Atmospheric Sciences Webinar Series Part 1 of 8: From the Past Into the Future

good morning or good afternoon or good evening depending on where you're coming to us from my name is Rob Reider director of engagement and membership here at aju we are proud along with the atmospheric sciences section to present this webinar series from the past into the future this is a webinar series that was presented as a session at the 2019 aju fall meeting due to the high demand the decision by the atmospheric sciences section Jim puerile as president and Paul Newman as the president-elect they decided to turn this into a webinar series and invite all 16 15 speakers to present this to you over the next few weeks so if you haven't registered for the other ones please go ahead and do so through the website otherwise we are ready to go here with today's first webinar our speakers today are going to be Allison Steiner who will be speaking to you on terrestrial biosphere atmosphere interactions and Kevin Trenberth who will be talking about Earth's changing energy budget just a couple of housekeeping notes before we get started with Allison's presentation the webinar will be archived for future viewing so you can take a look of that on the atmospheric sciences website and you will also be able to share the that archive with any colleagues that you think might be interested we also will have a Q&A session each presentation will take place for about 25 minutes and then you'll have an opportunity to use the technology using your dashboard to either raise your hand or ask a question to us through the GoToWebinar system without further ado I'm going ahead and introduce Allison Steiner Allison you can go ahead and start your presentation good morning good morning and thanks for this you need to give this presentation again and also to the atmospheric sciences section for organizing this session I'm Allyson Steiner from University of Michigan and I'll be talking about terrestrial biosphere atmosphere interactions and you know most atmospheric sciences tend to think about the Earth's surface predominantly as a lower boundary condition and the numbers that are frequently cited show that from the two-dimensional space land is taking up about maybe about a third of our Earth's surface and the remaining fraction is represented by oceans but vegetation and once we start thinking about the biota that's living on the Earth's surface that introduces a third dimension in terms of how we can think about the Earth's surface area and let's simply visualize this is often represented with a parameter Oona's leaf area index and I'm showing here an animation of monthly leaf area index as derived from the motive satellite and so essentially what that means is that the surface area that's provided by the structure of vegetation can often be many times larger than the ground area that the vegetation may occupy and so the example I'm showing on the left it uses the leaf area index or la I as a factor of three meaning that the leaf surface area is representing a factor of three greater than the ground surface and so we can see in this visualization is that we can see the greening of the southern hemisphere and the sin of the Northern Hemisphere in the summer and also the tropics as well as marginal changes within the southern hemisphere so if we actually plot this from a latitude '''l perspective this shows this bias where we can see a larger amount of leaf area index in the northern hemisphere and if we account for this surface area that means that in July about approximately half of the Earth's surface area can be increased over land when we take into account this interpretation of leaf area index and so what I'd like to talk about today is how this change in leaf surface area and the processes that are happening at the surface can influence both bio geophysical processes at the Earth's surface as well as biogeochemical processes and talk a little bit about the feedbacks that those types of processes can have with the atmosphere from the biophysical perspective then one of the first things that people think about is the surface energy budget we're going to hear more about the Earth's energy budget and Kevin's talk coming up next but from the lower boundary condition right we have in coming solar radiation from the Sun some of that gets absorbed some gets reflected and then some gets absorbed into the surface of the ground but most of that energy is being returned from the Earth's surface back to the atmosphere either in the form of sensible heat or latent heat fluxes and this ends up being an important point in terms of how we influence motions in the atmosphere in addition to the surface energy budget we can also think about this from the water budget perspective where we have precipitation in coming in from the atmosphere it can interact with the canopy you can get intercepted or fall through to the ground and infiltrate into the surface and then again some of that moisture is returned back to the atmosphere through latent heat fluxes of which transpiration is really one of the dominant mechanisms for that return of moisture and so predominantly today I'm going to focus on that how vegetation is influencing latent heat fluxes and what that means for atmospheric science on the other side of this diagram is the biogeochemical perspective and so in this regard now we're not just exchanging potentially energy or mass we're looking at exchanges or fluxes of different nutrients such as carbon or nitrogen or also some potentially short-lived climate forcing agents or ones that can influence greenhouse gas concentrations such as biogenic volatile organic compound emissions or VOCs as well as primary biological aerosol product particles and I'm predominantly going to focus today on seed box between the land surface in the atmosphere regarding VOCs and the primary biological aerosol particles so as we've tried to think about how we can capture these feedbacks within our suite of modeling and observational perspectives from the observations we can use into two observations such as flux net power observations or other ground-based monitoring sites aircraft campaigns are frequently used also to understand the exchange of these energy and mass with the atmosphere and also there's an emerging space towards using space-based observations to try to understand some of these land surface processes as well but to understand the feedback so it's often challenging to see these with observations and this is where Earth System models come in they're trying to represent a lot of these different processes as well as understand we can use them to probe and test different sensitivities to different feedbacks so what I like to do this talk is kind of focus on three different questions one is understanding what processes drive by a three atmospheric feedbacks the second is what challenges exist in identifying these feedbacks and finally what opportunities could improve their representation in predictive or system models so I'm going to start on the biophysical side of the diagram and because I'm talking about changes in this surface I'd like to talk a little bit about how we represent vegetation within our system models so starting with the very early first generation models the Manabi model back in 1969 it started to introduce a surface energy budget but there was no vegetation included in these models as models got more complex the second generation model started by Bob Dickinson with fats and pure cellars in 1886 the SIP started to introduce a vegetation canopy and to do so in order to not add too much complexity to the models they utilize something known as a big leaf parameterization where that leaf area index that I talked