- This week I would Professor Jack Williams,
who was born in Chicago, Illinois,
and attended University High School
in Sacramento, California,
where he later went to pursue his bachelor's
in geology at Oberlin College,
to finally obtain his PhD in geosciences at Brown University.
He came to Madison in 2004 and is here today to talk about the
ecological responses to climate change since the last Ice Age.
Please join me in welcoming Professor Williams
to Wednesday Nite @ the Lab.
[applause]
- Great. Thank you all.
It's really a pleasure to be here.
I do have degrees in geology and geosciences,
and if you're paying attention,
I'm now a professor in geography,
which has confused my family to no end.
They can never quite remember
which geo am I on any given day.
But the reason for that is, as you'll see,
that I really do a fairly interdisciplinary kind of work.
I study species responses to climate change.
So ecology, climatology, using the geological record
and using the sediments
we can find in the many lakes and mires around us,
as archives of past ecological and climatic history.
So that opening slide there gives you a bit of
a sort of taste of the scales
that we're going to be working on.
Looking from the last Ice Age, 21,000 years ago,
the last glacial maximum we call it,
where we had ice sheets sitting over North America.
Right here where we stand was under ice.
And then those ice sheets retreat, and,
as temperatures rise, as CO2 levels,
carbon dioxide levels in the atmosphere rise,
various species move north.
And so one of the things that we use as time period quite a bit
for is studying ecological dynamics in a warming world,
which has obvious comparisons to what's happening today.
So sort of a four-part, four-chapter structure here.
Give a bit of an intro first here,
then move into understanding a bit more about how we use
the past to gain insight into ecological dynamics and make
preparations for what's happening now and is expected to
happen in the future, give an overview of some of the key
lessons we've learned along the way,
and then finish a bit on this crossover from paleoecology,
which is the field of study that I'm representing here,
to conservation biology, how do we make informed management
decisions given this kind of information
from the geological record.
So, to start with and to give an overview of if you think, again,
sort of this context of a changing world,
rising temperatures, rising carbon dioxide concentrations.
Carbon dioxide now at 400 parts per million,
which we haven't seen since the Pliocene,
and it's still going up.
So if we then think about the fact that we expect temperatures
to rise and other kinds of climatic changes to go with
that, we then start to ask how we best conserve species of
concern, biodiversity, ecosystem services,
all kinds of things that you might want to adapt and manage
under these changing climates.
And, in ecology, we can think of some general areas of risk
that might come with those changing climates.
So the first one is habitat loss,
that if there are species that are endemic to, dependent upon,
the best competitors in, highest rates in population and transit
growth, other certain climate regimes and those climates
disappear, then we'd expect those species to maybe shrink in
population size, perhaps even be at risk of extinction.
Sometimes this is called the top of the mountain problem or the
polar bear problem because polar bears are very charismatic
species that are dependent upon arctic sea as a key habitat,
and as that arctic sea ice melts back, there is concern
about polar bears having their habitat diminished.
No one actually thinks, as far as I can tell,
that polar bears will go extinct,
but we do think that they'll have
reduced population sizes and so forth.
Then we have fast rates of change.
How, if climates change quickly,
if there are rapid rates of temperature rise
over the coming decades,
and the scenarios being, say, two to four degrees Celsius
temperature rise over this century, that's pretty fast,
the question becomes, how quickly can species keep up?
And so there, at the far right, as you can see here,
is some different estimates of rates of, let's see,
if I look at my cursor there, so we have these different bars
here representing the rate of dispersal ability
or mobility of different species.
How far can they move in sort of typicals, or populations,
kilometers per decade?
Some species can move quite far.
The large animals have high mobility.
Some species, the trees, can't move at all.
They have to throw propagules out
and reseed and move that way.
So they don't move as fast.
And then the various lines there
represents spatial rates of climate change.
Converting these estimates of temperature change in any given
area to how far will thermal zones move laterally.
If you're a tree, if you plant trees,
you may look at Arbor Day
and their maps of plant hardiness maps,
those plant hardiness zones are expected to shift
as temperatures rise and species will need to move
to keep up with those shifts.
There's also the question of rapid and abrupt changes.
So the first point to there was fast climate drivers
and can species keep up.
There's also the question of fast ecological responses.
Will species respond non-linearly?
Where are the tipping points?
And so this idea that there might be multiple stable states
represented conceptually by those balls there.
And that you might have one stable state, like a grassland,
and then you might push a system hard enough that it flips
another state, like a forest.
So there can be sort of back and forth between these states.
Down in the lower right there,
we have different parts of the world.
That figure looks a little washed out from here,
but that's a map of the world.
And those colored areas are different regions of the world
where we have observed system dynamics in the past
of these sort of abrupt shifts.
The Saharan Desert in Africa, North Africa,
shifting pretty quickly back and forth,
doing a grassland state and a desert state.
The North Atlantic circulation flipping on and flipping off,
speeding up and slowing down.
There are some parts of the Earth's system that seem to show
this kind of bi-stability, these quick flips in state.
And then the part that I have actually worked the most on,
and I'll develop all these a bit more as we go forward,
but the part that I've worked on the most,
and will develop the most here,
is this novelty challenge,
sometimes called the bottom of the mountain problem,
where, at the top of the mountain,
if you sort of look at that cartoon there,
that cartoon is supposed to represent sort of thermal zones,
cold blue, so cold at the top, warm is at the bottom,
and in a warming world those thermal zones move up-slope,
that those coldest environments at the top
move off the top of the mountain and disappear,
which is bad news for those species.
