Imaggeo on Mondays: A spectacular rainbow

Imaggeo on Mondays: A spectacular rainbow

Back in February 2005, François Dulac and Rémi Losno worked in the field in the very remote Kerguelen Islands (also known as the Desolation Islands). Located in the southern Indian Ocean they are one, of the two, only exposed parts of the mostly submerged Kerguelen Plateau.

Our work consisted in sampling atmospheric aerosols and their deposition by rain on the island, which is a meeting point for the roaring fourties (strong westerly winds found in the Southern Hemisphere between 40 and 50 degrees latitude) and the equally turbulent furious fifties (which occur at more southerly latitudes still).

The aim of the study was to evaluate the input of chemical elements (in very low concentrations) derived from continental soil dust, to the remote surface waters of the Southern Ocean. Given the scarcity of land areas at this latitude, the particles were expected to have travelled long distances before arriving at Kerguelen.

For example, iron – one of the major elements in the Earth crust and soils – is of particular interest in this oceanic area because it is a micro-nutrient that limits the productivity (and related CO2 sink) of the Southern Ocean.

The island’s air was often very clear and the horizontal visibility unusually high, as can be seen in the photo. It highlights that atmospheric aerosol concentrations (the mixture of solid and liquid particles from natural and anthropogenic sources) are very low in this environment. Field sampling and subsequent chemical analyses require constraining protocols adapted to ultra-traces in order to minimize contamination of samples and blank levels.

The unique atmospheric conditions also meant we had problems estimating distances: we often found ourselves underestimating the stretch between two points during our long walks between the base and our remote sampling stations. In addition, the combination of very clean air, low sun and fast running atmospheric low-pressure systems carrying water clouds at low-level over the cold ocean make rainbows relatively frequent.

Walking back to the base after changing samples, we were caught in a rain shower. Raindrops were almost falling horizontally due to the high wind speed, leaving the soil dry downwind of the stones and rocks lying on the ground. A few minutes later clouds had passed and sunlight reflecting and diffracting in the cloud droplets offered us a spectacular semi-circular rainbow.

It was particularly special because it displayed an infrequent combination of (i) the main, classic, bright rainbow that shows up at 138-140 degrees from the direction of the sunlight, (ii) a secondary rainbow due to double reflection of sunlight in droplets that appears higher on the horizon at an angle of about 127-130 degrees and with an inversion of colours compared to the main bow (red inside), and (iii) one supernumerary rainbow with pastel green, pink and purple fringes on the inner side of the primary bow.

This stacked rainbow is caused by interferences and was first explained in 1804 by Thomas Young. It indicates the presence of small, uniformly sized droplets.  The dark area visible here on the right-hand side between the primary and secondary rainbows is called the Alexander’s band, after the ancient Greek philosopher Alexander of Aphrodisias comments on Aristotle’s Meteorology treatise, published in the early 3rd century. It is due to a lack of light resulting from the fact that diffracted rays are either reflected back inside the primary rainbow (causing this area to be brighter) or outside the secondary rainbow.

By François Dulac, Laboratoire des Sciences du Climat et de l’EnvironnementCEA/LSCE, Gif-sur-Yvette, France

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at

Imaggeo on Mondays: A spectacular view of moss-covered rocks

Imaggeo on Mondays: A spectacular view of moss-covered rocks

Geology has shaped the rugged landscape of the Isle of Skye – the largest island of Scotland’s Inner Hebrides archipelago. From the very old Precambrian rocks (approximately 2.8 billion years old) in the south of the island, through to the mighty glaciers which covered much of Scotland as recently as 14,700 years ago, the modestly-sized island provides a snap-shot through Earth’s dynamic history.

A far cry from its modern cold, foggy and drizzly weather, back in the Jurassic age (250 million years ago, or so), the island was part of hot and dry desert. Over time, the sea encroached the low-lying plain, depositing sands and muds, and later sandstones, as well as thin limestones and shales across the island. The best examples of these rocks are found on the western side of the island, on the Strathaird Peninsula, but they can also be found on northern and eastern coastal stretches too.

