Aerosols, Climate and Poetry


Well when Mark asked me to do this I was
all set to come up with a real technical science lecture, but then he said “well
it’s got to have some non-science interest to it,” so I scratched my head
and came up with a title Aerosols, Climate and Poetry. Well aerosols and
climates easy that’s what I focused on for pretty much my whole career it’s the
poetry part that something about me that you probably never knew and certainly
never appreciated and probably still won’t appreciate it is I’m an
international prize winning poet. [applause] Hold your applause. So I went to Siberia in
November a couple of years ago for a workshop on Siberian aerosols you got a
question the sanity of somebody who voluntarily goes to Siberia in November,
but okay we can continue doing that. So you know as in any conference and
especially in Russia there’s a lot of toasts going on and after a few of those
they said well we’re gonna have a contest and everybody has to write a
poem, and they handed out pieces of paper with what the general subject of your
poem was supposed to be and mine was to write about the people of Tomsk. Tomsk, Russia which was where the conference was which was a bit of a challenge, but
I’d gone out at lunch time to eat lunch and I watched people feeding their
squirrels and so I wrote a poem about how nice the people of Tomsk were
because they took care of their squirrels. Now you probably want to hear
my poem don’t you well that lower right picture kind of explains why I’ve
managed to forget my poem. There was a fair amount of Russian vodka
involved in the process but I did bring my prize. Well I can pass it around if
you want to see it it’s a Christmas tree yarn. So aerosols and climate oh I’ll
come back to Siberia by the way, because there was a reason I went there.
What’s climate? It’s the average of weather over a long period of time, so
these people who want to criticize climate change by saying well you know
it’s snowing in Washington DC therefore it can’t be global warming. You know it
can be cold someplace but when we talk about climate especially global climate
we’re averaging over time, over many years and over the entire globe so even
though you have an unusually warm summer in Europe well somewhere else it may be
unusually cold and it’s those averages that people can’t do themselves really
very well. So what are aerosols? Tiny particles suspended in air and there are
all sorts of different kinds of particles they have come in different
sizes, different shapes, different chemical composition and their climate
effects depend very much on those properties of the aerosols. The soot
particle for example is a very special part of it of the climate puzzle because
that’s the strongest absorber of solar radiation in the condensed phase in the
atmosphere. So what are the effects? Well I’m really
only going to talk about one category of effects and that is the direct
interaction of particles with solar radiation, because they scatter light so
they redirect some of that incoming radiation into different directions
and they absorb light so the picture and the numbers there are the grand averages
for the Northern Hemispheric Indian Ocean for a three-month period in 1999
and we went down there and we both sat on an island and this is in the maldives sat on on an island and made
measurements for a few months, but also the National Science Foundation’s c-130
research aircraft went down and we had instruments on that and these numbers
are the average perturbation to the Earth’s radiation balance that were
attributable to aerosols due to the scattering and absorption. Seven watts
per square meter at the top of the atmosphere, so that’s essentially the
loss of energy to the Earth’s system. Seven, that doesn’t sound like a very big
number does it? Where’s where’s my straight man? Roses, what’s the incoming? [audience answer] Yeah about a thousand we’ll round it off,
but that’s that’s with the sun directly overhead midday. This is the average over
24 hours for several months. That cooling cooling at the surface is
those 23 watts per square meter that’s actually like about a quarter of the
amount of energy that the ocean is absorbing. So these are big numbers for
that particular region, so the effects: we warm the atmosphere because particles
like soot are absorbing solar energy they heat the atmosphere. Which also
means there’s less energy reaching the surface and that top of the atmosphere
effect then is the difference between those two. So this direct forcing that’s
just one part of the puzzle there are other aspects of the puzzle and I’ll
briefly touch on them later the biggest one is interactions with
clouds, because every single cloud droplet, every single ice crystal in the
atmosphere has formed on an aerosol particle so when you change the
properties of the aerosols you change the properties of the clouds. We’ve been
at this for a long time and this figure is from Scientific American about 25
