Geoengineering – how could we detect its cooling effect?

Eunice LoLeave a comment

Detecting sulphate aerosol geoengineering with different methods
Lo, Y. T. E. et al. Detecting sulphate aerosol geoengineering with different methods. Sci. Rep. 6, 39169; doi: 10.1038/srep39169 (2016).

Email: y.t.e.lo@pgr.reading.ac.uk

Sulphate aerosol injection (SAI) is one of the geoengineering proposals that aim to reduce future surface temperature rise in case ambitious carbon dioxide mitigation targets cannot be met.  Climate model simulations suggest that by injecting 5 teragrams (Tg) of sulphur dioxide gas (SO2) into the stratosphere every year, global surface cooling would be observed within a few years of implementation.  This injection rate is equivalent to 5 million tonnes of SO2 per year, or one Mount Pinatubo eruption every 4 years (large volcanic eruptions naturally inject SO2 into the stratosphere; the Mount Pinatubo eruption in 1991 led to ~0.5 °C global surface cooling in the 2 years that followed (Self et al., 1993)).  However, temperature fluctuations occur naturally in the climate system too.  How could we detect the cooling signal of SAI amidst internal climate variability and temperature changes driven by other external forcings?

The answer to this is optimal fingerprinting (Allen and Stott, 2003), a technique which has been extensively used to detect and attribute climate warming to human activities.  Assuming a scenario (G4, Kravitz et al., 2011) in which 5 Tg yr-1 of SO2 is injected into the stratosphere on top of a mid-range warming scenario called RCP4.5 from 2020-2070, we first estimate the climate system’s internal variability and the temperature ‘fingerprints’ of the geoengineering aerosols and greenhouse gases separately, and then compare observations to these fingerprints using total least squares regression.  Since there are no real-world observations of geoengineering, we cross-compare simulations from different climate models in this research.  This gives us 44 comparisons in total, and the number of years that would be needed to robustly detect the cooling signal of SAI in global-mean near-surface air temperature is estimated for each of them.

Figure 1(a) shows the distribution of the estimated time horizon over which the SAI cooling signal would be detected at the 10% significance level in these 44 comparisons.  In 29 of them, the cooling signal would be detected during the first 10 years of SAI implementation.  This means we would not only be able to separate the cooling effect of SAI from the climate system’s internal variability and temperature changes driven by greenhouse gases, but we would also be able to achieve this early into SAI deployment.

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Figure 1: Distribution of the estimated detection horizons of the SAI fingerprint using (a) the conventional two-fingerprint detection method and (b) the new, non-stationary detection method.

The above results are tested by applying a variant of optimal fingerprinting to the same problem.  This new method assumes a non-stationary background climate that is mainly forced by greenhouse gases, and attempts to detect the cooling effect of SAI against the warming background using regression (Bürger and Cubasch, 2015).  Figure 1(b) shows the distribution of the detection horizons estimated by using the new method in the same 44 comparisons: 35 comparisons would require 10 years or fewer for the cooling signal to be robustly detected.  This shows a slight improvement from the results found with the conventional method, but the two distributions are very similar.

To conclude, we would be able to separate and thus, detect the cooling signal of sulphate aerosol geoengineering from internal climate variability and greenhouse gas driven warming in global-mean temperature within 10 years of SAI deployment in a future 5 Tg yr-1 SAI scenario.  This could be achieved with either the conventional optimal fingerprinting method or a new, non-stationary detection method, provided that the climate data are adequately filtered.  Research on the effects of different data filtering techniques on geoengineering detectability is not included in this blog post, please refer to the article cited at the top for more details.

This work has been funded by the University of Reading.  Support has also been provided by the UK Met Office.

Note: So how feasible is a 5 Tg yr-1 SO2 injection scenario?  Robock et al. (2009) estimated the cost of lofting 1 Tg yr-1 SO2 into the stratosphere with existing aircrafts to be several billion U.S. dollars per year. Scaling this to 5 Tg yr-1 is still not a lot compared to the gross world product. There are practical issues to be addressed even if existing aircrafts were to be used for SAI, but the deciding factor of whether to implement sulphate aerosol geoengineering or not would likely be its potential benefits and side effects, both on the climate system and the society. 

 

References

Self, Stephen, et al. “The atmospheric impact of the 1991 Mount Pinatubo eruption.” (1993).

Allen, M. R., and P. A. Stott. “Estimating signal amplitudes in optimal fingerprinting, Part I: Theory.” Climate Dynamics 21.5-6 (2003): 477-491.

Kravitz, Ben, et al. “The geoengineering model intercomparison project (GeoMIP).” Atmospheric Science Letters 12.2 (2011): 162-167.

Bürger, Gerd, and Ulrich Cubasch. “The detectability of climate engineering.” Journal of Geophysical Research: Atmospheres 120.22 (2015).

Robock, Alan, et al. “Benefits, risks, and costs of stratospheric geoengineering.” Geophysical Research Letters 36.19 (2009).

