GeoLog | Anthropocene Archives

Living in a new Age

Robert Emberson September 14, 2018

The International Commission on Stratigraphy (ICS) has updated the timeline for Earth’s full geologic history, dividing the Holocene into three distinct periods. What does that mean for the Anthropocene? (Photo: East Khasi Hills in Megahalaya, India. The state is the namesake of the new geological age. Credit: Sai Avinash via Wikimedia Commons)

If you were suddenly told you were living in a different time period, what would your immediate reaction be? Changes in the calendar – even if it’s just terminology – have proven emotive in the past. In 1752, when England shifted from the Julian to Gregorian calendars, and 11 days were cut from 1752 to catch up, there are suggestions that civil unrest ensued.

Once again, the name of the period in which we live has recently changed; the Holocene is now subdivided into three parts, and we’re now living in the Meghalayan age, according to the International Commission on Stratigraphy (ICS). While there weren’t riots in the streets this time, it has proved controversial for some researchers.

The division of time into different epochs and eras is an important part of stratigraphy. While time marches on, ignorant of the names humans give to its divisions, defining periods like the Cretaceous and Jurassic helps scientists compare results from around the world, even where the fossil and sedimentary records differ. It also draws into sharp focus the globally significant differences between each period, often including the devastating mass-extinctions that mark the boundaries of a handful of these periods.

The Holocene has been for at least a century the term favoured to describe the period in which we live, with its beginning marked by the end of the last ice age. The date at which the Holocene began has been more and more closely defined by experts over time, to the now accepted value of approximately 11,650 calendar years before present. The Holocene period encompasses the emergence of human civilisation, and represents a period of relatively warmer, somewhat stable climate in comparison with the prior ice age.

After considerable debate, however, the ICS has decided that the Holocene should be further subdivided; now, the period from 11,650 and 8,200 years before present is the Greenlandian; the Northgrippian stretches from 8,200 to 4,200 years before present, and the Meghalayan defines the time between then and the present. Why did the Holocene need to be divided up as such? If it wasn’t broken, why fix it?

The International Commission on Stratigraphy (ICS) has updated the timeline for the earth’s full geologic history, dividing the Holocene into three distinct periods. What does that mean for the Anthropocene? (Credit: International Commission on Stratigraphy)

The distinctions between an ice age and a warmer period, also known as an interglacial period, are globally significant, and a good place to start when describing how Earth’s climate has changed over the past few hundred thousand years. The swings in global temperature and ice extent are large enough that we often ignore the subtler climate changes that occur within an interglacial or glacial period. However, sediment and fossil records from more recent eras are relatively well preserved (simply because those records have had less chance to be destroyed by other geological processes), and this enables us to explore more recent periods in finer detail. Looking within the Holocene, the transition between the Greenlandian and Northgrippian is marked by a dramatic cooling of the climate, while the Northgrippian – Meghalayan by an abrupt ‘mega-drought’ and cooling that affected the nascent agricultural societies developing at that time.

By dividing the Holocene into these bite-sized chunks, the ICS has drawn attention to these changes in the earth’s geological system and provided a global context to the climatic shifts of the last ten thousand years. It also helps emphasise that climate can and does change on timescales more abrupt that glacial-interglacial periods – something we need to remember when considering the likely effects of anthropogenic climate change.

The stalagmite from India with the GSSP for the base of the Meghalayan Stage (beginning of Meghalayan Age).https://t.co/ginCzDbKYS #Holocene #Meghalayan #GSSP pic.twitter.com/VV82P9AYVR

— IUGS (@theIUGS) July 14, 2018

So far, so scientific. So why have the changes upset some people? Well, there’s an elephant in the stratigraphic room that looms larger now that these changes have been officially ratified. If there’s anything that has marked out the Holocene as fundamentally different from other historical ages, it’s the growth of human society. In particular, we are now at a point in history where the actions of a specific species – humans – can have global effects on the stratigraphic record.

Humans have added large quantities of carbon dioxide to the atmosphere, sown radioactive isotopes across the oceans from nuclear bomb testing, and left waste deposits in environments from the top of Mt Everest to the middle of the Pacific Ocean. Many of these impacts could leave lasting traces in the sedimentary and fossil records, leading to some scientists calling for a new period of time – the Anthropocene. And this may not fit well with the ICS changes.

