When Wangari Maathai, who died of cancer on Sept. 25 in a Nairobi hospital, won the 2004 Nobel Peace Prize, not everyone was happy. Maathai was the first African woman to win a Nobel, chiefly for her work creating the Green Belt Movement — a (literally) grassroots effort to empower rural women in Kenya to plant trees and reverse a catastrophic trend of deforestation. Critics wondered why — at a moment when war raged in the Middle East and terrorism loomed across much of the world — the Nobel Committee should choose to bestow the prize on a mere environmentalist. Didn’t the world have bigger problems than the loss of a few trees?
(PHOTOS: Wangari Maathai, African Environmentalist and Nobel Laureate)
Those critics were wrong because they misunderstood what Maathai was doing — and what environmental values mean to the fate of the world. Maathai didn’t stop with tree planting. The Green Belt Movement inspired women to stand up for themselves against a corrupt and patriarchal government and see the forests — the natural wealth of Africa — as something they had a civic right to preserve, as Anna Lappé and Frances Moore Lappé of the Small Planet Institute wrote in the International Herald Tribune after Maathai won her Nobel:
Maathai’s genius is in recognizing the interrelation of local and global problems, and the fact that they can only be addressed when citizens find the voice and courage to act. Maathai saw in the Green Belt Movement both a good in itself, and a way in which women could discover they were not powerless in the face of autocratic husbands, village chiefs and a ruthless president. Through creating their own tree nurseries — at least 6,000 throughout Kenya — and planting trees, women began to control the supply of their own firewood, an enormous power shift that also freed up time for other pursuits.
(MORE: Has Environmentalism Lost Its Spiritual Core?)
Maathai bore a terrible price for her environmental and political activism. She was jailed and beaten — as were her followers — and her husband divorced her, claiming Maathai was too strong willed. She won a seat in the Kenyan parliament in 2002 and served for a time as the Deputy Minister of the Environment before she was pushed out of government in 2008 and ended up protesting in the streets once more.
Former U.N. Secretary-General Kofi Annan put Maathai’s life in perspective:
She will be remembered as a committed champion of the environment, sustainable development, women’s rights and democracy. Her contribution to all these causes will forever be celebrated and honored.
Wangari was a courageous leader. Her energy and lifelong dedication to improve the lives and livelihoods of people will continue to inspire generations of young.
If Maathai became known for her politics, at her core she was an environmentalist in the most traditional sense: one who saw the intrinsic value of the forests, the land, the water. She worried that something would be lost in the developing world’s hustle to grow rich, that on an increasingly urban planet — more than half the global population now lives in cities — we would find ourselves lacking some essential part.
(MORE: Wangari Maathai, Hero of the Environment)
“In Africa, we’re busy trying to catch up with the West and live the same kind of life we see on TV,” Maathai told me a little less than a year ago. “But we end up destroying the environment to get the things we perceive as development. We’ve become detached from nature. And as you move away from nature, you become lost.”
It’s a sobering thought as the global population grows and what was once wilderness dwindles. If nature’s wounds are our wounds, than we have become very sick indeed. But Maathai, I know, wouldn’t want us to despair — though we have no shortage of reasons to do so. She spent her life preaching a green gospel, working with her hands to ensure that we would realize we have a stake in nature — and therefore, in one another, as Maathai made clear in her 2004 Nobel lecture:
Today we are faced with a challenge that calls for a shift in our thinking, so that humanity stops threatening its life-support system. We are called to assist the earth to heal her wounds and in the process heal our own — indeed, to embrace the whole creation in all its diversity, beauty and wonder. This will happen if we see the need to revive our sense of belonging to a larger family of life, with which we have shared our evolutionary process.
In the course of history, there comes a time when humanity is called to shift to a new level of consciousness, to reach a higher moral ground. A time when we have to shed our fear and give hope to each other.
That time is now.
Maathai is gone. It’s up to the rest of us to heed her call.
MORE: 1o Questions: Wangari Maathai
Bryan Walsh is a senior writer at TIME. Find him on Twitter at @bryanrwalsh. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.