Category Archives: aerosols

Getting on my soapbox

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At 12 noon exactly I stepped onto my soapbox and surveyed the vast expanse of unpopulated concrete between me and the River Thames. 3 boxes to my right, another female scientist had already pulled in an audience with her flagella balloons. With a deep breath I lifted my empty water bottle high and started “Who can tell me what’s in this bottle?” Some people drifted in my direction, and I was off on my SoapboxScience adventure.

SoapboxScience involves 12 female scientists taking shifts on soap boxes on public thoroughfares talking about their research and their love of science. Sort of science street theatre. WITH NO POWERPOINT. In fact no power either. The project aims to raise the profile of science and female scientists amongst the general public via the style of public debate and discussion. For the past 4 years there has been an event in London, but this year there were also sister events in Swansea, Dublin and Bristol.

soapbox

My event was Sunday June 29th 2014. Our soapboxes were set up at Gabriel’s Wharf near the Southbank Centre in London. It was a beautiful sunny day, at least to start with! Sharing the first hour slot with me were experts on cheetahs, evolutionary biology and Mars exploration. My job was to spread excitement about particles in the atmosphere and their effects on weather and climate. We’d been told to prepare 10-15 minutes of “stand-up” material, with props if we wanted, and to expect people to stay listening to us for anywhere between 2 and 20 minutes. These are a few of the things I learnt from the experience:

  • Your opening pitch is really important to draw people to you.. asking a question that seems to have a simple answer but doesn’t worked well. As did a giant picture of jam donuts as a metaphor for coated soot particles (Thanks to @willtmorgan and his European Geophysical Union blog )
  • The prop that was the most useful was the one that I thought I would only use in an emergency – a set of 4 scanning electron microscope images of different aerosol particles. I got people to “pick a card” and asked the group to guess what it was. Then I spent 3 mins talking about that type of aerosol, making sure I included the main points (aerosols scatter sunlight and aerosols make clouds) in every case. However, this also meant people stayed to see all 4 pictures which meant the “dwell time” was at least 10 minutes.
  • Don’t make audience participation too contrived. I tried making an aerosol chains and balls out of humans to demonstrate the aging and coating process but it didn’t work so I dropped it after one attempt. I have an idea how to improve it for the future though so watch this space.
  • People will ask questions of all levels of sophistication – be prepared to tailor your answer appropriately
  • I prepared props that would work in the rain, but not in the wind – without my dedicated soapbox volunteer I’d have been in trouble

The scariest part was trying to stop people just walking past without stopping, but I think I talked to around 80 people in the hour I was on the box and there weren’t too many awkward gaps. The first time I looked at my watch was 45 minutes into my hour long slot, and then it was over way too soon. I’d do it again tomorrow if I could.

crowd

Sponsored in the past by L’Oreal UNESCO For Women in Science and ZSL, the two dedicated research biologists women who started it, Seirian Sumner and Nathalie Pettorelli have been successful in securing government funding for Soapbox for the next few years, and plan to put on events in other cities. Possibly even Reading…

Tales of the unexpected

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This post was originally an article written for the online Newsletter of theWeather Club  of the Royal Meteorological Society and is reproduced here with their permission)

I spend a lot of time reading scientific papers. They are one of the main ways in which science is communicated within the academic discipline, and also one of the ways in which academics productivity is measured. Away from work therefore, I generally find it hard to summon enthusiasm for reading anything vaguely science related. However, for Christmas this year I asked for 3 of the books on the shortlist for the Royal Society’s Winton Prize for Science Books prize. I looked forward to reading these initially because of my interest in science writing, but somewhat to my surprise I quickly found myself intrigued by the science within the first one.

 Image

“Bird Sense” by Tim Birkhead discusses the evidence that birds use each of seven senses; seeing, hearing, touch, taste, smell, magnetic sense, and emotion. It is hard to say why such a topic captured my imagination but its considerable distance from my own research area certainly contributed. Imagine my surprise then to find the familiar topic of dimethyl sulphide (DMS) and even a familiar name within such a book.

 

DMS is a gas that is most well known as a component of the smell produced when cooking cabbage or beetroot. It is also produced at sea when phytoplankton are eaten by zooplankton (e.g. krill), the gas being first dissolved in seawater and then released to the atmosphere. Once oxidised in the marine atmosphere it is a major natural source of sulphate aerosol in the marine atmosphere and may go on to affect clouds and have a significant impact on the Earth’s climate (therein lies the link to my research area). Oceanic DMS emissions account for something like 15% of the global sulphur emissions to the atmosphere and are a significant fraction of the sulphur emissions particularly in the southern hemisphere mid-latitudes. These emissions are a major player in the supposed CLAW feedback loop between atmosphere and ocean whereby climate change leads to changes in DMS emissions which then alter climate themselves, although the magnitude and even the sign of this feedback is the subject of much debate.

