Cabinets of Curiosity
Can 200 Million Year Old Fossils Predict Global Warming?
Plants and Fossils
Fossils of plants from only 20 million years ago look much like the plants we see around today. Plants from as far back as 420 million years ago were quite different, with no leaves, flowers or seeds. Plant fossils we find in Ireland are mostly from the period of time called the Carboniferous (360 - 286 million years ago) 1, 2, 3, 4. The period itself gets its name from all the plant fossils found in rocks of that age, usually as thick layers of coal, or 'seams', made of the chemical element carbon. Before about 200 million years ago, the most common kinds of plants were gymnosperms (meaning 'naked seed' - they produce neither flowers nor fruit). Today, living gymnosperms include pines and other conifers, and gingko trees. Most modern plants are angiosperms - flowering plants. Everything from clover to oak trees is in this biological group. However, they did not come to dominate the planet until after many kinds of ancient gymnosperms went extinct.
Fossil fuel and global warming
Fossil fuels (coal, oil and petroleum) are the transformed remnants of ancient plants. Coal seams are reservoirs for carbon, buried deep underground. Over the past 200 years these reservoirs have been excavated and burned almost to nothing. This has led to large quantities of carbon dioxide (CO2) being introduced into the atmosphere, which traps long wave radiation reflected from the ground by the sun, like a blanket. This causes an increase in the amount of heat in the atmosphere, which has a knock-on effect on the temperature of the Earth's surface and oceans: global warming. Global temperatures have been fluctuating for hundreds of millions of years, but it is unlikely that the global climate has ever changed as rapidly before as it is now.
Biodiversity and climate
Climate is very different to weather - weather changes daily. Climate changes over decades, and period of at least 30 years to be meaningful. To track climate change, we look at the average ground surface temperature and the ocean surface temperature. The current average for the Earth's climate is 19 degrees C (66 degrees F). There has been a 25% increase in carbon dioxide over the last 200 years. Current CO2 levels in the atmosphere are at about 360ppm (parts per million) - the highest it has been in 55 million years - and are expected to rise to 700ppm by 2100. Plants have a huge impact on how atmospheric carbon dioxide changes (for example, the opening of new leaves in spring causes a huge decrease in atmospheric CO2).
Plants as indicators of CO2 and Global warming
Scientists have produced climate models that can accurately predict future climates and atmospheres. Models predict that future temperatures will rise from anywhere between 1.9 degrees C to 4.5 degrees C in the next 100 years. To predict future climates we can also look into the past - from the fossil record we can see natural regeneration of ancient ecosystems in reacting to natural climate change in the past. In order to predict what will happen as a result of increasing global CO2, studies have been carried out on how plants respond to CO2 and how this has affected plant communities over time. By looking at the number of stomata (small holes in the leaf surface that allows CO2 in and water out), it is possible to identify how much CO2 is in the atmosphere. If CO2 levels are high, then the plant has a lesser need of stomata, so the numbers found on leaves are low. Conversely in an atmosphere with lower CO2 levels the plant will produce more stomata to avail of as much CO2 as possible. The shape of a plant's leaf also contains information about the environment in which the plant lives. In atmospheres of elevated CO2, leaves tend to be smaller. The shape of a leaf can also give us a clue as to the climate the plant was growing in. For example tropical plants tend to have long thin leaves, or broad leaves with holes in them. This is to allow air to cool the surface of the leaf if it gets too hot. Roughly 210 to 195 million years ago the earth saw a major extinction event - data from the period suggests that 95% of plant species and 70% of corals became extinct. Fossil leaf studies from this period (known as the Jurassic-Triassic boundary) found that at this time there was an increase in global CO2 levels. It is estimated that at the beginning of the period, CO2 levels where three times as high as they are today. By the end of the extinction event this was seen to rise to seven times current CO2 levels. According to climate models, this led to an average temperature increase of 2-3 degrees C over approximately 15 million years. This increase in temperature lead to a huge upheaval in plant communities - biodiversity of plants was seen to decline which would in turn have seriously affected the ecosystem at the time. Periods of major animal extinction have been offset by major extinction events in plants. Thus these results suggest that rapid climate change associated with increasing CO2 levels has a negative impact upon the environment.
Can 200 million year old fossils predict global warming?
We can't say for sure if 200 million year old fossils can predict global warming, but the trend we see in the fossil record is worrying. With a 2-3 degrees C rise in temperature over15 million years we witnessed a mass extinction event. What we could be facing now, according to predicted current climatic change, is an increase from anywhere between 1.9 degrees C to 4.5 degrees C over a much shorter time period. The last global warming event that we know about was a natural occurrence - caused probably by volcanism (volcano activity). We do know that for 2 million years in the 15 million year interval there was a very intense period of volcanism. This would have released large amounts of methane as well as CO2 into the atmosphere, adding to the global warming. The most important point is that a small climate change caused a major ecological change in the past. There are differences in today's ecosystems. In the modern plant kingdom angiosperms (flowering plants) are the dominant plant group, not gymnosperms. The Jurassic-Triassic boundary extinction may have paved the way for angiosperms to become the dominant plant form. We know that the more diverse a system can survive a serious extinction event. So conserving biodiversity is the key to protecting the environment. However, it is very probable that by the year 2100 we will see significant ecosystem changes in vegetation.
Our 1st speaker, Dr Jennifer McElwain.
Dr Jennifer McElwain, who completed her undergraduate degree at Trinity College Dublin, is curator of fossil plants at the Field Museum of Natural History, Chicago. Utilising the more than 80,000 fossil plants in the Field Museum's collections, McElwain is looking at how levels of atmospheric CO2 have changed over time and how these atmospheric changes have affected Earth's biodiversity. In the summer of 2002, she led an expedition to collect 200 million year old plant fossils in Greenland, which was then funded by National Geographic Society. The project has since also secured funding from the Field Museum and NASA. The fossils date back to a major extinction event (in geological time period known as the Triassic-Jurassic boundary), where 95 percent of all plant species and 70 percent of coral reefs went extinct. The researchers have already shown that rapid increases in CO2 contributed to this mass extinction when global temperatures rose by 5 degrees Centigrade to 7 degrees Centigrade higher than the present. 'The whole subject of climate change is very contentious,' says McElwain. 'We know we're burning fossil fuels and, in doing so, Earth is heating up. What we are uncertain about, however, is the role atmospheric CO2 plays in large-scale climate and biotic change. By looking back in time at the relationships between CO2, climate and biodiversity, we can gain a greater understanding of their interactions and use this information to make better predictions of possible climatic and biodiversity responses in a future higher CO2 world.'