Canada's federal government, in a pledge that skeptical climate campaigners called a triumph of hope over experience, promised on Friday to reverse years of emissions growth and get its global warming pollution back on a downward slope.

"This is a fair and ambitious target that is in line with other major industrialized countries and reflects our national circumstances," said the government's announcement of Canada's contribution to the goals of a new climate treaty the world is struggling to complete in Paris at the end of the year.

Canada's pledge was submitted formally to the United Nations Framework Convention on Climate Change, which has asked all countries to outline their promises as soon as possible.

The target falls short of what other leading industrial nations have promised, would do less than Canada has promised in the past, and would be hard to achieve without significantly scaling back industry's longstanding plans to expand production of tar sands oil.

The goal, announced by Leona Aglukkaq, environment minister in the Conservative federal government, would reduce Canada's greenhouse gas (GHG) emissions by 30 percent below 2005 levels by 2030.

By comparison, pledges announced by the United States would occur a bit faster—cutting up to 28 percent by 2025, enough to stay on track with its past commitments. And those offered by Europe would cut much deeper, to at least 40 percent below 1990 by 2030.

Canada's greenhouse gas emissions have climbed steadily since 2009, when it matched the United States in pledging reductions of 17 percent by 2020. Essentially all the backsliding is attributable to growth in tar sands oil production in Alberta. Other economic sectors and other provinces have done better at reducing emissions.

The only hope for Canada to meet this new target it is that some provinces are taking more ambitious steps to cut emissions. Ontario, for example, has just announced provincial targets that are far more dramatic than the federal goals.

In a related announcement describing new regulations that the Conservative federal government said it will impose on the fossil fuel industries, there was no mention of any attempt to rein in emissions from the tar sands projects in Alberta.

Instead, Canada said it would seek to match proposed rules, mostly voluntary, put forth recently by the Obama administration to cut in half the methane that leaks during production and shipping of oil and natural gas.

And it promised to address emissions from chemical and fertilizer production, as well as from natural gas-fired electricity generation.

Environmental advocates sharply criticized Canada's promises. Some said they doubted their sincerity. Others questioned their efficacy.

"These targets are a nice gesture, but for now that's all they are, because the numbers here simply don't add up," said Cameron Fenton, a spokesman for 350.org. "There's no way Canada can hope to cut emissions by a third while this administration is still pursuing every possible opportunity to dig up the tar sands."

"Canada's leaders have missed an opportunity to lay out a strong plan that would ramp up renewable energy and drive deeper cuts in their emissions," said David Waskow, international climate director of the World Resources Institute. "Canada should reconsider this lackluster proposal and demonstrate to the world that it's serious about combating the climate crisis."