But the bottom of the mountain has warmer than present
conditions than has ever been seen at that mountain before.
So now there's new climates that have not been seen
at that location before, and the question becomes,
how will species behave or respond
to those warmer than anything seen at present conditions?
Or, I'm focusing on temperature here,
but there might be other dimensions of climate.
More extreme precipitation regime events and so forth.
This is called novelty, and there's a map and right there,
sort of mapping out globally, areas of high climate novelty.
This is a paper we did about 10 years ago now.
And we did a sort of analysis of 21st century climates by the end
of this century versus climates at the beginning of the century
and identified places where the climates of the future had no
close counterpart in the climates of today and they tend
to occur in the tropics and subtropics.
The warmer world and those parts being at the leading edge
of a warming world becomes a question
of how well can we predict how species respond
to climates that are warmer than anything we see at present?
So that's the set up.
And these are all kinds of questions
that are ecological questions today
and, not coincidentally,
they are ones that can be addressed by looking at the past.
And that's a big part of what I do in my work is trying to work
with geological data and the geological record of past
climatic and ecological events and draw parallels and insights
into what's happening today.
So in this picture here, what we're seeing now is changes
in temperature, on the vertical axis,
and this is expressed as relative to the late
20th century, like 1960s, 1990s or so.
And positive values will be warmer than that reference point.
Negative values will be cooler than that reference point.
And the time scale is a little tricky here.
It actually changes its scaling, and this line here,
if I get my cursor back, represents today.
This is looking out 100 years in the future.
This is looking back over the last 150 years.
So this would be back to about 1860 or so.
This is basically the domain
for which we have weather station data,
instrumental data, direct observations of the climate
system and its change through time.
And what we see is that there's been a rising trend in
temperatures with some little stair steps along the way,
and we expect these trends to continue.
And this is being driven by the rising greenhouse gases from our
fossil fuel and land use and land cover change through the
emissions of greenhouse gases, carbon dioxide, methane,
and nitrous oxide, primarily.
We go further back in time, we can see there's been some
variations back here, but you can see that over this time
scale we've had a range of variation of plus or minus a
degree or so but nothing like what we expect to see over the next century.
And this is now going back to about 10,000 years ago.
So this is now back to 2,000.
This scale is changing here and back to about 10,000 years ago.
So this is a common challenge we face.
And I'm focusing on ecology but you could sort of extend
this challenge to any area of the world.
How do economic systems behave?
How will flood regimes in the greater Milwaukee area behave?
This general challenge, we're moving the system to a state
that's not like anything we've seen in recorded human history
and how do we best adapt and plan.
So in this challenge, we have sort of,
if you're a scientist trying to tackle this, I think it would be fair to say
you have four general classes of tools.
You can do experimental manipulations,
and these are from the Department of Energy's
Free Air Carbon Dioxide Enrichment experiments,
the FACE experiments, where they built towers around forest plots
and agricultural plots and grassland plots,
pumped CO2 in those areas, and then watched how the forests or
other ecosystems behaved under an enriched, ambient CO2 levels.
There's other kinds, you can do warming experiments and so forth.
We have numerical models and computational models that model
the atmosphere and the oceans and the cryosphere and the ice
sheets, how they behave under rising temperatures
or other changes of rising greenhouse gases
and forcing the climate system.
You can go to modern analog systems,
such as deep sea vents there.
People are using deep sea vents to study ocean acidification
because there's a lot of those, that's very acidic water
in the vicinity of those deep sea vents.
So if you want to know how deep ocean communities will behave
under rising CO2 levels and the rising CO2 concentrations
that will permeate into the oceans,
that becomes a system you can study.
And then the part that, again, that I'll develop further here
is going to the past and looking for geological time periods
that have some counterpart to today.
So to take that same diagram now,
and that's the same one I showed two slides ago,
and now expand it out.
So now we saw the last 10,000 years, which is here,
and now I've extended out to the last five million years.
And so this is going back to
500,000 years ago and back to five million years ago.
And now you can see when you sort of zoom out a bit further,
there's all kinds of climatic events happening
that have some interesting parallels
and are good model systems
for what's happening now.
And some of the key features you can see is that you can see
there's a slow drift of the Earth's system towards a cooler
state over this sort of five million time period.
And then you can see that over the last 500,000 years
there's been a very pronounced glacial interval
cycle, and I'll turn back to this in a little bit,
but we have these warm periods, cold periods,
warm periods, cold periods,
and these are pretty abrupt transitions.
And I'll zoom in to show you that some of these transitions
are similar in rate and magnitude
to what's expected over here.
And so obviously this is a cooler world than we're
expecting to have in the future, but the rate of change and the
amount of change is comparable from those time periods to
what's expected this century.
So now to go into that just a bit more here.
So now to kind of go from that framing to actually talking
a bit about these geological time periods.
This is another version of this data here.
This is what's confusing and annoying about my field
is that we aren't consistent about which way time goes.
Time is running from left to right in this plot.
Now it's running from right to left.
So that's older over there, and it's younger over here.
So that's 1.8 million years ago, at far right, to today.
We also, being geologists, we count back from the present,
so that's zero years ago at left
and 1.8 million years ago at far right.
So what you see when you look at this
is that there is this very regular climate variation.