about in the beginning could be used to describe a canopy in terms of both sunlit and shaded leaves in order to build in more processes and more realism into these models the third generations model started to introduce understanding how photosynthesis and stomata conductance or the opening of stomata that allow that transpiration of water vapor to occur to be coupled within models so by that manner these models tried to start to introduce these processes to allow for a more realistic representation the forest generation model started to introduce dynamic vegetation which would be allowing models over long timescales to be able to predict distributions of vegetation types from different processes as well as including much more complex ecosystem carbon balances in terms of the fifth generation or what we see now evolving with land surface models is the introduction in some of the global models of vegetation demographic models which can be really important in terms of how we understand vegetation changes due to climate change so as again modeling are one of the tools that we can use to try to understand these feedbacks so from the bio geophysical perspective I'd like to highlight two different types of feedbacks that we can often observe and most people are fairly familiar with the first has to do with local precipitation recycling so in this example for the figure on the Left changes in the land surface such as soil moisture can influence the evaporative fraction or that ratio of sensible latent heat flux which can then go on to influence processes within the planetary boundary layer affect the formation of clouds and precipitation which can then further feed back to the surface and this sort of local precipitation mechanism has been observed and quantified in many cemet semi-arid regions there's also emerging studies in terms of understanding what the contribution to the non-local moisture would be so as evaporation is occurring in one place locally but it can be transported via the atmosphere and moisture fluxes to influence precipitation in other regions and in this study by way and dermyer actually went to quantify what that non-local contribution would be so in the figure on the bottom the red boxes are ones that have identified a lot of non-local precipitation and then the moisture fluxes you can see our frequently located in different locations similar to precipitation we can also see feedbacks with temperature in terms of the non local and local misses well so with local temperature feedbacks it's a similar process where if perhaps we see soil drying that can change that fraction and increase sensible heat as opposed to latent heat and that can end to work to dry air within the planetary boundary layer and increase the evaporative demand another recent study here has shown that this process may not just be local and that heat can be affected and influence heat latitude mid wave mid latitude heat waves in other regions so we can also see this non-local response with respect to temperature so try to try to understand and disentangle these feedbacks the models become very important so how do we represent the forest canopy in that land surface area that I talked about at the beginning and how can that be used to understand these types of fluxes and identify this as one of the first challenges within terrestrial biosphere atmosphere interactions which is how do we represent the forest canopy within models so the leaf surface area that I talked about can drive processes such as transpiration right which is really a dominant component of that latent heat flux so this is a figure from a synthesis paper that used several different types of canopy models with different representations of the forest canopy some are the big leaves Sun leaves shade models that I showed in the earlier development others include multiple layers within the forest canopy and so by comparing all these different models this is showing you one result from this paper at the Duke Forest which is a flux net site and showing you the change in transpiration as simulated by the models over several years the observations are shown from the flux net site in terms of the black dots and you can see there's at least a factor of two difference between these models some models can capture some inter-annual variability but the model still struggle to capture REM or really capture a lot of that observed entry on your variability so in terms of this challenge one of the opportunities that's available is that a lot of the new satellite observations that are being launched for example the new suite right now that's including eco stress Jedi OC o3 and he's we are what are one way that we can try to improve our understanding of that lower boundary condition and how we represent vegetation canopies so while these aren't direct observations they can really provide important constraints for models but that leaf surface area isn't the only piece of the bio geophysical profit the bio geophysical processes that we still need to try to understand the second aspect of that is access to moisture especially for things like transpiration rates so soil moisture is another aspect that requires some attention we think about how soil moisture is evolved within our system models the first generation models were using a fairly similar fairly simple bucket model which allowed a certain amount of soil moisture content to be held within a bucket with inputs and outputs of precipitation evaporation and subsurface runoff as models advance the second generation we saw the addition of vertical structure within the subsurface and using Darcy's law to explain infiltration within the soil and then finally a lot of the newer third generation models have introduced detailed hydrology models such as top model Vic to better represent those surface processes we've also seen a big shift in terms of opportunities in terms of how remote sensing products as well can be used to understand surface soil moisture so this is a review paper showing you several of the different satellites that have been launched over the past few decades to try to understand surface or a mush or that first five centimeters of soil although I will highlight some of the challenges of this is this can be very difficult to remotely sense surface soil surface soil moistures through vegetation so in this figure the hatching shows all regions that we'd be blocked out by dense Vedic vegetation in which case the satellite would then be remotely sensing the canopy water and not the soil water content so this represents another challenge because typically that means that in order to interpret roots and soil moisture or the amount of water that vegetation can access from the deeper soil we still need models to be able to understand how that's working and why this challenge is important is because it sort of highlights how we still struggle to capture soil moisture flux relationships so in this example I'm showing you a recent study where we've looked at and compared observed transpiration fluxes or latent heat fluxes from several different flux net sites across the temperate to boreal transition region in the United States here we have these organized by plant functional type with deciduous trees on the left and evergreen sites on the right and so one of the things you can see that the deciduous sites many times the models under predicting that the gray boxes are much showing much higher latent heat fluxes don't we what we observe with two different versions of the community land model and for the Evergreen sites things will look a little bit better in terms of some of that of a model evaluation but if we look a little bit more closely on the temporal scale now I'm just showing