It?s painful to think about how profoundly global climate change is going to affect our gardens. But this is a problem we have to understand and get involved with rather than lapse into helplessness and depression.

We already know that we have to use water wisely so planting for drought tolerance has become a necessity. We know we need to attract native insects (especially native bumble bees), so we should use native plants as much as possible. And we know we have to comprehend what biodiversity means in every part of the country, and plant with that in mind.

But who knew that weeds, already the plant world?s equivalent to the schoolyard bully, were going to change so drastically as well? According to a study by the U.S. Department of Agriculture?s Research Service, the higher levels of carbon dioxide and the warmer temperatures expected in the next few years will increase not only the size of some weeds (up to four times taller) but also the virulence of what they produce. For example, with a doubling of carbon dioxide, there will be an estimated quadrupling of ragweed pollen. Pity the poor souls who are allergic to it and all those in the future who will join them with runny noses and watery eyes.

Another ruffian, poison ivy, is going to get bigger, become more toxic, spread faster and be harder to eradicate. With its signature three leaves, poison ivy infests forests and their fringes (called edge communities), elbowing aside native plants that have more sensitive responses to the environment.

Herbicides will be of little help in getting rid of these super weeds, because they are likely to knock out the very plants you want to save?the native plants that are a lifeline to beneficial bugs, birds, animals and, ultimately, people. The web of life and its interconnections are serious and complex, so don?t mess with them.

Recently, scientists from around the world gathered in Vancouver for the 5th International Weed Science Congress on the theme of ?Weeds?Local Problems/Global Challenge.? Their findings should prove fascinating reading. For more on the congress and the weed study, visit the Weed Science Society of America?s website.

But don?t be discouraged. Do sensible things to combat weeds. For large areas and persistent invaders, solarize?that is, put down thick layers of newspaper, cover with black plastic held down by bricks and leave it for a couple of months. The weeds will fry, root growth will be discouraged and you?ll have a tabula rasa for new planting beds. Plant your garden intensively, leaving little room for weeds, and mulch deeply to suppress weed growth. And get out there and get involved with every program that you can to help ameliorate climate change, from recycling to walking to work.