years ago and it’s a model calculation of the global distribution of the
perturbation of the energy balance. So if you can see the numbers at the bottom
these really dark parts of the map are minus 1 watt per square meter, 0 watts
per square meter, all the way up to 3 in the yellow and
this calculation is done for two components sulfate aerosols and carbon
dioxide warming. What you see is a very patchy picture from the aerosol side of
that that’s because particles don’t reside in the atmosphere very long so
that the atmosphere is not well mixed and that’s why you see so much cooling
the the bluish and darker blue colors in a few specific regions where there are a
lot of sulfur industrial sulfur emissions. Well that’s another part of
the problem of understanding how aerosols are affecting climate. Remember
there’s a whole bunch of different kinds of aerosols and we see very non-uniform
distributions. That means that in order to understand the climate effect we need
to be making measurements in a lot of different places. It’s very different
from the greenhouse gases. It turns out if you measure carbon dioxide up on the
Mauna Loa volcano in Hawaii, which is where Noah and Scripps
Institute of Oceanography have been making measurements for 50 some years,
that actual 1 point measurement can give you a pretty good handle on the global
average. Can’t do that with aerosols, so what I spent a lot of my career doing
was putting dots on the map. A few very few of those dots are sites where we’re
actually making the measurements ourselves going to the site, calibrating
instruments, fixing problems doing all the data analysis ourselves. Most of
those stars though are from other places other institutions that are making
measurements and our goal was first to recruit people to join in this effort
and then to make sure everybody is on the same page in terms of making
measurements the same way. This brings me back to Siberia,
because you’ll notice there are a lot of really big empty places- spaces- on this
map and Siberia is one of them and the reason why we went to Siberia was to get
that dot on the map. Well what do we do with these
measurements? One of the things that is done is use them to test models of
climate forcing by aerosols. Remember forcing is the word I’m using to
describe a perturbation of the radiation balance the blue line is what you get
with a model without aerosols in it just greenhouse gases, the black lines the
observations and all the the band of yellow is a whole range of different
model runs, but what you see is that blue line is very different from the
observations and it’s not until you start putting in observations of
aerosols into the model that you get much better agreement between what’s
observed and what the models predicting. And it’s these kind of results that lead
to the ever increasing confidence that come from the international assessments
of aerosol effects on climate. How many have heard of the Intergovernmental
Panel on Climate Change IPCC? A few, it’s the international organization that’s
coordinating assessments of climate effects- human effects on climate- and
it’s there are assessments or really represent consensus of a large number of
scientists from all around the world that consensus also involves governments
in terms of approving the final wording. And I’ve never been to one of those
meetings, but I understand that the discussions get pretty intense about
specific words that get used especially from countries who are so dependent on
combustion of fossil fuels for their economies. I did get to take part in one
of those IPCC assessments as one of the official US government reviewers so this
report huge report is generated and sent out for comment
and anybody can comment on it but then there was a panel of government
scientists who had to prepare the US government assessment. So this slide- and
what can you see that from back there?- going down from the the top what is
being shown is the radiative forcing, here’s the zero line going to the left
as a cooling, here’s minus one watt per square meter these are top of the
atmosphere global averages and the warming. So carbon dioxide up at the top
it’s got the biggest single bar and a fairly modest uncertainty range here.
Carbon dioxides number is a bit over one and a half watts per square meter,
so that’s what much of the fuss about carbon dioxide is about that one and a
half watt per square meter perturbation of the energy balance. So the assessment
and goes through a whole range of different gases that absorb infrared
radiation, because that’s where the effect of the gases is is absorption of
outgoing terrestrial radiation. The aerosols are down here in the bottom and
the different colors represent different types of aerosols. Remember that picture
I showed you of what electron microscope photographs of aerosols look like
they’re very different. Well that’s this it’s breaking them down into their effects.
