In a statement released on Tuesday, Johnston notes that the annual awareness day has been adopted by countries around the world.
"Its message transcends borders, politics and dogma … It can be understood in every language, translated a thousand times over from the most complicated scientific lexicon into the simplest, plainest terms: we must preserve the natural world in order to ensure our own survival."
This isn't the first time that Rideau Hall has taken official notice of Earth Day, which originated in the United States in 1970, but didn't cross the border to Canada until 1980.
Back in 2007, then Gov. Gen. Michaëlle Jean signed her name to an Earth Day-themed blog post that invited Canadians to submit ideas on how to "act ecologically and with green ethics in our everyday lives and in our communities."
Since then, however, April 22 appears to have passed without viceregal comment until last year, when Johnston became the first Canadian Governor General to issue a formal Earth Day statement, which lauded "the shared love of the land" that unites Canadians, while warning that it would be "a grave error to take all this for granted."
"I would like to wish everyone a most enjoyable and instructive Earth Day, as we all reflect on the wonders of the natural world and on effective ways to preserve them," he concluded.
This year, Johnston seems to be taking a distinctly more activist tone.
"The time has come when we can no longer progress with blinders on, ignoring the dire effects we have on our environment," he says.
"Nor can we simply lay the consequences of our actions — and inaction — at the feet of future generations."
Rideau Hall spokeswoman Marie-Eve Latourneau told CBC News the decision to include Earth Day on the list of events for which a statement would be prepared was made last year, and confirmed that Johnston "personally reviews all messages issued by [the] press office."
Critics have long complained about the Conservative government's record on the environment and climate change in particular, pointing to decisions to pull out of the Kyoto Protocol and to dismantle the National Round Table on the Environment and the Economy, the gutting of the Navigable Waters Act, and delays in introducing emissions regulations for the oil and gas industry.
The government's own reports show it is not on track to meet its own watered-down target for emissions reductions by 2020.
Recent Earth Day comments rare
A search of government news archives reveals that Paul Martin was the last prime minister to attend an Earth Day event — or, indeed, issue a statement at all.
In 2007, then Environment Minister John Baird spent April 22 planting trees at an Ottawa school.
At the time, he called Earth Day "a great opportunity to reflect and be proud of what we’ve accomplished and to think about how we can all continue to work to protect our environment."
"Canada's New Government is serious about tackling climate change and protecting the air we breathe, but we know we can't do it alone," he continued.
"Taking steps at home and teaching our children to protect the environment will be the key to securing a healthier future for all Canadians."
Last year, then Environment Minister Peter Kent marked Earth Day by launching an online oilsands environmental data monitoring portal.
"Today, as the world celebrates Earth Day and showcases commitments to protecting the environment, Canada is contributing and doing its part," he commented.
"With this portal, our respective governments are actively encouraging informed discussions and analysis on the impacts of oilsands development based on high-quality scientific information."