the Alaska Range

The Alaska Range, including its highest summit Denali, sits in Alaska somewhat exposed to air currents and weather patterns blowing in from the ocean. These glacier-covered summits therefore might be particularly sensitive to changes in the average temperature driven by greenhouse gases. To investigate how mountain glaciers in the Alaska Range are responding to a warming world, in 2013 a team led by scientists at Dartmouth University collected ice cores on Mount Hunter, a 4,257 meter high summit about 15 kilometers south of Denali itself. The first image shows the team collecting the ice cores on this slope, the second image shows what they were looking for. When the snow at the top of the winter ice melts, it will re-freeze when the temperature drops and create one of those dark blue layers; the other layers are white because they still contain air bubbles. By counting the number of dark blue layers and measuring their thickness, the team could figure out how often melting events were happening and how big they were.

Overall the team collected ice cores at this site that cover about 400 years of time. They found that, in the first 200 years of their core there are only a couple of melting events. By the time we reach the last few years, the number of melting events has increased by a factor of 57 and the amount of melting increased by a factor of 60. Many of those are found in years where the tropical Pacific Ocean is unusually warm, directly linking these new melting events to broader changes in the climate of the Pacific Ocean.

The scientists used modern records of temperature and melting events to convert the increase in melting to an estimated increase in temperature, and found that since the melting events became more common in the mid 1800s, this site has warmed by at least between 1.2-2 °C – a rate comparable to or higher than that observed around the world.

This is the first alpine record of melting events from this part of the world. It shows similar warming signals to those found elsewhere, showing that high altitude glaciers are affected by the same warming trends found elsewhere in the world.

-JBB

Original paper: https://bit.ly/2qlxJHx

Reference: https://bit.ly/2HpvbjD

Astronaut @colchrishadfield‘s video group has been presenting science regarding the threatened environment in the Arctic over the past few years. Here is the latest video in their sequence. Original caption:

Warm Arctic, Nasty North America

In recent years, North America has been hammered by severe winter weather. A few years ago, scientists at NOAA developed a “Winter weather misery index” called the Accumulated Winter Season Severity Index (AWSSI), which takes into account all the features of winter weather such as how much snow has fallen, the depth and extent of extreme cold snaps, and how long it has been since the last fall temperatures. Using recorded weather data from several dozen weather stations around the U.S., the scientists who created the index were able to characterize what a mild winter was at a certain location compared to an extreme winter, and the range in-between.

Not every winter has been extreme – the 2016 to 2017 winter was particularly mild around the country, but winters such as 2014-2015 and 2017-2018 have pushed many cities up to the “Extreme” level on that scale. For example, in January of this year, more than ½ of the sites in the Eastern U.S. were experiencing extreme winters.

There has been substantial discussion, including here at the Earth Story, about the cause of these extreme winters. It has not gone unnoticed by scientists that many of them, including noreasters like the one seen in this satellite photo from early March, were occurring at the same time as persistent warm periods hitting the Arctic. Once scientist at Rutgers University, Dr. Jennifer Francis, has published intriguing climate model results that suggest these states are linked; the warm conditions in the arctic allow weakening of the jet stream, as a consequence large bends form in the jet stream as major frontal boundaries move to the south, and these bends and frontal boundaries trigger severe weather.

When scientists see two things that seem to be happening at the same time, like warm weather in the arctic and cold weather in the states, an important first step is to assess whether the events are really correlated or if it just seems to be happening because we’re paying attention. To test whether warm weather in the Arctic really was correlated with severe winters in the U.S., Dr. Francis and colleagues compared the AWSSI misery index to two measurements that record how warm it is in the Arctic. One measurement is the actual arctic temperature averaged over the ice sheets, and the other records the height of a boundary in the atmosphere over the Arctic – a measure of how much energy is stored in the lower part of the atmosphere.

Sure enough, when the scientists tested for correlations between these indices, they found that there was a good correlation, particularly for the Eastern U.S. As the Arctic warmed, and particularly as air pressure increased over the Arctic, about 5 days later there was commonly a substantial increase in the AWSSI index, indicating a severe storm or severe wintry conditions. This correlation was the strongest in late winter, such as the time that noreasters like the one in this photo have lined up in 2018.

In this study, Dr. Francis’s group didn’t directly address the cause of the severe weather or why these are linked. They have other work suggesting that the linkage comes through the jet stream, but they limited this study to testing whether these weather events actually correlate statistically, and they do.

