The plants that cover the globe interact with climate in many ways. As manmade climate change progresses, the links will provide both good news and bad news for people — and plenty of controversy.
Newly released federal information sheds more light on plant-climate links, and provides fodder for all kinds of stories. Research and policy discussions are focusing on both natural plant systems and domesticated ones, especially agriculture.
Studies have shown that some plants in some situations can be large greenhouse gas emitters. Other studies have shown that some can be carbon sinks. Still other studies have shown that some can benefit from climate change — though maybe in ways that people won't like, such as increased weediness or allergenicity — while other studies show that some plants will suffer.
Some recent studies, data sources, and policy statements on this topic:
The US Dept. of Agriculture's Agricultural Research Service published in November 2009 a series of studies and articles. The findings illustrate significant plausible changes in weed invasiveness, pollen production, drought tolerance, and understory plant composition; chemical changes in forest litter; nutrient changes in crops; shifts in plants foraged by animals; alterations in certain diseases and insect pests; and harmful effects of ground level ozone that is expected to rise as temperatures generally increase. The studies were conducted in diverse settings, ranging from the East Coast to the Southeast to the Rocky Mountains, as well as Europe.
On the policy front, USDA Secretary Tom Vilsack outlined in a talk in Copenhagen a series of steps he is advocating for the Department. He addressed both the effects of climate change on agricultural yields, and the role agriculture and forests can play in mitigating climate change.
He pressed for better research on effects at the local level, and improved communication of that information to farmers; revamping crop and livestock production and water usage so that they are more responsive to more extreme climates; and improving knowledge of how, and whether, agriculture can help mitigate climate change, and helping farmers develop appropriate strategies and technology to implement what is learned.
- USDA: Press Release of Dec. 12, 2009, "Agriculture Secretary Tom Vilsack Highlights Role of Agriculture in Climate Change." 
One possible effect of climate change is shifts in water availability, both as precipitation and as surface and ground water. That will affect both the ability of crops to grow, and the availability of water for irrigation.
An improved picture of irrigation demand and associated aspects became available Dec. 3, 2009, when the USDA released its data from a 2008 survey. This is a follow-up to similar surveys conducted periodically (though the information and methodology continue to change, making comparisons with earlier surveys difficult).
- USDA: 2008 — Farm and Ranch Irrigation Survey;  press release, "USDA Study Finds 54.9 Million Acres of U.S. Farmland Now Irrigated." 
For the 2008 survey, there are 43 tables, covering topics such as acreage irrigated, amount of water used, costs, energy use (including solar), and water conservation practices (including use of recycled water). There is data at the state and regional level for each category, and trends from 2003 to 2008 can be covered at the national level (though not at the state level, since that data isn't directly comparable between the two surveys).
Irrigated acreage and water use went up 5% from 2003 to 2008, illustrating the nation's continuing thirst for water. The rise in water use came despite a small increase in use of more water-efficient systems, such as drip irrigation. The increasing stress on the nation's water was reflected in an average increase of five feet in well depth. Stress on the farmer's wallet was reflected in a total increase of 73% in pumping costs.