you two different sites and this is soil water content versus latent heat flux well the overall June July August total might be close to the observed we can see some differences in terms of the seasonal profile so in the observations here the June fluxes are shown to the right-hand side generally things are wetter and the fluxes are lower as we move into the summer with more available radiation the fluxes go up and we can see that drying throughout the summer season where we have lower soil water content as observed at the site in August and the model really struggles to either model with depending on which the amount of conductance parameterization you're using really struggles to capture that seasonal cycle at both the Evergreen and the deciduous sites this represents one of the challenges in terms of how we can think about if models are able to capture these feedbacks between the atmosphere and the land surface now I'm going to switch over to the biogeochemical side of the story and talk a little bit about biogenic PFC emissions and how they can influence feedbacks between the atmosphere and the terrestrial biosphere the biogenic PFC emissions are important they're carbon-based compounds that tend to be very reactive and can undergo a series of reaction in the atmosphere they get oxidized by the o8 radical and if sufficient nitrogen oxides are present they can form the greenhouse gas tropospheric ozone which is also harmful to human health additionally the set of reactions can produce a suite of oxidation products that have a lower volatility than the original emission and in many cases under atmospheric conditions they can partition to form secondary organic aerosol which can act as a forcing agent within the atmosphere as well so one of the most important be BOC emissions is one that's as known as isoprene C 5 H 8 and it's important because it's emitted globally at a very high rate and it tends to be very reactive so we look at how isoprene has been understood throughout the history of atmospheric science the first observations were actually published by a Georgian scientist in the 1950s although a lot of those publications were not read into the West until later after the iron curtain came down and then simultaneously a little bit later in the United States Fritz went in 1960 wrote a paper about the blue haze that was frequently observed in regions like the Blue Ridge Mountains and attributed to natural emissions from vegetation after IFS people started recognizing these compounds they found that they were also really important in terms of tropospheric ozone chemistry and this is important both from the rural perspective as well as very urban vegetated regions in urban areas like Atlanta and finding that it was a very important thing to factor in in terms of how we can work to abate high ozone concentrations after this finding for tropospheric chemistry was discovered we started to develop a lot of models in terms of regional and global emissions inventories and it's always been an important part of tropospheric chemistry models I would say in the last two decades it's gotten even more attention as new chemical mechanisms have been found to show that isoprene can also influence secondary organic aerosol formation so one of the challenges with isoprene is that it varies significantly with vegetation type so it goes much beyond what we've seen with plant functional types and how different types of trees are represented within our system models for the bhaiyyaji of physical processes for example when we look at deciduous trees species like poplar and Oaks tend to be very high isoprene emitters whereas enables for summer or not and so this ends up having a big impact in terms of how we try to improve their representation with their ear system models and intrepid spirit chemistry the vertical structure also matters quite a bit when we think about how we simulate forests we know that different species are at different locations within the forest canopy and when we've incorporated that into emissions estimates at a flux net site in northern Michigan the University of Michigan Biological Station we found that changing the vegetation species in their structure can change isoprene emissions by up to about 35 percent so the vegetation structure and where that surface area is is important for isoprene as well but perhaps more interesting from the feedback perspective is how climate controls isoprene so met isoprene emissions are dependent upon environmental factors such as light temperature and the soil moisture is another one that's thought to be true so for light and temperature the behavior of isoprene mimics photosynthesis although the temperature response curves are slightly different and you can emit more isoprene at higher temperatures than you can photosynthesize for soil moisture I've shown a parameterization that's here that's included in isoprene emission models but this still represents a large uncertainty because it's been very difficult to get a good handle on how soil moisture constrains isoprene from laboratory and field measurements so isoprene can be important from the perspective of how we try to understand these types of biogeochemical feedbacks between the atmosphere and the terrestrial biosphere so as we can see in this temperature response curve generally isoprene increases with increasing temperature however there's a limit to that isoprene emission and one interesting fact to note is that when people looked at the influence of ozone changes with temperature they've also noticed that there can be a plateau with respect to how ozone increases with increasing temperature so on the Left I'm showing you a figure from the south coast from observations from the south coast air Basin in California where with increasing daily maximum temperature we see an increase in the maximum one-hour ozone concentration but you can see over different decades that increase has slowly started to Plateau and one of the things that we've postulates postulated is that that may be due to the isoprene response under high temperatures another study using the geo-scan model found that this ozone suppression could occur other locations that the United States as indicated by the red dots and that study indicated that mere logical factors such as changes in the planetary boundary layer heighten stagnation events could be important as well so no matter what the driver is understanding this type of feedback is very important for the predictability of air quality the other feedback in addition to high temperature events would be that from isoprene and drought and so as I mentioned this is one that's been challenging to try to constrain with observations this research study used observational evidence to show that while in the early drought years in California from 2011 to 2013 we didn't see that much change in isoprene but when it when the cat state went into severe drought in 2014 and 2015 then we saw a substantial decrease in isoprene by about 50% and that led to about a 22% decrease in ozone production modeling studies that try to incorporate this effect and look at the effect of VOCs on drought on VOCs in subsequent SOA I've actually shown an increase in biogenic PSC emissions under drought in a subsequent increase in SOA and this sort of highlights this challenge of trying to understand drivers in these sort of isoprene climate feedbacks so the third challenge I'd like to highlight is that we really don't have a good handle yet on how biogenic BOC is going to respond under extreme events and this has implications for air quality as we move into warmer climates and finally the last point I'd like to make from this figure is that well we might understand the emissions of