This is one of the really cool things that got me excited about
paleoclimatology when I was a grad student and starting to
learn about it is that there's this very regular oscillation
in the Earth's system between what we call interglacials,
the warmer periods with smaller ice sheets, and the glacials,
the colder periods with larger ice sheets,
and you can see it far lower right there.
The ice sheets covering North America during a glacial period
in parts of Eurasia as well, and then the interglacial,
like the one we're in right now, with ice sheets
restricted to Greenland and Antarctica.
So we have this regular oscillation,
and if you actually were to do a periodicity analysis,
you would find out that there's a 40,000-year beat
back before a million years ago,
and it shifts to about 100,000-year beat.
Those big cycles are happening 100,000 years ago
or every 100,000 years.
And then they shift to a higher frequency back before.
Why it goes from 40,000 years ago to 100,000 years ago
is an area that people are still working on,
but we know, in general, that all that periodicity is being
controlled by variations in the Earth's orbit.
That the orbit varies at these timescales.
It changes from being more circular to more elliptical.
That's what that diagram there shows.
The tilt of the Earth changes from being more closer to
perpendicular to further away from perpendicular.
We wobble like a top wobbles.
And those three components of motion, the eccentricity,
the tilt, and the wobble, which we call procession,
affect the amount of sunlight we get at different latitudes.
That changing the amount of sunlight we get at different
latitudes and seasons directly controls the growth and melting
of those ice sheets and other parts
of the climate system as well.
So we have a very good understanding of this orbital,
what we call the orbital variations,
the orbital forcing of these ice ages
and their waxing and waning.
Okay, but this isn't a paleoclimatology talk.
This is an ecology and biogeography talk.
So this is really the structure that,
as an ecologist, we're working in.
What we're interested in less is what's causing these climate
variations, but how do species and ecosystems respond to them
and survive them because if you're a species that's been
around for any more than a few hundred thousand years,
you've had to live through multiple glacial and
interglacial cycles and you've had to be able to adapt to
and accommodate this kind of climate change in the past.
So now what I'm going to do is
zoom in into just one of these events.
That's the best study of them all because have lots of lakes
and mires and radiocarbon data of sediments that cover it.
And so this is the last deglaciation.
This is the last transition from the last glacial maximum
to the current interglacial, what we call the Holocene.
So now we're looking, time is now going that way again.
Oldest, 22,000 years ago, to present at far right.
Timescale or vertical scale again is temperature
as difference from present.
So this is a record from Greenland.
So this is telling us that Greenland was about 10 degrees
colder than present about 20,000 years ago.
And that about 10,000 years ago, it reached more or less modern
day or pre-Industrial Revolution temperatures,
and it's been more or less constant there ever since.
And what you can see is, of course,
you can notice very quickly that
it's not just a little linear ramp up.
There's some very abrupt changes along the way.
There's some distinct events, and we have given them names.
We call that first abrupt warming the Bølling warming,
as part of a broader event called the Bolling-Allerode.
And then there's that Younger Dryas,
which is that return to sort of near glacial conditions.
And then the abrupt end of the Younger Dryas,
which is the start of the Holocene,
the start of the current interglacial.
So lots of things are happening climatically.
Globally, temperatures rise by about
four to five degrees Celsius.
Some of those changes aren't what we would--
Sometimes you hear geologists say,
"Oh, things happened really fast in the past."
And people say, "Oh, yeah, you're a geologist,
"you're talking about millions of years, that's not meaningful."
These are really abrupt, even on human timescales.
People think basically it's Greenland and other high
resolution records that some of these abrupt shifts in the
climate of these areas could have been nine to 14 degrees
Celsius in one to 40 years.
In our own lifetimes would have been sort
of the comparable kind of rate of changes.
So these are big past climatic events, these aren't global.
These are North Atlantic, western Europe.
But in these areas, at least some regions,
we've had very rapid changes.
Ice sheets melt back over this time period.
That plotted upper right is showing this, I think,
this really beautiful diagram of the Laurentide Ice Sheet
and the Cordilleran Ice Sheets.
The dark blue is its furthest extent,
and then it's melting back over this sort of from
about 19,000 years ago to about 6,000 years ago.
The ice sheets are wasting away as temperatures rise.
Sea level rises because that water has got to go somewhere
and it winds up in the world's oceans.
So that's about 400 feet or so of sea level rise from the last
glacial max to the present.
And then novel climates emerge.
And what I mean here by novel climates is that if you actually
look at the ranges of climates that occurred at some points in
the past to the ranges of climates that happened today,
there are areas of non-overlap.
And the way to kind of show that visually is at that far right
plot there, where what we're looking at here is
just two simple temperature axes:
summer temperatures and winter temperatures.
And we're looking at that each location represents some
location in North America for three different time periods.
Red, being a projected [inaudible] set of climate model
simulations for what we think North American climates might
look like maybe 30 or 40 years from now.
Black would be the late 20th century, the recent past.
And then blue is 15,000 years ago.
And what you can see is that there's areas of non-overlap.
I don't know how well you can see it from your angle,
but there's an area over here, for example,
whereas we move into a warming world,
portions of climate space open up in North America.
These novel climates that aren't available to species in North
America today, presumably mostly in the southern parts
of North America, whereas, 15,000 years ago,
there's a whole other portion of climate space
that opens up back then.
This portion of climate space is more seasonal.
We have kind of warmer than present or similar to present
summer temperatures, and colder than present winters.
And the reason for why we have this sort of portion of climate
space open in the past that's not open today is because
of these changes in the Earth's orbit
and the way that affects temperature seasonality.