Fast-forward to the Tertiary period (approximately 60 million years ago) and the landscape changed dramatically. The calm tropical waters had made way for explosive eruptions, which vented lavas from crack’s in the Earth’s crust. The lavas blanketed large areas of the north of the island, covering the sediments deposited back in the Jurassic.

Long after the surface explosive activity ended, the cracks in the Earth’s crust continued to serves as pathways for molten magma to move below the surface. In the norther part of the island, the lava travelled sideways, pushing its way between the layers of Jurassic sedimentary rocks. The black lavas, layered between the lighter coloured limestones and sandstones (as pictured above), are in stark contrast with the present-day moss-covered cliffs.

The most spectacular examples of this layering of volcanic units atop sedimentary rocks can be seen not far from where this photograph was taken, at Kilt Rocks, in south Staffin. Visitors to the area can also enjoy Mealt waterfall, where water from Mealt Loch (the Scottish word for lake) tumbles spectacularly into the Sound of Raasay.

Marius Ulm, who captured today’s featured image, is a civil/coastal engineer meaning a totally different aspect of the geology captured his attention:

“From a coastal engineering point of view, what is interesting is the missing moss-cover at the cliff’s toe. There is a line which marks the transition where the rocks stop being covered by moss also indicates how high water regularly rises due to tides. It tells us the tidal range (difference between low and high water) reaches up to 5 m in this area.”

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at


GeoPolicy: COP23 – key updates and outcomes

GeoPolicy: COP23 – key updates and outcomes

What is COP23?

Anthropogenic climate change is threatening life on this planet as we know it. It’s a global issue… and not one that is easily solved. The Conference of the Parties (COP) provides world leaders, policy workers, scientists and industry leaders with the space to share ideas and decide on how to tackle climate change and generate global transformative change. COP23 will predominantly focus on increasing involvement from non-state actors (such as cities and businesses), how to minimise the climate impacts on vulnerable countries and the steps that are needed to implement the Paris Climate Change Agreement.

Hold on – what’s the Paris Climate Change Agreement…?

You’ve probably heard about the Paris Climate Change Agreement (often shortened to just Paris Agreement) before, but what exactly does it refer to?

During the COP21, held in Paris during 2015, 175 parties (174 countries and the European Union) reached a historic agreement in response to the current climate crisis. This Paris Agreement builds on previous UN frameworks and agreements. It acknowledges climate change as a global threat and that preventing the Earth’s temperature from rising more than 2°C should be a global priority. The only nations not to sign the agreement were Syria, due to their involvement in a civil war and their inability to send a delegation, and Nicaragua, who stated that the agreement was insufficiently ambitious. Both of these countries have since signed the agreement while the US has unfortunately made headlines by leaving it.

The Paris Agreement states that there should be a thorough action plan that details how the Paris Agreement should be implemented by COP24 in 2018. There is still a long way to go before this action plan is finalised but COP23 was able to make a strong headway.

You can learn more about the UN climate frameworks and Paris Climate Change Agreement here or read more about COP21 here.

What did the COP23 achieve?

Today is the last official day of the COP23 and while it is often difficult to determine whether large scale political events are successful until after the dust has settled, there are some positive signs.

1. Making progress on the Paris Agreement action plan

The COP23 has been described as an implementation and ‘roll-up-your-sleeves’ kind of COP. While the COP21 resulted in a milestone agreement, the COP23 was about determining what staying below 2°C actually entails – what needs to be done and when. Some of the measures discussed to keep us under 2°C included: halving global CO2 emissions from energy and industry each decade, scrapping the $500 billion per year in global fossil fuel subsidies and scaling up carbon capture and storage technology. Simple, right?

These actions are all feeding into the detailed “rulebook” on how the Paris Agreement should be implemented which will be finalised at COP24.

2. Cities have stepped up to the plate

Mayors from 25 cities around the world have pledged to produce net zero emissions by 2050 through ambitious climate action plans which will be developed with the help of the C40 Cities network. Having tangible examples of what net zero emissions looks like and how it can be achieved will hopefully encourage other cities to follow suit. For this reason “think global, act local” initiatives are also picking up steam.