VOCs under our current climate it could be that under warmer climates we actually induce other types of vo C missions that also could be reactive in influence of formation of aerosols and influence clouds so one of the opportunities for addressing this challenge again remote sensing can play a role in here we've actually seen most recently in the past year new retrievals of isoprene from space using the Chris satellite and also you know because that data records going to be short one of the important things is going to be to understand the long-term drivers this is going to retire long-term monitoring sites and there are very few records that we have of long-term measurements of isoprene fluxes one of the longest that we have is at the University of Michigan Biological Station although that is discontinuous and nature and this represents one of the the challenges as well in term of how we can try to understand these feedbacks the next biogeochemical feedback i'd like to focus on has to do with the introduction of aerosols to the atmosphere it is their short-lived climate for sir and we know that they can have both direct aerosol effects meaning that they can scatter and absorb incoming radiation and then they can also have indirect aerosol effects where these types of particles can act as cloud condensation condensation nuclei are also as ice nucleating particles that can influence the formation and persistence of clouds and hence the global energy budget so one that I'd like to focus on is that between aerosols and the forest canopy and light penetration so as we add aerosols to the atmosphere they can induce a direct effect which can actually work to overall reduce the total amount of radiation reaching the surface but it also can increase the amount of diffuse or scattered radiation so showing this looking at this this is a foetus on the photosynthetic response curve for photosynthesis and if we think about this upper and lower canopy and our upper canopy right the Sun leaves that are receiving a lot of that direct sunlight they might expect to see a reduction in the total amount of light that recently received due to the presence of aerosols however as that diffusive fet goes up we might expect that we would see more radiation reaching the lower canopy and if that lower canopy factor outweighs the upper canopy loss we could see an increase in productivity within the forest canopy due to the presence of aerosols or clouds so observational studies do suggest that we see a weak influence of diffuse light on fluxes and this is an example from a study that looked at they saw a weak decrease in carbon fluxes with increasing aerosol optical depth or essentially meaning that the forests are taking up more carbon under moderate aerosol loadings yet if that's true we should see a relationship with the surface energy fluxes that's something that's been harder to disentangle so there's a lot of slight variability within these responses but overall what we notice when we are looking at flux net observations was that increasing aerosol concentrations led to an overall decrease in surface energy fluxes which creates an inconsistency in terms of how we think about how forest canopies might respond to aerosol several recent modeling studies have promoted the importance of this diffuse defect again showing increases in GPP by aerosols in the study on the left across a lot of the northern hemisphere and another study which postulated a feedback directly related to biogenic vo sea emissions which could form their own secondary organic gara cells in influence and promote additional carbon uptake so one of the challenges I'd like to highlight is that what we see the models doing appears to overestimate this diffuse effect so if we look at this this is a figure of the total visible light on the x-axis as compared to gross primary production or gtp on the y-axis at the University of Michigan Biological Station these are colored by the diffuse fraction where yellow colors are showing higher diffuse fractions so generally at lower light levels we tend to see more diffuse but as you go up along into higher light levels you can still see that the diffuse radiation is influencing GPP throughout that distribution in contrast and we look at what the model doing and this is an example using the clm multi-layer model you can see a very different pattern with the diffuse radiation where a more diffuse very strongly promotes the GPP and this is leading us to start to think that the models actually meet the overestimating this diffuse effect within the model and then the last piece I'd like to highlight is this influence on the indirect effect and how these particles may affect clouds and so then that final challenge that I'd like to highlight is the inclusion of biological particles in cloud interactions and the reason why I'm highlighting these biological particles is because they're really important in terms of how we understand what the pre-industrial aerosol forcing looks like and this is one example from our research group here at Michigan where we've been looking at the emissions of primary biological particles such as pollen which are emitted very frequently in the northern latitudes by a lot of different types of vegetation atmospheric scientists have typically thought that pollen grains are too large to be important that important in the atmosphere however recent work has shown that once under moist conditions at relative humidities 80 percent or higher pollen grains can actually rupture and create lots of tiny particles which are organic in nature and can act as cloud condensation condensation nuclei and this could lead to a sort of aerosol indirect effect where we would increase the cloud droplet number concentration and have the potential to suppress rain so one of the opportunities I think here with respect to the biological particles is we have a lot of new measurement techniques coming online such as fluorescents and things like metabolomics that can probe important new constraints on biological particles because right now we really have a very poor understanding of these types of particles and their contribution within the Earth System so with that I'd just like to highlight again I've sort of brought up five challenges within this within this talk one is how we represent that forest canopy within our system models how those models are capturing soil moisture flux relationships and then from the biogeochemical side how VOCs might be changing and influencing atmospheric chemistry under extreme events these diffuse radiation effects on the canopy and finally these biologic aerosol cloud interactions and from that perspective in terms of needs for the community we're hoping that models are really be able to progress to be able to accurately capture these feedbacks because that'll really help in terms of predictive capacities for future or system model simulations and then the observations still represent a very important piece of that where the need for higher space and time resolution observations will be very crucial for identifying these feedbacks and so if fat I just place up some acknowledgments and I'd be happy to take any questions thank you thank you so much Alison really appreciate that great talk so we've got the questions are open for folks that would like to ask Alice in a question you're welcome to do so using the questions box go ahead and type your question I'll be happy to relay that to Allison or you can go ahead and raise your hand using your dashboard and we can then select you and if you've got a mic or if you're on our on the phone today you can ask Allison your question on the mic so we've got a for five minutes for QA so we'll let this sit for a bit