A research team examined a long-term owl roost. Owls prey on small mammals and the excreted remains of those meals that accumulated over the time, provide us an insight into the composition and structure of small mammals over the past 'millennia. The research suggested that when the Earth went through a period of rapid warming about 13,000 years ago, the small mammal community was stable and resilient. But, from the last quarter of the nineteenth century, human-made changes to the environment had caused an enormous drop in biomass and energy flow. This dramatic decline in energy flow means modern 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. Global warming is a frequently occurring natural phenomenon.

2. The impending global warming will not adversely affect small mammals.

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

Which of the above assumptions is/are valid ?