Tag: temperature

Insects will struggle to keep pace with global temperature rise – which could be bad news for humans

Posted on by janet.crompton

Animals can only endure temperatures within a given range. The upper and lower temperatures of this range are called its critical thermal limits. As these limits are exceeded, an animal must either adjust or migrate to a cooler climate.

However, temperatures are rising across the world at a rapid pace. The record-breaking heatwaves experienced across Europe this summer are indicative of this. Heatwaves such as these can cause temperatures to regularly surpass critical thermal limits, endangering many species.

In a new study, my colleagues and I assessed how well 102 species of insect can adjust their critical thermal limits to survive temperature extremes. We found that insects have a weak capacity to do so, making them particularly vulnerable to climate change.

The impact of climate change on insects could have profound consequences for human life. Many insect species serve important ecological functions while the movement of others can disrupt the balance of ecosystems.

How do animals adjust to temperature extremes?

An animal can extend its critical thermal limits through either acclimation or adaptation.

Acclimation occurs within an animal’s lifetime (often within hours). It’s the process by which previous exposure helps give an animal or insect protection against later environmental stress. Humans acclimate to intense UV exposure through gradual tanning which later protects skin against harmful UV rays.

One way insects acclimate is by producing heat shock proteins in response to heat exposure. This prevents cells dying under temperature extremes.

A ladybird drinking a speck of water on a narrow leaf.
Insects in warmer environments develop fewer spots to reduce heat retention.
mehmetkrc/Shutterstock

Some insects can also use colour to acclimate. Ladybirds that develop in warm environments emerge from the pupal stage with less spots than insects that develop in the cold. As darker spots absorb heat, having fewer spots keeps the insect cooler.

Adaptation occurs when useful genes are passed through generations via evolution. There are multiple examples of animals evolving in response to climate change.

Over the past 150 years, some Australian parrot species such as gang-gang cockatoos and red-rumped parrots have evolved larger beaks. As a greater quantity of blood can be diverted to a larger beak, more heat can be lost into the surrounding environment.

A colourful red-rumped parrot perched on a branch.
The red-rumped parrot has evolved a larger beak to cope with higher temperatures.
Alamin-Khan/Shutterstock

But evolution occurs over a longer period than acclimation and may not allow critical thermal limits to adjust in line with the current pace of global temperature rise. Upper thermal limits are particularly slow to evolve, which may be due to the large genetic changes required for greater heat tolerance.

Research into how acclimation might help animals survive exceptional temperature rise has therefore become an area of growing scientific interest.

A weak ability to adjust to temperature extremes

When exposed to a 1℃ change in temperature, we found that insects could only modify their upper thermal limit by around 10% and their lower limit by around 15% on average. In comparison, a separate study found that fish and crustaceans could modify their limits by around 30%.

But we found that there are windows during development where an insect has a greater tolerance towards heat. As juvenile insects are less mobile than adults, they are less able to use their behaviour to modify their temperature. A caterpillar in its cocoon stage, for example, cannot move into the shade to escape the heat.

Exposed to greater temperature variations, this immobile life stage has faced strong evolutionary pressure to develop mechanisms to withstand temperature stress. Juvenile insects generally had a greater capacity for acclimating to rising temperatures than adult insects. Juveniles were able to modify their upper thermal limit by 11% on average, compared to 7% for adults.

But given that their capacity to acclimate is still relatively weak and may fall as an insect leaves this life stage, the impact is likely to be limited for adjusting to future climate change.

What does this mean for the future?

A weak ability to adjust to higher temperatures will mean many insects will need to migrate to cooler climates in order to survive. The movement of insects into new environments could upset the delicate balance of ecosystems.

Insect pests account for the loss of 40% of global crop production. As their geographical distribution changes, pests could further threaten food security. A UN report from 2021 concluded that fall armyworm populations, which feed on crops such as maize, have already expanded their range due to climate change.

A damaged corn crop following an attack by fall armyworms.
The fall armyworm is a damaging crop pest which is spreading due to climate change.
Alchemist from India/Shutterstock

Insect migration may also carry profound impacts on human health. Many of the major diseases affecting humans, including malaria, are transmitted by insects. The movement of insects over time increases the possibility of introducing infectious diseases to higher latitudes.

There have been over 770 cases of West Nile virus recorded in Europe this year. Italy’s Veneto region, where the majority of the cases originate, has emerged as an ideal habitat for Culex mosquitoes, which can host and transmit the virus. Earlier this year, scientists found that the number of mosquitoes in the region had increased by 27%.