A new global standard for reporting cities’ greenhouse gas emissions has also been announced by the Global Covenant of Mayors for Climate and Energy. The system will allow cities to track their contributions and impacts using a quantifiable method. This will not only allow the UNFCCC to track the progress of cities more effectively but it may also result in a friendly competition with cities around the globe. It is also expected that all cities will have a decarbonisation strategy in place by 2020.

3. Phasing out coal by 2030?

19 Countries (ranging from Angola to the UK) have committed to phasing out unabated coal generation by 2030. Unabated coal-powered energy generation refers to the generation of electricity from a coal plant without the use of treatment or carbon capture storage technology (which generally reduces emissions from between 85-90%). With 40% of the world’s electricity currently being generated from coal, this commitment is clearly a huge step in the right direction that will hopefully put pressure on other nations and steer energy investment towards lower-emission sources.

4. There is the will to change… and the funding is there too!

One of the key features of the Paris Agreement was the amount of financial aid committed, 100 billion USD annually by 2020, from developed countries to support developing states mitigate their emissions. While this level of funding is still far from being reached, the aim to jointly mobilise 100 billion USD annually by 2020 was reiterated.

The French President, Emmanuel Macron, also announced that Europe will fill the funding gap in the IPCC budget that was left by the US’ withdrawal from the Paris Agreement.


The Green Climate Fund booth at the COP23 exhibition area. Credit: Jonathan Bamber


Other outcomes

Not only do COPs generally result in solid outcomes and agreements being made but they also go a long way to strengthen global unity and the belief that we are able to tackle climate change despite it being a huge and often daunting problem. This was also highlighted by Jonathan Bamber, the EGU President, who attended the event, “It was so impressive to see politicians, policy makers and scientists all striving hard to ensure that the world’s economies achieve the goals laid out in COP21 in Paris. There was a lot of energy for change and action and much less cynicism than I have witnessed at previous COP events. I really hope it helps steer us towards a more sustainable future“.

While these are just a few of the immediately obvious results from the COP23, I am sure that there will be more agreements and outcomes announced within the next few days. Keep tuned to the GeoPolicy Blog for more updates!

Further reading


GeoSciences Column: The dirty business of shipping goods by sea

“Above the foggy strip, this white arch was shining, covering one third of the visible sky in the direction of the ship's bow,” he explains. “It was a so-called white, or fog rainbow, which appears on the fog droplets, which are much smaller then rain droplets and cause different optic effects, which is a reason of its white colour.”

Shipping goods across the oceans is cost-effective and super-efficient; that’s why over 80% of world trade is carried by sea (according to the International Maritime Organisation). But the shipping industry also contributes significant amounts of air pollutants to marine and coastal environments.

A new study, published in the EGU’s open access journal Earth System Dynamics, reports on concentrations of sulphur, nitrogen, and particulate matter (PM), from 2011 to 2013, in the Baltic and North Seas – one of the busiest shipping routes in the world. The study aims to provide policy-makers with better knowledge about how shipping impacts local environments. The end-goal being better industry regulations and technology to make shipping more sustainable in the long-term.

The reality of shipping goods by sea

In the past two decades reduction pledges, like the Paris Climate Accord, and strict regulation have driven down air pollutants from land-based emissions across Europe, but greenhouse-gas emissions from the shipping industry are not subject to as strict international protocols.

And that’s a problem.

It is estimated that there are about half a million ships in operation at present, which together produce almost one billion tonnes of carbon dioxide each year (that’s more than Germany emits in the same period!). Over the past 20 years, emissions of pollutants from shipping in the Baltic Sea and North Sea have increased.

Worryingly, economic growth in the region means shipping is only set to increase in the future. In fact, the European Commission predicts that shipping emissions will increase between 50% and 250% by 2050.

Why should you care?

While cruising the high seas, ships emit a dangerous cocktail of pollutants. When burnt, their fuels emit sulphur dioxide and as ship engines operate under high pressure and temperature, they also release nitrogen oxides. Combined, they are also the source of particulate matter of varying sizes, made up of a mixture of sulphate (SO4), soot, metals and other compounds.