It actually has different effects on summertime
temperatures and insulation, incoming solar radiation,
and wintertime values.
So that opens up portions of climate space that species had
available to them 15,000 years go that they don't have today.
Okay, so that was all sort of setting the stage
and setting the context here.
Now to go into, okay, now we have kind of some understanding
of these times and places, let's go in
and how do we sort of study these time periods.
So this is kind of a starting point for that data we gather.
We go out in the field and we get muddy.
Go out into middles of mires, we set up floating platforms on
lakes, and we take long tubes of mud from those sediments.
Here's a cleaner looking team actually out on a lake here.
And this is from Horseshoe Lake just outside of St. Louis
by Cahokia, if you've ever been down to Cahokia,
we're working right outside of Cahokia there and getting a
record of environmental and vegetation history from Cahokia.
And so you can see that maybe there's a couple steel tubes
there, but it's about a meter- long steel collection barrel
that we drive down, a drive at a time,
bring back a meter of mud at a time.
And as long as that lake has been around,
it's been collecting mud,
and so we can take those cores of mud
back to the lab and analyze them.
So now we're extruding that core of, that long tube of mud.
We're going to wrap it in those, we're going to first wrap it in
cling wrap, and we're going to wrap it in those PVC.
It's got kind of a consistency of kind of a banana at the top,
down to a pencil eraser at the bottom as the bottom sediments
get more and more compressed and dewatered
by the weight of the above sediments.
So it has some cohesion and stability to it,
but we wrap it up and protect it and take it back to the lab.
So there we can, here's another one where, before we wrapped it,
just getting a quick photo of it.
And you can just see that
some of the sedimentological variations.
This is a lake that has dried out, obviously, at some point.
So you can see how the uppermost sediments at left
have become oxidized, they've been exposed to oxygen.
They're getting kind of rusty and iron-rich.
Whereas the blueish sediments at right,
that's reduced iron that hasn't been exposed to oxygen yet.
So just as a first pass,
visually we can start to get some insights
into the environmental history of that lake.
And then the kind of, what our field works with
are what we call proxies.
What we want to know about our past temperatures,
where do species live, past water pH,
but we don't have thermometers.
We don't have species traps or photo cameras.
What we have are proxies for these things.
So we use pollen as a proxy for the past plants.
We use various stable isotopes, like oxygen,
as a proxy for water balance or temperature and so forth.
And different labs work in different proxies.
Ancient DNA increasingly use a proxy as well.
And so my lab does pollen analysis.
We're actually celebrating the 100th anniversary,
this is a birthday centennial year.
Pollen analysis was invented, or not invented,
but initiated by Von Post, a Swede, in 1917.
So this has been around for a while.
But because it's been around for a while, it's a mature proxy,
and it's one that we've got a lot of data on over the last century.
So we can now work with large proxy networks of different
records from different places where people have been doing
this kind of work for a long time.
So the way it works is that plants produce pollen.
Some plants are relying upon wind dispersal,
so they throw that pollen up in the atmosphere.
And they hope that by chance some of that pollen they throw
up there will land on a female flower and perpetuate the species.
It's a very inefficient way of doing that,
but pollen is cheap and so they
do this sort of broadcast approach.
Some of that pollen settles on the lake,
settles down through the water column,
is captured at the mud at that bottom, and then,
as that mud accumulates up,
the older sediments are at the bottom,
they have pollen from when that lake formed
15,000 years ago or whenever,
and the uppermost sediments are the
most recent sediments deposited in the last few years.
We core it, we bring the mud back, and then,
under light microscopes and sometimes SEMs,
scanning electron microscopes, we identify the pollen to genus,
sometimes to species, sometimes to family.
And here's just some different photos for different pollen
grains as you'd see them under a light microscope.
So kind of just one quick example of this kind of work.
So here's one site in northwestern Indiana
where we have a beach.
And here's one lake sediment record.
And what we produced is called a pollen diagram recording,
from those lake sediments, all the different pollen
that we find from the different zones.
It tells us something about forest history
and change in this site.
Not only does my field go left to right versus right to left,
we also go up and down.
So now time is on a vertical axis here.
Oldest at the bottom, youngest at the top.
And that actually makes some sense
because that's the way the sediments are deposited.
The oldest sediments are at the bottom, the youngest sediments are at the top.
So this is kind of how a geologist often sees these things.
So each curve, then, represents the relative abundance,
usually what we do for any given horizon we might count 300 or
400 pollen grains, identify them to these different tree taxa,
and then we say what proportion of those we counted
were fir or spruce.
And so what we can see is each curve here represents a different taxa.
We can see that in northern Indiana,
15,000 to maybe 12,000 years ago,
there's a lot of spruce around there
and a smaller amount of fir.
And a little bit later pine comes in.
So we can see boreal forests.
The kind of forests that we find
in northern Wisconsin, southern Canada.
Those forests were occupying northern Indiana
15,000 to 12,000 years ago.
They disappear, pine comes in,
we get sort of a pine zone for about 1,000 years.
Pine disappears, you get oak,
that big, green curve at near far right.
Oak comes in, we get these oak dominated forests.
You can see that beech curve, it's flagged with beech up there.
Beech comes in around 7,000 years ago.
So we can see these sort of long-term changes in forest
history that are being very directly driven
by climate change, that as temperatures rise,
the boreal forests die out.
Those species effectively migrate north,
and then other species, like oak,
migrate in and become more abundant.
