And while some have speculated there is an ongoing feud between Charles and Harry, the royal did not omit praise for the Duke of Sussex.
"And my younger son, Harry, has passionately highlighted the impact of climate change, especially in relation to Africa, and committed his charity to being net zero," Charles wrote.
"The eyes of our children and grandchildren are judging us. Let ours be the generation that can. And does. As we enter a new year, there is not a moment to lose."
The statement follows reports from last month suggesting their father-son relationship is at an "all-time low".
The Sun reported the pair have "barely spoken" other than a handful of phone conversations throughout most of 2021.
At the time of the reports, Harry revealed in a statement, that he cut ties with his father's Saudi billionaire donor as he did not trust his "motives". The move was rumoured to have sparked tension between them.
Harry shared that he severed ties with the controversial Saudi billionaire, Mahfouz Marei Mubarak bin Mahfouz, a full year before his father cut off contact.
His statement came in the wake of an investigation into Charles' charity foundation after his aide Michael Fawcett, 58, was accused of orchestrating a knighthood for Mahfouz in return for charitable donations.
What may have also sparked tensions was the Duke and Duchess of Sussex's explosive interview with Oprah Winfrey in March, and Harry's additional comments in an Apple TV + documentary that he was determined to "break the cycle of suffering" he experienced.