Leaders from around the world are gathering in Glasgow, Scotland, to hammer out new pledges to fight climate change. The stakes are high. Scientists warn that heat-trapping emissions must fall dramatically by 2030. Otherwise, the world faces more extreme hurricanes, floods and droughts, likely displacing millions of people. Still, negotiations at the COP26 meeting are expected to be tough. Here are four reasons why.

#1 The world is not on track to avoid extreme climate change

Countries have already made pledges to cut their greenhouse gas emissions by moving away from burning fossil fuels. But added together, those pledges don’t reduce emissions enough to avoid the worst damage from climate change. Current policies put the world on track for around 4.8 degrees of warming by 2100, compared with global average temperatures in the mid-19th century.

Globally, the goal is to limit warming to 2.7 degrees Fahrenheit, which scientists say is a crucial difference. The world would still experience worsening heat waves and storms, but not as intense and dangerous. Coral reefs would have a shot at avoiding a massive die-off. But to achieve that, emissions need to fall about 45% by 2030, compared with 2010 levels. That means countries will need to commit to far more ambitious goals.

#2 Wealthiest nations contribute the most to climate change

The global goal is to reduce emissions, but questions remain about which countries should enact most of the reductions. Developing countries contribute a small fraction of the emissions from cars and power plants. But they’re enduring some of the worst damage from climate change, like island nations that face being erased by sea level rise.

The United Nations is calling on countries to be carbon neutral by 2050, which means if a country is still emitting greenhouse gas emissions, they’re being absorbed by forests or other means to keep them from entering the atmosphere. The world’s largest climate polluter, China, has committed to becoming carbon neutral only by 2060. The country plans to have emissions rise until 2030.

#3 U.S. bears the biggest historic responsibility for climate change

China holds the top spot for highest emissions currently, but history matters. Once emitted, carbon dioxide can last in the atmosphere for hundreds of years, trapping heat that raises global temperatures. That means emissions from burning fossil fuels over the past 150 years are responsible for the warming happening today. Over that period, the U.S. has cumulatively emitted the most of any country.

The U.S has committed to a 50% to 52% reduction in emissions by 2030, which would come about through a significant shift to renewable energy and electric cars. Some environmental groups say that falls short of the U.S.’s fair share. Even a 50% cut depends heavily on policies that Congress is currently hashing out in a budget deal. If an agreement isn’t reached, the U.S. will arrive at COP26 without a credible path to achieve its emission goals, potentially hurting the negotiations.

#4 Wealthier nations are falling short on promises for climate change funding

With hundreds of millions of people vulnerable to extreme weather like severe storms and droughts, developing countries secured a promise for $100 billion in climate finance annually from developed nations. The funding goes to projects like sustainable transportation and renewable energy, as well as helping communities prepare for more extreme events. Still, as of 2019, developed countries are still below the goal, which will be a point of contention in the COP26 negotiations.