I spoke with Helmut Weissert, President of the EGU Stratigraphy, Sedimentology and Palaeontology Division about these changes, and he suggested that the new changes devised by the ICS might shift the debate over the Anthropocene, at least in the short term:

“I am quite worried. After the introduction of the new subdivisions I cannot see how the Holocene working group soon will vote for a further subdivision of the Holocene. The Anthropocene working group is confronted with a difficult task. I can envisage that the Anthropocene will be used as an informal term, not officially defined and introduced into the Stratigraphic Chart. I use the term regularly in my writing and in talks, everybody understands the term, I can explain how man is a geological agent. So, we may have to continue using an excellent term which is not yet properly defined, but most people do not care about the definition.”

The Anthropocene is certainly an effective term to draw the attention of the wider public to the impact of society on global geological cycles. But from a stratigraphic perspective, it offers a number of challenges. Where and when, for example, should the beginning of the period be set? Changes in geological periods require specific chemical changes that can be identified globally and an internationally agreed upon reference point – a physical location – that defines the base of the section. There are many potential examples that could be chosen to define the beginning of human interference in the natural system; ice cores showing the uptick in carbon dioxide at the industrial revolution, or ocean sediments attesting to nuclear bomb tests in the 1950s. But the choice of which section to pick is fraught.

Each stratigraphic division needs a reference point that defines the split between the prior time period and the one in question. Here, a ‘golden spike’ defines the base of the Ediacaran period (635 million years ago) in the Flinders Ranges of South Australia. (Credit: Bahudhara via Wikimedia Commons)

Moreover, preservation is a crucial part of stratigraphy; how much of human impact will in fact be preserved, especially after further anthropogenic changes? What if we clean up the environment? What if we dredge the ocean floor for rare metals, and, in doing so, extirpate the signal of the 1950s nuclear bomb tests? What if we melt the ice caps that record the incipient CO2 increases from the industrial revolution? Sure, these changes may be recorded elsewhere, but how can we be sure a reference stratigraphic section will remain intact?

And this brings us to a perhaps more philosophical point: what if the human impact on the natural system we see today is only a fraction of what is to come? Any Anthropocene we define now would be based only upon the impact to date, but future changes may make these seem small in comparison. What would come after the Anthropocene? The question echoes that of 20^th century philosophers, asking what comes after Post-Modernism? Perhaps instead of stratigraphy, we should look to written history and recorded data to better contextualise our impact.

Whether we end up defining our current era as the Meghalayan, the Anthropocene, or something else, it seems clear that the debate has drawn increased attention to the short-term climate changes – and in particular those driven by human intervention. A better public appreciation of our role within the natural system is a vital step in limiting damaging future climate change.

by Robert Emberson

Robert Emberson is a Postdoctoral Fellow at NASA Goddard Space Flight Center, and a science writer when possible. He can be contacted either on Twitter (@RobertEmberson) or via his website (www.robertemberson.com)

July GeoRoundUp: the best of the Earth sciences from around the web

Olivia Trani August 1, 2018

The Mars Express spacecraft probing the southern hemisphere of Mars. Credit: ESA/INAF/Davide Coero Borga.

Drawing inspiration from popular stories on our social media channels, as well as unique and quirky research news, this monthly column aims to bring you the best of the Earth and planetary sciences from around the web.

Major stories

Signs of water 55 million kilometres away

Last week scientists announced that they have found signs of existing water on Mars, offering new hope to the possibility of uncovering life on the Red Planet’s subsurface.

Radar observations made by the European Space Agency’s Mars Express satellite, suggest that a liquid lake is buried 1.5 kilometres beneath an ice cap situated near the south pole of Mars. Scientists think that this body of water is likely a few metres deep and 20 kilometres across, “nearly three times larger than the island of Manhattan,” reported Scientific American.

A schematic of how scientists used radar to find what they interpret to be liquid water beneath the surface of Mars. (Credit: ESA)

For the last 12 years the Mars Express satellite has been taking measurements of Mars by sending beams of radar pulses into the planet’s immediate interior. As these waves bounce back, the brightness of the reflection gives information on the material lying beneath Mars’ surface.

The researchers involved came across this discovery while analysing three years worth of data collected by the spacecraft.

“The bluer the colors, the brighter the radar reflection from the material it bounced off. The blue triangle outlined in black in the middle is the purported lake,” reported Science News.

