The Duke of Cambridge has called for action on the "clear and urgent" challenge faced by the environment.
Speaking at the Tusk Conservation Awards at the Empire Cinema in Leicester Square, William said the trade in wild animal parts was "disgraceful and baffling", while praising leading conservationists.
The Duchess of Cambridge was scheduled to attend the event with her husband, but due to an undisclosed matter regarding their children, William attended the event alone.
"Earlier today, Catherine and I spent some time with the nominees and finalists. Their bravery, single-minded determination, and commitment to African conservation is deeply, deeply humbling," he said.
William presented three awards at the annual ceremony held by Tusk, a charity which supports wildlife conservation work across Africa.
He used his speech closing to praise the "hugely important" work of the nominees before calling for action on climate change and other environmental threats.
He said: "As we approach the start of a new decade, the challenge ahead of us is clear and urgent.
"Climate change, human population growth, exploitation of natural resources, and habitat loss all pose major threats to the precious balance of our natural world."
William said his father the Prince of Wales had rung alarm bells about the state of the environment for many years.
"Right now, young people the world over are ringing that planetary alarm bell louder and with more determination than ever before," he added.
"My generation and those following are acutely aware that we cannot simply carry on as we are.
"We have to move faster and more effectively to find ways to balance our demands on this planet with the nature we share it with."
The duke has been the patron of the Tusk charity since 2005 and visited its projects in Namibia and Tanzania last year.
During the event, he presented a Conservation award, given to an emerging leader in conservation, a Wildlife Ranger honour, and the Prince William Award for Conservation in Africa – a lifetime achievement prize.
William said there had been reductions in the illegal ivory trade, but added: "We have a long way to go in eradicating the trade in other animal parts which is endangering species.
"The fact that there is a demand for animal parts such as lion parts and rhino horn in the 21st century is disgraceful and baffling."
After the ceremony, William attended a reception at the National Portrait Gallery with charity supporters, including television star Bear Grylls.
Grylls told the PA news agency: "Tonight was celebrating some real unsung heroes, their stories were amazing.
"The work these guys do is inspirational, it's the real front line of conservation in Africa, respect."
A Kensington Palace spokeswoman would not discuss further the reasons behind Kate's decision not to attend the event, but said the Cambridges had been present at an afternoon tea event with the Tusk winners at Kensington Palace.
The duke and duchess have three children, eldest son Prince George, aged six, daughter Princess Charlotte, aged four, and their youngest child Prince Louis, who is almost 19 months old.
With the couple able to leave their children to attend the afternoon event, it is not thought the health of the youngsters was an issue.