The Arctic is rapidly warming; the area is more than 2 °C warmer than it was only 3 or 4 decades ago. This warmth is hitting the whole area; for example, 2018 saw the lowest winter ice extent on record, breaking records set only a year or two ago, and the hottest Arctic winter temperatures ever recorded happened in February (https://tmblr.co/Zyv2Js2Vb3E_y). This work supports the idea in previous studies that as the arctic warms, one end result is severe winter weather over the United States. Scientists will still have work to do to understand the details of these interactions and how they will evolve as the arctic continues to shift, but as of right now, when it’s warm in the Arctic winter, it’s a mess down in North America.

-JBB

Image credit: NOAA/GOES-East http://bit.ly/2DqOUf1

Original paper: http://go.nature.com/2FzygQB

References: http://bit.ly/2HwWOWG http://wxch.nl/2tMCkr6 AWSSI Scale: http://bit.ly/2tKveTZ http://bit.ly/1lpm7z7

Pine Island Glacier collapse inevitable

This image was taken by the MODIS instrument on NASA’s Terra satellite on January 5th, 2014, and it shows an iceberg in Antarctica’s Pine Island Bay. The iceberg began as a crack in Pine Island Glacier last November and broke away as a piece the size of Singapore in early January.

The Pine Island Glacier is a major feature of West Antarctica. Western Antarctica is covered by an ice sheet. When snow falls on top of that ice sheet, it pushes older ice out towards the coast through a series of “ice streams”. The Pine Island glacier is one of these ice streams; about 20% of West Antarctica’s ice flows through its channel and you can even see streaks at the bottom-right of this image marking its flow direction.

The Pine Island glacier is also one of the least stable in Antarctica. Over the last 20 years it has shrunk rapidly, contributing several millimeters worth of sea level increase over that time. New research published in the journal Nature Geoscience suggests this is just the beginning, and over the next few decades a large portion of this glacier is going to collapse.

This type of ice stream typically starts on land and moves out to sea. It pushes ice out to sea, forming a shelf of ice floating offshore. Further up, there is a “grounding line” – the point at which the glacier goes from sitting on land to floating on the oceans. Above the grounding line the glacier is anchored to rocks at the base; below the grounding line the glacier is exposed to the waters of the ocean.

Much of the melting of this glacier over the last 20 years is due to the ice shelf shrinking. When warmer waters come up beneath the ice shelf, they cause ice to melt and to break away as icebergs, and as the ice shelf shrinks the glacier begins flowing faster as the sea ice helps hold the rest of the glacier in place.

But the Pine Island glacier is unique in an important way; its grounding line sits on an underwater ridge. The rocks that this glacier was hanging on to had another bay behind them where the waters got deeper. Water from the warming ocean couldn’t get into this bay because the glacier was grounded farther out to sea, but this setup created a precarious situation.

What would happen if the glacier lost its grounding point on this underwater ridge? The glacier would lose all of its support. The next possible grounding point is tens of kilometers farther up. If the glacier lost contact with this underwater ridge, the glacier would become extremely unstable.

New research just published in the journal Nature Geoscience says that is exactly what has happened. Based on radar surveys taken through the ice, the Pine Island Glacier has now lifted completely off this ridge. Warmer waters from the open ocean are now free to flow along the entire base of this glacier; it is no longer pinned in place and has crossed a point of no return.

Using models for how ice flows over topography, the scientists modeled the behavior of this glacier without the pinning point and project that it is in an irreversible retreat. The glacier will melt at the base weakening it and over time ice will break off until it retreats tens of kilometers to its next grounding point. The current structure of this glacier is going to collapse.

The Pine Island Glacier is already the largest contributor to sea level rise on the Antarctic Continent. Based on these models, the scientists project that over the next 20 years, it is likely that this glacier will contribute 3 to 5 times as much to sea level rise as it did during the last 20 years and possibly more.

The unsupported part of this glacier is going to die. It will retreat back to the new grounding line, dumping large amounts of water into the ocean and causing flow from the continental ice sheet to accelerate.

