[Jessica] Being in Arizona and working on climate change, it's personal.
We think about it every day.
We think about 10 years
from now, 20 years from now, will I still be able to be here?
What will it look like? Will we build water infrastructure?
And so it really brings it home for me to be able to work on
both past, present and future climate here in a place
that is on the frontlines of climate change.
I'm Dr. Jessica Tierney.
I'm a professor in the
Department of Geosciences at the University of Arizona.
And I'm a lead author on the recently released
sixth assessment report by the Intergovernmental Panel
on Climate Change.
In the last several decades,
there's always been a representative
from the University of Arizona involved with the IPCC reports.
So I'm the latest in a long tradition of Arizona
climate scientists participating in this global effort.
The report that I was a part
of is the first working group in this report.
We focus on assessing how climate has changed.
So what has happened in the past? What's happening right now
and what will happen
in the future under different emission scenarios.
So a major difference from the report that came out
in 2013 is the attribution of extreme events
to human influence. That is new.
So whenever we look back into the past
and we find evidence of a warm climate,
we always find that CO2 is high.
It's always one for one CO2 in temperature.
When CO2 is high, the planet is warm.
When CO2 is low.
It's cold over and over again.
CO2 is really the master dial on the earth's climate system.
There's a large range of what people call natural
climate variability changes in the climate
that would occur without human interference.
How do we separate that from
what's related to human emissions?
We can take a climate model and we can run it and see
what would have happened in the 20th century without humans,
and what we find from that experiment
is that since about 1950, humans are responsible
for all all of the increase in global temperatures.
Humans are warming
the climate faster than pretty much anything
we know about in Earth's history.
The rate is truly unprecedented.
So what that means is we're seeing climate move
into a new state at such a speed that ecosystems by MS
and people will struggle to adapt just because it's
happening so fast.
So if you look at where we're headed
already, the levels of CO2 in the atmosphere are higher
than anything we've seen in three million years.
So this is why going back
deep into geological history is really important.
What happens to the water cycle?
What places in the world experience more severe drought
or more severe flooding?
And so in order to do this, of course, we don't
have two monitors. They go back millions of years. Right.
So we have to use tricks from chemistry and biology
to be able to go back in time
and tell things like temperature and how wet or dry it is.
So my research focuses actually on looking at fossils, fats.
So it turns out that
fats are preserved in rocks for millions of years.
They just don't break down.
So if we take marine
sediments, for example, there are actually algae
and they change the structure of their lipid fat cell membrane
in response to the temperature
of the water, and that fat is preserved in the mud.
And so what we do in my lab is we'll go in and we will extract
all these fats out of a sample, will
focus on the one that we know responds to temperature
and we'll measure it.
And so with that calibration, then we can take ourselves back
into the past again, going back millions of years.
We're able to tell what is the temperature
of the surface ocean.
Another class is actually
based on the waxes that are produced by plants.
Leaf waxes, we call them.
So plants, their leaves are quite waxy.
You might notice, especially in desert plants, that
there's a thick layer of wax
coating and a lot of our plants here in Arizona.
So why are they interesting?
Well, it turns out the chemical
signature of the leaf waxes relates to the water cycle
and can tell us something about how rainfall
has change in the past.
[Thunder sound]
So we have a big research project focused on understanding
how the North American monsoon system has changed through time.
The system accounts for about half of the rainfall
that falls in Tucson.
And so we really want to know how climate change
is going to affect the monsoon.
What we've seen so far is evidence that the monsoon system
is more intense during past warm
climates. Now, how does this way
into the ongoing drought in the region?
The problem is, even though rainfall is going up
and down, temperatures are going up in Arizona.
And as it gets hotter and hotter, the atmosphere
becomes thirstier.
So the atmosphere itself is demanding more moisture
out of the soil.
It's actually evaporating more moisture out of the soil
and away from plants, and it makes the climate drier.
This is a phenomenon we call hot drought
because it can be driven by temperatures alone.
You can still have precipitation
go up and down year to year, yet
see the emergence of this long term drought.
We're just going to walk into the desert and see what we find
is, of course, a lot of my
students are really worried about climate change.
And so they come into my class and we learn about
how the system works.
All the climate changes that have happened
in the past and then what we might face in the future.
And it's easy to get trapped into this sort of
zone of despair.
So what I do like to remind students of is
there still is hope and we still have choices.
I guess I'm sort of a a practical optimist
in the sense that I know that some of the trajectories
might be too ambitious, but I also think there's great value
in doing everything we can to get on a better trajectory.
All these little different choices and engagements add up
and they can make a difference moving forward.