Insect species incapable of migrating may also become extinct. This is of concern because many insects perform important ecological functions. Three quarters of the crops produced globally are fertilised by pollinators. Their loss could cause a sharp reduction in global food production.

The vulnerability of insects to temperature extremes means that we face an uncertain and worrying future if we cannot curb the pace of climate change. A clear way of protecting these species is to slow the pace of climate change by reducing fossil fuel consumption. On a smaller scale, the creation of shady habitats, which contain cooler microclimates, could provide essential respite for insects facing rising temperatures.The Conversation

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This blog is written by Hester Weaving, PhD Candidate in Entomology, University of Bristol. This article is republished from The Conversation under a Creative Commons license. Read the original article.

Hester Weaving

 

 

Telling the story of temperature

Posted on by janet.crompton

 

Image credit: Brigstow Institute

 

What is the most extreme temperature you have experienced?

Take your time and have a moment to think about it.

What was happening that day? Where were you? Which of your senses feature in the memory? Do any emotions come back to you?

While you’re thinking about it, I’ll tell you a little bit about the Temperature Life Stories project that I brought to COP26 on 1st November 2021.

We all experience temperature differently. The hottest day I remember might be very different from the hottest day you remember. Where we have been, when we were there and our specific circumstances at a given moment all affect the physical temperatures we have lived through. We have lived different temperature life stories.

Why does this matter? Even in the UK, in Glasgow where world leaders will be meeting for COP26, which we often think of as being cold and driech, some people will be at risk from extreme temperatures. Meanwhile, for some of us that have always lived in and become acclimatised to temperate climate zones, we may never appreciate the searing strength of heat experienced by others on a daily basis. What does “1.5 °C or 2 °C of global warming above pre-industrial temperatures” even mean for ourselves or individuals like us elsewhere in the world? Expressing our differences in circumstances in creative ways can help build new understandings and narratives of how we will live with temperature extremes in a warming world.

The Temperature Life Stories project explored these questions. By digging into global temperature data, the same data that informs global temperature targets, we produced temperature life story graphs for both individuals and our collective of research participants. As individuals we may never ‘feel’ the global average temperature, but our experience is part of that bigger picture. Memories and experiences of temperature were explored through poetry, with exercises designed by Caleb Parkin (Bristol City Poet, 2020-2022), and a host of other creative methods from the wonderful (and hidden) talents of our research participants.

Of course, there were and will be contradictions too. The temperature that the data says we lived through might not match what we remember as being the most extreme of days. But that’s okay: unreliable narrators are part of storytelling, aren’t they?

So back to COP26, what was Temperature Life Stories doing there? Of course, I would have loved to have run a series of poetry workshops with international COP26 delegates to take the temperature of the conference, but unfortunately for them, time is more of the essence. For that reason, I settled for a providing a tiny morsel of the project as a taster at the COP26 Green Zone.

I asked attendees to spare just one key memory from their temperature life story. Something that stood out for them. I asked for them to describe it in just a few lines, which could be as poetic or as factual as they pleased. I asked them where and when the memory occurred (being as specific as they could or wanted to be).

Often, relative warmth appears in the memories: perhaps not extreme in a global sense, but enough to seem unusual to locals and visitors alike in Yorkshire, the Hebridies, alpine and polar environments. Sometimes a lack of snow says as much as burnt brown grass. Travel appears regularly, making up a key part of temperature life stories – both the biting cold of northern climates after a lifetime spent nearer the tropics and vice versa. Even a momentary blast of air changing connecting flights in Qatar can give a glimpse of what temperatures are possible. We don’t expect similar blasts of heat to hit us getting off the train in Birmingham, but recent summer heatwaves featured regularly in memories too, and in with them that same wall of heat. Finally, there are emotions too: nostalgia about climates of home or childhood not being the same when people return after time spent away, sadness for places of significance lost in wildfires, weeks of unbroken heat and sunshine “both amazing and terrifying”.

Using this collection of memories, a bespoke map of experience, emotions and stories in space and time will be produced for the COP26 conference. An alternative story of a warming world. Keep an eye on Brigstow channels in the coming weeks for this.

So what about you? Have you been thinking of your memory of temperature? Maybe it was during last summer’s heatwave. Maybe you were on holiday. Maybe you were stuck in an unairconditioned bus in a traffic jam. Maybe the heat was emotional, not physical: passion, anger or embarrassment. There is no right or wrong answers – every story is different.