Previous observations, made by NASA’s Curiosity rover for example, have found lake beds on the planet’s exterior, signifying that water may have flowed on Mars in the past. However, if this new finding is confirmed, it would be the first discovery of an existing stable body of water, one of the conditions believed to be necessary for life to thrive.

Context map: NASA/Viking; THEMIS background: NASA/JPL-Caltech/Arizona State University; MARSIS data: ESA/NASA/JPL/ASI/Univ. Rome; R. Orosei et al 2018 (distributed via ESA)

“We are not closer to actually detecting life,” said Manish Patel from the Open University to BBC News, “but what this finding does is give us the location of where to look on Mars. It is like a treasure map – except in this case, there will be lots of ‘X’s marking the spots.”

In their study, published in Science last week, the team remarked, “there is no reason to conclude that the presence of subsurface water on Mars is limited to a single location.”

Northern hemisphere feels the heat

In other news, the two words best describing the northern hemisphere this summer could very well “hot” and “dry,” as a series of heat waves have taken hold of several regions across Europe, Asia, North America and northern Africa. Many countries this month, including Japan, Algeria and Canada, have even experienced record-breaking temperatures.

A look at how this year’s heatwave has changed the colour of our vegetation in just one month (Credit: ESA)

For some places, above average temperatures and dry conditions have helped fuel devastating wildfires. More than 50 wildfires have swept through Scandinavian forests this summer, many well within the Arctic Circle, causing Sweden to request emergency aid from nearby countries.

Smoke rises from a wildfire in Enskogen. (Credit: Swedish Environmental Protection Agency/Maja Suslin)

A major wildfire also ignited near Athens, Greece this month, resulting in more than 85 death, with dozens still missing. While Greek officials claim that there are “serious indications” that the flames were brought upon by arson, they also note that the region’s climate conditions were extreme.

To many scientists, this onslaught of hot and dry conditions is a taste of what may soon become the norm. Of course, these conditions (in Europe, for example) are partly due to weather. “The jet stream – the west-to-east winds that play a big role in determining Europe’s weather – has been further north than usual for about two months,” reports the Guardian, leading to sweltering conditions in the UK and much of Europe, while leaving Iceland cool and stormy.

However, scientists say that heatwaves in the northern hemisphere are very much linked to global warming. “There’s no question human influence on climate is playing a huge role in this heatwave,” said Myles Allen, a climate scientist at the University of Oxford, to the Guardian in the same article.

A recent assessment on the ongoing heat wave in Europe reports that these conditions are more likely to occur due to climate change. “The findings suggest that rising global temperatures have increased the likelihood of such hot temperatures by five times in Denmark, three times in the Netherlands and two times in Ireland,” said Carbon Brief.

What you might have missed

Geologists have given a name to Earth’s most recent chapter: Meghalayan Age. The announcement was made earlier this month when the International Union of Geological Sciences updated the International Chronostratigraphic Chart, which classifies Earth’s geologic time scale. The new update has divided the Holocene Epoch (the current time series which began 11,700 years ago, when the Earth was exiting its last ice age) into three stages: the Greenlandian, the Northgrippian, and then Meghalayan.

The latest version of the International Chronostratigraphic Chart/Geologic Time Scale is now available! New #Holocene subdivisions: #Greenlandian (11,700 yr b2k)#Northgrippian (8326 yr b2k)#Meghalayan (4200 yr before 1950) https://t.co/IhvZHfHnWh #ChronostratigraphicChart208 pic.twitter.com/8Pf9Dnct7h

— IUGS (@theIUGS) July 13, 2018

The Meghalayan Age represents the time between now and 4,200 years ago, when a mega-drought led to the collapse of many civilisations across the world. The middle phase, Northgrippian (from 8,300 years ago to 4,200 years ago), is marked by an sudden cooling event brought on by massive glacial melt in Canada that affected ocean currents. Finally the oldest phase, Greenlandian, (from 11,700 years ago to 8,300 years ago) is marked by the end of the last ice age.

The recent update has created some unrest in the geosciences community. “There is still an active debate about assigning a new geologic slice of time to reflect specifically the influence of humans on the planet,” reported BBC News. Some scientists say that the new divisions conflict with the current work being done on proposing a new epoch classification, famously called the ‘Anthropocene,’ which would be marked by the beginning on significant human impact on Earth’s geology and ecosystems.