-JBB

Original article: http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2094.html

Image credit: NASA/GSFC/Jeff Schmaltz/MODIS Land Rapid Response Team http://www.flickr.com/photos/gsfc/11949193796/

Read more: http://www.bbc.co.uk/news/science-environment-25729750 http://www.independent.co.uk/environment/climate-change/pine-island-glacier-melting-past-the-point-of-no-return-9059347.html http://www.reportingclimatescience.com/news-stories/article/pine-island-glacier-committed-to-irreversible-decline.html_ _

Sea level rise is speeding up

As we all know one of the more disturbing consequences of the current bout of human induced global warming is the rise in sea level, due both to the expansion of the ocean's waters as they warm and to the rapid increase in glacier and ice sheet melting worldwide. Working out how fast it is happening and whether the rate of rise is accelerating is one of the most vital areas of research for our mitigation efforts, since if the rise is swift evacuating all the worlds coastal cities and replacing the infrastructure is going to be even more of a nightmare than it is already going to be (think Shanghai, Mumbai, New York, Holland, Bangladesh, London etc, the lowest projected rise by 2100 involve s shifting 150 million people, at least). We need the best and most refined projections in order to help us cope with the monumental changes that loom over our heads like a sword of Damocles, the only unknown variant being the speed of the increase.

Earlier measurements were based on tide gauges, which provide good local information but are hard to calibrate between each other, partly because various factors (such as local tectonics making a block of rock rise or sink or isostatic rebound after the removal of ice sheets) can confuse the result. Adding insult to injury tide gauges are all coastal, and so knowledge of what is happening in the open ocean was limited, until satellite based radar reflectance altitude measurements came into being.

Researchers looked at the last 25 years worth of such measurements from 4 generations of satellites (the latest being JASON 3, launched in 2016) from the entire globe to try and establish what is happening, and the results are illustrated in the accompanying graphic. While the data see-saws a bit the white line illustrates the long term trend and shows that the rise is indeed accelerating (and will probably continue speeding up at a faster rate with increasing warming and greenhouse gas levels) by 0.084mm yearly, with the authors noting that they have been as conservative in their estimations as the data allows. Sudden collapses in ice sheets (documented in the geological record) and other similar potential events are not included..

The last time CO2 stood at 400ppm there was no ice on Earth, that adds up to 70-80 metres of total rise already locked in unless we somehow manage to reverse the process we have inadvertently started. The only real question is how fast the water is going to rise around our increasingly beleaguered civilisation.

Loz

Image credit: John Fasullo

http://bit.ly/2F08iFH Original paper: http://bit.ly/2H8X1zY

Climate models correctly interpreted Holocene climate

When used to make a scientific prediction, a good model is one that tells you something you don’t know because you don’t have the best data. You put in everything you do know, the basic laws of chemistry and physics and everything else you can do to calibrate it, run the model, and see what it tells you about the world. Figuring out what areas they need to better understand is one of the best uses of models. When there is a disagreement between a model result and data about something, a scientist would ask why the model and the data are disagreeing. It might mean that there is something missing from the model, it might mean that there is something missing with the data currently available.

During the latter part of the Holocene, the time after the ice sheets had fully collapsed, climate models consistently suggested that global temperature remained mostly constant. This time of unusually constant global climate is the time humans built much of their civilization; cities are located where they could find food, water, and resources during this stable climate. However, the available temperature data from a 2013 study showed that the world was slowly cooling during this time, contradicting the model results.

To try to resolve this discrepancy, researchers led by a scientist at the University of Wyoming collected hundreds of pollen samples from around lakes in North America, including the one in this photo. Pollen is a direct record of the type of plants growing in an area, and also can be used as a temperature record. When they analyzed these pollen records, they found that there was a cooling trend, but it was mostly isolated to North America. It turns out that the climate models were right; they were hitting the right temperature and because the measured data was focused on North America, it was underestimating global temperature.

In other words, the model result was accurate and the real world data needed to be updated to bring it in accordance with the model.

The worry with the model being right is, of course, today. That same climate model suggests that without greenhouse gases released by humans, the world would have been cooling for the last several centuries. Furthermore, the last decade was warmer than any decade in their entire model reconstruction, and that’s before the last 3 years that have been dramatically warmer than the last decade. The model data told us where in the geologic record we needed to acquire more data, and that same model is now telling us that humans have ended the long era of a stable climate where we built our civilization.

-JBB

Image credit: David Foster http://bit.ly/2o9EjjQ

References and original paper: https://www.nature.com/articles/nature25464 http://science.sciencemag.org/content/339/6124/1198 http://www.pnas.org/content/111/34/E3501