If you have a memory and want to add it to our collective COP26 story, you can add it here (https://forms.office.com/r/HnwesuwJqg). We’ll ask you for the same information as the Green Zone participants an all memories and data recorded is anonymous.

Together we can rewrite a new story of our warming world. One which shows our vulnerabilities, frailties and fears but also our lighter moments, hopes, achievements. We have a complex relationship with the weather and climate we experience. Sometimes a graph can’t say it all.

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This blog is written by Cabot Institute member Dr Alan Kennedy-Asser from Brigstow Institute funded Experimental Partnership “Temperature Life Stories: Feeling the heat”. This blog has been reposted from the Bristow Institute blog with kind permission from the Brigstow Institute. View the original blog.

Humanity is compressing millions of years of natural change into just a few centuries

Posted on by janet.crompton
The near future may be similar to the mid-Pliocene warm period a few million years ago.
Daniel Eskridge / shutterstock

Many numbers are swirling around the climate negotiations at the UN climate summit in Glasgow, COP26. These include global warming targets of 1.5℃ and 2.0℃, recent warming of 1.1℃, remaining CO₂ budget of 400 billion tonnes, or current atmospheric CO₂ of 415 parts per million.

It’s often hard to grasp the significance of these numbers. But the study of ancient climates can give us an appreciation of their scale compared to what has occurred naturally in the past. Our knowledge of ancient climate change also allows scientists to calibrate their models and therefore improve predictions of what the future may hold.

Recent climate changes in context.
IPCC AR6, chapter 2

Recent work, summarised in the latest report of the Intergovernmental Panel on Climate Change (IPCC), has allowed scientists to refine their understanding and measurement of past climate changes. These changes are recorded in rocky outcrops, sediments from the ocean floor and lakes, in polar ice sheets, and in other shorter-term archives such as tree rings and corals. As scientists discover more of these archives and get better at using them, we have become increasingly able to compare recent and future climate change with what has happened in the past, and to provide important context to the numbers involved in climate negotiations.

For instance one headline finding in the IPCC report was that global temperature (currently 1.1℃ above a pre-industrial baseline) is higher than at any time in at least the past 120,000 or so years. That’s because the last warm period between ice ages peaked about 125,000 years ago – in contrast to today, warmth at that time was driven not by CO₂, but by changes in Earth’s orbit and spin axis. Another finding regards the rate of current warming, which is faster than at any time in the past 2,000 years – and probably much longer.

But it is not only past temperature that can be reconstructed from the geological record. For instance, tiny gas bubbles trapped in Antarctic ice can record atmospheric CO₂ concentrations back to 800,000 years ago. Beyond that, scientists can turn to microscopic fossils preserved in seabed sediments. These properties (such as the types of elements that make up the fossil shells) are related to how much CO₂ was in the ocean when the fossilised organisms were alive, which itself is related to how much was in the atmosphere. As we get better at using these “proxies” for atmospheric CO₂, recent work has shown that the current atmospheric CO₂ concentration of around 415 parts per million (compared to 280 ppm prior to industrialisation in the early 1800s), is greater than at any time in at least the past 2 million years.

chart showing climate changes over history
An IPCC graphic showing climate changes at various points since 56 million years ago. Note most rows show changes over thousands or millions of years, while the top row (recent changes) is just a few decades.
IPCC AR6, chapter 2 (modified by Darrell Kaufman)

Other climate variables can also be compared to past changes. These include the greenhouse gases methane and nitrous oxide (now greater than at any time in at least 800,000 years), late summer Arctic sea ice area (smaller than at any time in at least the past 1,000 years), glacier retreat (unprecedented in at least 2,000 years) sea level (rising faster than at any point in at least 3,000 years), and ocean acidity (unusually acidic compared to the past 2 million years).

In addition, changes predicted by climate models can be compared to the past. For instance an “intermediate” amount of emissions will likely lead to global warming of between 2.3°C and 4.6°C by the year 2300, which is similar to the mid-Pliocene warm period of about 3.2 million years ago. Extremely high emissions would lead to warming of somewhere between 6.6°C and 14.1°C, which just overlaps with the warmest period since the demise of the dinosaurs – the “Paleocene-Eocene Thermal Maximum” kicked off by massive volcanic eruptions about 55 million years ago. As such, humanity is currently on the path to compressing millions of years of temperature change into just a couple of centuries.

