evidence: Top scientists say the world’s ice sheets are melting more rapidly than expected and that world leaders must ramp up their climate ambitions to avoid a catastrophic rise in sea levels. [...] New studies suggest that melting ice sheets are a greater cause for concern than the IPCC had considered. [...] Meanwhile, scientists revealed new research that suggests the collapse of the West Antarctic Ice Sheet might already be inevitable and that Greenland’s glaciers are melting at five times the rate they were 20 years ago. And another group of scientists found that the remaining carbon budget to limit warming was far smaller than once thought. At the current pace, the scientists believe global average temperatures will reach 1.5 degrees Celsius above preindustrial levels in about six years.