A research team examined a long-term coral reef sediment core. Coral growth bands and the mineral remains that accumulated over time provide us an insight into the composition and structure of reef fish communities over the past millennia. The research suggested that when the Earth went through a period of rapid warming about 8,000 years ago, the reef fish community was stable and resilient. But, from the last quarter of the twentieth century, human-made changes to the ocean environment had caused an enormous drop in coral cover and reef complexity. This dramatic decline means modern reef ecosystems are not adapting as easily as they did in the past.

On the basis of the above passage, the following assumptions have been made:

1. Ocean warming is a frequently occurring natural phenomenon.

2. The impending ocean warming will not adversely affect reef fish communities.

3. Humans are responsible for the loss of the reef ecosystem's natural resilience.

Which of the above assumptions is/are valid?