What ancient pollen has to say about climate change in the future

Around 56 million years ago, Earth’s climate underwent a major climatic transition. A huge release of carbon into the ocean and atmosphere raised atmospheric carbon dioxide (CO₂) concentrations – which meant temperatures going up by 5 to 8°C and rising sea levels.

Do you sound familiar?

This event is called the Paleocene–Eocene Thermal Maximum(PETM) occurred over a few tens or thousands of years. However, the causes and effects of this transition remain a matter of debate.

Some possible causes of the large carbon release include massive volcanic activity, sudden releases from the ocean floor, or melting of permafrost in Antarctica.

Evidence for the PETM is mostly found in ancient marine sediments. But, if this period is to be used as a learning tool, we will need to see what might have happened. Climate change crisis currentlyIt is important to understand the land’s history.

There is not much information available about how the PETM climate affected life on land. Our research team used fossil pollen from around the globe that was preserved in ancient rocks to reconstruct how climate and terrestrial vegetation changed over this period.

Our New researchI am the leader Dr Scott WingThe Department of Paleobiology, Smithsonian’s National Museum of Natural HistoryPublished in the journal Paleoceanography, Paleoclimatology, demonstrates that an increase in the concentration of atmospheric CO₂ played a major role in shifting Earth’s climate and plant life.

We could see a similar increase in the coming centuries as a result of anthropogenic (that is caused by humans) increases in CO₂.

A recently developed approach was used to understand how terrestrial plants changed and moved over the period. It is based on fossilized pollen that has been preserved in ancient rock materials. It relies on the distinctive, species-specific appearances of pollen grains that can be seen under a microscope.

The distinctive appearance of pollen evolved to aid in the use of plants’ pollination strategies. Because each species has unique pollen, it means we can compare fossil pollen with modern pollen to find a match – as long as the plant family hasn’t gone extinct.

This means that fossil pollen can be easily assigned to many modern plant families. Each modern plant has its own climatic requirements. We assume that their ancient relatives had similar climates.

We omitted data from plant groups that we knew had evolved following the PETM to give more confidence in this assumption. These species may not have settled into the climate preference they have today.

We can reconstruct past climates and ancient floral communities by using pollen that has been preserved in rocks for tens or millions of years.

This is the first time that we have used this approach globally to fossil samples taken from 38 PETM sites across all continents, with the exception of Antarctica. This new pollen analysis has shown that PETM plant communities differ from pre-PETM plant community at the same sites.

These changes in floral composition are a result massive plant migrations. However, the types of plants involved vary by region.

When we say plant migration we mean plant movement, as the seeds that are spread grow better in one place and climate than in another – in this case at higher, cooler latitudes over lower, warmer ones.

Plants can move over 500 m each year, so they can travel huge distances over thousands.

For example, in the Northern Hemisphere, the bald cypress swamps of Wyoming were replaced by subtropical palm-dominated tropical forests. Similar happened in the Southern Hemisphere where wet-temperate podocarp trees were replaced with subtropical palm forests.

Each species was assigned a classification based on its climate. Köppen climate type. Examples include tropical rainforest, temperate summer, polar tundra, and arid desert.

This shows that the PETM brought warmer and drier climates towards the poles of both hemispheres but a warmer and dryer climate to the mid-latitudes.

We collaborated with the following organizations to explore the geographic extent of these shifts: Dr Christine ShieldsFrom the US National Centre for Atmospheric ResearchAnd Dr Jeffrey KiehlAt the University of California to run climate model simulations.

These simulations were created using data derived from Community Earth System Model (version CESM1.2)

These simulations were very similar to the climate data that we found in pollen. This included the expansion of temperate at the expense of colder climate types towards the poles, as well as the expansions of temperate and tropicalclimates in mid-latitudes.

So, if our current CO₂ levels continue to rise, warming and melting permafrost which could release more stored carbon to the atmosphere as it may have done 56 million years ago, we will once again see these mass shifts in vegetation in response to dramatic changes in local climate conditions.

The speed at which climate change is occurring and the availability of suitable areas for plants to migrate will affect how well the vegetation can move.

Where the plants go, so too will the animals that rely on them (if they can) – perhaps in some cases humans included.

Understanding the huge shifts in climate and our potential future gives us insight into our future. Is it possible to work together to prevent the negative consequences of climate change?

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