Small animals in a forest
Many mammals, like these horse-ancestors ‘Eohippus’, first appeared after a sudden warm period 55 million years ago.
Daniel Eskridge / shutterstock

Distant past can held predict the near future

For the first time in an IPCC report, the latest report uses ancient time periods to refine projections of climate change. In previous IPCC reports, future projections have been produced simply by averaging results from all climate models, and using their spread as a measure of uncertainty. But for this new report, temperature and rainfall and sea level projections relied more heavily on those models that did the best job of simulating known climate changes.

Part of this process was based on each individual model’s “climate sensitivity” – the amount it warms when atmospheric CO₂ is doubled. The “correct” value (and uncertainty range) of sensitivity is known from a number of different lines of evidence, one of which comes from certain times in the ancient past when global temperature changes were driven by natural changes in CO₂, caused for example by volcanic eruptions or change in the amount of carbon removed from the atmosphere as rocks are eroded away. Combining estimates of ancient CO₂ and temperature therefore allows scientists to estimate the “correct” value of climate sensitivity, and so refine their future projections by relying more heavily on those models with more accurate climate sensitivities.

Overall, past climates show us that recent changes across all aspects of the Earth system are unprecedented in at least thousands of years. Unless emissions are reduced rapidly and dramatically, global warming will reach a level that has not been seen for millions of years. Let’s hope those attending COP26 are listening to messages from the past.

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This blog is written by Cabot Institute for the Environment member Dan Lunt, Professor of Climate Science, University of Bristol and Darrell Kaufman, Professor of Earth and Environmental Sciences, Northern Arizona University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Dan Lunt

 

 

Read all blogs in our COP26 blog series:

Will global food security be affected by climate change?

Posted on by janet.crompton

The Intergovernmental Panel on Climate Change (IPCC) has just released an important report outlining the evidence for past and future climate change. Unfortunately it confirms our fears; climate change is occurring at an unprecedented rate and humans have been the dominant cause since the 1950s. Atmospheric carbon dioxide (CO₂) has reached the highest level for the past 800,000 years, which has contributed to the increased temperatures and extreme weather we have already started to see.

As a plant scientist, I’m interested in the complicated effects that increased temperatures, carbon dioxide and changes in rainfall will have on global food security. Professor David Lobell and Dr Sharon Gourdji wrote about some of the possible effects of climate change on crop yield last year, summarised below alongside IPCC data.

Increased CO₂

Plants produce their food in a process called photosynthesis, which uses the energy of the sun to combine CO₂ and water into sugars (food) and oxygen (a rather useful waste product). The IPCC reports that we have already increased atmospheric CO₂ levels by 40% since pre-industrial times, which means it is at the highest concentration for almost a million years. Much of this has accumulated in the atmosphere (terrible for global warming) or been absorbed into the ocean (causing ocean acidification) however it may be good news for plants.

Lobell and Gourdji wrote that higher rates of photosynthesis are likely to increase growth rates and yields of many crop plants. Unfortunately, rapid growth can actually reduce the yields of grain crops like wheat, rice and maize. The plants mature too quickly and do not have enough time to move the carbohydrates that we eat into their grains. 

High temperatures

The IPCC predicts that by the end of the 21st century, temperatures will be 1.5C to 4.5C higher than they were at the start of it. There will be longer and more frequent heat waves and cold weather will become less common.

Extremely high temperatures can directly damage plants, however even a small increase in temperature can impact yields. High temperatures means plants can photosynthesise and grow more quickly, which can either improve or shrink yields depending on the crop species (see above). Lobell and Gourdji noted that milder spring and autumn seasons would extend the growing period for plants into previously frosty times of year allowing new growth periods to be exploited, although heat waves in the summer may be problematic.

 
Image credit: IPCC AR5 executive summary
 

Flooding and droughts

In the future, dry regions will become drier whilst rainy places will get wetter. The IPCC predicts that monsoon areas will expand and increase flooding, but droughts will become longer and more intense in other regions.

In flooded areas, waterlogged soils could prevent planting and damage those crops already established. Drought conditions mean that plants close the pores on the leaves (stomata) to prevent water loss, however this means that carbon dioxide cannot enter the leaves for photosynthesis and growth will stop. This may be partly counteracted by the increased carbon dioxide in the air, allowing plants to take in more CO₂ without fully opening their stomata, reducing further water loss and maintaining growth.

 
Image credit: IPCC AR5 executive summary
 

These factors (temperature, CO₂ levels and water availability) interact to complicate matters further. High carbon dioxide levels may mean plants need fewer stomata, which would reduce the amount of water they lose to the air. On the other hand, higher temperatures and/or increased rainfall may mean that crop diseases spread more quickly and reduce yields.

