[clydethefrog]

You are right, but your premise is probably different. They were indeed wrong. They were too conservative.

Some historical perspective:

1990: 1st Assessment

Little observational evidence for a detectable human influence on climate

1995: 2nd Assessment

The balance of evidence suggests a discernible human influence on global climate

2000: 3rd Assessment

Most of the observed warming over the last fifty years is likely* to have been due to the increase in greenhouse gas concentrations

* > 66% chance

2007: 4th Assessment

Most of the observed increase in global average temeratures since the mid-20th century is very likely* to to the observed increase in anthopogenic greenhouse concentrations

* > 90% chance

2016

It is extremely likely** that human influence has been the dominant cause of the observed warming since the mid-20th century.

** > 95% chance

2021: It is indisputable that human activities are causing climate change, making extreme climate events, including heat waves, heavy rainfall, and droughts, more frequent and severe.