Improving Formality and Coherence

Read the following passage:

In recent years, many scientists have expressed concerns about the effects of climate change on global ecosystems. They argue that not only are weather patterns becoming more unpredictable, but also the habitats crucial for countless species are facing unprecedented threats.

However, some skeptics claim that the issue of climate change is exaggerated. They often point to natural climate fluctuations that have occurred throughout Earth's history as evidence that current concerns may be overstated.

Which of the following options best maintains the formal tone of the passage while improving its overall coherence?