My name is John Magnuson,
and I've been studying ice for quite some time.
I began studying ice 20 or 30 years ago
and have found it to be a fascinating signal
about how our world is changing.
(drill whirring)
The ice records on our local lakes here
have been recorded since the 1850s.
And they were not being recorded for scientific purposes.
(on screen): It's about 17 inches thick here.
(voiceover): They were not being recorded by scientists.
They were being recorded for practical reasons
by people who lived in the area.
And in particular, we had ice plants on each of the lakes.
Now, that wasn't a plant where you made ice;
it's a plant where you would cut ice, store it in sawdust
and use it for refrigeration during the summer.
And here in Wisconsin, the Madison lake records
are now kept in the state climatology office
and they're responsible
for making these measurements every year.
One of the first things that stand out
is that the average duration of ice cover 150 years ago
was, on average,
about a month longer in the mid-1800s than today.
Winter as measured by ice duration
has been getting shorter and shorter.
The other thing that you see is it's a very noisy graph,
with more extremely short ice covers in recent years.
There are some very short winters and very long winters,
often right after the other.
Those variations make it difficult
to see the long-term trend
unless you have a long-term data like we have for Lake Mendota.
That noise is a difference in weather from year to year--
differences in how warm the winter's been
or how cold the winter's been.
People often mistake
these differences in weather between winters
as a change in the climate.
Differences both in weather and climate are important to us.
Is it a short winter, a long winter?
Responding to differences in winter ice cover
is like deciding whether to put on a raincoat
when you go outside.
You don't ask, "Has climate changed?"
to put on a raincoat that day.
You ask, "Is it raining today?"
"Is there ice on the lake today?"
"Can I walk on that ice today?"
"Can I go ice fishing today?"
That's weather.
Is the ice not as safe now on average
as it was 150 years ago?
Are winters with extremely short ice cover more common now
than 150 years ago?
That's climate change.