If there's any group that doesn't have to be sold on the idea that government must address the effects of climate change, it's farmers.

"Anybody who's paying attention knows the climate has already changed," says Daniel Sumner, director of the UC Agricultural Issues Center at UC Davis.

And farmers, of course, pay excruciatingly close attention to the weather.

They know how many summer days their crops have to endure 100-plus degree heat. They know how sensitive some specialty crops are to nighttime temperatures that aren't low enough, and how changes in the dew point can affect crop production.

California farmers know that the most important storage of water for irrigation is the snowpack in the Sierra, and they are aware that even a slight elevation drop in the snow level can have enormous consequences on the amount of water that will be available for their fields.

Northern California vintners shudder when they note even a slight rise in nighttime low temperatures or a slightly more frequent retreat of the marine influence from San Francisco Bay on the precious grape-growing microclimate of the Napa Valley.

California farmers are also aware that theirs is a global industry and that the effects of climate change on distant locales can have profound effects on them.

For California almond growers, the biggest worry about climate change may not be its local effects but rather its effects on the other side of the world. Their business model would collapse, Sumner notes, "if the climate changes somewhere in China so that almonds become an ideal crop for them."

Sumner was among the speakers on Monday at a daylong conference in Sacramento on climate change challenges to California agriculture, a conference that included remarks by Gov. Jerry Brown.

As did his predecessor, Brown has made confronting climate change a central focus of his administration. The reason, he said at the conference, is that models show California will be "at the epicenter" of climate-change effects in the United States. "It is a real existential threat to individual and collective well-being."

Brown noted that the state faces two imperatives. It must act to limit climate-change effects by reducing carbon emissions, and it must also cope with the effects. "We have to adapt," he said.

Environmentalists applaud California's leadership on the issue. Even the anti-fracking protesters outside the conference acknowledged Brown's leadership in one arena even as they faulted him on another front. Their repeated chant: "Climate leaders don't frack."

Those protesters and other green activists might have shuddered at some suggestions offered at the conference of the steps California agriculture must take to adapt.

UC Berkeley professor David Zilberman argued that it's time to think less about defending against climate change. "We really need to talk about the protection of society," he said.

For California agriculture, he argued, that means taking advantage of the state's historic strength. "In California, we're very good at using new technology and adapting," he said.

That should mean, he argued, a greater reliance on genetically modified organisms -- new grains to feed cattle to reduce their methane emissions, new varieties of crops that are resistant to heightened threats of pest infestation, new grape vines engineered to better withstand hot days.

As for dealing with the effects of climate change on California's water supply, Zilberman was direct about what needs to be done: "We have to build dams."

UC Berkeley professor Max Auffhammer underscored the climate-change driven effects on water availability. Projections about reductions in the Sierra snowpack are, he said, "really, really worrisome."

All agreed that dealing with climate change is a tough political issue. Conservatives unwilling to acknowledge the overwhelming science on global warming will continue to fight efforts to slow climate change by reducing carbon emissions. Liberals will likely resist steps that might be needed to adapt to irreversible changes that have already taken place -- steps such as increased reliance on genetic engineering to help agriculture adapt and a greater emphasis on water storage.

As Brown noted, it's a difficult political issue on which to engage voters.

"It's a challenge that doesn't capture the imagination of momentary events," Brown said. "We must pursue a series of paths over a long period of time."

Auffhammer likened society's reluctance to tackle climate-change challenges to the resistance of so many to begin seriously planning for old age. "It's a little like planning for retirement," he said. "We know that at some point our health is going to get bad. We know that with certainty."