With the recent declines in numbers of monarch butterflies leading to the popular insect becoming a candidate for listing as an endangered species, more and more gardeners are thinking about growing milkweed. Milkweed, after all, if the only kind of plant monarch caterpillars can eat, and so growing milkweed in your garden means you’re providing monarchs with a nursery and larder for their young.

But there’s a problem: there are about 140 known species of milkweed, some of them potentially invasive in California wildlands. In fact, not all milkweeds are of equal benefit to monarch butterflies. There’s even some thought that one popular tropical milkweed may be harming North American monarchs by changing their migration habits.

Fortunately, there are fifteen species of California native milkweed that gardeners can choose from to give monarchs a helping hand. Not all of them are readily available in nurseries, but with a little searching you should be able to find at least one species appropriate for your part of the state.

Image credited to Marshel Hedin

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Stanford University scientists have found that the economic damage caused by a ton of CO2 emissions–often referred to as the “social cost of carbon–could actually be six times higher than the value that the United States uses to guide current energy regulations, and possibly future mitigation policies.

A new study by Frances Moore and Delavane Diaz finds that the ‘social cost’ of one ton of carbon dioxide emissions may not be $37, as previously estimated by a recent U.S. government study, but $220.

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