And then, a little bit later, sometimes species take a little
while to get there, beech comes in and is establishing by what
we call the mid-Holocene about 7,000 years ago.
So that's just one site.
And, of course, one site gives you a lot of information
about temporal history at one location.
It's also a lot of work.
Someone's got to sit there at the scope
and count these pollen grains.
And so what our community has moved to is creating community,
what we call community curated data repositories.
And the one that-- Oops. Hold on.
Mozy's nagging me. Sorry. Okay.
So what we've built are databases to house our data so
we can move from sort of single point temporal analyses to
multi-point spatial temporal analyses to look at rain shifts
and range migrations.
This is a resource at Neotoma Paleontology Database.
The URL is there.
It's one that I'm one of the PIs involved in building this
and helping build both the infrastructure
and then the contributing of data to it.
And so what this lets us do then are things like this,
where now what we're looking at here
is an animated map of North America.
This is an earlier visualization that goes back
to a paper published in 2004.
We're working on creating some updated versions of this,
but it's still a great visualization
so I still use it a lot for talks.
And what we're looking at here is
every frame is a thousand years.
We're stepping forward a thousand years in time.
So the first thing to pay attention to is
you can watch the ice sheets retreat.
You can watch the ice-free corridor open up
between the Cordilleran and Laurentide Ice Sheets.
You can watch Florida shrink because as sea level rises,
areas with low relief, like the eastern seaboard, lose the most.
So Florida is quite large and loses a lot of land area
between the last glacial maximum and present.
The west coast, not so much happens.
So you watch sea level rise and ice sheets melt,
but then the main thing that's supposed to show here is the
forest dynamics and showing how spruce migrates north.
It used to be, spruce used to be growing south of us
20,000 years ago, and it's northern range
was right around here.
And then as temperatures rise, the southern spruce populations
die out, the northern spruce populations expand into new
areas, and the whole population moves northwards.
This is some of our best evidence.
And when we talk about species migrating and moving in response
to climate change, it's this kind of data
that that concept is founded upon.
Now, of course, we're starting to see species shift their
ranges in response to current climate change.
That's happening around us now.
But the best documented data we have for how species respond to
these sorts of long and large climate changes
come from this kind of data.
So, okay, everything I've been showing you
has been very data-centric.
Out in the field working with the mud,
in the lab counting the pollen, making maps.
Straight up from the data but, of course,
in the sciences you really work from two directions.
You have the empirical lines of evidence and then modeling your
theoretical lines of evidence, and you've got sort of the intersection between the two,
which is where the interesting science happens.
And on the modeling side a very common tool,
of course there's all kinds of different ecological models out
there, a very common one that gets used all the time is what's
called species distribution models, SDMs.
They're called environmental niche models.
And what you basically do is you take some set of occurrences
where a species is found out in the environment,
you then overlay that set of occurrences with the
environmental characteristics, the topography, the temperature,
precipitation and other variables,
and you build a predictive model that predicts the species
occurrence or abundance as a function of environment,
what we call a response curve, the response of a species to
that environment, and then you say,
well, what if the environments were to change?
What if we have a global warming or some other degree of climate
change using a climate model to give us that scenario?
And then you say, well, this is where we think
a species would be in the future.
So we use this sort of approach all the time
to predict how species will respond.
Where should we conserve habitat?
What's the risk of extinction
using these kinds of modeling approaches?
And just as one example, this is just one of many papers,
this is just one synthesis paper coming with estimates of how
many species do we think will go extinct over the coming century
in response to the different climate scenarios.
So the X axis is how much temperature rise will there be
relative to sort of 1800s, pre-industrial baseline.
And then what percent of species will be predicted to go extinct.
And this is a meta analysis of many different studies,
and they all predict some degree of extinction,
some just a few percent, some quite alarmingly,
20% to 40%, but there's a fair cloud there.
And then some, the red line being some fitted curve to that.
And a general sense that the more we have temperature change,
the more we stress species, the more we change environments
around them, the higher the rates of extinction.
And those SDMs I showed you are part of the backbone
that predict these kind of responses.
And so one thing-- Of course, the challenge with this is that,
we can't test these predictions, right?
Or we have to wait 90 years to see how many species have gone
extinct by the end of the century,
taking no action in the meantime.
That's not a very satisfactory approach to doing things.
What we can do instead of a model testing ground
is what we call hindcasting.
We can take these models that are usually run from the present
into the future and instead run them from the present back to
the past and see how well they do there.
So this is one set of analyses where we actually ran it
forward, but we ran it forward starting from 15,000 years ago.
We said, okay, let's take this model,
start it from 15,000 years ago, before the last deglaciation,
before the climate changes happen, and then say, okay,
how well will that model predict
where that species would be today?
And so here's the distribution of oak at lower left.
The colors are kind of ugly,
but the greens are areas of high oak abundances.
Oak was generally further south
in Florida and so forth, southeastern US.
And then, as temperatures rise, it expands northward.
The lower right side, yeah, the lower right
is what's been modeled for its expansion.
The upper right is what we observe from the modern
botanical and pollen data.
And we get a pretty good fit between the two.
So this actually a case where the hindcasting works,
where this species distribution model is able to predict a
northward range expansion of this set of taxa of this genus
in response to climate change.
What we can also find out, though, is that, you know,
if we actually do an analysis of how good was that fit,
the correlation between what was modeled and what was observed,
and we say how far back do we start the model and then predict
it forward, we find that the correlation is pretty good
if there's not much time separation.