Links we liked

Ursula B. Marvin (1921–2018): this bold mineralogist and feminist bucked norms that deemed geology unsuited for women
Updating maps swiftly after natural disasters: satellite imagery and artificial intelligence could help speed disaster relief by quickly mapping landslides
Does soil really affect wine’s flavour?: The idea that a vineyard’s soil lends a wine its flavour is becoming increasingly popular – but is there any scientific basis?
How Kilauea—and other volcanoes—produce amazing and frightful weather: Volcanic tornadoes, choking fog, “laze,” lightning, hail, waterspouts and even frost are created above hot eruptions

The EGU story

This month we released not one but two press releases from research published in our open access journals. The findings from both studies have important societal implications. Take a look at them below.

New study: oxygen loss in the coastal Baltic Sea is “unprecedentedly severe”

The Baltic Sea is home to some of the world’s largest dead zones, areas of oxygen-starved waters where most marine animals can’t survive. But while parts of this sea have long suffered from low oxygen levels, a new study by a team in Finland and Germany shows that oxygen loss in coastal areas over the past century is unprecedented in the last 1500 years. The research was published in the European Geosciences Union journal Biogeosciences.

New study puts a figure on sea-level rise following Antarctic ice shelves’ collapse

An international team of scientists has shown how much sea level would rise if Larsen C and George VI, two Antarctic ice shelves at risk of collapse, were to break up. While Larsen C has received much attention due to the break-away of a trillion-tonne iceberg from it last summer, its collapse would contribute only a few millimetres to sea-level rise. The break-up of the smaller George VI Ice Shelf would have a much larger impact. The research was published in the European Geosciences Union journal The Cryosphere.

And don’t forget! To stay abreast of all the EGU’s events and activities, from highlighting papers published in our open access journals to providing news relating to EGU’s scientific divisions and meetings, including the General Assembly, subscribe to receive our monthly newsletter.

Geoscience hot topics – Part II: the Earth as it is now and what its future looks like

Laura Roberts-Artal December 11, 2015

The Waxing Earth from a Geostationary Perspective. Credit: Maximilian Reuter (distributed via imaggeo.egu.eu)

What are the most interesting, cutting-edge and compelling research topics within the scientific areas represented in the EGU divisions? Ground-breaking and innovative research features yearly at our annual General Assembly, but what are the overarching ideas and big research questions that still remain unanswered? We spoke to some of our division presidents and canvased their thoughts on what the current Earth, ocean and planetary hot topics will be.

Because there are too many to fit in a single post we’ve brought some of them together in a series of posts which will tackle three main areas. The first post focused on the Earth’s past and its origin, while today’s post will focus on the present Earth and its future. The final post of the series will explore where our understanding of the Earth and its structure is still lacking. We’d love to know what the opinions of the readers of GeoLog are on this topic too, so we welcome and encourage lively discussion in the comments!

Sustainable development

As populations across the globe continue to grow, geoscientists have a key role to play in sustainable development. The demands placed on planet Earth to supply our societies with anything from drinking water to food and energy are ever rising. Managing these resources in a way that ensures we can meet the needs of current and future generations is one of the biggest challenges faced by scientists and policy makers worldwide.

Humanity’s pursuit of a sustainable future, where our activities do not contribute to increased greenhouse gas emissions to the atmosphere (something which has be high on policymakers agenda’s recently) will open new, important, avenues of research. Goals need to be achieved so that food, energy and water resources are available for future generations and methods must be found to exploit resources in a way that minimises the impact on the environment.

Producing fuel for a growing population
The boundaries of technology and our knowledge of where and how resources can be exploited will be pushed as the demands for energy increase. Traditional oil and gas resources will continue to be exploited, but new emerging technologies and fuel sources will mean a shift to lesser known research areas.

Angelo De Santis, President of the Earth Magnetism and Rock Physics (EMRP) Division adds that: “Such fields as rock physics, geomagnetism and rock magnetism will have a role to play in future resource exploration.”

Perusing the programme of the 2016 General Assembly gives a flavour of some of the emerging avenues of research in this field. Take for instance deep geothermal reservoirs: this little know source of renewable energy provides an alternative to conventional fuel sources, with the potential to reduce fossil-fuel consumption as well as curbing greenhouse-gas emissions. Yet, the understanding of how to engineer the reservoirs so that they remain productive and safe over long time-scales is still being developed, and having better handle on the rock physics and mechanics of the reservoirs would help in this regard.