and see what questions come in okay Richard if you're okay I'm going to go ahead and unmute you so you can ask Alison your question oh wait oh it's not allowing me to unmute you for some reason Richard shows that you're connected to audio hmm attendee is muted click to unmute is showing that your self muted I think that could be why it's not allowing me so if you can unmute yourself there you go there you go Richard welcome all right yeah great talk I didn't hear any mention of wildfires I would assume that's also biogeochemical feedback there's a lot of feedback going both ways including what types of plants you're gonna end up with after one fire yeah absolutely I think you know there's a lot of interest in the atmospheric chemistry community on this biogeochemical side in terms of what types of trace gasses and particles are increasing the one study that I highlight the UA and Ungar study they actually did that look at diffused radiation specifically from fires and also from anthropogenic emissions if you're interested in that feedback specifically for fires and then in terms of you know succession I think that's something were there dynamic vegetation models you know over long timescales could be looking at that change in vegetation composition as well so do these fifth-generation models you were talking about that include the types of plans are there fully interactive that they will also adjust with the developing climate and so I think it depends on the model so some of the you know in terms of dynamic vegetation model there's one of the biggest differences I would say across our system models is how they do represent fire in terms of both what ignites fires where they occur and then what impact that has on the vegetation so I would say some of them do include that type of feedback and some do not there's a lot of variability there right okay thank you muted now sorry no other questions coming in at the moment if anyone has any other questions feel free to do so in the questions pane or raise your hand and we can go ahead and call on you so it's probably didn't hear me thank Richard for his question because I was muted let's see I've got about one more minute before we move to Kevin's presentation for questions looks like might have another question yeah sorry more comment I don't know whether you are aware of arms the do EE atmospheric radiation measurement program will move the mobile facility from elect up to the southeast us and they're currently looking for input on siding where that should be located this is a five-year deployment of a very a lot of atmospheric instrumentation and they're focusing on the southeast us and that's an area that should be of prime interest to you too yes I'm actually on the project team for the site selection meeting last week yeah we're really I'm really excited about the prospect of that new site yeah okay thank you so we are at time for Allison Allison thank you so much for your great presentation really appreciate it we do have a link that I share to Allison's abstract so you can feel free to go ahead and take a look at that and again we'll be sharing this recording with you all so anything you may have missed you'll be able to catch again so I'm going to go ahead and turn the presentation over to Kevin Trenberth Kevin good morning good afternoon everyone let's see if we can get this going here we go I think it's good well I'm going to talk about this changing energy budget as such and what the implications are on a global basis and then toward the end on a regional basis and so the big picture is the course we have the sun shining radiation onto the planet earth which is which is more like a sphere and as a result there's a lot more radiation received near the tropics and much less at high latitudes whereas the outgoing long-wave radiation depends upon temperature at absolute temperature and is much more uniform and so we get a distribution of net radiation on the left side of this panel which requires heat transports by especially the atmosphere and the ocean in order to balance the overall radiation budget this is work that I've done in conjunction with John Fasulo and young-shin Zhang and Li Jing Chang in particular so one reason this is an interesting topic is because of the diversity of different kinds of energy and the complexity that occurs so the incoming radiation is a shortwave radiant energy and it gets transformed into internal heat which relates to the temperature potential energy which relates to gravity and height latent energy which relates to phase changes and kinetic energy which relates to motion and all of these can be moved around in various ways by both the atmosphere in the ocean in particular they can get stored and sequestered by the various components in the climate system and ultimately they get radiated back to space as long wave radiation infrared radiation and with an equilibrium climate there is a balance between these overall flows of energy and they drive the weather systems and the currents in the ocean but they can also be perturbed through climate change so here's the overall picture of how the global mean surface temperature is changing this is actually the NOAA record I've got on here the pre-industrial temperature and you can see that 2016 is the warmest year on record I've got 2019 and here which is the second warmest on record there's a general increasing trend it's a bit more ragged as you go back in time and some of that is artificial because of less complete observations but there is still quite large natural variability so we can add to this the annual values of carbon dioxide before 1957 these are based upon bubbles of air and ice cores and after 1957 this is based upon the more in the lower record and I've put these together in a way to suggest that there's a relationship between them because we can prove that there is the pre-industrial by it was 280 parts per million by volume and the zero line on both of these curves is the 20th century average and so now we're up at 410 parts per million by volume and and there's a striking relationship between them now half of that increase has occurred since 1985 so this is during the lifetime of probably everyone who's listening listening here and it's accelerating it's not decreasing in spite of things like the Kyoto Protocol or the Paris agreement and so this is a real problem however I would argue that the most fundamental measure that the climate is changing is actually the Earth's energy imbalance one of the reasons that's important is that it is the net result of all the complicated feedbacks you know the main approach that's used to climate change is to estimate what is often referred to as radiative forcing put it into a climate model simulate all of the complicated feedbacks and there are many which we don't do very well like clouds and aerosols and so on and some that Alison talked about and here we're looking at the end result of all of these and so this has a tremendous advantage in many ways so this is a schematic of the overall flows of energy through the global climate system annual average as a function of the vertical and I'm not going to dwell on most of these but I will focus on the top values which are given to an extra decimal point because the energy imbalance here is 0.9 watts per square meter the only difference between this version and the 2009 version we published is that we have included the scattering and reflection of the downwelling long wave radiation which actually helps us balance the surface energy budget better and so this relates to the surface emissivity of the oceans of 0.97 so here's the more regional aspects the absorbed solar radiation is given at this is 2002 2016 the outgoing long-wave