Most of them are cooling but black carbon the soot is a warming effect so
you’ve got to put all of those pieces together to get the overall effect of
the aerosols, and then there’s the effect on clouds that I mentioned briefly with
the biggest uncertainty bar of all and these letters over here the level of
confidence in those assessments the lowest confidence of all. Another effect
is absorbing particles falling in snow which leads to a change in the
reflectivity of snow, which means it’ll melt faster. So this is putting together
those different numbers with their uncertainties to get a probability
distribution of the radiative forcing watts per square meter.
Greenhouse gases here centered on about 3 or a bit over 3 watts per square meter
plus aerosols down around minus 1 watt per square meter and then the total
human and caused climate forcing with a pretty wide uncertainty range. What were
the consequences of that uncertainty range and why are then we putting so
much effort into making those measurements? It comes back to the
concept of climate sensitivity so I had to put one equation my talk. Climate
sensitivity is the temperature change the change in global mean surface
temperature associated with a given radiative forcing a given perturbation
in the radiation budget. It’s normally expressed as degrees centigrade
associated with a doubling of carbon dioxide since pre-industrial times. Don’t
worry too much about the different color bands because those are all associated
with different scenarios emission scenarios that were considered in the
IPCC report, but I want you to look at the range of these values. So what’s
being plotted is the equilibrium temperature change, and equilibrium is
something in the climate system that takes a long time, versus the
concentration of greenhouse gases as an equivalent concentration of carbon
dioxide. The two curves the lower bound curve the
upper bound curve show the range of climate sensitivity that is considered
to be most likely in the IPCC assessments and it’s a pretty wide range
from about two degrees to four and a half degrees and it’s interesting that
range has not, over several decades of research, that range has not decreased
very much in spite of a huge amount of effort being put into it. And what that
reflects is not a failing of the researchers trying to quantify that but
it means it’s reflects that they’ve learned more and more about what they
didn’t know. What’s what’s the phrase “the unknown unknowns” is that what we
use? That’s what’s associated with the fact that that uncertainty
range hasn’t changed a lot, but there’s a lot of talk about well let’s try and
stabilize the temperature change to a degree and a half for maybe two degrees
centigrade. If you look at this horizontal line to two degree increase
since pre-industrial times. As a function of the greenhouse gas level if the
sensitivity is at the high end of that range that stabilization concentration
is down around 380 parts per million. How many of you know what the current
concentration of carbon dioxide in the atmosphere is? [audience answer] Yeah you’re back when we
were at Harvey Mudd it’s a bit over 400 now and continuing to rise. Well so we’re
already committed to that two degrees if the climate sensitivity is up there on
the high end of the range. Forget about one and a half degrees that they talk
about, that’s even less probable if the climate sensitivity is on the low end of
the range we’re down around 550 for that
stabilization so what that means is all right want to hold it to two degrees
we’ve still got a few years before we got to quit emitting co2, but the end
result is one way or another if we want to avoid major warming of the climate
we’ve got to quit burning carbonaceous fuels. So how do you get that sensitivity?
That’s such a key number it’s not something that gets programmed into a
computer model rather it’s an emergent property of the model where it’s the
some effect of all the processes all the feedbacks in the model lead to this
these numbers in the range of two to four and a half degrees that’s one way
to get at it another way to get at it is to pick an event or a time period where
you think you understand the forcing and you think you understand the temperature
response to that forcing. Take a volcano for example, that’s a major perturbation
in the in the climate system and I actually skip past that on my slide
showing the model results earlier because if you notice the big dips at
certain times in that those were volcanic eruptions. But if you know the
forcing and the temperature change associated with it you can estimate the
sensitivity. Well the point is if you’re going to know the forcing you’ve got to
be measuring the aerosols and you’ve got to do a really good job. So I promised
you poetry and I have a real poem for you now that I want to conclude with: Frogs in a pot, are we deluding ourselves that we’re not? I remembered this poem
well I told my sister about this poem well I told her the Siberia story first
and then I told her the story here I told her this poem and her comment was
fairly pithy and it was there was a little bit more Russian
vodka that was needed in my poetry endeavors so with that, thank you very
much.

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