Climate change deniers often argue that the climate change we're seeing now is just part of Earth's natural cycle, and isn't being caused by humans. But new research suggests that climate change is happening faster than it has at any other time in our planet's history -- and scientists are worried.

Scientists at the University of Bristol recently took a closer look at past periods of climate change in an effort to compare them with what's happening today, and to investigate whether Earth has ever seen the same level of rapid ocean acidification that's currently beginning to threaten marine life worldwide.

In an interview with Phys.org, Dr. David Naafs, the study's lead author, explained that during the period that most closely resembles what's happening to the climate right now, environmental change "appears to have been far slower than that of today, taking place over hundreds of thousands of years, rather than the centuries over which human activity is increasing atmospheric carbon dioxide levels," and that last time it happened, "it is extremely unlikely that widespread surface ocean acidification occurred" as a result.

The study's co-author Professor Daniela Schmidt reiterated to Phys.org that the rate of environmental change occurring today seems to be unprecedented in Earth history. "This is another example that the current rate of environmental change has few if any precedents in Earth history," she said, "and this has big implications for thinking about both past and future change."

Professor Rich Pancost, one of the study's senior authors, also told the outlet that this could make it difficult to predict what will happen as Earth continues to warm up faster than it ever has -- and what will happen if the oceans continue to grow increasingly acidic as a result.

"Testing the risks associated with the pace of modern environmental change is proving problematic, due to a lack of similar rapid changes in the geological past," Pancost said. "Consequently, these risks, in this case to the marine ecosystems on which so many of us depend, remain associated with profound uncertainty. Decreasing CO2 emissions, as recently agreed in Paris, will be necessary to avoid these risks."