radiation is in the second panel and the net the sum of these two is given at the bottom the top two panels both have quite distinctive cloud signatures hi cloud is bright and it reflects radiation that it also emits at lower temperatures and as a result this tremendous amount of cancellation between these two and we don't see that a lot of the cloud signatures in many places in the net except where there's low strata cumulus and also in desert regions so the overall energy imbalance is around about let's just round it off to one watt per square meter and for to get a sense of what that means the Christmas tree light is about 0.4 watts globally if you add up this one watt per square meter that's about 500 terra watts a terawatt is ten to the twelve twelve zeros after the value and for comparison the u.s. in 2018 electric consumption was about one point two eight terawatts and the global electricity generation is estimated to be about five point seven terawatts and so the energy imbalance is a factor of eighty five to ninety times the global electricity generation now that tells you that this energy imbalance is really very very large and in fact the direct effects of humans are small except locally in cities and it's mainly through the interference of the of the with the natural flows of energy through the climate system that it matters for climate change then the second aspect of this is that one watt per square meter is quite small compared the overall compared with the overall flow of energy through the climate system which is you know the difference between the incoming solar and the reflected and the outgoing long-wave radiation of both of order two hundred and forty watts per square meter and so one part in two hundred and forty means you can't go outside and say oh i can feel global warming you it's not how climate change is experienced instead it has to accumulate and it does so under certain circumstances because it's always in the same direction so what happens to this extra heat that we've got well it warms the land in the atmosphere it goes into the ocean and that the ocean expands it melts land ice and both of those then raise sea level it melts sea ice and warms the waters and it evaporates moisture and causes changes in rainstorms and clouds and this is the main complication that exists but a lot of this amazingly balances out over a period of about five months and it turns out that over ninety percent some 93 percent ends up going into the ocean so one place that the energy accumulates is in the melting of ice so glaciers have melt there's a lot of pictures like the one I've shown you here of Muir glacier and also Arctic sea ice is down over 40 percent this is the September value at the at the peak of the summertime loss of Arctic sea ice and the overall rate is 13 percent per decade so the this is one place that the energy accumulates there was some spectacular melting in Greenland last summer in 2019 especially around early August and the picture on the left is from the NS idct website showing water rushing down Mulan's and and creating channels in the ice and the ice is also showing up as being quite dirty if we estimate the overall of effects of the melting of ice it turns out to be about fourteen terawatts so globally that's about point zero three watts per square meter and of course this is partly because the coverage of snow and ice is over a fairly small portion of the globe so what about land well if the land is wet a lot of the heat goes into evaporation evapotranspiration but in a drought the heat can accumulate it only takes one little rainstorm and a lot of the accumulation effects tend to vanish and so the heat goes into firstly drying and then secondly heating and as the temperature rises so the evaporative demand of the atmosphere also increases and if you have one watt per square meter over a month and you accumulate that that's equivalent to 720 watts per square meter over one hour in other words to 720 hours in a month and 720 watts is the equivalent to the power of a small microwave oven one square meter is about 10 square feet so let's say it's one microwave oven at full power every square foot over the planet for six minutes no wonder things catch on fire now this is a physical argument this is not trying to deal with the awful datasets and the statistics of how fire wildfire in Australia or or or California or in southern Europe is changing instead this is a physical argument and it says that things have to dry out and it has consequences for the risk of wildfire so the non Oshin component overall is about point zero seven watts per square meter so what about the oceans the ocean heat content so we've updated this curve now through 2019 2019 is the warmest year overall for the oceans by quite a substantial amount 2018 is second 2017 is third 2015 is fourth and there's a small dip where are we here in in in 2016 and and that was because of the big El Nino event that occurred at that time and that put extra heat into the atmosphere especially through evaporation and and latent heating of the atmosphere and it took heat out of the ocean but even that big El Nino effect is relatively a small blip in the overall ocean heat content I put the mana lower record on top of this to suggest that there's a relationship between the two and the uncertainty of the ocean heat content record increases as you go back before about 1990 which is when altimetry began the sea level measurements from space whoops there we go so we can also measure the distribution of this in the ocean this is not quite up to date but the biggest warming is in the Southern Oceans and in the North Atlantic there are some places where it's cooled and that relates to the ocean circulation which which is a little bit like that so some of the heat gets carried down and some of the cooler waters from below get get brought up but you know it's warming just about everywhere over over the oceans and this is the these are somewhat smooth values but this looks at different layers 0 to 300 300 700 meters and you can see the main penetration of heat has really not occurred below about 300 meters until after about the late 1980s or thereabouts and that's gradually penetrated deeper and deeper and 93% it pretty much matches what's happening at the top of the atmosphere with regard to radiation so a consequence of this is that sea level rises this is the overall sea level rise record and this is affected by El Nino there's a big blip here which was a La Nina event a trained a lot over Australia and formed a big lake called Lake here and took about five millimeters of water out of the global ocean but there are also other parts of the world North America and and parts of Asia that had large amounts of snow and and water on land at that time and in general during El Ninos it's there are it's more drought over land so this is again evidence of the ocean heat content increasing as well as the melt of ice so the challenge is then are can we say a lot more about what's going on if we do this locally so here's the extra challenges that exist we have the radiation at the top of the atmosphere and at the surface you've got the evaporative fluxes and the sensible heat fluxes and so the net surface flux is given by the sum of these three and there's a small component from precipitation sensible heat which we actually take into account as well and then what's going on in the atmosphere is balanced by the radiation at the top of the atmosphere and the surface fluxes the divergence of the atmospheric heat transports or in transport sand in the ocean it's we certainly have to take into account the storage term there whereas in the atmosphere it's relatively small this slide here don't have