Overall Lobell and Gourdji state that climate change is unlikely to result in a net decline in global crop yields, although there will likely be regional losses that devastate local communities. They argue that climate change may prevent the increases in crop yields required to support the growing global population however.

The effect of climate change on global crop yields is extremely complex and difficult to predict, however floods, drought and extreme temperatures will mean that its impact on global food security (“when all people at all times have access to sufficient, safe, nutritious food to maintain a healthy and active life”) will almost certainly be devastating.

On the basis of the IPCC report and the predicted impact of climate change on all aspects of our planet, not just food security, it is critical that we act quickly to prevent temperature and CO₂ levels rising any further.  

 

This blog is written by Sarah Jose, Biological Sciences, University of Bristol

You can follow Sarah on Twitter @JoseSci
Sarah Jose

Warming up the poles: how past climates assist our understanding of future climate

Posted on by janet.crompton
Eocene, by Natural History Museum London

The early Eocene epoch (56 to 48 million years ago), is thought to be the warmest period on Earth in the past 65 million years. Geological evidence from this epoch indicates that the polar regions were very warm, with mean annual sea surface temperatures of > 25°C measured from geological proxies and evidence of a wide variety of vegetation including palm trees and insect pollinated plants found on land. Unfortunately, geological data from the tropics is limited for the early Eocene, although the data that does exist indicates temperatures only slightly warmer than the modern tropics, which are ~28°C.  The reduced temperature difference between the tropics and the poles in the early Eocene and the implied global warmth has resulted in the label of an ‘equable’ climate.

Simulating the early Eocene equable climate with climate models, however, has not been straightforward. There have been remarkable model-data differences with simulated polar temperatures are too cool and / or tropical temperatures that are too hot; or the CO2 concentrations used for a reasonable model-data match being outside the range of those measured for the early Eocene.

There are uncertainties in both geological evidence and climate models, and whilst trying to resolve the early Eocene equable climate problem has resulted in an improved understanding of geological data, there are uncertain aspects of climate models that still need to be examined.  Climate processes for which knowledge is limited or measurements are difficult, such as clouds, or which have a small spatial and temporal range are often simplified in climate models or parameterised. These uncertain model parameters are then tuned to best-match the modern observational climate record. This approach is not ideal, but it is sometimes necessary and it has been shown that the modern values of some parameters, such as atmospheric aerosols, may not be representative of past climates such as the early Eocene, with their removal improved the model-data match.

However, a climate model that can simulate both the present day climate and past more extreme climates without significant modification potentially offers a more robust method of understanding modern and future climate processes in a warming world. We have conducted research in which uncertain climate parameters are varied within their modern upper and lower boundaries in order to examine whether any of these combinations is capable of the above. And we have found one simulation, E17, from a total of 115, which simulates the early Eocene equable climate and improves the model-data match whilst also simulating the modern climate and a past cold climate, the last Glacial Maximum reasonably well.

This work hopefully highlights how paleoclimate modelling is a valuable tool in understanding natural climate variability and how paleoclimates can provide a test bed for climate models, which are used to predict future climate change.

This blog has been written by Nav Sagoo, Geographical Sciences, University of Bristol.

Why the Pliocene period is important in the upcoming IPCC report

Posted on by janet.crompton

Critical to our understanding of the Earth system, especially in order to predict future anthropogenic climate change, is a full comprehension of how the Earth reacts to higher atmospheric CO2 conditions. One of the best ways to look at what the Earth was like under higher CO2 is to look at times in Earth history when atmospheric CO2 was naturally higher than it is today. The perfect period of geological history is the Pliocene, which spans from 5.3 – 2.6 million years ago. During this time we have good evidence that the Earth was 2-3 degrees warmer than today, but other things, such as the position of the continents and the distribution of plants over the surface, was very similar to today.

There is therefore a significant community of oceanographers and climate modellers studying the Pliocene, many of whom were in Bristol last week for the 2nd Workshop on Pliocene climate, and one of the main points of discussion was the exact value of CO2 for the Pliocene.

80 top scientists from 12 countries gathered for the 2nd Workshop on Pliocene climate on 9-10 September 2013 at the University of Bristol

The imminent release of the first volume of the 5th assessments of the IPCC is also expected to include sections on Pliocene climate.

Today we published a paper in Philosophical Transactions of the Royal Society A which therefore represents an important contribution to the debate. Several records of Pliocene CO2 do exist, but their low temporal resolution makes interpretation difficult. There has also been some controversy about what these records mean, as some show surprisingly high variability, given what we understand about Pliocene climate.