If we take climates from 2,000 years ago
and predict to present, we get a pretty good match.
And if we go back to, say, climates from 14,000 years ago
and then ask the model to predict to present,
we're not getting down to a correlation of 0.5 or so.
So there is a sense that model performance degrades the further
you go back in time, the more climates change
between your starting point and your end point.
Okay, so that's kind of going from the modeling side.
And I'll come back to that with a few slides near the end.
So, okay, from this kind of work, what have we learned?
This is kind of, I'll go through each of these in turn here.
But talking about sort of we can see that species are clearly
sensitive to climate change.
We can see that species move in response to climate change.
They do so individualistically.
And we also see that species that we don't have much evidence
of climate driven extinctions except for the large animals,
the mammoths and the other large animals that are probably being
affected by a combination of climate and human action.
We see this emergence of novel ecosystems in response to those
novel climates and, as I'll come back to,
this challenge of ecological forecasting.
Okay, so now I'm going to go through each of those in turn
with a few slides.
So this question about rates of response, this really matters.
If temperatures are going to rise by several
degrees over this century, how quickly can species adapt?
Should we be moving species through what's managed called a
system migration or managed relocation?
Should we sit back and let them adapt on their own?
Let nature takes its course or some set of other options?
And so one thing we can see from the Paleo data is that when
climates change, you very clearly get strong local
responses and often very strong fast responses.
And this plot here, again time being vertical now,
oldest at the bottom,
this record here is a temperature record.
So this is going back.
Remember that Greenland ice core and those fast changes we saw
around the Bolling-Allerode and the Younger Dryas?
This is one of those events.
So there's a very fast warming here in Greenland
about nine to 14 degrees Celsius in a few years.
Probably not quite as big a warming as at this location.
But what you can see is temperatures rise
and almost instantly, from a geologist's perspective,
the communities turn over.
They go from a sage, sedge plant community,
kind of an open tundra, to a juniper woodland
within the span of a few decades.
So very quickly this plant community is changing
and turning over response to that temperature forcing that it
receives, but several centuries later, pine shows up.
So there's both called the fast responses of sort of local
community turnover, and then the slower responses,
where pine probably was not anywhere near this site when
these temperatures changed.
It was probably hiding out in various refugia down in the Alps
and had to expand northward to this location.
And trees don't get up and move,
so it took a few centuries for pine to get there.
So we can see this is an example of what we call a delayed
response or a lag response, where it takes a few centuries
for the force of ecological effect of that rising
temperature to be felt at this site.
We've already walked through this point,
the idea that that was at one site and then we can sort of
step back and look at the continent and see that species
accommodate climate change by moving.
They try to stay within their thermal zones of their climatic
optima or ranges of tolerance, and one way they do so is by
moving spatially as the environments change around them.
Moreover, I've only been showing you spruce,
mostly because it's a nice kind of iconic one,
but if you actually were to look at other taxa and start to look
at how they respond, what you start to see
is that different species respond to different rates
and in different directions.
And so we can see that that spruce again, northwards shift.
We look at ash.
Ash doesn't really move much of anywhere.
It expands a little bit north.
There's a bit of a northern range to it.
But mostly what ash does, it goes from being not very
abundant to being really abundance,
between 15,000 and 13,000 years ago,
and then not being very abundant again.
And so it's a completely different trajectory from what
we see from that sort of simpler story of sort of northward
expansion with rising temperatures.
And notice that today we think of spruce being up in Canada and
northern Wisconsin and ash being parts of southern Canada
and the eastern deciduous forests.
So we think it'd be used as largely disjunct species
from different biomes or ecosystems.
But if you've been an ecologist walking the landscapes
15,000 to 13,000 years ago, you would have thought that spruce
and ash were just found as a normal association.
And so the mixtures of species change.
What we start to mean by novel communities,
or reshuffling in novel mixtures.
As climates change, each species follows its own path.
And as a result you get this mixing of and breaking down
of exiting community around you and new ones emerging.
We should expect the same sort of things happen in the future.
We should expect that because of this,
some of these co-evolutionary relationships
should be pretty weak.
If your neighbors are changing all the time,
maybe you're not tightly co-evolved with the other
species around you, and so we're starting to think about some of
those implications for co-evolutionary relationships.
And, again, this sort of prediction question.
Another point that's, I think, of real interest is that if you
actually look at the last 1.8 million years,
even going further back, one thing you don't see a lot of
are species extinctions.
Species extinctions are there.
They're not nothing, but they're not very common either.
And you can make a good case and they not much above,
back to what a sort of typical background rate,
species are kind of always coming and going
and that might be sort of typical.
And when you do see extinctions happen,
they often tend to be at the cold periods.
That sometimes species die out either locally or regionally
during the cold glacials but not as much evidence of extinction
during the warm glacials.
So there's some sense that there's a bit of asymmetry here
where the colder periods are more special for species and can
drive extinctions more than the warmer periods.
This is sometimes called the Quaternary conundrum there
because I just showed you a few slides ago these predictions of
large rates of 15% extinction rates over this
century in response to 21st century climate change, and yet,
when we look at the geological record,
we just don't see that much of it happening.
But the obvious counterexample to that,
I've been focusing mostly on plants so far,
but there was these very large animals roaming these
landscapes, we used to have mastodons all over the place
around here, and those mastodons aren't here anymore.
The mammoths aren't here, the camels aren't here,
the horses, all over North America.