“Geothermal energy methods“. Licensed under Public Domain via Commons.

Ensuring the integrity of any reservoir be it conventional or unconventional, requires collaboration. Seismology has a large part to play here too. Away from the well-known and exciting work being carried out on understanding earthquakes, the field of ‘ambient noise’ seismic data has the potential to revolutionise our understanding of Earth dynamics and can be applied to monitoring changes in zones of natural and induced (minor tremors caused by human activity) seismicity in oil & gas reservoirs and also geothermal fields, highlights P. Martin Mai, President of the Seismology (SM) Division.

In seismology, ambient noise, or “background noise” recorded on seismic instruments refers to the seismic energy that is continuously generated by various natural (e.g. ocean waves, wind, etc) and man-made (traffic, industrial activities) processes. Classically, seismology wants to avoid any noise contamination of seismic recordings, as the noise masks or even destroys the desired “deterministic” signals from earthquakes or exploration-driven seismic excitations. However, experimental and theoretical work over the last ~10 yrs has shown that the mathematically predicted relation between “noise” and the Earth elastic properties can be applied to use “noise” for making inference about Earth structure. “Ambient noise” studies in seismology have been used, for instance, to infer properties of the Earth crust and how it may change on small scales (like in earthquake fault zones) over time, but ‘ambient noise tomography’ also helps to unravel Earth properties in the upper mantle (down to ~150 km depth). Research in ambient-noise seismology requires dense seismic recording networks that continuously record the subtle movements of the ground. Advanced processing and interpretation techniques then allow to also, for instance, monitor the processes within, and thus the state, or geothermal or oil & gas reservoirs.

Raw materials

A new rural landscape in Irpinia. Credit: Sabina Porfido (distributed via imaggeo.egu.eu)

According to Chris Juhlin, President of Energy, Resources and Environment (ERE) Division, it will be crucial for scientists in this field not only to focus on establishing how energy can be produced in a way that will continue to allow societies to live comfortably, but also establish where the resources to produce and supply energy will come from.

The advantages of exploiting resources, such as solar, wind, geothermal energy and nuclear energy over fossil fuels are clear: their emissions of greenhouse gases to the atmosphere are limited. That being said, an often overlooked fact is that they still require natural resources in order to operate.

Juhlin uses wind turbines as an example to illustrate the point: “Wind turbines require significant amounts of rare earth metals, as well as steel, to be built. These metals need to be mined and the mining operation produces CO2.”

Both mining of metals and storage of nuclear waste require that sophisticated geological, geochemical and geophysical surveying methods are available. Not only that, when finding and choosing new locations to mine for resources and store waste, looking at the bigger picture is also important. How these human activities will affect the ecosystems in which they take place will take on greater significance as the loss of habitats and biomes increases.

Juhlin emphasises that: “It is important to understand how a decision at local level may affect the energy balance on a global level.”

Defining a new geological epoch – The Anthropocene

That humans will leave their mark on Earth is undeniable. Human kind has already caused extinctions, polluted oceans and the atmosphere, as well as influenced land use and biodiversity. But pin-pointing the exact time at which our actions became a major geological agent is a source of heated debate.

Traditionally, new epochs are defined by an abrupt change in the chemistry of rock strata which signifies the occurrence of a major geological or palaeontological event. However, in the case of defining the age of humans, the Anthropocene, the lack of a rock record makes applying this traditional approach difficult.

Nevertheless, since it was introduced in 1980s and popularised in the past decade or so, the notion of the Anthropocene epoch has been gaining momentum and opened up further research questions.

Helmut Weissert, President of the Stratigraphy, Sedimentology, and Palaeontology (SSP) Division, says that comparing the role humans have played versus past natural variations is becoming increasingly important. Take an example: what role have humans played in accelerated soil erosion vs. natural variations? Equally, what role has humankind played in affecting the global biogeochemical cycles? By comparing current changes with natural changes recorded in marine and lake sediments we may better understand the role humans have played in shaping the modern Earth.

An exotic solution?

The scientific consensus is that in order to minimise our impact on the planet, while at the same time moving towards zero net emissions of greenhouse gases by the second half of this century, a combination of approaches are needed. While renewable resources and nuclear energy will provide energy which has minor contributions to greenhouse-gas emissions, it is just as important to reduce and find ways to deal with emissions from burning fossil fuels (think carbon capture and storage).

