Norwegian Jan Egeland, a former UN humanitarian chief now head of his country's refugee agency, says without a concerted political push to end the war, the West could face decades of terrorism.
His assessment comes as the world prepares this week to mark the fourth anniversary of the war.
Egeland and various humanitarian groups across the globe called Wednesday for a diplomatic solution to a festering conflict that has destroyed the security of millions of people.
Egeland agrees with the failing grade given to the United Nations Security Council on Wednesday in a joint report by Oxfam, Save the Children and World Vision.
While Canada and other western countries debate anti-terror laws in the wake of attacks at home, Egeland says they ignore Syria at their peril.
He says if countries don't force the issue of a solution to the Syria crisis many of the millions of children forced from their homes and deprived of school — and hope — will become tomorrow's terrorists.
"It will be biggest political mistake of this generation if we continue like now, because we will create a huge problem for generations to come," Egeland said Wednesday in a telephone interview from Norway. "Because we sow so much bitterness, we will harvest enormous problems."
He says the West must also spend more to address the continuing humanitarian catastrophe.
"Countries like Norway and Canada that take few refugees and also have a limited investment there in terms of humanitarian work — we provide cents per refugee, per day — we will meet the consequences of this policy in potentially decades to come."
Canada has contributed more than $700 million to the Syrian crisis since 2012 and has committed to resettle 10,000 Syrian refugees by 2017.
The joint Oxfam, Save the Children and World Vision report documented a declining situation that it blamed on the Security Council, whose five permanent, veto-wielding members include Russia, a Syrian ally.
The report said 76,000 people killed last year brought the war's death toll to 220,000. Meanwhile, 5.6 million children are in need of aid, a nearly one-third increase from 2013.
Also since 2013, the amount of international aid money for Syrian refugees has fallen off dramatically. Last year, donations covered only 51 per cent of what was needed.
The organization Handicap International said in a separate report Wednesday that tens of thousands of Syrians,"an entire generation of injured and maimed people," need orthopedic devices or rehabilitation services.
Egeland said he hasn't given up hope for a negotiated settlement.
His 30-year career in international diplomacy has included seeking ways to end conflicts in Darfur, Lebanon and Congo and dealing with natural disasters such as the 2004 South Asian tsunami and Hurricane Katrina in the United States.
The world must exert collective pressure on Russia, Iran, Saudi Arabia and the U.S. to force a negotiated resolution among the many armed factions, including the Syrian government, he said.
"There hasn't been such a catastrophe affecting so many people, so badly, in my time," he said.
"We've sunk to depths that are unheard of."