AGU Fall Meeting – Posters and Protests

Rebecca Emerton1 Comment

Email: r.e.emerton@pgr.reading.ac.uk

From 12th to 16th December 2016, the annual American Geophysical Union (AGU) Fall Meeting took place at the Moscone Centre in San Francisco. AGU remains the largest Earth and Space Science conference in the world with more than 25,000 scientists.

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Overlooking the Poster Hall in Moscone South

At the 2016 Fall Meeting, I was one of around 8000 students who arrived in San Francisco to present one of the 15,000 posters that would be displayed over the course of the week. While I knew that AGU is one of the largest Earth science conferences, and had indeed spent hours on the plane fine-tuning my schedule to choose which of the ~200 hydrology sessions (let alone the meteorology sessions also related to my work) I would attend, the scope and diversity of the research presented throughout the week really sunk in when I stood on the mezzanine overlooking the poster hall on the first day of the conference.

I was lucky enough to be awarded an AGU student travel grant in order to present my latest PhD research that I’ve been working on at the University of Reading, in collaboration with the European Centre for Medium-Range Weather Forecasts (ECMWF), and funded by NERC as part of the SCENARIO Doctoral Training Partnership. My work maps the historical probability of increased (or decreased) flood hazard across the globe during ENSO (El Niño and La Niña) events, using the first 20th Century ensemble river flow reanalysis, created at ECMWF as part of this work. But more on that another time!

blogpostscreenshotUnlike other conferences I’d presented at, the poster sessions at AGU span half a day – while you are only expected to be there to discuss the work for two hours, it’s inevitable that you get caught up in discussion and I saw many presenters (myself included) who stuck by their poster for the full 4.5 hours! I thoroughly enjoyed my poster session, where several familiar faces dropped by for an update on my work, and others stopped to pose new questions and make a few suggestions for improvements to my maps (wait, why didn’t I think of that?!). As a student presenter, I could also register for the Outstanding Student Poster Award – which means that my poster was anonymously judged, and I will soon be receiving  feedback on my poster and presentation – an opportunity I was excited about to make sure I continue to improve the way I communicate my research.

For me, some of the sessions that were highlights of the conference included  ‘Global Floods: Forecasting, Monitoring, Risk Assessment and Socioeconomic Response‘, ‘Large-scale Climate Variability and its Impact on Hydrological Systems, Water Resources and Population‘, ‘Forecasting Hydrology at Continental Scale‘, ‘Transforming Hydrologic Prediction and Decision Making: Uncertainty’ and ‘ENSO Dynamics, Observations and Predictability in light of the 2015-2016 El Niño Event‘. With such a range of science being presented, there’s also plenty of opportunity (well, so long as you haven’t double- or triple-booked sessions in your schedule already!) to listen to talks outside of your own field – which is how I ended up in an 8am talk on operational earthquake forecasting and early warning. It was brilliant to learn about forecasting natural hazards outside of hydrology and meteorology!

There was also the social aspect that’s a big part of any conference – networking, networking and more networking! While it can be daunting, particularly at a conference of this size, to find and introduce yourself to scientists in your field whose work you’ve read but you’ve never met, I was pleased to first bump into some friendly faces who in turn introduced me to the new faces. Plus, it’s an AGU tradition that ‘AGU beer’ is served at 3.30pm sharp and the conference centre fills with groups of friends and colleagues in heated debates and discussions about anything from volcanoes to Jupiter’s magnetosphere.

It was impossible not to notice, however, the many more politically-themed conversations than would normally be overheard at such an event, as a result of uncertainty about the future of science in light of the recent US presidential election. While I was in the middle of research discussions at my poster, a ‘Stand up for Science‘ rally took place a few blocks away from the conference centre, where scientists donned lab coats and held signs – “stand up for science”, “ice has no agenda – it just melts” – protesting to raise awareness of the challenges, and to support science. You can read the Guardian article here.

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All in all, AGU was a brilliant chance to present and discuss part of my research that I had just finished – it was certainly overwhelming and tough to choose which sessions to stop by (which meant I missed one or two presentations that sounded great), but I would recommend it for showcasing your work (and receiving feedback via the OSPA) and meeting scientists in your field that you wouldn’t normally bump into at conferences in Europe, especially if you can apply for one of AGU’s travel grants to help cover the costs of getting there.

P.S. You can watch presentations from the AGU Fall Meeting 2016 on the website.

Of course, I couldn’t fly all the way out to California and not find time to explore San Francisco a little.