Sketch illustrating the process of cloud seeding. Cloud seeding by DooFi. Distributed via Wikimedia

Geoengineering might provide a more exotic solution to the problem. The premise behind it is to use technology to counter the effects of a warming climate. Proposed solutions include reflecting sunlight into space to cool the planet, cloud seeding, scrubbing CO2 out of the atmosphere, … But at this stage, the majority are deemed unrealistic; not to mention that there is an ongoing ethical debate as to whether they should be used at all and that the consequences of their implementation are also largely unclear

So it seems, the presence of human kind on Earth has paved the way for an astonishing period of research, not only in the geosciences but also in other fields, fuelling an exciting opportunity for cross-disciplinary investigation. And the time is most certainly now, if we are to minimise the mark we leave on the planet while at the same time ensuring a sustainable future for generations to come.

By Laura Roberts Artal, EGU Communications Officer in collaboration with EGU Division Presidents

Next time, in the Geosciences hot topics short series, we’ll be looking at our understanding of the Earth as we know it now and how we might be able to adapt to the future.

GeoTalk: Nick Dunstone, an outstanding young scientist

Laura Roberts-Artal December 17, 2014

Nick Dunstone, the winner of a 2014 EGU Division Outstanding Young Scientists Award, who studies the Earth’s climate and atmosphere, including how they are impacted by natural variation and anthropogenic emissions talks to Bárbara Ferreira, the EGU Media and Communications Manager, in this edition of GeoTalk. This interview was first published in our quarterly newsletter, GeoQ.

First, could you introduce yourself and tell us a bit about what you are working on at the moment?

My name is Dr Nick Dunstone and I am a climate scientist working at the Met Office Hadley Centre in the UK. Here I work within the Monthly to Decadal Climate Prediction group which focuses on developing regional climate prediction capability for all areas of the globe. The monthly to decadal timescale (often referred to as ‘near-term’ prediction) is an emerging and challenging field of climate prediction which attempts to span the void between shorter term weather forecasts (days to weeks) and longer term climate projections (many decades to centuries) using numerical climate models. So, similar to a weather forecast, near-term climate predictions are initialised close to the observed state of the climate and yet, similar to a climate projection; they also include the projected changes in external forcings such as greenhouse gases, anthropogenic aerosols and the solar cycle. Much of my research over the last few years has concerned the amount of predictability in the climate system arising from slowly varying internal processes (for example, slowly varying ocean dynamics) versus how much is driven by external forcings (e.g. anthropogenic emissions).

Earlier this year, you received a Division Outstanding Young Scientists Award for your work on the coupled ocean-atmosphere climate system and its predictability. Could you tell us a bit more about the research you have developed in this area?

Some of my work has considered the role of internal ocean dynamics in driving predictability in the atmosphere. Often we think of the tropical regions as being the engine of the climate system, driving some of the variability in the mid-latitude atmosphere. However, this is not always the case and especially on longer timescales (multi-annual to decadal), the mid-latitudes can drive tropical variability. My colleagues and I illustrated this using a set of idealised climate model experiments that tested the impact of initialising the state of different parts of the world’s oceans. The results showed that it was key to initialise the ocean’s sub-surface temperature and salinity (and so density) in the high latitude North Atlantic to have skill in predicting the multi-annual frequency of model tropical Atlantic hurricanes. This is intimately linked to correctly initialising the model’s Atlantic meridional overturning circulation, and to the question of what sub-surface ocean observations would be needed to do this. I have also worked on how external forcings, such as anthropogenic emissions from industrial pollution, may impact regional climate variability.

A lot of the work you have developed focuses on the anthropogenic impact on the Earth’s atmosphere and climate. What does your research tell us about the extent of the impact of human activities on the Earth’s natural systems?

