Many countries have agreed to stronger limits on greenhouse gas emissions in the lead-up to international climate talks next week, a crucial step in avoiding catastrophic storms, floods and droughts.

But those pledges don't go nearly far enough to rein in the heat-trapping pollution destabilizing the climate, according to a new report from the United Nations Environment Programme. The shortfall is casting a shadow over negotiations that scientists say are pivotal for putting the brakes on warming.

After disappearing from international climate cooperation under former President Donald Trump, the U.S. is seeking to return as a world leader at the COP26 climate summit in Glasgow, Scotland. In April, the Biden Administration announced a new national commitment: reducing emissions 50-52% by 2030, compared to 2005 emissions levels.

As part of its comeback, the U.S. has been encouraging other countries to strengthen their pledges, too. Special Climate Envoy John Kerry has done an international tour to drum up support. But all together, the total cuts in heat-trapping emissions offered by countries are only incrementally better — a 7.5% improvement by 2030 over earlier pledges.

But global emissions need to fall 55% by 2030 compared to previous pledges, the report says, to limit warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) by 2100.

Studies show that holding warming to 1.5 degrees Celsius greater than temperatures in the mid-19th century is a crucial threshold. The world would still experience more intense rainfall and heat waves if average global temperatures warmed that much, but they would not be as devastating as with higher temperatures. Coral reefs would have a shot at avoiding a global die-off.

So far, human activity, such as burning fossil fuels and deforestation, have raised global temperatures about 1 degree Celsius, or around 2 degrees Fahrenheit.

Without a significant shift in policies, global temperatures will hit around 4.8 degrees Fahrenheit, a level where dangerous heat waves could be more than 10 times more likely, and sea level rise would displace millions of people along coastlines. Last week, the Department of Defense warned that extreme climate change is a national security issue, as disasters fuel conflict and human migration abroad.

After a temporary dip during COVID-19 lockdowns, global greenhouse gas emissions are on the rise again. Overall, emissions are expected to grow 16% by 2030, compared to 2010 levels, according to another report this week from the U.N, driven by some of the largest polluting countries.

China has reaffirmed its goal of reaching net zero emissions by 2060, but emissions wouldn't begin falling until 2030. The country says it will stop financing new coal-fired power plants in other countries, a significant source of global emissions, though it has not said when that would occur.

But within its own borders, coal power still dominates and the COVID-19 recovery surge in manufacturing is only boosting demand. China accounted for 27% of global emissions in 2019, according to the Rhodium Group, about the same amount as all developed countries combined.

Brazil's emissions are also expected to keep rising due to continued deforestation of the country's rainforests, which releases carbon dioxide into the atmosphere.

Even with its new climate promise, the U.S. may arrive at the Glasgow talks without a convincing path to achieve it. The Biden Administration is counting on new incentives and tax breaks in the Congressional budget package to speed the transition to renewable energy. But with a thin margin in the Senate, objections from Sen. Joe Manchin, a West Virginia Democrat with personal financial ties to the fossil fuel industry, have put the policies in a precarious spot.

Solar and wind power have become cheaper than burning coal, leading to significant growth in renewable energy. But the trend isn't happening fast enough to avoid extreme climate change. A new United Nations report finds that fossil fuel use worldwide in 2030 needs to be half as much as what it's likely to be, in order to limit warming to 2.7 degrees Fahrenheit.