Image

Thus DMS is an important component of the marine atmosphere, but what does it have to do with bird senses? Seabirds in particular travel over very long distances to search for food, but many unerringly navigate safely back to their breeding grounds. Well, it could be that DMS is in fact providing a smell map by which seabirds can find their way home. Even more fascinating is the fact that this link was made via a chance encounter of biologist Gaby Nevitt with an atmospheric scientist, Tim Bates. Following an injury on a research cruise, Nevitt stayed on the ship whilst it was being prepared for a DMS transect cruise and saw the measurements of DMS across the ocean by Tim’s group. Subsequently, Nevitt and colleagues measured elevated heartbeats in birds exposed to air containing DMS and noted that the flight patterns of albatrosses were consistent with birds attempting to locate a breeding ground by smell, i.e. zigzagging across a plume rather than flying in a straight line (which would be more consistent with navigating by sight). So, far from escaping from work, I found aerosols deep in the depths of a book about bird behaviour, and a story of two science worlds colliding to produce a step change in understanding. I wonder what I will find in the other two books?

ImageImage and more information from the Nevitt Lab

Bird Sense What it’s like to be a bird by Tim Birkhead, Bloomsbury Press 2013
Bonadonna et al (2006) Journal of Experimental Biology, 209, 2165-9

Aerosols in the IPCC 2013 Summary for Policymakers

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Whilst I don’t approve of “cherry picking” from important reports such as the IPCC WG1 Summary for Policymakers (SPM) that was published today, I do need to look particularly for the updates to the quotes from previous reports that have motivated much of what I do in my day to day job. Previously, the IPCC (2007) report said that aerosols were one of the most uncertain aspects of climate change. So what does the new report bring?

As I’ve said in my previous post, the IPCC have considered a phenomenal number of new publications since 2007. There has been a particularly large research effort since 2007 in trying to understand how aerosols affect climate, and to better represent them in models. The full WG1 report available on Monday 30th September 2013 will have an entire chapter concerning aerosols, and aerosol-cloud interactions, but the relevant parts that made it to the SPM are interesting.

1. Improved estimates of radiative forcing (perturbation to the energy balance of the planet) due to aerosols indicate a weaker net cooling relative to 1750 than was included in the last IPCC report (AR4)

2. The radiative forcing (RF) of the total aerosol effect in the atmosphere, which includes cloud adjustments due to aerosols is -0.9 [-1.9 to -0.1] Wm-2 with medium confidence and results from a negative forcing from most aerosols and a positive contribution from black carbon absorption of solar radiation. There is high confidence that aerosols and their interactions with clouds have offset a substantial portion of global mean forcing from well-mixed greenhouse gases. They continue to contribute the largest uncertainty to the total RF estimate

3. Climate models now include more cloud and aerosol processes, and their interactions, that at the time of the AR4, but there remains low confidence in the representation and quantification of these processes in models.

4. Observational and modelling evidence indicates that, all else being equal, locally higher surface temperatures in polluted regions will trigger regional feedbacks in chemistry and local emissions that will increase peak levels of ozone and PM2.5 (medium confidence). For PM2.5, climate change may alter natural aerosol sources as well as removal by precipitation, but no confidence level is attached to the overall impact of climate change on PM2.5 distributions.

5. A lower warming target, or higher likelihood of remaining below a specific warming target will require lower cumulative CO2 emissions. Accounting for warming effects of increases in non-CO2 greenhouse gases, reductions in aerosols, or the release of greenhouse gases from permafrost will also lower the cumulative CO2 emissions for a specific warming target

6. Solar Radiation Management (SRM) “geo-engineering”: Modelling indicates that these methods, if realizable, have the potential to substantially offset a global temperature rise, but they would also modify the global water cycle and would not reduce ocean acidification. If SRM were terminated for any reason, there is high confidence that global surface temperatures would rise very rapidly to values consistent with the greenhouse gas forcing. SRM methods carry side-effects and long-term consequences on a global-scale.