In the last couple of years we have examined the possible impact of anthropogenic aerosol emissions on multi-decadal changes in climate variability. We found that when the latest generation of climate models include the historical inventory of anthropogenic aerosol emissions, they are capable of better reproducing the phases of observed multi-decadal variability in North Atlantic temperatures. In our Met Office Hadley Centre climate model, we find that this is principally due to the inclusion of aerosol-cloud interactions. When aerosols are present in clouds they can modify the cloud droplet size (known as the 1^st aerosol indirect effect), increasing the reflectivity of the clouds and hence decreasing the amount of solar radiation reaching the ocean surface. Variations in aerosol emissions from North America and Europe due to socioeconomic changes (e.g. rapid post-war industrialisation in the 1950s and 1960s and then the introduction of clean-air legislation in the 1970s and 1980s) then drive fluctuations in North Atlantic temperatures in our climate model. Furthermore, we also showed that the frequency of model North Atlantic hurricanes is also driven primarily by anthropogenic aerosol changes and that it is in phase with the observed changes in Atlantic hurricane frequency. Further work needs to be done to understand if this aerosol mechanism is truly operating in the real world. If so, then our work suggests a significant role for humans in unwittingly modulating regional climate variability (especially in the North Atlantic) throughout the 20^th century. This also has profound implications for the next few decades, as North America and Europe continue to clean-up their industrial aerosol emissions, whilst the impact of short-term increases in aerosol emissions from developing economies (e.g. China and India) also needs to be studied. Of course, at the same time, the signal of greenhouse gas warming is likely to become more dominant with associated climate impacts.

What is your view on having the Anthropocene accepted as a formal geological epoch? Do you think there are scientific grounds to define the Anthropocene in such a way, or at least in what your research area is concerned?

This is an interesting question but not one that I’ve thought very much about! From a climate scientist perspective, I think it is fairly obvious that we have entered a time when the human fingerprint extends to all (or at least very nearly all) environments on Earth. We see the fingerprint in the concentration of greenhouse gases and water vapour in the atmosphere, land and sea-surface temperatures, deep-ocean warming, ocean sea-level rise, ocean acidification, etc… If physical climate changes alone were the main criterion, then surely there would be no doubt that we have entered a new epoch. Beyond this though, the wider Earth biological system is also being impacted by human activity. For example, previous epochs have also been defined based upon mass species extinction, so there may also be a case here for viewing the Anthropocene as a time when the actions of humanity have led to species extinction. Of course there are then questions about how to define the beginning of this new epoch. Many suggest a geophysical marker such as the 1940s and 1950s when radionuclides from nuclear detonations first became present. Or would it be when the atmospheric CO2 concentration started to rise above pre-industrial levels in the early nineteenth century? Or would it be earlier still, when we started significantly altering the land-surface via large-scale deforestation? Then when would the Anthropocene end? Could we envisage a time in the future when we effectively remove our influence on the climate system, e.g. returning the atmospheric constituents to pre-industrial ratios? Or, rather more grimly, would the Anthropocene only truly be over when our species itself becomes extinct? Whilst these are very interesting ‘dinner-table’ type discussions, from a working climate scientist viewpoint the definition seems largely academic and we’d probably be better off investing our time into researching how we are changing the planet and predicting the associated climate impacts!

On a different topic, according to your page on the Met Office website, you started your career in science as an astrophysicist. Could you tell us a bit about how you made the transition from astrophysics to climate science, highlighting any difficulties you may have had with making such a career change and how you overcame them? What advice would you have for young scientists looking to make a similar move?

To a large extent I think ‘science is science’! Many of the skills are very transferable, especially between physical, computationally based, subjects, where numerical modelling skills are essential. I’ve now met a surprising number of climate scientists who are ex-astronomers, or from some other branch of physics. I think what you need most of all is the drive for learning new things, and making new discoveries, about the physical world in which we live. I found that this is very transferable, applying equally to astrophysics and climate science. I think you settle into a subject slowly and even though I’ve been working in climate science for over 6 years now, I still have lots to learn about our existing understanding of climate system, and that’s exciting. The important thing to realise however, is that you can still make important and useful contributions to a new field quite quickly, especially one as broad as climate science, given the right guidance or supervision.

Finally, could you tell us a bit about your future research plans?

We need to progress both our understanding of natural (internal) variability in climate models and improve the fidelity of important climate teleconnections (processes linking variability in one part of the climate system with climate impacts in a remote region). At the same time we need to progress our understanding of the relative roles of external vs internal forcing in driving variability and extremes in the climate system. On the shorter (seasonal) timescales I am interested in what drives the year-to-year variability in the winter North Atlantic Oscillation, which our latest Met Office seasonal climate prediction systems can now predict with surprisingly good skill. Much of this work I hope to develop during my new post as manager of the Global Climate Dynamics group in the Met Office Hadley centre that I will start in December.

Interview conducted by Bárbara Ferreira

EGU Media and Communications Manager and GeoQ Chief Editor