 

 

From foehn to intense rainfall: the importance of Alps in influencing the regional weather

Ambrogio VolontéLeave a comment

Email: a.volonte@pgr.reading.ac.uk

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Figure 1: View from Monte Lema (Italy-Switzerland) looking West. The Lake Maggiore region and the southern Alpine foothills are visible in the foreground whereas Monte Rosa and the Pennine Alps behind them are partially hidden by a characteristic foehn wall.  (A. Volonté, 4 January 2017)

The interaction between atmospheric flow and topography is at the origin of various important weather phenomena, as we have already seen in Carly Wright’s blog post. When a mountain range is particularly high and extended it can even block or deflect weather systems, as it happens with the Alps. For example, in Figure 1 we can see the main Alpine range with its over-4000m-high peaks blocking a cold front coming from the north. The main ridge acts as a wall, enhancing condensation and precipitation processes on the upstream side (stau condition) and leaving clear skies on the downstream lee side, where dry and mild katabatic foehn winds flow. The contrast is striking between sunny weather on Lake Maggiore and snowy conditions over Monte Rosa, just a few miles apart. The same phenomenon is shown in Figure 2 with a satellite image that highlights how a cold front coming from northwest gets blocked by the Alpine barrier. A person enjoying the sunny day in the southern side of the Alps, if unaware of this mechanism, would be very surprised  to know that the current weather is so different on the other side of the range.

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Figure 2: Satellite image (MODIS-NASA) over the Alps and Po Valley on 22 October 2014
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Figure 3: same as Figure 1 but on 13 December 2016

A comparison with Figure 3 helps to notice that in Figure 2 the shape of the cloud band closely mirrors the mountain range. As an additional remark,  this comparison shows that foehn bring clear skies even in the Po Valley, having blown away the typical mist/fog occurring in the region in Autumn and Winter months in high pressure regimes. The  stau/foehn dynamics is actually very fascinating, and you can read more about it in Elvidge and Renfrew (2015 ) and in Miltenberger et al. (2016), among others. Unfortunately, the interaction of weather systems with the Alps can often trigger very damaging phenomena, like heavy and long-lasting precipitation on one side of the slope, and this is what the rest of this post will be focused on. In fact, the most recent event of this kind just happened at the end of November, with intense and long-lasting rain affecting the southern slope of the Alps  and causing floods particularly in the Piedmont region, in northwestern Italy ( Figure 4).

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Figure 4: River Tanaro flooding in the town of Garessio, 24 November 2016 (Piedmont, Italy). Source: http://www.corrierenazionale.it
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Figure 5: rainfall accumulated between 21 and 26 November 2016 in the Piedmont region. Source: Regional Agency for the protection of the Environment – Piedmont

Figure 5 shows that the accumulated rainfall in the event goes over 300 mm in a large band that follows the shape of the southern Alpine slope in the region (see map of Piedmont, from Google Maps), reaching even 600 mm in a few places. This situation is the result of moist southerly flow being blocked by the Alps and thus causing ascent and consequent precipitation to persist on the same areas for up to five days. It is quite common to see quasi-stationary troughs enter the Mediterranean region during Autumn months causing strong and long-lasting moist flows to move towards the Alps. Hence, it is crucial to understand  where the heaviest precipitation will occur. In other words, will it rain the most on top of the ridge or on the upstream plain? What processes are controlling the location of heavy precipitation with respect to the slope?

The study published by Davolio et al. (2016), available here and originated from my master degree’s thesis, tackles this issue focusing on northeastern Italy. In fact, the analysis includes three case studies in which heavy and long-lasting rain affected the eastern Alps and other three case studies in which intense rainfall was mainly located on the upstream plain. Although all the events showed common large-scale patterns and similar mesoscale settings, characterised by moist southerly low-level flow interacting with the Alps, the rainfall distribution turned out to be very dissimilar. The study highlights that the two precipitation regimes strongly differ in terms of interaction of the flow with the mountain barrier. When the flow is able to go over the Alps the heaviest rain occurs on top of the ridge. When the flow is instead blocked and deflected by the ridge (flow around), creating a so-called barrier wind, intense convection is triggered on the upstream plain (Figure 6) .

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Figure 6: Schematic diagram of the key mechanisms governing the two different wind and precipitation patterns over NE Italy. (a) Blocked low-level flow, barrier wind, convergence and deep convection over the plain, upstream the orography. (b) Flow over conditions with orographic lifting and precipitation mainly over the Alps. From Davolio et al. (2016)
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Figure 7: cross section going from the Adriatic Sea to the Alps in one of the events simulated. Equivalent potential temperature is shaded, thick black lines indicate clouds while arrows show tangent wind component. See Davolio et al. (2016)

The key mechanism that explains this different evolution is connected to the thermodynamic state of the impinging flow. In fact, when the southerly moist and warm air gets close to the Alpine barrier it is lifted above the colder air already present at the base of the orography. It can be said that the colder air behaves as a first effective mountain for the incoming flow. If this lifting process triggers convection, then the persistence of a blocked-flow condition is highly favoured (see Figure 7). On the contrary, if this initial lifting process does not trigger convection the intense moist flow will eventually be able to go over the ridge, where a more substantial ascent will take place, causing heavy rain on the ridge top. This study also looks at numerical parameters used in more idealised analyses (like in Miglietta and Rotunno (2009)), finding a good agreement with the theory.

