"Then it dropped off the cliff in 2007, and this year we have surpassed that level. And in addition to the extent of sea-ice, what remains is thinner than it used to be."

Measurements from submarines, drilling and satellites suggest that the ice is about one-third of its thickness 30 years ago, a change Meier describes as "remarkable." Almost all the ice that melted used to be first-year ice," he says; now, multi-year ice 10 to 12 feet thick is breaking up and melting.

The consensus among scientists is that the declining Arctic ice cover is now irreversible and accelerating. Some models predict that the North Pole will be ice-free in the summer within a decade; others project sometime between 2030 and 2050.

"It used to be -- 10 years ago -- that we spoke about 'if' rather than 'when' the Arctic would be ice-free in summer. Now, it's the other way round," Meier said.

It may seem a long way from the fields of Iowa or Ukraine, but what happens in the Arctic doesn't stay there. The region is often called the Northern Hemisphere's refrigerator.

"Sea-ice reflects much of the sun's energy back into space," Meier said. "When it's no longer there, dark ocean water absorbs the energy, which then warms the water and further melts the ice."

It's like leaving the fridge door open. The only way to restrain the process would be to moderate temperature increases, which in turn would depend on lowering carbon dioxide emissions.

Just how that affects weather patterns is only now being explored, but in 2009, the National Snow and Ice Data Center noted that "some numerical simulations indicate that the loss of the sea-ice cover may lead to changes in storm tracks and rainfall patterns over Europe or the American West."

Research this year by Jennifer Francis at the Institute of Marine and Coastal Sciences at Rutgers University shows that enhanced Arctic warming slows atmospheric jet streams, which tends to prolong weather patterns.

In other words, it entrenches drought in some areas.

Drought: the new norm?

A new study published in Nature-Geoscience suggests that drought in the western U.S. between 2000 and 2004 may have been the worst in nearly a millennium, depleting water resources and causing significant declines in river flows and crop yields.

There is yet another effect. Plants grown in North America do a good job absorbing carbon dioxide from the atmosphere, offsetting carbon emissions.

"Our study shows the turn-of-the-century drought reduced plant uptake by half in western North America," said Kevin Schaefer of the National Snow and Ice Data Center, one of the authors.

Drought in the American Northwest may "trigger a whole host of significant water resource challenges in a region already subject to frequent water shortages," Schaefer said.

From long-term imponderables back to short-term action. A further surge in commodity prices may lead the G-20 to convene its Rapid Response Forum within the next month in an effort to prevent the bottlenecks in 2007 and 2008 that led to food riots.

Buyers -- and insurance underwriters -- await the next U.S. Agriculture Department crop report due Wednesday with trepidation. The insurance bill from the subpar crops on American farms this year probably exceeds $18 billion, according to underwriters.

There are already ominous signs: Last week, the price of soybeans was close to 1,800 cents per bushel (up from about 1,300 cents in June) as Brazilian exports sagged. And in a sign that some buyers are worried grain supplies may tighten, one Mexican buyer last month made the fourth largest single purchase of U.S. corn since 1991, according to the Financial Times.

There's also demand for corn from ethanol producers, now that U.S. gasoline is not far shy of $4 a gallon.

If Russia were to introduce a grain export ban, as it did in 2010 to restrain prices at home, global prices would probably accelerate. In the face of market forces, the G-20 has few tools.

In the meantime, there are always silver linings amid the dark warnings. Here are two. Drought in the Midwest has sharply reduced the runoff of nitrates into the Mississippi River and down into the Gulf of Mexico. As a result, the "dead zone" of algae bloom has shrunk dramatically to an estimated 1,580 square miles, from about 3,400 square miles a year ago.

One of the photographs in a recent Atlantic gallery shows the enterprising Joseph Perazzo of Grass is Greener Lawn Painting turning a parched lawn in New Jersey into a picture of emerald green.

"Miracle Results" proclaims his sign. Maybe that's what we need.