Here are two stories of small effects that may have a large impact, but that climate models haven’t included in their projects until now. They may look geeky but these things MATTER.
High CO2 Levels Cause Plants To Thicken Their Leaves, Could Worsen Climate Change Effects
Plant scientists have observed that when levels of carbon dioxide in the atmosphere rise, most plants do something unusual: They thicken their leaves.
And since human activity is raising atmospheric carbon dioxide levels, thick-leafed plants appear to be in our future.
But the consequences of this physiological response go far beyond heftier leaves on many plants. Two University of Washington scientists have discovered that plants with thicker leaves may exacerbate the effects of climate change because they would be less efficient in sequestering atmospheric carbon, a fact that climate change models to date have not taken into account.
In a paper published Oct. 1 in the journal Global Biogeochemical Cycles, the researchers report that, when they incorporated this information into global climate models under the high atmospheric carbon dioxide levels expected later this century, the global “carbon sink” contributed by plants was less productive — leaving about 5.8 extra petagrams, or 6.39 million tons, of carbon in the atmosphere per year. Those levels are similar to the amount of carbon released into the atmosphere each year due to human-generated fossil fuel emissions — 8 petagrams, or 8.8 million tons.
“Plants are flexible and respond to different environmental conditions,” said senior author Abigail Swann, a UW assistant professor of atmospheric sciences and biology. “But until now, no one had tried to quantify how this type of response to climate change will alter the impact that plants have on our planet.”
In addition to a weakening plant carbon sink, the simulations run by Swann and Marlies Kovenock, a UW doctoral student in biology, indicated that global temperatures could rise an extra 0.3 to 1.4 degrees Celsius beyond what has already been projected to occur by scientists studying climate change.
“If this single trait — leaf thickness — in high carbon dioxide levels has such a significant impact on the course of future climate change, we believe that global climate models should take other aspects of plant physiology and plant behavior into account when trying to forecast what the climate will look like later this century,” said Kovenock, who is lead author on the paper.
Scientists don’t know why plants thicken their leaves when carbon dioxide levels rise in the atmosphere. But the response has been documented across many different types of plant species, such as woody trees; staple crops like wheat, rice and potatoes; and other plants that undergo C3 carbon fixation, the form of photosynthesis that accounts for about 95 percent of photosynthetic activity on Earth.
Leaves can thicken by as much as a third, which changes the ratio of surface area to mass in the leaf and alters plant activities like photosynthesis, gas exchange, evaporative cooling and sugar storage. Plants are crucial modulators of their environment — without them, Earth’s atmosphere wouldn’t contain the oxygen that we breathe — and Kovenock and Swann believed that this critical and predictable leaf-thickening response was an ideal starting point to try to understand how widespread changes to plant physiology will affect Earth’s climate.
“Plant biologists have gathered large amounts of data about the leaf-thickening response to high carbon dioxide levels, including atmospheric carbon dioxide levels that we will see later this century,” said Kovenock. “We decided to incorporate the known physiological effects of leaf thickening into climate models to find out what effect, if any, this would have on a global scale.”
A 2009 paper by researchers in Europe and Australia collected and catalogued data from years of experiments on how plant leaves change in response to different environmental conditions. Kovenock and Swann incorporated the collated data on carbon dioxide responses into Earth-system models that are widely used in modeling the effect of diverse factors on global climate patterns.
The concentration of carbon dioxide in the atmosphere today hovers around 410 parts per million. Within a century, it may rise as high as 900 ppm. The carbon dioxide level that Kovenock and Swann simulated with thickened leaves was just 710 ppm. They also discovered the effects were worse in specific global regions. Parts of Eurasia and the Amazon basin, for example, showed a higher minimum increase in temperature. In these regions, thicker leaves may hamper evaporative cooling by plants or cloud formation, said Kovenock.
Swann and Kovenock hope that this study shows that it is necessary to consider plant responses to climate change in projections of future climate. There are many other changes in plant physiology and behavior under climate change that researchers could model next.
“We now know that even seemingly small alterations in plants such as this can have a global impact on climate, but we need more data on plant responses to simulate how plants will change with high accuracy,” said Swann. “People are not the only organisms that can influence climate.”
The research was funded by the National Science Foundation and the UW.
For more information, contact Swann ator firstname.lastname@example.org.
Grant numbers: AGS-1321745, AGS-1553715.
Climate Models Fail To Simulate Recent Air-Pressure Changes Over Greenland
Climatologists may be unable to accurately predict regional climate change over the North Atlantic because computer model simulations have failed to accurately include air pressure changes that have taken place in the Greenland region over the last three decades.
This deficiency may mean regional climate predictions for the UK and parts of Europe could be inaccurate, according to new research published today.
Researchers compared real data with simulation data over a 30 year period and found that the simulations on average showed slightly decreasing air pressure in the Greenland region, when in fact, the real data showed a significant increase in high air pressure – or so-called ‘Greenland blocking’ – during the summer months. These simulations are widely used by climate scientists worldwide as a basis for predicting future climate change.
The findings raise serious questions about the accuracy of regional climate projections in the UK and neighbouring parts of Europe because meteorological conditions in those regions are closely linked to air-pressure changes over Greenland.
Researchers warn that record wet summers in England and Wales such as those experienced in 2007 and 2012 could become more frequent if Greenland air pressure continues to strengthen over the next few decades, but such a trend might not be predicted due to inaccurate regional climate simulations.
The study, carried out by the University of Lincoln, UK, and the University of Liège in Belgium, also concluded that current models of melting on the Greenland Ice Sheet – a vast body of ice which covers more than 80 per cent of the surface of Greenland – may significantly underestimate the global sea-level rise expected by 2100.
Professor Edward Hanna led the study with Dr Richard Hall, both from the University of Lincoln’s School of Geography, and Dr Xavier Fettweis of University of Liège. Professor Hanna said: “These differences between the estimates from the current climate models and observations suggests that the models cannot accurately represent recent conditions or predict future changes in Greenland climate.
“While there is natural variability in the climate system, we think that the recent rapid warming over Greenland since the early 1990s is not being fully simulated by the models, and that this misrepresentation could mean that future changes in atmospheric circulation and the jet stream over the wider North Atlantic region may not be properly simulated.
“Until now, no-one has systematically examined the projections to see how they represent the last few decades and future changes – up to the year 2100 – from a Greenland regional perspective. Previous work reported a tendency for global warming to result in a slightly more active jet stream in the atmosphere over the North Atlantic by 2100 but our results indicate we may actually see a somewhat weaker jet, at least in summer.”
The research is the first to systematically compare global climate model data and observational data of air pressure changes for the Greenland region. The study, Recent changes in summer Greenland blocking captured by none of the CMIP5 models has been published in the European Geosciences Union journal, The Cryosphere.