The authors of the Earth System Dynamics paper, led by Björn Clareman of the Department of Earth Sciences at Uppsala University, found that international shipping in the Baltic Sea and the North Sea was responsible for up to 80% of near-surface concentrations of nitric oxide, nitrogen dioxide and sulphur dioxide in 2013.

Total emissions of SOx and deposition of OXS (oxidized sulphur) from international shipping in the Baltic Sea and North Sea in 2011. From B.Claremar et al., 2017.

In addition, the team’s simulations show that PM from shipping was distributed over large areas at sea and over land, where many people will be exposed to their harmful effects. The highest concentrations are found along busy shipping lanes and big ports. In total, shipping was responsible for 20% of small sized PM (known as PM2.5) and 13% of larger particles (PM10) during the studied period.

These pollutants have harmful effects on human health: It is thought that living close to the main shipping lanes in the Baltic Sea can shorten life expectancy by 0.1 to 0.2 years. Sulphur oxides in particular, cause irritation of the respiratory system, lungs and eyes; while a 2007 study estimated that PM emissions related to the shipping industry cause 60,000 deaths annually across the globe.

Environmentally, the effects of shipping pollution are concerning too. Deposition of nitrate and sulphate causes the acidification of soils and waters. The brackish waters of the Baltic Sea make them highly susceptible to acidification, threatening diverse and precious marine ecosystems.

The current problem

Legislating (and then monitoring and enforcing) to limit the negative impact of shipping emissions is tricky given the cross-border nature of the industry. For instance, currently, there is no international regulation for the emission of PM. However, the International Maritime Organisation’s (as well as others; see Claremar, B., et al., 2017 for details of all regulations) does impose limits on sulphur and nitrogen emissions from ships (in some parts of the world).

Low-sulphur fuels and switching to natural gas are an effective way to control emissions. However, operators can also choose to fit their vessels with an exhaust gas treatment plant, or scrubber, which uses sea water to remove sulphur oxides – the by-products of high-sulphur fuels. So called open-loop scrubbers release the dirty exhaust water back into the ocean once the tank is cleaned. The practice is known to increase ocean acidification globally, but particularly along shipping lanes.

As of 2021, the transport of goods via the North and Baltic Seas will be subject to the control of nitrogen and sulphur emissions, which could decrease nitrogen oxide emissions by up to 80%. However, the study highlights that the continued use of scrubber technology will significantly offset the benefits of the new legislation. If cleaner alternatives are not implemented, total deposition of these harmful particles may reach similar levels to those measured during the 1970s to 1990s, when shipping emissions were largely unregulated.

By Laura Roberts Artal, EGU Communications Officer


Those who have an interest in this subject might want to contribute an EU Public consultation on the revision of the policy on monitoring, reporting and verification of CO2 emissions from maritime transport. The International Maritime Organisation (IMO) adopted the legal framework for the global data collection system (IMO DCS) in July 2017. This Consultation is now reviewing the situation and would like input on things such as the monitoring of ships’ fuel consumption, transparency of emission data and the administrative burden of the new system. While the Consultation is not specifically aimed toward scientists, it may interest EGU researchers who are working in the marine, climate and atmospheric sciences sectors.


Refences and resources

Claremar, B., Haglund, K., and Rutgersson, A.: Ship emissions and the use of current air cleaning technology: contributions to air pollution and acidification in the Baltic Sea, Earth Syst. Dynam., 8, 901-919,, 2017.

Lower emissions on the high seas. Nature, 551, 5–6, https://doi:10.1038/551005b, 2017

Corbett, J. J., Winebrake, J. J., Green, E. H., Kasibhatla, P.,Eyring, V., and Lauer, A.: Mortality from ship emissions: a global assessment, Environ. Sci. Technol., 41, 8512–8518, 2007.

Dashuan, T., and Shuli, N.: A global analysis of soil acidification caused by nitrogen addition, Environ. Res. Lett., 10, 024019, https://doi:10.1088/1748-9326/10/2/024019, 2015

What is Ocean Acidification? Ocean Facts by NOAA

Reducing emissions from the shipping sector, Climate Action by the European Commission