Increasing concentrations of CO2 and other gases seem likely to warm the earth in the next century. The article examines opportunities to prepare for the consequences, focussing on options that are rational even if one is skeptical about global warming. Some responses can be postponed. But many low-cost opportunities will slip away if we fail to act; and reaching a consensus on what is fair is easier when the consequences seem remote. It concludes that some changes in land use and water allocation should be implemented today, even if effective dates are several decades in the future.