It’s one of those science stories that at first appears rather irrelevant: A study out of Woods Hole Laboratory has found that poison ivy will become more common if our world continues to heat up from global warming. But the
study actually gives us an indication that a warmer world will really be like – and it won’t be springtime in Paris.
Research has shown that plant growth tends to increase under higher carbon dioxide levels. So, for six years, researchers with the Marine Biological Laboratory of Woods Hole pumped extra carbon dioxide into three test areas
of pine forest in North Carolina. By adding more of the most common greenhouse gas to the test forest, researchers hoped to simulate conditions we’re expected to see in our atmosphere by the middle of this century.
Their findings, published in the Proceedings of the National Academy of Sciences, report that when CO2 levels for the experiment were raised by about 50 per cent, poison ivy growth more than doubled – far exceeding
average plant increases. This is because vines respond especially well to increased carbon dioxide levels. Instead of storing the carbon in a woody stalk or trunk, as most plants do, vines simply grow more shoots and leaves, which provides them with more access to sunlight for photosynthesis – so they grow more quickly.
Interestingly, the poison ivy did not only grow twice as fast, it became more poisonous. Researchers say it is unclear why this occurs, but it may have something to do with the way the ivy produces the most noxious form of
urushiol, the vine’s poison that irritates our skin. Other studies have found that global warming could increase other irritants as well – such as pollen levels in the air, making life more miserable for hay-fever sufferers.
One can imagine the humourous headlines resulting from such studies: “Life in future more irritating, scientists say” or “Global warming makes world more annoying,” but there is more to the story. For example, increased vine
growth in forests also has a climate feedback effect. As vines grow faster, they can choke out woody plants such as trees, which store far more carbon in their trunks. So, rather than soaking carbon out of the atmosphere and
storing it, these forests could soon start turning it over rapidly and make global warming worse.
In fact, our climate contains a number of such feedback loops, where a change brought on by warmer weather causes another change, which exacerbates the problem. As Canada’s frozen tundra melts, for example, it
could cause the soil to release methane, which is an extremely powerful greenhouse gas. This, in turn, could again make global warming worse.
Also in the North, if global warming reduces snow and ice cover, it will expose the darker earth below. Without the bright white snow to reflect some of the sun’s radiation back into space, the ground will absorb more
light and heat, again potentially leading to increased temperatures.
Our climate is a complex system, intimately connected to the entire biosphere and all life within it. Small changes here or there can have repercussions down the line. Seemingly minor alterations can have cascading
and unintended consequences. It would be foolish to assume our climate will change slowly in a simple, linear fashion.
We hear so much about the most dramatic problems global warming is expected to cause, such as rising sea levels, extinction of species and more frequent or extreme weather events, that it’s easy to dismiss less
provocative studies. But they are all part of a story we need to understand if we are to prepare for a different world tomorrow, and make the changes necessary to prevent some of those problems from occurring today.