To summarise, we can say that the Alpine range is able to significantly modify weather systems when interacting with them. Thus, an in-depth understanding of the processes taking place during the interaction, along with a coherent model is necessary to capture correctly the effects on the local weather, being either a rainfall enhancement, the occurrence of foehn winds or various other phenomena.

References

Davolio, S., Volonté A., Manzato A., Pucillo A., Cicogna A. and Ferrario M.E. (2016), Mechanisms producing different precipitation patterns over north-eastern Italy: insights from HyMeX-SOP1 and previous events. Q.J.R. Meteorol. Soc., 142 (Suppl 1): 188-205. doi:10.1002/qj.2731

Elvidge A. D., Renfrew, I. A. (2015). The causes of foehn warming in the lee of mountains. Bull. Am. Meteorol. Soc. 97: 455–466, doi:10.1175/BAMS-D-14-00194.1.

Miglietta M. and Rotunno R., (2009) Numerical Simulations of Conditionally Unstable Flows over a Mountain Ridge. J. Atmos. Sci., 66, 1865–1885, doi: 10.1175/2009JAS2902.1. 

Miltenberger, A. K., Reynolds, S. and Sprenger, M. (2016), Revisiting the latent heating contribution to foehn warming: Lagrangian analysis of two foehn events over the Swiss Alps. Q.J.R. Meteorol. Soc., 142: 2194–2204. doi:10.1002/qj.2816

Met Festivities.

KajaLeave a comment

The Christmas period is a busy time for many and PhD students are no exception. Below are quick highlights from the department written by three of our PhD students. Read below to learn more about our recent Royal Meteorological Society South-East local centre meeting, the adventures of the Met Choir, and the much-anticipated departmental pantomime.

“Will we have a white Christmas in Reading this year? What does the term “white Christmas” even mean? Both of these questions were addressed at the beginning of the Royal Meteorological Society’s local south-east centre meeting on the 7th of December by the department of meteorology’s recently retired Ross Reynolds.

The evening began with inevitable mince pies and a poster showcase by eight PhD students from a variety of research areas, which initiated lively discussions. The Met choir singers added to the festive spirit with a repertoire of carols before the oral presentations began.

First up was Jake Gristey, whose research project investigates satellite constellations to measure energy flux in and out of the Earth’s atmosphere. Updating the satellite constellation will allow satellites to measure outgoing energy flux to a higher accuracy than any instrument has done previously, allowing for an accurate calculation of Earth’s radiation budget. Eunice Lo spoke about a geoengineering method, Sulphate Aerosol Injection (SAI) which involves releasing sulphate particles into the atmosphere with the aim of increasing the Earth’s albedo. The idea is based on historical volcanic aerosol release which led to a decrease in global temperatures. Eunice is basing her studies of the effects of SAI on a future world following a particular economic scenario. Our last speaker of the evening was James Shaw, who researches the modelling of atmospheric transport over terrain. He is currently developing a new mesh for numerical transport schemes over mountains, with a focus on the accurate representation of near-surface cells.

The meeting exhibited the huge variety of research happening in the department and was an overall success. This was the last local-cente meeting of the year, with the next one taking place on 11th January 2017.”

Kaja Milczewska, K.M.Milczewska@pgr.reading.ac.uk

“An important part of the festive season for PhD students is the infamous Met Pantomime. Twice a week we all get together over our lunchtimes to practice and perfect all the jokes accrued by the members of the department this year. Although planning begins in September, it’s only come December when it all comes together. That crazy wig arrives from Amazon and we’ve created oversized comic props from all the cardboard Hobbycraft can spare. The jokes and jibes get funnier every time we practice them and staff just keep providing more and more material (oh no they don’t!). There’s definitely an undercurrent of excitement – and a little apprehension – as the big evening draws near. This years’ comic spectacle: Snow White and the Research Dwarves, complete with lights, sound, and a fantastic buffet.”

Sarah Bentley, S.Bentley@pgr.reading.ac.uk

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“This year the meteorology choir have been busy rehearsing for performances both within the department and externally. A recently formed tradition and definite highlight has been singing for the residents of the Lakeside care home as well as for the annual department Christmas celebration. We also have been lucky enough this year to perform at a local and national meeting of the Royal Meteorological Society. The choir is open to all, regardless of musical ability and we have members ranging from students all the way up to head of department.”

Samantha Buzzard, s.c.buzzard@pgr.reading.ac.uk

Merry Christmas and Happy New Year from the Social Metwork.

Stationary Orographic Rainbands

Carly Wright1 Comment

Email: c.j.wright@pgr.reading.ac.uk

Small-scale rainbands often form downwind of mountainous terrain. Although relatively small in scale (a few tens of km across by up to ~100 km in length), these often poorly forecast bands can cause localised flooding as they can be associated with intense precipitation over several hours due to the anchoring effect of orography (Barrett et al., 2013).   Figure 1 shows a flash flood caused by a rainband situated over Cockermouth in 2009.  In some regions of southern France orographic banded convection can contribute 40% of the total rainfall (Cosma et al., 2002).  Rainbands occur in various locations and under different synoptic regimes and environmental conditions making them difficult to examine their properties and determine their occurrence in a systematic way (Kirshbaum et al. 2007a,b, Fairman et al. 2016).  My PhD considers the ability of current operational forecast models to represent these bands and the environmental controls on their formation.

