The United Nations is warning that most countries have failed to uphold promises to make deep cuts to greenhouse gas pollution, in order to avoid the most catastrophic effects of climate change.

Under the 2015 Paris Agreement on climate, countries are required to submit details of their plans to cut greenhouse emissions, called "Nationally Determined Contributions," or NDCs, to the UN, which then calculates their total impact. The goal is to keep average global temperatures from rising beyond 3.8 degrees Fahrenheit (2 degrees Celsius), and ideally, no more than 2.7 degrees, compared to pre-industrial levels.

"We need about a 45 to 50 percent decrease by 2030 to stay in line with what the science shows is necessary," says Rachel Cleetus, policy director for the Climate and Energy Program at the Union of Concerned Scientists.

Yet according to a new report issued by the UN on Friday, the NDCs submitted so far actually will allow global emissions to keep rising, increasing by 16 percent by 2030, compared to 2010 levels. According to the UN's Intergovernmental Panel on Climate Change, meeting the more ambitious target of a 2.7 degree Fahrenheit temperature rise would require eliminating fossil fuels almost entirely by 2050.

"It's a sobering, sobering summary," Cleetus says. "We are so far off track from where we need to be."

The U.S. has updated its climate plan to the UN, promising to cut greenhouse emissions in half by 2030, compared to 2005 levels.

Cleetus says the American pledge is a "significant contribution, but the reality is, we have to deliver, to help ensure that those emissions reductions actually happen." Some of the policies and programs that the Biden Administration is counting on to reach that goal, such as a clean electricity standard, have not yet made it through Congress.

The UN report does include one small bit of hopeful news for advocates of climate action. More recent updates to countries' NDCs tend to be more ambitious, perhaps signaling a growing willingness to abandon fossil fuels.

The UN is still waiting for updated plans from many countries. "There are some real laggard nations that we hope to hear from," Cleetus says. They include China, which is the largest emitter of greenhouse gases, as well as Japan, Australia, South Korea, and Brazil.