Eocene

• Warming at the poles, especially the Arctic, has been three to four times faster than the rest of the globe.
• Climate models simulate this effect, but when tested against the past 40 years of warming, these models fall short.
• This is a problem because these are the same models used to project into the future and forecast how the climate will change.
• Read more:
  Climate explained: why is the Arctic warming faster than other parts of the world?

Back to the future

• For us, this means we can use Earth’s history to find out how well our climate models perform.
• We can test our models by simulating episodes in the past when Earth was much warmer.
• The advantage of this is that we have temperature reconstructions for these episodes to evaluate the models, as opposed to the future, for which measurements are not available.
• Carbon dioxide (CO₂) concentrations ranged between 900 and 1,900 parts per million (ppm), compared with 415 ppm today.

Polar stratospheric clouds

• In 1992 American paleoclimatologist Lisa Sloan suggested polar stratospheric clouds might have caused extreme warming at high latitudes in the past.
• They are also called nacreous or mother-of-pearl clouds for their vivid and sometimes luminous colours.
• This suggests polar stratospheric clouds could be one of the missing puzzle pieces.
• In our research we use one of them and find that under certain conditions, the additional warming due to these polar stratospheric clouds exceeds 7°C during the winter months.

Implications for future projections

• This suggests the standard climate models are better at predicting the future than the past.
• Looking into the past is a way of broadening our horizon and learning for the future.
• Read more:
  When Greenland was green: rapid global warming 55 million years ago shows us what the future may hold

Katrin Meissner receives funding from the Australian Research Council. Deepashree Dutta received funding from the Australian Research Council and the Australian Government Research Training Program Scholarship. Martin Jucker receives funding from the Australian Research Council.