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Figure 1: Flash flood event caused by a rainband situated over Cockermouth, Cumbria, UK in 2009

 

What is a rainband?

  • A cloud and precipitation structure associated with an area of rainfall which is significantly elongated
  • Stationary (situated over the same location) with continuous triggering
  • Can form in response to moist, unstable air following over complex terrain
  • Narrow in width ~2-10 km with varying length scales from 10 – 100’s km

 

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Figure 2: Schematic showing the difference between cellular and banded convection

To examine the ability of current operational forecast models to represent these bands a case study was chosen which was first introduced by Barrett, et al. (2016).  The radar observations during the event showed a clear band along The Great Glen Fault, Scotland (Figure 3).  However, Barrett, et al. (2016) concluded that neither the operational forecast or the operational ensemble forecast captured the nature of the rainband.  For more information on ensemble models see one of our previous blog posts by David Flack Showers: How well can we predict them?.

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Figure 3: Radar observations of precipitation accumulation over a six hour period (between 3-9 am) showing a rainband located over The Great Glen Fault, Scotland on 29 December 2012.

Localised convergence and increased convective available potential energy along the fault supported the formation of the rainband.  To determine the effect of model resolution on the model’s representation of the rainband, a forecast was performed with the horizontal gird spacing decreased to 500 m from 1.5 km.  In this forecast a rainband formed in the correct location which generated precipitation accumulations close to those observed, but with a time displacement.  The robustness of this forecast skill improvement is being assessed by performing an ensemble of these convection-permitting simulations.  Results suggest that accurate representation of these mesoscale rainbands requires resolutions higher than those used operationally by national weather centres.

Idealised numerical simulations have been used to investigate the environmental conditions leading to the formation of these rainbands.  The theoretical dependence of the partitioning of dry flow over and around mountains on the non-dimensional mountain height is well understood.  For this project I examine the effect of this dependence on rainband formation in a moist environment.  Preliminary analysis of the results show that the characteristics of rainbands are controlled by more than just the non-dimensional mountain height, even though this parameter is known to be sufficient to determine flow behaviour relative to mountains.

This work has been funded by the Natural Environmental Research Council (NERC) under the project PREcipitation STructures over Orography (PRESTO), for more project information click here.

References

Barrett, A. I., S. L. Gray, D. J. Kirshbaum, N. M. Roberts, D. M. Schultz, and J. G. Fairman, 2015: Synoptic Versus Orographic Control on Stationary Convective Banding. Quart. J. Roy. Meteorol. Soc., 141, 1101–1113, doi:10.1002/qj.2409.

— 2016: The Utility of Convection-Permitting Ensembles for the Prediction of Stationary Convective Bands. Mon. Wea. Rev., 144, 10931114, doi:10.1175/MWR-D-15-0148.1.

Cosma, S., E. Richard, and F. Minsicloux, 2002: The Role of Small-Scale Orographic Features in the Spatial Distribution of Precipitation. Quart. J. Roy. Meteorol. Soc., 128, 75–92, doi:10.1256/00359000260498798.

Fairman, J. G., D. M. Schultz, D. J. Kirshbaum, S. L. Gray, and A. I. Barrett, 2016: Climatology of Banded Precipitation over the Contiguous United States. Mon. Wea. Rev., 144,4553–4568, doi: 10.1175/MWR-D-16-0015.1.

Kirshbaum, D. J., G. H. Bryan, R. Rotunno, and D. R. Durran, 2007a: The Triggering of Orographic Rainbands by Small-Scale Topography. J. Atmos. Sci., 64, 1530–1549, doi:10.1175/JAS3924.1.

Kirshbaum, D. J., R. Rotunno, and G. H. Bryan, 2007b: The Spacing of Orographic Rainbands Triggered by Small-Scale Topography. J. Atmos. Sci., 64, 4222–4245, doi:10.1175/2007JAS2335.1.

What is loss and damage from climate change?

Hannah YoungLeave a comment

Characterizing loss and damage from climate change
James et al., 2014. Nature Climate Change, 4, 938–939. doi:10.1038/nclimate2411

Email: h.r.young@pgr.reading.ac.uk

Under the United Nations Framework Convention on Climate Change (UNFCCC), countries negotiate how to address the impacts of anthropogenic climate change through mitigation and adaptation. Despite these efforts, climate-related events still cause huge impacts across the globe every year. Impacts can be particularly  devastating in developing countries and this is what the relatively new area of ‘loss and damage’ in the negotiations aims to address.

