If you head east to El Centro from San Diego, Interstate 8 takes you through arid scenery, climbing to 4,000 feet through barren mountains so fast that your ears pop. Then comes the oasis.

As you head down rapidly out of the mountains once more toward El Centro you hit a sign that tells you that you have reached sea level. Green fields and palm trees, stacks of hay drying in the fierce sun -- 90 degrees Fahrenheit even in November -- surrounded on all sides by rocky hills and the desert.

We knew before coming here that this was an agricultural region, but the lush greenery amid such a scorched landscape took us by surprise. This is where much of America's lettuce, spinach and other vegetables come from in the winter. There are also large cattle feed lots here too, which launch a frontal assault on your olfactory system long before you see them.

But you don't have to wander far from the fields to find the desert and its fine reddish, beige sand and realise just how incongruous the lush green fields are. Particularly when you feel the sun beating down on you when much of the northern hemisphere is already feeling the first cold of winter.

This is all made possible by water rights this area has from the Colorado River. As this part of the desert is below sea level in some parts, the water flows downhill and an irrigation system delivers it to 500,000 acres of farmland.

Without this water the fields would no doubt revert to desert in short order.

Some 97 percent of the water diverted to the area around El Centro goes toward farming and city manager Ruben Duran says the city is looking at ways to conserve water in a place where "mild dehydration is a natural state for most people."

But while people here talk in terms of conservation and wise use of water, they can also remind you that water rights in El Centro and Imperial County have been upheld twice by the Supreme Court and that no one can take them away.

"Water is always a concern," said Tim Kelley, head of the Imperial Valley Development Corporation, a public private partnership set up to diversify the local economy. "But those water rights belong to us. And if you don't like it, you can take us to court."

Photos by Lucy Nicholson

Photo by Kris Krüg

(Updated below with Michael Pollan's response)

You want some petroleum with that Big Mac?

Journalist and food writer Michael Pollan broke down the hidden cost of America's best-known burger on Saturday to an eager audience at the Poptech conference. He traced the Big Mac's origins all the way back to the oil fields, used to make fertilizer that is crucial to the corn grown for cows in massive feeds lots.

“Our meat eating is one of the most important contributors we make to climate change," said Pollan, who is best known for his book "The Omnivore's Dilemma."

"A vegan in a Hummer has a lighter carbon footprint than a beef eater in a Prius.”

It's a great line and quite a mental image, one that wowed the audience and quickly spread on Twitter. Too bad it's not true.

Gidon Eshel and Pamela Martin of the University of Chicago published a 2005 paper in the journal Earth Interactions that looked at the relative carbon footprints of plant-based and red-meat diets.

They found that the difference between an heavy meat-eating diet and a vegan diet was about 2 tons of carbon dioxide equivalent per person per year. The difference between a Prius and an SUV (they used a Suburban, which gets about the same mileage as a Hummer) was 4.76 tons per year.

Pollan's claim, said Eshel, "is emphatically wrong. If you're looking at the mean American driving habits and eating habits, it's not even close."

"In my heart I'm flatly on the Pollan side, but I'm a scientist and I don't like to play fast and loose with numbers," he added. "It's like death panels in the healthcare debate. We don't want to get into hyperbolic statements that are numerically unsound."

To be sure, the calculations behind food-related carbon footprints can be complex. The impact of a Big Mac includes the carbon footprint of the cattle feed and the fertilizer used to grow it, the fuel burned to get the animal to a feedlot and then to market, and the animal's emissions of methane gas, which can be 20 times more potent than carbon dioxide as a greenhouse gas.

UPDATE: Michael Pollan has asked Poptech not to post his presentation without removing the statistic about the vegan Hummer driver.

"After digging in to it further, and consulting Gidon Eschel, I don't feel comfortable defending it," he wrote to Reuters in an email. "It's much more important to keep the focus on the central thrust of the environmental case against eating industrial meat, which is not in dispute and certainly does not stand or fall on the case of the vegan Hummer driver."

