Nations have delayed curbing their fossil-fuel emissions for so long that they can no longer stop global warming from intensifying over the next 30 years, though there is still a short window to prevent the most harrowing future, a major new United Nations scientific report has concluded.

Humans have already heated the planet by roughly 1.1 degrees Celsius, or 2 degrees Fahrenheit, since the 19th century, largely by burning coal, oil and gas for energy. And the consequences can be felt across the globe: This summer alone, blistering heat waves have killed hundreds of people in the United States and Canada, floods have devastated Germany and China, and wildfires have raged out of control in Siberia, Turkey and Greece.

But that’s only the beginning, according to the report, issued on Monday by the Intergovernmental Panel on Climate Change, a body of scientists convened by the United Nations. Even if nations started sharply cutting emissions today, total global warming is likely to rise around 1.5 degrees Celsius within the next two decades, a hotter future that is now essentially locked in.