Most empirical studies have been conducted in laboratory or greenhouse settings; though, these environments may be too simplified to detect conflicting selection present in complex natural communities (e.g., Shaw et al. 1995).
In past seasons, Golden Land, a farm created out of an empty field five years ago, obtained at least enough permits to work its greenhouses, though bureaucratic tangles in Russia's temporary work visa program reduced the quota this year.
Soil is a key component in the world's greenhouse gas systems, though often overlooked.
The greenhouse gas initiative, though, turned out to be piggybacking on a larger economic force, the relative price of fuels.
The risk of hurricanes in Florida makes it harder for growers there to set up greenhouse cultivation, though growers elsewhere do not have that concern.
Most research suggests that corn ethanol offers modest benefits in lowering emissions of climate-altering greenhouse gases, though production of ethanol has contributed to rising food prices.
For greenhouse gases, though, Mr Bush has done no more than leave open the possibility of a trading scheme some time after 2012, when the new strategy will be reviewed.Putting off the day of reckoning for as long as possible (and well beyond Mr Bush's term of office) may have seemed the easiest option to Mr Bush.
But it will not have much impact on emissions, and therefore on the speed of climate change, because it does not require developing countries to cut their emissions, and because America did not ratify it.The United States is the world's biggest producer of greenhouse gases, though not for long.
On broad environmental issues, Mr. Clinton's single most important adviser, particularly on global warming, was Vice President Al Gore, who took the lead in hammering home the 1997 Kyoto accord on the reduction of so-called greenhouse gases, though that deal has yet to be ratified by Congress.
Theoretically, one can achieve removal of non-CO2 greenhouse gases, though literature on this is scarce.
Also, current law lets polluters meet some of their obligation to cut greenhouse gases though what are called "offsets" -- activities like planting and protecting forests, which remove carbon dioxide from the air.