"Thanks for your doggedness on this matter, which we can hope will stop this meme before it hurts somebody," he added.

The blogger Fat Knowledge did a separate calculation of the numbers after Eshel and Martin's paper was published, and concluded:

Going from a Mad Meat Eater diet to a Vegan diet saves 6.5 tonnes of CO2 a year while going from a Hummer to a Prius saves 6.4 tonnes. Given a margin of error on the values, I call that a tie.

The numbers have also shifted as gas mileage improves. Using Eshel and Martin's calculations with the current EPA mileage statistics, a 2010 model Hummer getting 14-15 miles per gallon has a carbon footprint of 4.3 to 4.7 tons per year, depending on whether it's an automatic or manual transmission model. (The EPA's own carbon footprint calculations, which include the manufacture of the vehicle, are significantly higher)

A 2010 Prius getting 50 miles per gallon has a footprint of 1.4 tons. The difference is 2.6 to 3.3 tons per year -- not very far from the 2 ton difference between a meat-eater and a vegan.

Click her for more Poptech coverage.

Historically, prices of natural resources lag equities, which typically front run the economic cycle by between 18 to 24 months. The change is also partly due to the tumbling dollar, a major driver in recent weeks.

The natural resources sector is also one of the last to price in economic expansion. But not this time.

Global capacity utilisation rates in petroleum products and mining between 2002 and 2007 averaged more than 90 percent. Analysts estimate those levels fell to 80 percent -- still very high -- in July 2009.

In contrast, utilisation rates among manufacturing companies was estimated at around 65 percent last July from about 80 percent between 2002 and 2007. Equivalent numbers for the auto sector were 45 percent and 80 percent respectively.

The large output gap in manufacturing and the auto sector means production can ramp up easily without any bottlenecks when the global economy sees stronger growth, albeit from low levels.

Not so in commodities, where firms are running a tight ship.

Corporations have said they see themselves as part of the fight too, particularly when it comes to research. But Robert Thompson, a former World Bank official, says he’s pessimistic the private sector will be able to contribute enough. “Their shareholders won’t stand for them solving all the problems of the developing countries, and giving it away,” he told Reuters.
    
“It’s going to take subsidies or at least a public sector contribution to engage their research horsepower,” said Thompson, now an agriculture professor with the University of Illinois, who has pushed for more spending on agricultural development for 40 years.
    
Agribusiness should be motivated to get involved in developing countries because they represent a future growth market for their products, Thompson said. “They should be willing to accept lower return on their own investments as an investment in the longer term, but we have to keep the short time horizon of the U.S. investment community in mind,” he said.
    
“Shareholders are brutal on companies that don’t meet their short-term profit expectations. In that sense, perhaps some of the European companies like Syngenta, BASF or Bayer … may have a little more license, if you will, to take a longer-term perspective than some of the U.S. publicly traded companies.”

Below: Bill Gates addresses World Food Prize forum in Des Moines, Iowa.

He warned that if the United States doesn't move forward on clean energy, it risks falling behind China where the government is spending almost $100 billion a year to support renewable energy and clean energy efficiency.

And China is not doing it just to address climate change issues, but because it sees an economic opportunity. "They're really focusing investing in the clean energy field to serve the needs of the world," Locke said at the Reuters Washington Summit.

"And so that's why it's very important that we pass clean energy legislation because there's so many investors, entrepreneurs, venture capitalists who are sitting on the sidelines waiting for that certainty," he said. "They just want to know what the rules of the game are, what the tax incentives are, what the tax rules and regulations are before they commit."

The longer the U.S. government takes to pass comprehensive energy legislation, "the farther ahead the Chinese will be and we certainly do not want 10 years from now Shanghai and other parts of China to be the Silicon Valley of the clean energy field," Locke said.

He agreed with President Barack Obama's equation. "The president has said that the country that leads in the clean energy sector will lead the world economy, I believe that's true," Locke said.

For more news from the Reuters Washington Summit, click here.

Photo credit: Reuters/Jonathan Ernst (Commerce Secretary Gary Locke at Reuters Washington Summit)