MADISON, Wis. -- On Earth Day, an important Wisconsin conservationist being remembered for a legacy that reminds us of the challenges to come.

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The historic work of Aldo Leopold, and those who've followed him, is now telling people more about the world we live in today and showing us how climate change might be happening in our own backyard.

Leopold spent a great deal of time at a farm in Sauk County. Readers of his book, "A Sand County Almanac," might know the place that he wrote from as "the Shack." But beyond his essays, Leopold kept meticulous notes on the dates and times of when he observed things happening in nature, like the blooming of wildflowers and the return of birds. That work was continued by his daughter after his death in 1948. She kept records from 1975 to 2004, WISC-TV reported.

Now, Stanley Temple, a University of Wisconsin professor emeritus and senior fellow at the Aldo Leopold Foundation, is looking at the numbers, and he said that they give a greater glimpse at climate change.

"Quite a few things were happening earlier, some things were unchanged, but the most dramatic result that could be observed in the data was that there were many things, especially early spring wildflowers that were blooming almost two weeks earlier than they did in Leopold's time," said Temple.

Temple said that everything from wildflower blooms to the first frost are happening at an earlier date, in some cases more than a month before Leopold noted them.

"Given that the climate is warming, you might have predicted that some events would be happening earlier in the year now that spring is arriving earlier and it is warmer, and that's what his notes demonstrate very graphically," he said.

Temple said that some of the patterns of animals haven't changed. He said that robins come earlier than usual because of the warmth, while woodthrushes, who migrate based on daylight, show up at the same time.

Even one of Leopold's key symbols in "A Sand County Almanac" is out of sync. In his "Prairie Birthday" essay, compass plants bloomed July 15.

"Now, if you were to keep track of when compass plants bloom, they're almost three weeks earlier and are now blooming in June," said Temple.

What's the lesson to be learned from this? Leopold said that it was to live within the land.

"The Shack was a place where Leopold tried to accomplish what he described as the oldest task in human history, which was to live on a piece of land without spoiling it," said Temple.

That lesson is being taught by the Aldo Leopold Legacy Center. It's been called the "greenest building in the world" by the U.S. Green Building Council. The center is run by solar energy and is considered "carbon neutral," WISC-TV reported.

It seems even Leopold might have wanted to leave a reminder of the need. The tiny bloodroot flower has been blooming for two weeks just outside the door of the Shack. Its first bloom of spring was the last thing Leopold noted on the day that he died -- April 21, 1948.

For those interested in reading Aldo Leopold's records and papers, the full text of all the Shack journals are online. The University of Wisconsin is in the process of making his essays, field journals and other documents digital, and available worldwide. To see what's available, visit here.