In 2013, the UNFCCC established the Warsaw International Mechanism (WIM) to “address loss and damage associated with impacts of climate change, including extremes events and slow onset events, in developing countries that are particularly vulnerable to the adverse effects of climate change” (UNFCCC, 2013). Two decades of negotiating went into forming this mechanism, since the first calls from small island developing states in the early 1990s to address the effects of sea level rise.

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Island states such as Vanuatu in the South Pacific have been requesting support for the impacts of sea level rise since the early 1990s. Source: Meredith James/Flickr/CC BY-NC-ND 2.0

The WIM states it will address the impacts of both extreme events (such as floods and heatwaves) and slow onset events (such as sea level rise). However, as yet, there is no official definition of what loss and damage will actually encompass. In our commentary in Nature Climate Change (James et al., 2014), we considered one aspect of defining loss and damage: whether loss and damage would need to be attributed to anthropogenic climate change. As the text of the WIM describes “loss and damage associated with the impacts of climate change” and the UNFCCC’s definition of climate change is that which is “attributed directly or indirectly to human activity” (UNFCCC, 1992), this could imply that there would need to be proof that impacts from events were caused by anthropogenic climate change.

If this were the case, impacts would first need to be attributed to particular events (e.g. the infrastructure damaged by a particular flood), and then the event would need to be attributed to anthropogenic climate change. For slow-onset events like sea level rise, the science attributing these to anthropogenic climate change is well-established. However for individual events it is much more challenging to say how climate change had an influence. Extreme event attribution can, for some types of events, estimate how anthropogenic climate change affected the probability of the particular event occurring. This generally relies on large ensembles of climate model simulations, which are necessary to estimate the probabilities of such rare events, and studies therefore rely on the ability of the models to represent the processes that produce the extreme event in question. Observations are also necessary to both to validate the model simulations and define the extreme event to be studied, which are not always available, particularly in developing countries. Up to now, studies attributing specific events have been carried out on an ad hoc basis in the aftermath of particularly extreme events, rather than more systematically. They have also mainly focussed on events in developed countries, rather than the developing countries the WIM aims to assist.

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Typhoon Haiyan caused devastation in November 2013 as the WIM was being negotiated. It was used as an example of loss and damage, but without any consideration of whether anthropogenic climate change played a role. Is this an important consideration? Source: DFID/Flickr/CC BY 2.0

While the attribution of events to anthropogenic climate change could be relevant to addressing loss and damage, it is controversial in negotiations. This is in part due to its perceived association with compensation claims. However we suggest that, somewhere along the line, the question of causality is likely to come up, to establish just what the loss and damage being addressed is. Attribution may or may not have a role to play here. What is key is that as event attribution science is continuing to develop, scientists and policymakers need to have opportunities for conversations about what information the science can provide and how this could be applied if it was deemed necessary for policy.

Since writing our commentary we have continued to research this science-policy interface. We have investigated what is understood about event attribution science by stakeholders associated with loss and damage negotiations and how they think it could be relevant (Parker et al., 2016). We have also investigated how policymakers and practitioners are defining ‘loss and damage’, as this still has no official definition and there are differing perspectives among those looking to address loss and damage. Our aim is that by better understanding this policy context, the science will be able to develop in ways that are most relevant to the needs of decision makers and, if deemed relevant, ultimately help to address loss and damage in vulnerable regions.

This work forms part of the ACE-Africa project, for more information see http://www.walker.ac.uk/projects/ace-africa-attributing-impacts-of-external-climate-drivers-on-extreme-weather-in-africa/ 

References

James, R., Otto, F., Parker, H., Boyd, E., Cornforth, R., Mitchell, D., & Allen, M. (2014). Characterizing loss and damage from climate change. Nature Climate Change, 4, 938-939, doi: 10.1038/nclimate2411.

Parker, H. R. , Boyd, E., Cornforth, R. J., James, R., Otto, F. E. L., & Allen, M. R. (2016). Stakeholder perceptions of event attribution in the loss and damage debate. Climate Policy, doi: 10.1080/14693062.2015.1124750.

UNFCCC (1992). Article 1: Definitions

UNFCCC (2013). Decision 2/CP.19: Warsaw International Mechanism for Loss and Damage Associated with Climate Change Impacts FCCC/CP/2013/10/Add.1

Showers: How well can we predict them?

David Flack1 Comment

Email: d.l.a.flack@pgr.reading.ac.uk

Showers are one of the many examples of convective events experienced in the UK, other such events include thunderstorms, supercells and squall lines. These type of events form most often in the summer but can also form over the sea in the winter. They form because the atmosphere is unstable, i.e. warm air over a cooler surface, this results in the creation of thermals. If there is enough water vapour in the air and the thermal reaches high enough the water vapour will condense and eventually form a convective cloud. Convective events produce intense, often very localised, rainfall, which can result in flash floods, e.g. Boscastle 2004.

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Boscastle flood 2004 – BBC News

Flash floods are very difficult to predict, unlike flood events that happen from the autumnal and winter storms e.g. floods from Storms Desmond and Frank last winter, and the current floods (20-22 November). So often there is limited lead time for emergency services to react to flash flood events. One of the main reasons why flash floods are difficult to predict is the association with convective events because these events only last for a few hours (6 hours at the longest) and only affect a very small area.