We sampled a deep ocean core taken by the Ocean Drilling Program in the Carribean Sea. Cores such as this record the ancient envrionment as sediment collects over time like the progressive pages in a book, and by analysing the chemical composition of the layers a history of the Earth System can be discovered. The approach that Badger et al take is to use the carbon isotopic fractionation of photosynthetic algae, which has been shown to vary with atmospheric CO2.

What this study revealed is that atmospheric CO2 was actually quite low, at around 300 ppm for much of the warm period. What was also revealed was that CO2 was relatively stable, in contrast to previous work. This implies that in the Pliocene the Earth must have been quite sensitive to CO2, as small changes in atmospheric CO2 drove changes in climate. The study of Badger et al doesn’t explicitly reconstruct climate sensitivity but it does have important implications for future change.

The paper is published in a special volume of Philosophical Transactions of the Royal Society A, edited by Bristol scientists Dan Lunt, Rich Pancost, Andy Ridgewell and Harry Elderfield of Cambridge University. The volume is the result of the Warm Climates of the Past – A lesson for the Future? meeting which took place at the Royal Society in October 2011. The volume can be accessed here: http://bit.ly/PTA2001

This blog is written by Dr Marcus Badger, School of Chemistry, University of Bristol.
Marcus Badger

Oligocene discussion day

Posted on by janet.crompton

On the 16th of May, the University of Bristol held a half-day meeting devoted to the discussion of the Oligocene epoch (34 to 23 million years ago [Ma]). The Oligocene is a period of relative climate stability following the establishment of permanent ice sheets on Antarctica (34Ma). By the early Miocene (23Ma), atmospheric CO2 was low enough to allow the development of northern hemispheric ice sheets1. As a result, the Oligocene may have been the only time in the Cenozoic era (65-0Ma) during which a unipolar glaciation could exist.

Despite this, the Oligocene has received little attention from the Cenozoic palaeoclimate community. The aim of this event was to promote awareness of the Oligocene and encourage future research within this field.

Ellen Thomas, currently in Bristol on sabbatical from Yale, and David Armstrong-McKay, from the National Oceanography Centre (NOC), began the morning session with a series of talks devoted to the late Eocene and early Oligocene. Ellen discussed the Eocene-Oligocene transition (34Ma) from both a modern2 and historical3 perspective while David outlined the competing hypothesis put forward to explain the event4.   Dierderik Liebrand, also from the NOC, followed this with a talk on late Oligocene and early Miocene (24-19Ma) cyclostratigraphy5.  Following lunch, Bridget Wade gave an hour-long seminar on the Eocene-Oligocene boundary (34Ma)6 and the middle Oligocene (24-30Ma)7. Bridget’s talk doubled as a departmental seminar in the School of Geography.

Figure 1: A compilation of benthic foraminifera oxygen isotope values. During the Oligocene, this reflects a combination of ice volume and temperature7

The event was hosted by Gordon Inglis, a PhD student in the School of Chemistry, and was funded by Professor Rich Pancost (Global Change) and Professor Paul Valdes (School of Geography).

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For more information, please consult the following references:

  1. Zachos, et al. (2008) An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics: Nature, v. 451, p. 279-283
  2. Liu, Z. et al (2009) Global cooling during the Eocene-Oligocene transition: Science, v. 323, p. 1187-1190
  3. Kennett and Shackleton (1976) Oxygen isotopic evidence for the development of the psychrosphere 38 Myr ago: Nature, v. 260, p. 513-515
  4. Merico, A, et al. (2008) Eocene/Oligocene ocean de-acidifiation linked to Antarctic glaciation by sea level fall: Nature, v. 452, p. 979-982
  5. Liebrand, D., et al. (2011) Antarctic ice sheets and oceanographic response to eccentricity forcing during the early Miocene: Climate of the Past, v. 7, p. 869-880
  6. Wade, B., et al (2011) Multiproxy record of abrupt sea-surface cooling across the Eocene-Oligocene transition in the Gulf of Mexico: Geology, v. 40, p. 159-162
  7. Wade, B. And Palike, H., (2004) Oligocene climate dynamics: Palaeoceanography, v. 19, PA4019

Unprecedented melting of the Greenland Ice Sheet

Posted on by janet.crompton

Three Cabot Institute researchers provide their own insights on the highly publicised news story about the extent of melting observed on the Greenland Ice Sheet.