time to go this into any detail but this is how we do these calculations we use the reanalysis and do the calculations of all of these terms in considerable detail we've learned how to do these quite wellness critical that we actually balance both the water and dry mass budgets as well and and this involves processing in our case many terabytes of data and if you go to the latest reanalysis easy ra.5 actually petabytes of data so this is a huge task so the result then here's the radiation at the top of the atmosphere that I showed you before here's the total heating that goes on in the atmosphere actually this is not heating it also includes moistening and so that explains why the subtropics tend to be emphasized because there's a lot of evaporation that goes on in into the subtropics and then we see the large fluxes into the atmosphere over the Kuroshio and over the Gulf Stream in the wintertime in particular and that's a lot of fascinating details in here so why are these different most people often think that this is what's going on in the atmosphere it's not this is the this is the climate system this is what's going on in terms of heating the atmosphere and then the differences between these is the net surface flux and that's what we get out of this and just about all of the features that are in here appear to be real and so the blue areas are where heat is going into the ocean and the red areas are where heat is coming out of the ocean and as a result there has to be a transport by the ocean from the blue areas to the red areas something something like this and so if you look at the Arctic that's nearly all reddish or orange and the North Atlantic the blue area and the Atlantic is not sufficient to compensate for that and this very little flow through the Bering Strait and as a result some of the heat in the Atlantic actually comes from the Pacific all the way around South America or sometimes even around Africa into the Atlantic and we can do calculations of this kind of thing which is really very interesting because we cannot get direct measurements of what the ocean is doing from in situ measurements within the ocean so here's what we're doing here we're calculating the divergence of the energy flux using this formula and then what we're going to do is to take zonal averages for the moment and do the meridian all he trots flux by integrating this quantity from where we start off with the North Pole for the Atlantic and the Arctic for the Bering Strait in the Pacific and we started in the South Asia for the Indian Ocean and then goes southwards and then we have often an imbalance at the Antarctic coast and we have to reconcile that with the top of the atmosphere radiation budgets we have ways of doing that then the one of the complications for the Indian and Pacific Oceans is the Indonesian through flow and there is a net flow from the Pacific into the Indian Ocean and a net flow around Australia like this which means the the mass budgets of the Indian Ocean and the Pacific Ocean are not closed by themselves and so heat transports are not as well defined under that circumstance in fact they're really not well defined but what we've done is to do a calculation of this nature his his the global his the atmosphere his the ocean with some error bars on it as the meridian all transports and then the ocean is the same value over here divided up into the Atlantic the Pacific and the Indian and now we've added in this component from the Indonesian through flow which we have as a function of time and as I say this is a bit artificial because the mass budgets of these are no longer closed but this is this is what you get when you do that kind of thing and over the Southern Oceans of course all these things are combined because of the Antarctic circumpolar current so one of the things we've been able to do now for the first time I would say is to estimate meridian or heat transport this is the annual mean annual cycle this is global the end of Pacific and the Atlantic here and let's see these are the you know the main transports that are occurring and so in the Atlantic it's northwards year-round except maybe in September and October that's when it's the warmest in the Northern Hemisphere and so there's no requirement as much for the ocean to transport heat northwards but otherwise the Atlantic's transporting heat north was most of the year and certainly in middle attitudes of the northern hemisphere the indo-pacific however has a very large annual cycle which actually maximizes near eight degrees north which is where the ITCZ occurs rather than on the equator a very large amplitude and we can see that being reflected in the global values and so we can also look at this from the standpoint of the Pacific and the Indian Ocean where we have accounted for the Indonesian through flow and again we see in the Pacific this very large annual cycle of Meridian all heat transport that has profound influences on the on the climate system eight petawatts is the annual cycle that's huge then of course we can look at the time series of these things and so we can go through here through 2016 this is the twelve months running mean values so that we've got the total values here and down the bottom I've taken out the mean annual cycle and so we're looking at the departures the anomaly so-called and you know it looks fairly blobby and you say oh isn't this noise well actually it's not all of these things turn out to coincide with El Nino events and they're dominated in the in the Pacific Ocean so we'll look at that in just a second here so has the Atlantic the Atlantic has quite substantial variability the biggest variations are associated with the North Atlantic Oscillation these changes and and this record here that we've devised can be validated at at 26 28 north with the rapid array in the ocean and has quite good agreement although we have slightly different trends which may relate to the homogeny of homogeneity of the two different records but we think we think this is a pretty good depiction of what's going on in the North Atlantic and the main coherent transports are from the equator to about 45 degrees north this is the indo-pacific and the South would transport in the southern hemisphere the north would transport and here you can see the 2015-16 El Nino event showing up and what I'm going to focus on in the last part of this talk is the across equatorial transports the end of hemispheric exchanges and so now we can produce time series of these things and so here's the global value in black and you can see there's quite large inter-annual variability quite large fluctuations here and his 2015-16 it just went off the scale in fact quite quite remarkable associated with the 2015-16 El Nino event if we break that down this is what the Atlantic is doing across the equator here's the Indian and and his the Pacific down here and so the Pacific you can see is dominant in terms of the variability with regard to the global you know there's a tremendous amount of work going on with regard to what is called the a mock the Atlantic Meridian all overturning circulation but in the tropics and subtropics the what's going on in the Pacific is much much greater than anything in the Atlantic the Atlantic comes into its own in the higher latitudes of the Northern Hemisphere we've also got down here the atmospheric and the total top of the atmosphere component and and and there's some numbers down the bottom here and on the right-hand side I've just shown you some of the correlations between these curves so the Pacific is correlated point 9 7 with the global top of the atmosphere is hardly correlated at all that the global cost requite oriole transports and the Atlantic and Indian Oceans