One of the aspects of forecasting the weather that researchers look into is the predictability of certain events. My PhD considers the predictability of convective events within different situations in the UK.

The different situations I am considering are generally split into two regimes: convective quasi-equilibrium and non-equilibrium convection.

In convective quasi-equilibrium any production of instability in the atmosphere is balanced by its release (Arakawa and Schubert, 1974). This results in scattered showers, which could turn up anywhere in a region where there is large-scale ascent. This is typical of areas behind fronts and to the left of jet stream exit regions. Because there are no obvious triggers (like flow over mountains or cliffs) you can’t pin-point the exact location of a shower.  We often find ourselves in this sort of situation in April, hence April showers.

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Classic convective quasi-equilibrium conditions in the UK – scattered showers on 20 April 2012 – Dundee Satellite Receiving Station

On the other hand in non-equilibrium convection the instability is blocked from being released so energy in the system builds-up over time. If this inhibiting factor is overcome all the instability can be released at once and will result in ‘explosive’ convection (Emanuel, 1994).  Overcoming the inhibiting factor usually takes place locally, such as a sea breeze or flow up mountains, etc. so these give distinct triggers and help tie the location of these events down. These are the type of situations that occur frequently over continents in the spring and often result in severe weather.

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Non-equilibrium convection – convergence line along the North Cornish Coast, 2 August 2013 – Dundee Satellite Receiving Station

It’s useful having these regimes to categorise events to help determine what happens in the forecasts of different situations but only if we understand a little bit about their characteristics. For the initial part of my work I considered the regimes over the British Isles and found that  we mainly have convective events in convective quasi-equilibrium (showers) – on average roughly 85% of convective events in the summer are in this regime (Flack et al., 2016). Therefore it is pertinent to ask how well can we predict showers?

To see how well we can predict showers, and other types of convection, the forecast itself is examined. This is done by adding small-scale variability into the model, throughout the forecast, to determine what would happen if the starting conditions (or any other time in the model) changed. This is run a number of times to create an ensemble.

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Deterministic forecast vs Ensemble forecast schematic, dotted lines represent model trajectories, the bright red represents the truth, darker red represents the forecast

Using ensembles we can determine the uncertainty in the weather forecast, this can either be in terms of spatial positioning, timing or intensity of the event. My work has mainly considered the spatial positioning and intensity of the convection, and is to be submitted shortly to Monthly Weather Review. The intensity in my ensemble shows similar variation in both regimes, suggesting that there are times when the amount of rainfall predicted can be spot on. Most of the interesting results appear to be linked to the location of the events. The ensembles for the non-equilibrium cases generally show agreement between location of the events, so we can be fairly confident about their location (so here your weather app would be very good). On the other hand, when it comes to showers there is no consistency between the different forecasts so they could occur anywhere  (so when your app suggests showers be careful – you may or may not get one).

So I’ll answer my question that I originally posed with another question: What do you want from a forecast? If the answer to this question is “I want to know if there is a chance of rain at my location” then yes we can predict that you might get caught by a shower. If on the other hand your answer is “I want exact details, for my exact location, e.g. is there going to be a shower at 15:01 on Saturday at Stonehenge yes or no?” Then the answer is, although we are improving forecasts, we can’t give that accurate a forecast when it comes to scattered showers, simply because of their very nature.

With forecasts improving all the time and the fact that they are looking more realistic it does not mean that every detail of a forecast is perfect. As with forecasting in all areas (from politics to economy) things can take an unexpected turn so caution is advised. When it comes to the original question of showers then it’s always best to be prepared.

This work has been funded by the Natural Environmental Research Council under the project Flooding From Intense Rainfall, for more project details and project specific blogs visit: www.met.reading.ac.uk/flooding

References

Arakawa, A. and W. H. Schubert, 1974: Interaction of a Cumulus Cloud Ensemble with the Large-Scale Environment, Part I. J. Atmos. Sci., 31, 674-701.

Emanuel, K. A., 1994: Atmospheric convection, Oxford University Press, 580 pp.

Flack, D. L. A., R. S. Plant, S.L. Gray, H. W. Lean, C. Keil and G. C. Craig, 2016: Characterisation of Convective Regimes over the British Isles. Quart. J. Roy. Meteorol. Soc., 142, 1541-1553.  