 

Chris Vernon, Ph.D student in the Bristol Glaciology Centre, studying the mass balance of the Greenland Ice Sheet

Last week NASA released new images of the Greenland ice sheet generated from satellite data showing that between the 8th and 12th of July 2012 the area of the ice sheet’s surface that was melting had increased from about 40 percent to an estimated 97 percent.  On average during the summer approximately half of the ice sheet experiences such surface melting and this expansion of the melt area to include the highest altitude and coldest regions was described as “unprecedented” by the scientists at NASA.  Such widespread melting has not been seen before during the past 34 years of satellite observations and melting at Summit Station, near the highest point on the ice sheet, has not occurred since 1889 based on ice core records.

The Greenland ice sheet gains mass from rain and snowfall and loses mass by solid ice discharge to the ocean (iceberg calving) and runoff of surface melt water.  During the period 1961-1990 these processes are thought to have been in balance with the ice sheet’s mass stable (Rignot et al., 2008).  During the last two decades, however, both ice discharge and liquid runoff have increased resulting in the ice sheet losing mass over this period at an accelerating rate (Velicogna, 2009, Rignot et al., 2011). Changes to these two processes have contributed approximately equally to recent mass loss (van den Broeke et al., 2009).  Whilst these NASA images do not provide data about how much snow and ice have melted or the direct effect on mass balance, they do indicate a significantly larger area of the ice sheet has been melting.

While this melting is an extreme weather event, associated with a series of unusually warm fronts passing over Greenland this summer, new research on the ice sheet’s albedo from Jason Box, a researcher with Ohio State University’s Byrd Polar Research Center, shows summer albedo has been decreasing over the last decade.  This reduced reflectivity, particularly at high elevations, is associated with warming related feedbacks and means more energy is absorbed at the surface for melting leading Box to suggest earlier this year that it is reasonable to expect 100% melt extent within another decade of warming (Box et al., 2012).  His latest albedo data are available here: http://bprc.osu.edu/wiki/Latest_Greenland_ice_sheet_albedo.

 

References (some behind paywall)

BOX, J. E., FETTWEIS, X., STROEVE, J. C., TEDESCO, M., HALL, D. K. & STEFFEN, K. 2012. Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers. The Cryosphere Discuss, 6, 593-634.

RIGNOT, E., BOX, J. E., BURGESS, E. & HANNA, E. 2008. Mass balance of the Greenland ice sheet from 1958 to 2007. Geophysical Research Letters, 35.

RIGNOT, E., VELICOGNA, I., VAN DEN BROEKE, M. R., MONAGHAN, A. & LENAERTS, J. 2011. Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise. Geophysical Research Letters, 38.

VAN DEN BROEKE, M., BAMBER, J., ETTEMA, J., RIGNOT, E., SCHRAMA, E., VAN DE BERG, W. J., VAN MEIJGAARD, E., VELICOGNA, I. & WOUTERS, B. 2009. Partitioning Recent Greenland Mass Loss. Science, 326, 984-986.

VELICOGNA, I. 2009. Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE. Geophysical Research Letters, 36.

 

Liz Stephens, Research Assistant in flood risk and co-author of article: ‘Communicating probabilistic information from climate model ensembles-lessons from numerical weather prediction’ soon to be published in WIRES Climate Change

The story of the unprecedented extent of melting of the Greenland ice sheet no doubt forms an important discussion point amongst scientists and those concerned about future climate change in the Arctic. However, for me it demonstrated the problems of clumsy communication; causing confusion that led some to think that the entire ice sheet had melted, and accusations of sensationalism from climate change sceptics (see http://sfy.co/a1AS for examples).

My main grievance is in the use of colour in the images. This may be the standard colour bar used by the NASA scientists, but it is too emotive for those not used to what is being referred to. At first glance the white area suggests ‘this is ice’, and the red, ‘we should be really scared that this is no longer white’.  In my opinion the colour white should not be used because it is evocative of what is ice rather than what is freezing ice, and so more neutral colours should be used to distinguish areas of melting from areas of freezing ice.

Additionally, I think that some of the language used is problematic; scientists need to be careful not to assume that people understand what is meant by the terms ‘ice sheet’, ‘area’, ‘surface’ etc., so that people don’t think that the entire volume of the ice sheet has disappeared.  Further, the subheading of the Guardian article – 97% surface melt over four days – is misleading, because the images refer to the area of the ice sheet that is undergoing melting and not the rate of melting itself, and so is not a direct indication of any volume of ice lost.