are negatively correlated you can see the Pacific in the Indian by the way they both go up and down together through here but then the Pacific goes crazy in 2015/16 and that greatly influences any of these correlations so here's the overall schematic of the flow of energy across the equator in the three different oceans this flow through here one one petawatt and redistribution over the Southern Oceans there's a flow up into the Arctic and the North Atlantic and you know dispersed through the through the Arctic and on the right-hand side I've got the the overall changes showing up and then this is the vertical depiction the top of the atmosphere is given here that's separate from the atmosphere here we've gotten the overall atmosphere transporting heat into the southern hemisphere the ocean is transporting heat northwards so that's mainly in the Atlantic there's a flux into the Northern Hemisphere and into the into the southern hemisphere oceans to compensate for those but this is a net imbalance here which is point zero five watts 500 500 watts in this case which means that the Southern Ocean is warming more than the Northern Hemisphere Ocean and that's mainly because the Southern Ocean is bigger than the Northern Hemisphere Ocean so this these numbers all differs somewhat from previous previously published versions it turns out it depends a lot on the period and whether you've got the 2015-16 El Nino event included also we've got revised atmospheric energy transports and better representation of the ocean heat content and so the differential storage between the oceans is also an important thing to take into account so I'm going to close out by just emphasizing the potential for these kinds of methods to come into play of special note is the extremely large values here in 2016 associated with the El Nino event and the big changes in the internal Indonesian through flow and the values range from minus 0.3 to 1.2 petawatts for the 12-month running mean in terms of the transports murray only and if you don't include 2016 the ranges is certainly a lot less and so these the US energy imbalance has implications for the future you know if I had longer we could link these to marine heat waves and and hurricanes which and you know there are profound consequences in both hemispheres they bring in new kinds of information and in fact there's a lot of information in the coupled system that's not being utilized in many analyses and it also constrains many data sets because these things have to add up and it also constrains models that can be used to validate models and thank you very much thank you Evon really appreciate that so we've got some we've got a question coming in here for you again you're able to ask your questions using the questions area of your dashboard or feel free to raise your hand and we can unmute you so you can ask Kevin your question live first question is coming in from Priscilla was the calculation of MHT using daily reanalysis data regarding what year the MHT and mama Lee's were made well IIIi showed that we have we have these Maria heat transports for every month and so we do this every month from 1979 on through 2017 as where we've got it now maybe we've gotten some for 2018 and what I emphasized here was the 12-month running means sort of annual values that tends to eliminate some of the noise that occurs and so we have a little bit less confidence in the individual monthly values than we do in the the annual values but these values are available from our website and one of our publications has a URL where you can go and access all of these data as time series thank you Kevin thank the question Priscilla we've got another question coming in from Janek or Yannick I apologize could there be a contribution of human power generation eg hydroelectricity worldwide to influence the global energy budget yes so I had this this brief mentioned here that we actually talk about how much sorry it was the where was it oh it was the comparison I had with this one of these ones here right let's see this one I actually had the comparison between the energy imbalance at the top of the atmosphere versus the u.s. total electricity consumption not just hydroelectric power and also the total global electricity generation is really quite small compared with these you know quite modest changes in the top and the top of the atmosphere radiation associated with the increases in greenhouse gases in the atmosphere and so energy consumption can be important locally these values can get up to around 20 or 30 watts per square meter in big cities and so you have an urban heat island effect but on a global basis they're relatively small did I answer the question thank you Kevin any other questions for Kevin we've got about one more minute to go so for coming from Amy what are the main reasons behind 20:19 anomalies 2019 is the last year on record and so that since this talk was given originally in December 2019 I didn't actually have those but here we we certainly have got 2019 values for the ocean heat content and you know it's global warming it's increases in greenhouse gases in the atmosphere but it's the is the primary thing that's happening and a lot of that heat ends up in the ocean with the Argo array we can now measure that much more precisely but there is interesting variability spatially over-over around the globe in 2017 one of the warmest spots was in the Gulf of Mexico and one of the consequences with hurricane javi in 2018 one of the warmest spots in the global ocean was off of the Carolinas and the result was hurricane Florence with tremendous amounts of rainfall and so on and then there are these marine heat waves the thing called the blob and there was a major marine heat wave off of Tasmania in the South Tasman Sea in association with the 2015/16 El Nino event because of the changes in the currents around Australia and so all of these kind of things come into play and help us understand why the local climate is varying the way it is all right unfortunately that all the time we have I do see a couple other questions that have come in I will share those with Kevin offline so that Kevin can respond but for now unfortunately we do have to end this webinar before I do that though I want to thank Kevin and Allison very much for their presentations today I've shared the links to their abstracts so you're welcome to reach out to them if you have any other questions or reach out to us here at AG you were happy to pass along your questions to them we do have a couple of things I want to thank Jim Hiro and Paul Newman from the atmospheric sciences section leadership they were integral in bringing this forward and working with Ag staff to get this webinar produced so I appreciate them taking the time and effort to do that you can find the seven other webinars in this series at their website where you can go ahead and register if you haven't already if you're interested in getting involved with this section you can also reach out to them as well they're always looking for for new folks to help out with different projects like this one and my information at the bottom there if you have any questions for a GU staff anything we can do to help we are here to answer your questions so with that I will go ahead and end today's webinar again thank you to our speakers and to Atmospheric Sciences leadership for presenting this webinar with Ag you everybody have a great day thank you all

Channel: AGU

Views: 1,614

Keywords: American Geophysical Union, AGU, Atmospheric sciences, atmospheres, Webinar, atmosphere, Fall Meeting, Meetings and events, Special events, Research and news, Atmospheric science

Id: 6y7EhoJKLLU

Length: 66min 9sec (3969 seconds)

Published: Fri Mar 06 2020