And, worldwide, we do have a major extinction event,
but it's very much concentrated on the big animals.
We lose about two-thirds of all the big animals worldwide
starting about 45,000 years ago up until the recent past.
In North America, we lose about 34 genera and this long-running
question about what doesn't end.
And I'm of the personal mindset that it is some combination
of climate change and human dispersal, right?
Humans are moving out of Africa
beginning around 100,000 years ago or earlier,
they spread into Europe, into the southeast Asia,
into Australia by about 40,000 to 50,000 years ago,
into the Americas by about 15,000 years ago.
And, interestingly, it's not a perfect correspondence.
It's not as if the early hypotheses were this blitzkrieg
hypothesis that when people showed up,
very quickly they hunt down the animals.
And now it looks like there's often a period of coexistence
for several thousands of years, but then the animals do die out.
And, for me, the telling point is that we don't see waves of
large animal extinctions during all these previous glacial and
interglacial cycles going back the last million years.
It's only the most recent one where these extinctions happen.
And, to me, that's sort of one of the key signals that it's
this new factor of climate change plus this new predator,
new large animal on the landscape that's causing these
extinctions to happen.
It's also telling that if you look at
which animals go extinct, it's the very large ones.
And those bar charts over there are showing the blue,
it's rated by body size there, and then the vertical axis is
the number of species that go extinct, or, sorry,
the number of taxa in that body size.
And so what you can see is that
the red ones are the ones that go extinct.
The blue ones are the ones that survive.
And so the extinctions are very heavily concentrated
on the big N, the animals that will be the easiest to find,
the most resources for early hunters to get.
And the timing and pattern is consistent as well.
Okay, so we see this idea of novel ecosystems
that I talked about.
Species, and I'll show in a moment,
a good case he made
that these novel communities are forming in part to response to
the novel environments that they encounter that exist in the past
that don't exist today.
And one way of looking at this, going back to this point about
seasonality, remember what I showed you at far right there,
that 15,000 years ago climates in the past were more seasonal
than they are today.
Now look to the far left
and look at where ash is found today.
And that middle plot here,
I don't know how well you can see it,
but there is this black set of dots and,
maybe a little harder to see, a set of gray dots here.
This is the climate space of North America.
And what this figure should be showing is that we have,
the black dots is where ash is present in North America.
The gray dots is where ash is not present
but those climates exist.
And then, for much of ash's range,
we have some constraints
that ash cannot be found in these areas.
We don't find ash in these areas at least.
But over here ash is right up against the edge
of the North American climate envelope.
It's found right in the middle of North America,
which is as seasonal as it gets in North America.
So there's some sense that ash could expand into these
climates, these more seasonal in terms of climates,
if those were to exist.
They don't exist now, but these climate models suggest
that they did exist in the past.
And so some of these sort of spruce, ash assemblages,
and some of these other no analog communities
that formed we think are forming
in response to this heightened climate
and temperature seasonality
of this sort of late Pleistocene time period.
So one consequence then, as I showed you-- Oops.
I don't have-- Oh, yeah, so I showed you a map a few moments
ago about oak, I'm looking at how oak does.
This is another map for Fraxinus.
This isn't quite as clean as the other one I showed you ago.
But, again, here's the modeled distribution of ash
15,000 years ago.
We take that model, predict it forward to present,
and the model basically thinks that ash shouldn't exist at
present or should exist only at very low abundances.
Where, in fact, we know that ash does exist at present.
And so this is a good--
And the correlation between these two maps is terrible.
It's, you know, 0.09 correlation.
And so this is a good example
where the model is not matching to the data.
It's having a hard time taking these novel climate phases
of the past and then basing predictions on them into the
climates of today and the species of today.
Just like that oak plot, we saw that, in general,
predictions based on more recent time periods do better,
predictions based on earlier time periods do worse, but now,
if we look down here, the correlation, again, is very low.
And so, basically, if you--
What this is telling us is if you take the set of climates
that we know for 14,000 years ago
and the known distributions of ash from 14,000 years ago,
build a predictive model based on this data
and relationships, that model has little or no
predictability to today.
And so that is an example of how these novel climates
can confound these models because, again,
they're statistical models.
They're not very good at extrapolation into the unknown.
This is a case where they're really breaking down
in these sorts of situations.
And one more just kind of visualizations around this,
this is showing the sort of total climate space of North
America 15,000 years ago, the total climate space of North
America 1,000 years ago, and then the black dots being the
places of high ash abundances.
And so what you can see is this portion of climate space
that opens up down here is also a place
where we're finding lots of ash.
The ash is really preferentially occupying these highly seasonal
climates, these climates that don't exist today.
And so, again, this is sort of these signals that as climates
change and new portions of climate space open up,
species are able to respond to and occupy these spaces and are
sometimes our ecological forecasting models have a hard
time predicting these novel climates
and community responses to them.
Okay, so those are some of the lessons,
some of kind of the big kind of things we can take away from
what we see from the geological record.
And now just a few slides at the end about what should we do.
What kind of things can we--
We take this information and bring it
to bear on current challenges.
In general, if you're thinking about climate change and you're
sort of working at a high level thinking about sort of policy
options, there's sort of two general options.
One is mitigation, which you try to mitigate or prevent climate
change by reducing our greenhouse gas emissions.
And the other one is adaptation, where you try to increase our
resilience to climate change.
When I first came into the field, you know, 20 years ago,
adaptation was viewed as kind of a taboo,
that we shouldn't be thinking about adaptation,
we should be really focusing our efforts on mitigation.
