What if you needed a heart transplant, but you put off surgery until you became so weak an ambulance had to deliver you to the emergency room? By that time, you would be in immediate danger.

That's a lot like what's happening with global warming. Unless you're a scientist studying atmospheric chemistry, or you're paying very close attention to the global warming debate, the Earth doesn't appear to be in immediate danger. But when scientists go looking for telltale warnings, they find them everywhere.

Make no mistake, climate change is an imminent danger, and that unpleasant fact will become increasingly clear over the coming decades. The longer we wait to address climate change, the harder it becomes to fix the problem. Every year's delay compounds the effort, and the danger. Although it often isn't immediately apparent, the effects of global warming are already showing. Sea ice in the Arctic Ocean is getting thinner every year, and may disappear entirely by 2030. If that happens, it would be the first time in recorded history. Glaciers are in retreat on every continent, potentially drying up the water supplies for hundreds of millions of people. Extreme weather like severe flooding is becoming more common.

Continuing to delay the environmental care we urgently need will make the future much, much worse. Projections show the inland United States will warm up roughly 40 percent faster than the global average, with profound implications for American agriculture. In 2007, the prestigious Science magazine published research that "predicted a permanent drought by 2050 in many parts of the country," creating 1930s Dust Bowl-like arid conditions from Kansas to California. Another study found that without action to address climate change, by 2100 Oklahoma will see temperatures above 110 degrees for 60 to 80 days a year — within the lifetime of many children born today.

Just as emergency room care is always more expensive, waiting to address climate change will cost prohibitively more. Suppose we pass cap-and-trade climate legislation this year, with the law taking effect in 2012. To comply with the emissions target by 2020, businesses would need to cut annual emissions by roughly two percent per year.

Now let's look at another scenario: say we pass a cap-and-trade bill in 2010, and it doesn't take effect until 2014. To meet the same target, emissions would have to fall by 4.3 percent per year — over twice as fast — year after year until 2020, just to get to the same place.

Of course, the most expensive option of all is doing nothing — in a future of unconstrained global warming, the costs to agriculture, health, the world's infrastructure, and the environment would be unlike anything ever experienced in human history.