I also don’t like some of the phrasing used, particularly, ‘had thawed’. This is perhaps misleading, because if 97% of the ice sheet surface ‘had thawed’, then perhaps some might think that only 3% of the ice sheet surface would be left. I would probably go for an image caption of:

“The area of the Greenland ice sheet surface that was melting on July 8, left, compared to July 12th on the right.”

Subtle changes to the language can make it clear that this is an unusual weather event that could be indicative of climate change, rather than the ice sheet starting to disappear for good.

 

Jon Hawkings, Ph.D student in the Bristol Glaciology Centre, studies the chemistry of glacial meltwaters

During the course of my stay at the University of Bristol-led field site near Leverett glacier in south-west Greenland, I witnessed the start of what has since been identified as one of the most significant Greenland melt years over the past century. Over that time Leverett glacier’s subglacial drainage river, fed by the melting ice sheet surface together with stored meltwater from the bed, had altered from a small stream to a raging torrent. Although this is usual for a glacial river during a melt season in Greenland, the scale of change was unprecedented. Temperatures around camp far exceeded my expectations. I packed expedition gear expecting Arctic summer temperatures of around 10°C – a little higher than I had previously experienced in the northerly island archipelago of Svalbard. What I experienced were temperatures sometimes reaching 20°C. In our camp mess tent where we cooked and ate our meals the temperature would sometimes exceed 30°C – shorts and t-shirt weather – were it not for the thousands of mosquitoes that were thriving in the warmer weather. In June I often found myself processing samples in the science tent with beads of sweat on my brow.

When the discharge of the river exiting the margin of Leverett glacier hit around 500 m3/s in late June (over six times that of the average River Thames discharge when flowing through London), it was evident to all of the camp that the 2012 melt season was going to be much larger than in previous years. Over the period that Leverett catchment has been studied (2009-), river discharge usually reaches a high of 405 m3/s, and that was in early August – more than a month after this high (and therefore after a month’s more melt). At that time a bridge crossing the glacial meltwater river in the nearest town, Kangerlussuaq, approximately 25 km downstream (Watson River, fed by Leverett glacier and two other large glaciers in the area), had to be closed as the amount of water deemed it unsafe. I’ve recently been informed that discharge of Leverett river has subsequently hit more than 800 m3/s since I left camp – nearly twice that of the previous high. At the same time Watson River discharge at Kangerlussuaq was nearly double its previous high (3500 m3/s – more than the average discharge of the Nile), and in dramatic fashion has washed away the same bridge that was closed in 2010 (see http://www.guardian.co.uk/environment/picture/2012/jul/27/glaciers-flooding?newsfeed=true# and http://www.guardian.co.uk/environment/2012/jul/25/greenland-glacier-bridge-destroyed-video?newsfeed=true). Although a trend for higher melt season discharge has been observed, locals and scientists in the Kangerlussuaq area have all been taken aback by the magnitude of change experienced this year (http://www.ouramazingplanet.com/3254-greenland-flooding.html).

As this was my first field season in Greenland it was difficult for me to grasp the scale of change from previous years. Ben Linhoff, an isoptope geochemist from Woods Hole Oceanographic Institute in Massachusetts, USA, has been in camp during the 2011 and 2012 melt seasons, and was surprised by the difference in temperature and river size between the two years. He has documented the scale of change on his Scientific American blog (http://blogs.scientificamerican.com/expeditions/tag/following-the-ice/), and in a short video with Andrew Tedstone of the University of Edinburgh (http://www.whoi.edu/page.do?pid=80757&cl=82073&tid=5122). Ben comments that air temperatures in camp are substantially warmer than in 2011 and that glacial moraine deposited by Leverett glacial hundreds of years ago (possibly during the Little Ice Age) was being eroded by Leverett river – likely for the first time in decades. Dave Chandler, a University of Bristol researcher, camped within the ice sheet interior, 40km from the margin, has also been surprised by the warm temperatures. During the 2011 melt season he found that the temperature on the ice very rarely exceeded freezing at night. In contrast, the temperature has stayed above freezing throughout most of June and July at a similar point on the ice this year. Higher temperatures and the lack of freezing conditions on the ice sheet interior mean that more glacial ice has melted on the surface. This water is then thought to be routed to the bed through conduits know as moulins. At the bed the meltwater joins a large subglacial channel that flows under the ice and exits the glacier via a portal such as that which exists on Leverett glacier. The discharge of these subglacial rivers is thus indicative of the amount of ice melt.

 

 

 
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