When I was working on the latest edition of my textbook in 2001, I was struck by the fact
that there were really no good examples of climate change, the effects of climate change,
anywhere from the eastern United States.
The examples were all very far away like polar bears in Canada or wildflowers in the Swiss Alps.
So beginning in 2002 with my students we started to look for the effects of climate change.
We found that there's a wealth of information about how warming temperatures is affecting
the flowering times of plants, the leafing out time of trees and shrubs, and the arrival
of birds in the spring.
Six months after we started our project, a former B.U. graduate student in philosophy
told us about Thoreau's records.
In the 1850s he made very detailed observations in Concord about when plants flowered, and
when they were leafing out, and also when birds arrived in the spring.
We're studying the same species that Thoreau studied and by comparing his observations
of leafing out with when these species are leafing out today in Concord we can see the
effects of climate change.
We start to come to Concord towards the end of March, beginning of April.
We're looking for the first individual of that species to leaf out.
The white pine, which is an evergreen species, is still not leafed out. We still have these
very small buds where the leaves are just coming out.
Leafing out time is very important because it changes a lot of variables in the Spring.
So when leaves come out it's when the plant starts photosynthesizing and when nutrients
are used up from the soil.
Also leaves are an important food source for many insects which can be in turn a food source
for bird species, and changing the time of those leaf availability can really alter the
presence of other species that depend on them.
The leaf-out is occurring on average about 17 days earlier now than it was during Thoreau's time.
The flowering time is about anywhere from about 10 days to about two weeks that the
plants are now flowering earlier than in Thoreau's time.
We find that certain species of plants in particular are not able to respond to this
changing climate and are going extinct.
One-quarter of the wildflower species which were present in Concord 150 years ago and
that Thoreau would have seen aren't present here anymore,
and another one-third of them are now very rare and are probably likely to go extinct
within the next few decades.
107 centimeters.
Okay.
Fifty-two...fifty-three...fifty-four...fifty-five. Fifty-five.
I've been doing much field work at the base site of the Boston Area Climate Experiment.
The base site provides us with kind of an on-the-ground experimental way of demonstrating
how those different temperatures actually affect flowering and leafing out on the ground
in a very controlled experimental set-up.
So we have all these different combinations of either not changing the temperature or
increasing the temperature by different amounts,
and either keeping the normal amount of rainfall or decreasing it by 50 percent or increasing
it by 50 percent.
And so this is an un-heated plot right here. We can see that the milkweeds are growing up,
but they're not really finishing their life cycle quite yet.
They're not flowering yet. You have a lot of flower buds in close.
And then from here we'll go to a heated plot. This is actually a six-degree centigrade increase
plot so it's about almost you know nine or ten degrees Fahrenheit.
And this plant is in full flower here. It's actually warmer, dramatically warmer, because
of the heaters here, and that's just stimulated these plants to just grow much faster.
So how many plots had dandelions on them?
I think this year was more like 15, and last year was more like 20.
Pretty big difference between the two years.
Yeah.
I started working last year with a group from the geography department to get a different
perspective on leafing out.
And we asked them if they were interested in working with us of comparing when plants
are leafing out using remote sensing with what we're observing on the ground, and they
were very interested in doing this as well.
They can give us the leafing out times in Concord over the last 11 years using remote sensing.
Each one of these different approaches that we have of remote sensing, historical information,
and then this work from the Boston Area Climate Experiment also gives us different ways of
estimating how climate change will be affecting the leafing out time of the forest and the
ability of a forest to begin photosizing in the spring.
And what we really want to come out of this with is a very clear idea of how comparable
these three methods are.
And this will result in much more accurate models being created of how climate change
will be affecting forest growth in this region and the ability of the forest to absorb carbon
dioxide.
If Thoreau could return to Concord today, I'm sure he would be pleased to learn how
important his notebooks have been to the study of climate change.