All in all, I’m probably not out of a job just yet…

You can find the 18 key IPCC headlines that were agreed by 110 governments in the form of tweets by @piersforster and storify form courtesy of Mark Brandon @icey_mark

The WG1 summary for policymakers is available here

Climate forcing: The impact of aerosols on mid-century temperature hiatus

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This post is based on our recent paper: “The influence of anthropogenic aerosol on multi-decadel variations of historical global climate” by Laura Wilcox, Ellie Highwood and Nick Dunstone, which appeared in Environmental Research Letters. One of our main conclusions was:

  • Mid-century (1950s-1960s) temperature hiatus, and coincident decrease in precipitation, is likely to have been influenced strongly by anthropogenic aerosol forcing.

Here I describe how we came to this conclusion, and use an analogy with Newton’s laws of motion to describe the competing influences on climate.

Background: An increase in aerosol concentration (the particulates) in the atmosphere generally acts to cool the global climate, as sunlight is reflected back to space – we refer to this as the aerosol direct effect. Aerosols can also change the properties of clouds, making them more reflective, or last longer – this is the “indirect effect”.  There have been lots of recent studies linking aerosol changes to changes in important parts of our climate system: e.g.  Atlantic temperatures, Sahel rainfall and hurricanes.

But aerosol has played an important role in the historical changes of global temperature too. Unlike recent greenhouse gas changes, the sign of the influence of aerosols on global mean temperature has varied over time. Whilst greenhouse gas concentrations in the atmosphere have been growing consistently over the past 250 years, aerosol emissions and concentrations have a much more complex history. As aerosols can be washed out by rain, they last for only a few days to weeks if they remain in the lowest part of the troposphere. This means that the pattern globally is very non-uniform (see figure of Aerosol Optical Depth (AOD) below from NASA)  and that high concentrations tend to be close to emission regions. Thus if the emissions change over time (e.g. clean air act  in Europe reducing aerosol emissions on the grounds of improving air quality since 1960s), this would be seen in the time series of aerosol in the atmosphere too.

aerosol_depth

The timeseries of aerosol from climate models (we have to do it from models because although we have some idea of the changes in emissions, we have only been able to look at what aerosol is actually in the atmosphere globally for around 20 years) looks like the figure below which is taken from Wilcox, Highwood and Dunstone (2013). Thus there have been times of increase, and times of much smaller change.

wilcox2013_blogfig1

What does this mean for the influences on global temperature? Let’s picture the global mean temperature as a floating ball. According to Newton’s laws of motion, this ball will remain stationary unless a net force acts upon it. Now imagine all the possible things that could be pushing the temperature higher (increases in greenhouse gases, decrease in aerosol) as a force on one side of the ball, and all the things that could be pushing the temperature lower (increase in aerosol) on the other side. If “cooling” influences win at any time, then the ball will move towards cooler temperatures. If stronger cooling influences exist, then it will move faster. If cooling and warming influences are more equal, then the ball will stay still, and we would see little trend in global mean temperature. See what we mean in an animation

What did we do?
We used a technique especially developed to deal with noisy timeseries, called Ensemble Empirical Mode Decomposition . This works by decomposing a noisy timeseries into a set of oscillating functions, as shown in figure 2.

wilcoxblogfig2

We applied this technique to the timeseries of global mean temperature, rainfall, and the hemispheric gradient of temperature. We used simulations that included all things likely to affect climate change (greenhouse gases, anthropogenic aerosols, solar changes, volcanoes), as well as simulations that only included some of these things. We also separated models by the types of aerosol effect that are included.

What did we find out?

Using the different simulations, and imagining that the line in this animation  represents the position of the “global temperature ball”, we can show how the influences from aerosol, greenhouse gases and natural forcings changes over time, the arrows in this animation are the forces pushing on the ball.
Because adding up the simulations with single forcings produce the same total temperature time series (by coincidence?), we can put a percentage on the contribution due to each forcing. Aerosol forcing accounts for over 50% of the variability before 1970, and in excess of 70% in the 1940s-1960s.

wilcoxblogfig3

What’s next?
One of the big uncertainties in the future is how aerosol emissions will change. The climate model simulations we have access to have assumed that aerosol emissions will decrease dramatically by the year 2100. Thus in the global mean aerosol will move from being a cooling push to being a warming push. Thus we will enter a period unlike all others in the recent past, where both greenhouse gases and aerosols are pushing in the same direction. There are enough non-linearities in the climate system to make us think that we might see some new types of changes – particularly in rainfall and circulation patterns. We will look at these competing influences for specific regions, and in the future, using EEMD and other techniques. Should be interesting!