Conflicting news about weeds and climate change

Will weeds be more aggressive if the climate warms up – or won't they?

The bad news is that global warming is increasing the aggressiveness of some weeds, says the Weed Science Society of America. The good news is that some scientists in Australia don't necessarily agree.

Once summer's heat and humidity soar, I don't want to think about weeds. And I imagine I'm not alone in feeling that way. Unfortunately, the weeds are there and have to be dealt with.

If the Weed Science folks are right, that's going to get more difficult:

They point out that the rising amount of carbon dioxide in the atmosphere caused by increased temperatures is expected to help vegetables and grains grow more quickly and produce greater yields.

Unfortunately, that impact could be even more pronounced in weeds than in good crops.

So, how much faster will the weeds grow with warmer temps and higher carbon dioxide levels? About four times more, several studies by the USDA's Agricultural Research Service showed.

Interestingly, the Monitor has been reporting this since 1995.

But wait a minute, say researchers at the School of Plant Science at the University of Tasmania. Their seven-year study suggests that for many weeds, the increase in growth caused by more CO2 is offset by the rising temperatures.

"When you add warming to an experiment as well, the warming actually knocks the weeds out very strongly," said Mark Hovenden.

He specifically mentions that bane of suburban lawns – dandelions.

Dr. Hovenden also adds a caveat to the belief that carbon dioxide will increase good plant growth across the board. That will be dependent on ample summer rainfall, he says.

A third voice – Arthur Weis, a professor of ecology and evolutionary biology at the University of California at Irvine – conducted studies that predict that weeds will evolve to cope with climate change.

So here you have a group of scientists saying climate change will probably make it harder and more expensive to control weeds, which will dramatically increase the pollen in the air.

And a different group says their experience shows that climate change slows weed invasion.

And, lest that get you feeling hopeful – another study shows how quickly weeds can adapt to global warming.

If you'll excuse me, I'm going to slip on my heavy-duty garden gloves and pull some weeds while I think about all this. That's when I do my best thinking.

Note added on 6/29: You may want to look at Tom Christopher's article, "Can Weeds Help Solve the Climate Crisis," in The New York Times Magazine.

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