 

Discovering COP22

The Social MetworkLeave a comment

Email: j.f.talib@pgr.reading.ac.uk

Over the past two weeks 25,000 delegates have been gathering in Marrakech to discuss mitigation and adaptation for climate change. On the 4th November 2016 the Paris Agreement came into force and as a result discussions during the conference debated its implementation. The Walker Institute and the Department of Meteorology (University of Reading), with the support of the NERC SCENARIO doctoral training partnership and an UNFCCC partnership, supported two PhD students to be official UN observers at COP22, and enabled remote participation with students back at Reading University. To find out more about our work with COP22 continue reading this blog post and check out:

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Today (18/11/16) the UK government are set to announce that the United Kingdom has ratified the Paris Agreement. Yesterday, Boris Johnson (UK foreign secretary) signed the Paris Agreement after no objections were raised by the House of Commons or House of Lords. The United Kingdom in accordance with the Intended Nationally Determined Contributions (INDCs) of the European Union, are set to reduce greenhouse gas emissions by 40% by 2030 relative to 1990 emission levels. Today also marks the end of the 22nd Conference of the Parties (COP) for the United Nations Framework Convention on Climate Change and here are some quick summary points that PhD students took away from observing the process in Marrakech:

1) The significance of the Paris Agreement.

“Now that we have Paris, we need to take action immediately”

Teresa Anderson, ActionAid UK.

The Paris Agreement marks a change in the intentions during the COP process. Due to the success and ratification of the Paris Agreement more discussions can be based on the adaptation and mitigation against climate change, rather than negotiating global targets on climate change prevention. The Paris Agreement states that a global response is needed to respond to the threat of climate change and that global temperature rise should be kept well below 2°C and that efforts should be pursued to limit the global temperature rise to 1.5°C. COP22 Marrakech, began by stating that this is the “COP of Action”, and therefore the focus seen during side events, negotiations, dignitary speeches and press conferences was on the need for action.

“Countries have strongly supported the [Paris] Agreement because they realize their own national interest is best secured by pursuing the common good. Now we have to translate words into effective policies and actions.”

Mr Ban Ki-Moon, Secretary General of the United Nations.

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2) A continued effort is needed to concentrate on the individual.

As SCENARIO PhD students we were challenged to understand the process that takes place during a UNFCCC conference. To do this we interviewed many conference delegates including policymakers, research organisations, industry experts, entrepreneurs, environmental consultants and funding sources to name a few. A common theme that ran through most of our interviews is that action is needed to prioritise the individual as well as thinking in terms of national- and community-level. To ensure the successful mitigation and adaptation to climate change, strategies need to come into place that protect the rights of the individual. This poses a global challenge, stretching from protecting the livelihoods of indigenous cultures and those impacted by sea level rise on low-lying islands, to supporting workers who rely on the non-renewable energy industry. In terms of climate research we need to ensure that we make our scientific conclusions accessible on an individual-level so that our work has a greater impact.

“a key goal for us is making climate change research accessible to the user community”

Clare Kapp, WMO Press Office Communications Leader.

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3) Action is needed now, however the Paris Agreement only implies action post-2020.

Throughout our attendance in plenary meetings and side events there was an emphasis that whilst the Paris Agreement is an important stepping stone to combatting climate change, action is needed before 2020 for the Paris Agreement to be reached. Currently INDCs are proposed for between 2021-2030, however for the intended global temperature targets to be achieved it was argued that action is needed now. Although, pre-2020 action raises much contention, with the most popular argument against pre-2020 action being that more time and effort is needed for negotiations to ensure that a better understanding of national efforts to climate change mitigation is determined.

“We need to take action before 2020. Working for action post-2020 is not going to be enough. We need to start acting now.”

Honduras Party Representative.

“We need more time to work on the rule book for the Paris Agreement. Discussions on this should continue.”

Switzerland Party Representative.

4) There is a difference in opinion on whether 1.5°C can be reached.

For me the most interesting question we asked conference delegates was “do you think the target of 1.5°C can be reached?” This question brought a difference of opinion including some party members arguing that the change in our non-renewable energy dependence is far too great for the target to be achieved. Meanwhile, other political representatives and NGO delegates argued that accepting the target is unachievable before even trying makes negotiations and discussions less successful. There was also anticipation for the future IPCC report titled, Special Report on Global Warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways.

“Of course we want to fight for 1.5°C, why fight for 2°C? It just makes sense to fight for 1.5°C”

Martina Duncan, Party Representative for Grenada.

COP22 has been a fantastic opportunity for PhD students in our department to interact and understand the process that takes place during a UNFCCC conference. Whilst the past couple of weeks have been dominated by the results of the US election and the associated uncertainties, there has been an increasing global recognition of climate change and that action should be taken. In the next few years the challenge to mitigate and adapt towards climate change will be an increasing priority, and let us hope that these annual UNFCCC conferences are key stepping stones for climate change action.

“This is a problem people are recognising, and that it is time to change”

Jonathan Pershing, US Climate Envoy

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Thank you all those who have supported our work at COP22 this year. Thank you to the Walker Institute, NERC SCENARIO doctoral training partnership and UNFCCC for this brilliant opportunity. Thank you to all those who have supported us with publicity including NERC, Royal Meteorological Society, members of staff and PhD students at the University of Reading and Lucy Wallace who has ensured the appropriate communication of our project. Plus a huge thanks to all delegates and staff at COP22 who volunteered their time to talk to us.