But increasingly, these are seen as not either/or,
it's and/both kind of situations because you want to avoid the
really high end climate scenarios that might cause a
four-degree or five-degree warming this century that would
cause all kinds of harm to low-lying areas, small islands,
heat waves, you know, droughts, etc., and, you know,
rates of adaptation for species and so forth,
you want to avoid those outcomes, and mitigation does that for you.
It moves you away from the high- end climate change scenarios
down to the lower end or middle end climate change scenarios.
Whereas, adaptation recognizes that climate change
is already underway, climate change is happening.
It's been underway for the last several decades.
And now it's just a question of how much climate change
we'll have, and at what point we'll level out
or maybe start to reverse things.
And so the Paris Accords said
we need to stay at 1.5 degrees Celsius.
So that would put a limit around here or so.
So there's different scenarios and pathways to get there,
but no matter what there's going to be some amount of climate
change and some amount of adaptation needed to those.
And so adapt to what you can't avoid.
And so if you think about, from an ecological perspective,
one thing to recognize is that, again,
species accommodate climate change by moving,
but that's actually been sort of a hard concept for us.
We have legal restrictions in place.
We think about invasive species, there's some species you can't
move across certain boundaries.
And I'm certainly not advocating for wholesale movement
of species across continents.
We know about all the issues of moving exotic species into
places they'd never been before.
But within continents, within regions,
we should recognize that species have moved in the past and they
will move in the future and doing things like adaptive
planting, looking for seed sources from populations maybe
not in the current area where you're trying to reseed a
species, but to the south of it.
And so organizations like the US Forest Service are starting to
change guidelines so that simply sort of taking a seed from the
current areas, they start to look for seed sources a bit
further south and so forth.
Some places, like in Alberta, foresters in Alberta are
actively planting species outside of their historic ranges
in the expectation that by the times those trees come to
maturity 60 or 80 years from now,
the climates that they'll grow up in will be the climates
favorable to them and so they're doing sort of proactive planting
for future forestry and harvesting.
This gets in this topic of managed relocation.
And so sometimes if you're worried that a species habitat
will entirely disappear or largely disappear as a result of
climate change, maybe due to sea level rise or other factors,
moving these vulnerable populations,
picking them up from one place to north.
This, again, can cause concern.
I tend to be of the perspective that this is a natural process,
it's just one that we haven't seen happen much
because we haven't see that much climate change happen
in our human lifetimes.
And so this is the kind of thing I tend to support
as a way that's congruent with past climate change
and past adaptations to it.
And also recognize that what we think of as a normal or natural
set of species around us may be a temporary phenomenon.
Species move, associations come and go,
and then as climates change we should expect these shifting
associations to happen in the future.
Some species moving faster than others,
some species being more temperature sensitive
or rainfall sensitive or extreme sensitive,
and so we'll expect to see this reshuffling of species.
This has led to this concept of novel ecosystems,
and there's a bit of an argument about that right now.
And there's a couple of quotes about that argument.
And so Hobbes, for example, is arguing that novel ecosystems,
the concept of novel ecosystems is based upon
the fact of novel ecosystems.
He's saying already we can see that some ecosystems have
departed entirely from their historical analogues.
Whereas other have argued, no, no, no,
we can keep things in a current state.
We shouldn't sort of wave the white flag of surrender,
but accept these unavoidable and widespread irreversible changes.
And so there's been an argument about this.
What should we be conserving to? What should we be maintaining?
I, again, tend to favor more of the former perspective.
That these are dynamic systems that are systems in changing
and we should look for ways to facilitate those changes,
one that best promotes biodiversity and the services
that we depend upon.
And, again, we expect that climates are changing,
we expect novel climates over the century.
So this is very much a real process
for us all to be wrestling with.
We are wrestling with in the professional sector and I think
it's worth bringing out to the broader community as well.
And if we look around, I've been focusing here on climate change,
but if you think about it, there's, of course,
all kinds of other factors transforming these ecosystems.
There's been invasive species.
There has been land use and legacies of past land use.
So the Parthenian rangelands is an example of a toxic, you know,
invasive species that we generally try to
limit its spread.
Puerto Rico is an example of an area that was widespread sugar
plantations, is now reforesting.
And as it's reforesting, it's becoming this interesting blend
of native and exotic species, apparently with, you know,
not major negative ecosystem or biodiversity consequence.
If anything, biodiversity may have gone up in some of these
areas with this mixture of natives and exotic.
Isle Royale is being a relatively pristine area
but one that nonetheless is changing in many ways.
And the corral triangles as an area that is changing
and is threatened by rising temperatures,
ocean acidification, and so forth.
And so we can recognize that the world is changing,
we can recognize that novel ecosystems are emerging.
Some of these we might view as more positive than official,
others we might view as more negative or ones to try to
reverse, but, nonetheless, we should recognize that we are in
this changing world and that we should seek to facilitate
certain kinds of change and mitigate or reverse others.
Okay, so that's, I've kind of worked through
these points here already.
But, again, this perspective
that comes out of paleoecology of the world
has always been in flux.
Now new changes are happening.
We are accelerating the rate of change.
And, in general, I would say that prudence would dictate
that we try to slow down rates of climate change,
we try to stabilize the climate system,
but we should also accept that change is underway
and that those rates of change lead to adaptation needs,
and those adaptation needs can be grounded
in the lessons from the past.
Thank you. Thanks a lot.
[applause]