The province already has a goal to reduce greenhouse gas pollution by 15 per cent below 1990 levels by 2020 and 80 per cent below 1990 levels by 2050.
On Thursday, it said it was committing to a new mid-term target to reduce emissions by 37 per cent below 1990 levels by 2030.
"Climate change is already hurting our environment, causing extreme weather like floods and droughts, and hurting our ability to grow food in some regions," the Ministry of the Environment and Climate Change said in a statement.
"Over the near term, it will increase the cost of food and insurance, harm wildlife and nature, and eventually make the world inhospitable for our children and grandchildren."
Earlier this year, the province announced a cap-and-trade system for carbon emissions, said it was ending coal-fired electricity generation, and electrifying and improving Ontario's commuter rail network.
Based on greenhouse gas reporting data, the ministry says Ontario has met its 2014 target of six per cent below 1990 levels.
Ontario uses 1990 as a baseline year for its targets, which is common in the international community and aligns with the United Nations Framework Convention on Climate Change.